Hip joint replacement navigation system and method

Abstract

It is an objective to provide accurate measurements of a patient's leg length and joint offset, and to provide for those leg lengths and joint offsets to be visualized using conventional equipment. [Solution] A hip joint navigation system is provided that includes a base having at least one channel disposed therethrough for receiving a pin for attaching the base to a pelvis. An attachment feature is disposed on the upper surface. A registration jig is configured to couple with the base and engage an anatomical landmark. In some aspects, a patient-specific jig system for hip joint replacement is provided that includes an engagement surface configured to closely mate with the acetabular bone contour of a particular patient and a registration feature configured to be in a predetermined orientation relative to the patient's acetabulum when the jig is coupled with the acetabular bone contour of the particular patient. In other aspects, a method of using the system is provided.

Description

Technical Field

[0001] [Incorporation by Reference to Prior Applications] Any or all applications for which foreign or U.S. priority is claimed are identified in the application data sheet filed with this application, which includes U.S. Provisional Application No. 62 / 118,987, filed Feb. 20, 2015, and U.S. Non-Provisional Application No. 14 / 643,864, filed Mar. 10, 2015. These applications are incorporated herein by reference in accordance with 37 C.F.R. § 1.57.

[0002] This application is directed to the field of hip joint replacement, and more particularly to surgical instruments and methods for guiding pre-treatment of bone in connection with surgical instruments.

Background Art

[0003] Hip joint replacement surgery is common and has become increasingly common over the years. One problem that continues to exist with hip joint replacement surgery is the relatively high incidence of improper placement of the cup component and the ball component of the artificial hip joint. For example, the cup component is optimally positioned in a particular alignment with a plane including the rim of the acetabular fossa of the pelvis. For a variety of reasons, an unacceptably high percentage of patients have the cup component of the artificial hip joint outside the range of alignment with this plane.

[0004] Unfortunately, the misalignment can lead to immediate dislocation of the hip joint within one year of the implantation surgery. This is particularly problematic because it can take months to recover from hip joint surgery. Patients who undergo revision soon after the initial implantation will surely be dissatisfied with their care and will undergo additional, redundant surgeries. Of course, all surgeries carry some risk. Those improper outcomes are not satisfactory for the patient and, overall, are not useful to the healthcare system.

[0005] Furthermore, in cup placement during complete hip replacement surgery, the inclination and anterior tilt angles are relative to the anterior pelvic plane (defined as the plane formed by the two anterior superior iliac spines (ASIS) and the pubic symphysis). While these anatomical features are visible / palpable when the patient is in the supine position, the majority of total hip replacement surgeries are performed via a posterolateral approach with the patient in some lateral decubitus position. In this case, many of these landmarks are inaccessible and not visible. Historically, navigation for posterior approach hip replacement surgery has been performed by recording the anatomical features of the anterior pelvic plane. Once the patient is initially in the supine position and this plane is recorded by a navigation computer, the patient is moved to the lateral decubitus position to perform the hip surgery. This allows navigation to be performed directly against the recorded anterior pelvic plane. This approach to hip navigation is a suboptimal method for the flow of surgery. This is because the extra movement of the patient from supine to lateral position takes up more time for surgeons and staff, requires breaking sterility, and necessitates re-draping. This is one of the key reasons why hip navigation is not adopted by the majority of the market.

[0006] Furthermore, altered leg length is a common patient condition resulting from hip replacement surgery and is a common cause of medical malpractice lawsuits arising from hip replacement surgery. Some hip replacement surgeries require accurate measurement of the patient's leg length and joint offset, and since these measurements are often difficult to visualize using conventional equipment, there is an opportunity to improve surgeons' ability to perform these measurements using computer technology. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] U.S. Patent No. 8,118,815 [Patent Document 2] U.S. Patent Application Publication No. 2010 / 0076505 [Patent Document 3] U.S. Patent No. 8,057,479 [Patent Document 4] U.S. Patent Application No. 13 / 011815 [Overview of the project] [Problems that the invention aims to solve]

[0008] There is a need for improved systems and methods to provide proper alignment of the patient's anatomical structure and the components of the hip joint during hip replacement surgery. This may include modular systems with low-profile components. This may include camera components designed to read length measurements. This may include techniques for measuring leg length and joint offset. This may include techniques for placing one or more points on a fixed femoral tracker. [Means for solving the problem]

[0009] In some embodiments, a hip joint navigation system is provided. The hip joint navigation system may include a fixture comprising a fixation base configured to be fixed to the patient's pelvis. The hip joint navigation system may include an optical component connected to the fixture and having at least one degree of freedom relative to the fixation base. In some embodiments, the optical component is configured to project light toward a portion of the patient's limb. In some embodiments, the optical component is configured to determine the orientation of the limb before and / or after surgery.

[0010] The hip joint navigation system may include an inertial sensor connected to a fixture and having at least one degree of freedom relative to a fixed base. In some embodiments, the optical component and the inertial sensor are separate components. In some embodiments, the optical component and the inertial sensor are integrated into a single housing. In some embodiments, the inertial sensor is connected to the fixture to enable multi-axis motion between the inertial sensor and the fixed base. In some embodiments, the optical component is connected to the fixture to enable multi-axis motion between the optical sensor and the fixed base. In some embodiments, the optical component is rotatable around an axis in addition to multi-axis motion. In some embodiments, the optical component is configured to be positioned independently of the inertial sensor.

[0011] In some embodiments, the optical component is coupled to a fixture to allow multi-axis movement between the optical sensor and a fixed base. In some embodiments, the optical component is rotatable around an axis in addition to multi-axis movement. In some embodiments, the optical component comprises a laser. In some embodiments, the optical component is configured to move up and down in pitch to adjust the position of the light along the limb. In some embodiments, the optical component is configured to tilt toward and away from the pelvis to sweep the light along the limb. In some embodiments, the optical component is configured to swivel from side to side to sweep the light across the limb. In some embodiments, the optical component is configured to rotate to change the orientation of the plane relative to the limb. The hip joint navigation system may include a probe coupled to a fixture.

[0012] In several embodiments, a method for performing hip replacement surgery is provided. This method may include the step of positioning the patient's limb in an extended position. This method may include the step of attaching an optical component to the pelvis adjacent to the hip joint. This method may include the step of projecting light onto the limb to illuminate a portion of the limb away from the hip joint. This method may include the step of recording the position of incidence of the light. This method may include the step of replacing the hip joint, or a portion thereof, with a prosthetic hip joint. This method may include the step of projecting light onto the limb to confirm the orientation of the femur relative to the pelvis.

[0013] This method may include a step of recording a portion of the proximal thigh adjacent to the hip joint. This method may include a step of recording a portion of the proximal thigh adjacent to the hip joint to confirm leg length and / or joint offset. In some embodiments, the step of recording a portion of the proximal thigh includes recording the femur at the greater trochanter. This method may include a step of attaching a multi-joint member to the pelvis and connecting an optical component to the multi-joint member. In some embodiments, the multi-joint member comprises a ball joint. This method may include a step of articulating an optical component to direct a laser beam to a portion of the limb. This method may include a step of locking an articulated member into a fixed structure and maintaining that fixed structure while replacing the hip joint. In some embodiments, the recording step includes marking points on the surface of the limb that coincide with the light. In some embodiments, the recording step includes capturing photographic images of the light and the limb. In some embodiments, the step of projecting light onto the limb to confirm the orientation of the femur relative to the pelvis includes reconstructing the recorded position by aligning the limb with the incident light. This method may include a step of constraining the movement of the foot relative to the lower limb during light projection. In some embodiments, the optical components are housed within a housing that includes an inertial measuring unit. This method may include a step of connecting the optical components and the inertial measuring unit to a fixture. This method may include a step of adjusting the optical components independently of the inertial measuring unit. In some embodiments, the optical components and the inertial measuring unit are separate components. This method may include a step of connecting the fixture to the pelvis, where the inertial measuring unit has at least one degree of freedom relative to the pelvis. In some embodiments, the optical components have additional degrees of freedom relative to the pelvis. This method may include a step of connecting the fixture to the pelvis, where the optical components have at least one degree of freedom relative to the pelvis.

[0014] In some embodiments, a method for performing hip replacement surgery is provided. This method may include the step of attaching an optical component to the pelvis adjacent to the hip joint. This method may include the step of recording a portion of the proximal thigh adjacent to the hip joint. This method may include the step of projecting light from the optical component onto the limb to confirm the agreement between the preoperative orientation of the femur and pelvis and the postoperative orientation of the femur and pelvis. This method may include the step of recording a portion of the proximal thigh adjacent to the hip joint to confirm the postoperative leg length and / or joint offset.

[0015] The method may include the step of connecting the optical components and the inertial measuring unit to a fixture. The method may also include the step of adjusting the optical components independently of the inertial measuring unit. In some embodiments, the optical components and the inertial measuring unit are separate components. The method may include the step of connecting the fixture to the pelvis, where the inertial measuring unit has at least one degree of freedom relative to the pelvis. In some embodiments, the optical components have additional degrees of freedom relative to the pelvis. The method may include the step of connecting the fixture to the pelvis, where the optical components have at least one degree of freedom relative to the pelvis.

[0016] In some embodiments, a hip navigation system is provided. The hip navigation system may include a base comprising a base through which at least one channel for receiving a pin for attaching the base to the pelvis, and a mounting feature disposed on its upper surface. The hip navigation system may include a recording fixture connected to the base and configured to engage with anatomical landmarks. In some embodiments, a hip navigation system is provided. The hip navigation system may include a base comprising a base comprising at least one channel through which a fastener for attaching the base to the pelvis is disposed, and the base comprises a mounting feature disposed on its surface. The hip navigation system may include a recording fixture connected to the base and configured to engage with anatomical landmarks.

[0017] In some embodiments, the base has a bottom surface configured to be positioned on the pelvis, the bottom surface having two channels for receiving a screw-type member for at least one channel to engage with the pelvis. In some embodiments, the base has a bottom surface configured to be positioned on the pelvis, the bottom surface having two channels for receiving a fastener for at least one channel to engage with the pelvis. In some embodiments, the mounting part has a latch feature for detachably securing the tower to the base. In some embodiments, the mounting feature has a latch feature for detachably securing the tower to the base. In some embodiments, the tower has a lower end configured to be secured to the mounting part and an upper end configured to be secured to an inertial sensor assembly. In some embodiments, the upper end is positioned at an angle (e.g., 35 degrees) with respect to the lower end of the tower. In some embodiments, the upper end is positioned at an angle of about 35 degrees with respect to the lower end of the tower. In some embodiments, the mounting feature is positioned between the lower and upper ends of the tower, and the mounting feature is configured to be connected to a recording fixture. In some embodiments, a secondary mounting feature is positioned between the lower and upper ends of the tower, and this secondary mounting feature is configured to connect to a recording fixture. In some embodiments, the mounting feature includes a ball joint for detachably securing the tower to a base. In some embodiments, the tower includes a lower end configured to be fixed to a mounting section and an upper end configured to be fixed to an inertial sensor assembly. In some embodiments, the upper end is positioned at an angle of about 35 degrees with respect to the lower end of the tower. In some embodiments, a secondary mounting feature is positioned between the lower and upper ends of the tower, and this secondary mounting feature is configured to connect to a recording fixture. In some embodiments, the recording fixture includes an elongated member configured to connect to a base, a housing having at least two degrees of freedom with respect to the elongated member, and a probe slidably disposed through the housing. In some embodiments, the probe includes a distal portion inclined with respect to its proximal portion.In some embodiments, the probe is substantially straight along its length. In some embodiments, the probe includes a machine-readable feature positioned on its side. In some embodiments, the machine-readable feature includes a binary code or other symbol. In some embodiments, the recording fixture housing includes a sensor mounting section configured to be releasably attached to a sensor unit for positioning the sensor unit for reading the readable feature. The hip navigation system may include a sensor unit adapted to optically detect a machine-readable feature on the probe when coupled with the sensor mounting section.

[0018] In some embodiments, a femoral fixture is provided. The femoral fixture may include a base configured to reliably connect to the proximal surface of the femur. The femoral fixture may include a reference coordinate system member configured to be positioned on the base, having a plurality of reference coordinate system targets. In some embodiments, a femoral fixture is provided. The femoral fixture may include a base configured to reliably connect to the proximal surface of the femur, the base including a plurality of recording points. The femoral fixture may include a reference coordinate system member configured to contact the plurality of recording points. In some embodiments, the base has at least one hole through which it is configured to receive a screw pin for securing the base to the femur. In some embodiments, the base has at least one hole through which it is configured to receive one or more fasteners for securing the base to the femur. In some embodiments, the member is detachably attached to the base and comprises an elongated upright member and an inclined portion configured to be generally oriented along the long axis of the femur. In some embodiments, the reference coordinate system member comprises an elongated upright member and an inclined portion configured to be oriented generally along the long axis of the femur. In some embodiments, the base is configured to be attached to the proximal femur within an incision before hip dislocation. In some embodiments, the reference coordinate system member is accessible by a reference probe connected to the pelvis during use. In some embodiments, the reference coordinate system member is connected to the pelvis during use.

[0019] In some embodiments, the system includes a femoral fixture and provides a module for comparing the anatomical placement of the hip joint before and after surgery. In some embodiments, this module is adapted to compare the anatomical placement of the hip joint before and after surgery using anatomical landmark information obtained from the acetabular rim. In some embodiments, this module is adapted to include multiple recording points on the rim of the acetabular shell implant in order to calculate the center of rotation (COR) of the hip joint. In some embodiments, this module is adapted to calculate at least one of the following: a change in angle between the pelvis and the femur, a change in leg length, and joint offset. In some embodiments, if a threshold for joint angle, leg length, or offset is exceeded, the system displays an error message along with guidance on repositioning the femur. In some embodiments, this guidance advises the user to abduct / addduct, flex / extend, and / or internally / externally rotate the femur. In some embodiments, the base and reference coordinate system member are located on opposite sides of the same member. In some embodiments, this same member comprises a slender plate structure. In some embodiments, this member is configured to be thin to conform to the femur.

[0020] In some embodiments, a sensor unit for orthopedic navigation is provided. This sensor unit may include a housing having an elongated structure. This sensor unit may include an inertial sensor at least partially disposed within the housing. This sensor unit may include a camera at least partially disposed within the housing, the camera being oriented transversely to the longitudinal axis of the housing. In one embodiment, the sensor unit has a transparent area on its side surface.

[0021] A sensor unit with a camera disposed within a housing can be combined with one or more other components within one or more systems. A system including the sensor unit can be coupled to a jig that includes a coupler for holding the sensor unit fixed relative to a device to be observed by the camera. The sensor unit can be oriented in its width or height extending along an expandable probe. The jig can include a sliding bearing to enable the probe to be moved while the probe moves along a range and passes through a field of view area towards which the camera is directed. The probe can include a binary code or other symbols that can be read by the camera. In another system, the sensor unit is coupled to a user interface device. The user interface device can be positioned within the surgical field during use. The user interface device can be coupled to a jig configured to be attached to a bone, for example, the pelvis, during use.

[0022] In some embodiments, an orthopedic navigation method is provided. The method can include detecting the orientation or position of a probe using an inertial sensor. The method can include detecting the extension of the probe using a camera. In some embodiments, the camera is positioned directly above the probe.

[0023] In some embodiments, a patient-specific jig system for hip replacement is provided. The patient-specific jig system can include an engagement surface formed to closely couple with the bone contour of a particular patient's acetabulum. The patient-specific jig system can include a recording feature configured to be in a predetermined orientation relative to the patient's acetabular fossa when the jig is coupled to the bone contour of a particular patient's acetabulum.

[0024] This patient-specific jig system can include anatomical engagement portions. This patient-specific jig system can include a recording portion disposed outside the anatomical engagement portion and disposed in a region outside the acetabular rim. The patient-specific jig system can include a recording channel extending from the front surface of the recording portion toward the rear surface of the recording portion.

[0025] This patient-specific jig system can include a mounting base that is coupled to the pelvis adjacent to the acetabular fossa and is configured to be spaced apart from the closest part of the jig when the engagement surface engages the acetabular bone contour. This patient-specific jig system can include an inertial sensor device. In some embodiments, the recording feature comprises a recess extending from the exposed surface of the jig. This patient-specific jig system can include a channel extending from the front face of the jig to the rear side, the channel being configured to receive a mounting pin of a navigation system. This patient-specific jig system can include at least two channels extending from the front face of the jig to the rear side, the channels being configured to receive a mounting pin of a navigation system. In some embodiments, the channels are arranged in an orientation relative to the plane of the acetabular fossa.

[0026] In some embodiments, a patient-specific method is provided. The method can include the step of coupling a patient-specific jig to the edge of the acetabular fossa. The method can include the step of recording a surrogate orientation of the plane of the acetabular rim using an inertial sensor device coupled to the patient-specific jig. The method can include the step of removing the patient-specific jig from the acetabular fossa. The method can include the step of orienting the acetabular shell within the acetabular fossa using an impactor and the inertial sensor device, and during the orientation, the inertial data from the inertial sensor device is used to confirm the proper orientation of the acetabular shell.

[0027] In some embodiments, the inertial sensor device is a first inertial sensor, further comprising mounting a base on the pelvis adjacent to the acetabular fossa, and connecting a second inertial sensor to the base, the second inertial sensor being fixed to the pelvis. In some embodiments, the base is mounted in a position independent of the patient-specific fixture. In some embodiments, the second inertial sensor is configured to track pelvic movement and generate an output that eliminates errors caused by pelvic movement. In some embodiments, the second inertial sensor includes a display that provides a user interface. This method may include the step of connecting the first inertial sensor to the base in order to relate the orientation data of the first inertial sensor to the reference coordinate system of the second inertial sensor. In some embodiments, mounting the base includes inserting at least a fixing pin through the patient-specific fixture along an axis positioned at a predetermined angle corresponding to the reference coordinate system of the second inertial sensor. In some embodiments, mounting the base includes inserting at least two fixing pins through a patient-specific fixture along axes positioned at predetermined angles corresponding to the reference coordinate system of a second inertial sensing device. In some embodiments, recording includes connecting the inertial sensor device to the impactor and connecting the impactor to the patient-specific fixture. In some embodiments, recording includes linking the distal portion of the impactor to the fixture's recorded features at a specific predetermined angular position. In some embodiments, recording includes aligning the inertial sensing device with orientation symbols on the patient-specific fixture before connecting the impactor to the patient-specific fixture. This method may include the step of connecting the inertial sensor device to the impactor. This method may include the step of changing the orientation of the impactor in response to an output reflecting inertial data generated by the inertial sensing device. This method may include the step of aligning the acetabular shell to a target anterior tilt angle. This method may include the step of aligning the acetabular shell to a target tilt angle. This method may include a step of aligning the acetabular shell to a target anterior tilt angle.

[0028] In several embodiments, a method for performing hip replacement surgery is provided. This method may include the step of positioning the patient in a supine position with the leg at the hip joint in an extended position. This method may include the step of attaching a laser projection device to the pelvis adjacent to the hip joint. This method may include the step of projecting laser light onto the leg to illuminate a portion of the leg away from the hip joint. This method may include the step of recording the incident position of the laser light. This method may include the step of recording a portion of the proximal thigh adjacent to the hip joint. This method may include the step of replacing the hip joint with an artificial hip joint. This method may include the step of projecting laser light onto the leg and / or foot to confirm the orientation of the femur relative to the pelvis. This method may include the step of recording a portion of the proximal thigh adjacent to the hip joint to confirm the leg length and / or offset.

[0029] This method may include the steps of attaching a multi-joint member to the pelvis and connecting a laser projection device to the multi-joint member. In some embodiments, the multi-joint member comprises a ball joint. This method may include the step of articulating a laser projection device to direct a laser beam to a portion of the foot of the leg. This method may include locking the articulated member into a fixed structure and maintaining this fixed structure from the step of projecting a laser beam onto the leg to illuminate at least a portion of the leg away from the hip joint, to the step of projecting a laser beam onto the leg and / or foot to confirm the orientation of the femur relative to the pelvis. In some embodiments, recording includes marking three points on the surface of the leg and foot that coincide with the laser beam. In some embodiments, recording includes capturing the laser beam and photographic images of the leg and / or foot. In some embodiments, recording a portion of the proximal thigh includes recording the femur at the greater trochanter. In some embodiments, the step of projecting a laser beam onto the leg and / or foot to confirm the orientation of the femur relative to the pelvis includes reproducing the recorded position by aligning the incident light with the leg and / or foot. This method may include, in at least one of the steps of recording the incident position of the laser beam and projecting the laser beam onto the leg and / or foot to confirm the orientation of the femur relative to the pelvis, the step of restraining the movement of the foot relative to the leg. In some embodiments, the laser projection device is housed in a housing that includes an inertial measuring unit.

[0030] In some embodiments, a method for performing hip replacement surgery is provided. This method may include the step of attaching a laser projection device to the pelvis adjacent to the hip joint. This method may include the step of recording a portion of the proximal thigh adjacent to the hip joint. This method may include the step of projecting laser light from the laser projection device onto the leg and / or foot to confirm the agreement between the preoperative orientation of the femur and pelvis and the postoperative orientation of the femur and pelvis. This method may include the step of recording a portion of the proximal thigh adjacent to the hip joint to confirm the leg length and / or offset.

[0031] Those features, embodiments and advantages, as well as other features, embodiments and advantages, are described below with reference to the drawings. This is intended to be illustrated but is not intended to limit the present invention. In the drawings, similar reference numerals consistently indicate corresponding features throughout similar embodiments. [Brief explanation of the drawing]

[0032] [Figure 1] This is a perspective view of a hip joint navigation system applied to a patient, illustrating the measurement of leg length and / or joint offset after artificial hip joint implantation. [Figure 2] Figure 1 is an image of the anatomical structure of the hip joint illustrating some examples of anatomical landmarks that can be used in navigating a prosthetic hip joint using the navigation system. [Figure 3] This figure shows the first anatomical landmark, in this case the navigation base assembly connected to the ilium on the patient's pelvis. [Figure 4] Figure 3 is a perspective view illustrating the first orientation detection device and the second orientation detection device connected to the base assembly. [Figure 5] Figure 1 is a perspective view of the navigation system illustrating a technique for synchronizing multiple orientation and / or position detection devices in the navigation system. [Figure 6]Figure 1 is a perspective view of the navigation system connected to the pelvis, illustrating the stage of recording femoral landmarks before femoral resection. [Figure 7] This figure shows the anatomical structure after the femoral head has been removed, and the optional steps for synchronizing multiple inertial sensors in the navigation system. [Figure 8] This diagram illustrates the steps involved in recording anatomical landmarks located on the acetabular rim of the pelvis. [Figure 9] This diagram illustrates the steps involved in recording other anatomical landmarks located in relation to the acetabular rim of the pelvis. [Figure 10] This diagram illustrates the initial placement of the impactor in the acetabular fossa. [Figure 11] This diagram illustrates an artificial hip joint placement system including an inertia detection device. [Figure 11A] This figure illustrates an embodiment of an impactor assembly. [Figure 11B] This figure illustrates an embodiment of an impactor assembly. [Figure 11C] This figure illustrates an embodiment of an impactor assembly. [Figure 12] This diagram illustrates the steps involved in navigating the placement of the cup portion of an artificial hip joint. [Figure 13] This is a perspective view of another embodiment of the hip joint navigation system. [Figure 14] This is a detailed view of the system in Figure 13, showing the state in which the camera records the linear position of the recording arm. [Figure 15] This figure shows a modified example of the embodiment shown in Figures 13 and 14, in which the rotational direction and linear position can be acquired by a camera that views the radial scale. [Figure 16] This is an exploded view of an assembly showing a tilt / rotation mechanism adapted to allow the camera to track at least one rotational position. [Figure 17] This diagram illustrates a modification system configured to navigate posterior approach hip replacement surgery. [Figure 17A] This diagram illustrates a modification system configured to navigate posterior approach hip replacement surgery. [Figure 17B] This diagram illustrates a modification system configured to navigate posterior approach hip replacement surgery. [Figure 17C-1] This diagram illustrates a modification system configured to navigate posterior approach hip replacement surgery. [Figure 17C-2] This diagram illustrates a modification system configured to navigate posterior approach hip replacement surgery. [Figure 18] This is a perspective view of a hip joint navigation system applied to a patient. [Figure 19] Figure 18 is a perspective view of the fixing pins of the system. [Figure 20A] Figure 18 illustrates an embodiment of the fixed base. [Figure 20B] Figure 18 illustrates an embodiment of the fixed base. [Figure 20C] Figure 18 illustrates an embodiment of the fixed base. [Figure 20D] Figure 18 illustrates an embodiment of the fixed base. [Figure 20E] Figure 18 illustrates an embodiment of the fixed base. [Figure 20F] Figure 18 illustrates an embodiment of the fixed base. [Figure 20G] Figure 18 illustrates an embodiment of the fixed base. [Figure 20H] Figure 18 illustrates an embodiment of the fixed base. [Figure 21A] This figure illustrates an embodiment of the first assembly shown in Figure 18. [Figure 21B] This figure illustrates an embodiment of the first assembly shown in Figure 18. [Figure 21C] This figure illustrates an embodiment of the first assembly shown in Figure 18. [Figure 21D]This figure illustrates an embodiment of the first assembly shown in Figure 18. [Figure 21E] This figure illustrates an embodiment of the first assembly shown in Figure 18. [Figure 21F] This figure illustrates an embodiment of the first assembly shown in Figure 18. [Figure 21G] This figure illustrates an embodiment of the first assembly shown in Figure 18. [Figure 22A] This figure illustrates an embodiment of the second assembly shown in Figure 18. [Figure 22B] This figure illustrates an embodiment of the second assembly shown in Figure 18. [Figure 22C] This figure illustrates an embodiment of the second assembly shown in Figure 18. [Figure 22D] This figure illustrates an embodiment of the second assembly shown in Figure 18. [Figure 22E] This figure illustrates an embodiment of the second assembly shown in Figure 18. [Figure 22F] This figure illustrates an embodiment of the second assembly shown in Figure 18. [Figure 23A] Figure 18 is a diagram illustrating an embodiment of the orientation detection device. [Figure 23B] Figure 18 is a diagram illustrating an embodiment of the orientation detection device. [Figure 23C] Figure 18 is a diagram illustrating an embodiment of the orientation detection device. [Figure 24A] Figure 18 illustrates an embodiment of the femoral tracker. [Figure 24B] Figure 18 illustrates an embodiment of the femoral tracker. [Figure 25A] This is a diagram of a hip joint navigation system applied to a patient. [Figure 25B] This is a diagram of a hip joint navigation system applied to a patient. [Figure 25C] This is a diagram of a hip joint navigation system applied to a patient. [Figure 26A] Figure 25A illustrates an embodiment of the fixed base. [Figure 26B]Figure 25A illustrates an embodiment of the fixed base. [Figure 26C] Figure 25A illustrates an embodiment of the fixed base. [Figure 27A] Figure 25C illustrates an embodiment of the femoral tracker. [Figure 27B] Figure 25C illustrates an embodiment of the femoral tracker. [Figure 27C] Figure 25C illustrates an embodiment of the femoral tracker. [Figure 27D] Figure 25C illustrates an embodiment of the femoral tracker. [Figure 27E] Figure 25C illustrates an embodiment of the femoral tracker. [Figure 28A] Figure 25C illustrates an embodiment of the femoral tracker. [Figure 28B] Figure 25C illustrates an embodiment of the femoral tracker. [Figure 28C] Figure 25C illustrates an embodiment of the femoral tracker. [Figure 29] This is a diagram showing the X-ray image taken before surgery. [Figure 30] This diagram illustrates the preoperative position of the patient for posterior approach techniques. [Figure 31] This diagram illustrates the structure of the system shown in Figure 18. [Figure 32] This is a diagram illustrating anatomical landmarks recorded in several embodiments. [Figure 33] This diagram illustrates the first set of points on the edge of the shell. [Figure 34] This figure illustrates anterior approach hip replacement surgery and a hip replacement navigation system configured for various aspects of such surgery. [Figure 35] This figure illustrates anterior approach hip replacement surgery and a hip replacement navigation system configured for various aspects of such surgery. [Figure 36A]This figure illustrates anterior approach hip replacement surgery and a hip replacement navigation system configured for various aspects of such surgery. [Figure 36B] This figure illustrates anterior approach hip replacement surgery and a hip replacement navigation system configured for various aspects of such surgery. [Figure 37] This figure illustrates anterior approach hip replacement surgery and a hip replacement navigation system configured for various aspects of such surgery. [Figure 38] This figure illustrates anterior approach hip replacement surgery and a hip replacement navigation system configured for various aspects of such surgery. [Figure 39] This figure illustrates the position of the system in Figure 18 during the forward approach. [Figure 40] This diagram illustrates the position of another hip navigation system during an anterior approach. [Figure 41] This diagram illustrates the position of another hip navigation system during an anterior approach. [Figure 42] This diagram illustrates the position of another hip navigation system during an anterior approach. [Figure 43] This diagram illustrates various embodiments of a method that includes patient-specific positioning jigs. [Figure 44] This diagram illustrates various embodiments of a method that includes patient-specific positioning jigs. [Figure 45] This diagram illustrates various embodiments of a method that includes patient-specific positioning jigs. [Figure 46] This diagram illustrates various embodiments of a method that includes patient-specific positioning jigs. [Figure 47] This diagram illustrates various embodiments of a method that includes patient-specific positioning jigs. [Figure 48] This diagram illustrates various embodiments of a method that includes patient-specific positioning jigs. [Figure 49] This diagram illustrates various embodiments of a method that includes patient-specific positioning jigs. [Figure 50] This diagram illustrates various embodiments of a method that includes patient-specific positioning jigs. [Figure 51] This diagram illustrates various embodiments of a method that includes patient-specific positioning jigs. [Figure 52] This diagram illustrates various embodiments of a method that includes patient-specific positioning jigs. [Figure 53] This diagram illustrates an embodiment of a method that includes a patient-specific positioning jig. [Figure 54] This diagram illustrates an embodiment of a method that includes a patient-specific positioning jig. [Figure 55] This diagram illustrates an embodiment of a method that includes a patient-specific positioning jig. [Figure 56A] This diagram illustrates an embodiment of a method that includes a patient-specific positioning jig. [Figure 56B] This diagram illustrates an embodiment of a method that includes a patient-specific positioning jig. [Figure 56C] This diagram illustrates an embodiment of a method that includes a patient-specific positioning jig. [Figure 56D] This diagram illustrates an embodiment of a method that includes a patient-specific positioning jig. [Figure 56E] This diagram illustrates an embodiment of a method that includes a patient-specific positioning jig. [Figure 56F] This diagram illustrates an embodiment of a method that includes a patient-specific positioning jig. [Figure 57] This diagram illustrates an embodiment of a method that includes a patient-specific positioning jig. [Figure 58A] This diagram illustrates an embodiment of a method that includes a patient-specific positioning jig. [Figure 58B] This diagram illustrates an embodiment of a method that includes a patient-specific positioning jig. [Figure 59] This diagram illustrates an embodiment of a method that includes a patient-specific positioning jig. [Figure 60] This diagram illustrates an embodiment of a method that includes a patient-specific positioning jig. [Figure 61A] This diagram illustrates an embodiment of a method that includes a patient-specific positioning jig. [Figure 61B] This diagram illustrates an embodiment of a method that includes a patient-specific positioning jig. [Figure 62] This diagram illustrates an embodiment of a method that includes a patient-specific positioning jig. [Figure 63] This diagram illustrates an embodiment of a method that includes a patient-specific positioning jig. [Figure 64] This diagram illustrates a method for defining a patient-specific safety zone during hip joint repositioning surgery. [Figure 65] This figure shows an embodiment of a system for short-range optical tracking. [Figure 66] This diagram illustrates various anatomical landmarks that can be used in a variety of ways, including navigating by landmarks. [Figure 67] This diagram illustrates various anatomical landmarks that can be used in a variety of ways, including navigating by landmarks. [Figure 68] This is a pre-operative image that can be used to improve positioning in hip replacement surgery by providing patient-specific data. [Figure 69] This is a diagram of a hip replacement surgery navigation system applied to the pelvis in a posterior approach. [Figure 70] This is a diagram of a hip replacement surgery navigation system applied to the pelvis in a posterior approach. [Figure 71] Figures 37-38 show a modified hip replacement surgery navigation system applied to the pelvis in an anterior approach. [Figure 72] Figures 37-38 show a modified hip replacement surgery navigation system applied to the pelvis in an anterior approach. [Figure 73] This figure illustrates a first embodiment of the pin fixing device. [Figure 73A] This figure illustrates a first embodiment of the pin fixing device. [Figure 74]This figure illustrates a second embodiment of the pin fixing device. [Figure 74A] This figure illustrates a second embodiment of the pin fixing device. [Figure 74B] This figure illustrates a second embodiment of the pin fixing device. [Figure 75] This figure illustrates a third embodiment of the pin fixing device. [Figure 75A] This figure illustrates a third embodiment of the pin fixing device. [Figure 75B] This figure illustrates a third embodiment of the pin fixing device. [Figure 76] This diagram illustrates a modular system having optical components. [Figure 77] This diagram illustrates a modular system having optical components. [Figure 78] This diagram illustrates a modular system having optical components. [Figure 79] This diagram illustrates a modular system having optical components. [Figure 80] This diagram illustrates a modular system having optical components. [Figure 81] This diagram illustrates a modular system having optical components. [Figure 82] This diagram illustrates a modular system having optical components. [Figure 83] This diagram illustrates a modular system having optical components. [Figure 84] This diagram illustrates a modular system having optical components. [Figure 85] This diagram illustrates a modular system having optical components. [Modes for carrying out the invention]

[0033] Various systems and methods that can be used to improve patient outcomes by increasing the possibility of proper hip joint positioning are discussed below. These systems may focus on inertial navigation techniques, short-range optical navigation, or a combination of inertial and optical navigation.

[0034] [I. Hip joint navigation using inertial sensors] The systems and methods described below can improve the placement of a prosthesis using navigation in relation to referencing multiple anatomical landmarks, and incorporate specially adapted preoperative fixtures based on a combination of imaging and landmark referencing. These hip replacement surgeries generally guide the prosthesis to an orientation within the acetabular fossa that minimizes the possibility of dislocation due to impingement of the femoral neck over the bone around the cup or acetabular fossa, or other reasons related to the suboptimal orientation of the prosthesis. Various techniques utilize the population average of appropriate placement, while others accept patient-specific modifications. Similarly, various techniques for recording and confirming the position and / or orientation of the femur before and after implantation are discussed in this specification. This is useful for controlling leg length and joint offset at the end of surgery.

[0035] [A. Navigation using multiple inertial sensors and fixtures for referencing anatomical landmarks via a posterior approach] Currently, the majority of hip replacement surgeries are performed via a posterior approach. In this approach, the patient is positioned to the side, with the anterior pelvic plane oriented perpendicularly, for example, perpendicular to the plane of the operating table on which the patient is positioned. Many surgeons performing hip replacement surgeries are familiar with this approach and will immediately recognize the innovative advantages in terms of anatomical orientation when the patient is in this position.

[0036] [1. Rear approach: A system using an orientation detection device connected to the probe] Figures 1 and 4 show the hip joint navigation system 100. This hip joint navigation system 100 is configured to navigate hip joint surgery by referencing anatomical landmarks without requiring preoperative imaging or other inputs, except those discussed below, although these do not necessarily need to be excluded. The hip joint navigation system 100 attached to the pelvis in a posterior approach is shown in Figure 1. Figure 4 shows an early stage of surgery after the hip joint navigation system 100 has been attached to the pelvis, before the joint has been dislocated. Figure 1 shows a later stage of some modifications of the technique to which the hip joint navigation system 100 is adapted. As will be further discussed below, such modifications include recording the femur before and after the joint is replaced to confirm the relative position and / or orientation of the femur, e.g., leg length, joint offset, and rotational orientation of the femoral neck.

[0037] The hip joint navigation system 100 includes a recording jig 104, a positioning assembly 108, and a landmark acquisition assembly 112. The positioning assembly 108 is rigidly connected to the hip joint in the illustrated structure, so that hip joint movement causes corresponding movement of sensors in the positioning assembly 108, as discussed below. Detecting this movement allows the hip joint navigation system 100 to rule out patient movement as a cause of navigation errors. The landmark acquisition assembly 112 provides a maximum range of controlled movement and, in cooperation with the sensors in the positioning assembly 108, a maximum range of sensors capable of tracking movement. Additional details of the system, apparatus, sensors, and methods are described in U.S. Patent No. 8,118,815; U.S. Patent Application No. 2010 / 0076505; and U.S. Patent No. 8,057,479, all of which are incorporated herein by reference as a whole for all purposes. The sensors in the alignment assembly 108 and the landmark acquisition assembly 112 preferably transfer data between them, and in some cases wirelessly transfer the data to external devices and monitors using Bluetooth®, Wi-Fi®, or other standard wireless telemetry protocols.

[0038] The recording jig 104 includes a fixation cannula 124 having a distal end, which can be advanced into the pelvic bone at an anatomical location, an anatomical landmark, or another selected location. In the illustrated technique, the fixation cannula 124 is fixed by a pin 132 which is driven into the ilium on the pelvis through the fixation cannula 124 (as seen in Figure 3). The distal end 128 of the pin 132 is shown in Figure 1.

[0039] Furthermore, as will be discussed below, the fixation cannula 124 can be connected to other bones in other techniques by a posterior approach. For example, the fixation cannula 124 can be connected to the ischium or pubis in other techniques. In some techniques, the fixation cannula 124 is attached to the pelvic bone rather than a landmark. The hip joint navigation system 450 discussed below in relation to Figures 17-17C-2 can be used such that the fixation member 466 is connected at a point above the uppermost point on the acetabular rim. In certain techniques, the fixation member 466 is approximately 10 mm above the uppermost point on the acetabular rim. In such techniques, three or more anatomical landmarks located around the acetabulum can be acquired as will be discussed below. When the fixation cannula 124 is connected to a landmark, two additional landmarks are acquired in some embodiments as will be discussed below. In other modifications, a clamp can be used to connect to a bone without requiring the pin 132 to be driven into the bone through the fixation cannula 124. For example, if the bone is thinner in the area where system 100 is to be fixed, placing the pin may be disadvantageous. Figure 2 shows the area where a clamp can be used below point "A" on the ischium. One reason for attaching or clamping the fixation cannula 124 away from the landmark is that the landmark may not be visible or accessible before dislocating the hip. If the clinician wants to use system 100 to reference the femur (as discussed below), attaching or clamping the fixation cannula 124 away from the landmark may be necessary.

[0040] Figure 1 illustrates the stages toward the end of a navigated hip joint transplant surgery, which are discussed in detail below. Several preceding stages include the stage of removing the joint to be replaced, the stage of navigating the hip joint, the stage of preparing the implantation site for the prosthesis, and the stage of positioning the joint, as will be discussed in detail below. As will be discussed further below, Figure 1 illustrates the techniques for ensuring that these stages are performed correctly.

[0041] Figure 2 shows several anatomical structures related to the various methods and systems of the present invention. In some embodiments, the navigation system 100 is configured to determine appropriate anatomical features to assist in the proper placement of the artificial hip joint. For example, a plane including at least a portion of the patient's acetabular rim can be located using the system 100. In reality, the acetabular rim may not be flat due to the development of osteophytes. In other words, in relation to the present invention, determining an anatomical plane, for example, estimation of the plane, can be an approximation of the actual topography, and the plane may include substantial fragments, such as a large portion of the acetabular rim surface, or several other methods for estimating appropriate anatomical features. Preferably, the determined anatomical landmarks are used to confirm the correct placement of at least the cup, preferably the correct placement of the complete artificial hip joint.

[0042] Figure 2 also illustrates several anatomical landmarks that can be used to approximate the acetabular rim or other planes associated with the acetabular rim. In many patients, the acetabular rim is not well defined due to injury, the progression of arthritis, or other conditions. Therefore, approximating the acetabular rim for those patients involves calculating a plane in system 100 that may refer to most or all of the actual acetabular rim, but may not include most or all of the actual acetabular rim. The defined plane is located adjacent to the acetabular rim, but more importantly, it has known anterior and posterior tilt angles with respect to the anterior pelvic plane. For example, three points can be used to estimate the plane of the acetabular rim. In one technique, some or all of the points illustrated in Figure 2 are used.

[0043] As illustrated in Figure 2, the three landmarks are defined as "A," "B," and "H." Landmark "H" is located on the ilium, at a distance from the acetabular rim sufficient to avoid irregular bone growth due to injury, progression of arthritis, or other conditions, for example, 1 cm above the uppermost point on the acetabular rim. Landmarks "A" and "B" can be located on the ischium and pubis, respectively, and can similarly be spaced away from the acetabular rim to avoid the injured / affected area. Each of these landmarks is preferably sufficiently close to the acetabular rim. However, they are sufficiently close to the acetabular rim because they are within the standard open area, e.g., the area exposed by surgical resection. Other landmarks that may be used include the anterior insertion point of the transverse acetabular ligament relative to the ischium, the midpoint of the inferior surface of the acetabular notch, the anterior superior iliac spine, the anterior inferior iliac spine, the convergence of the acetabular fossa and anterior inferior iliac spine, and other landmarks illustrated in Figures 66 and 67. In the techniques discussed below, the ilium, pubis, and ischium are all used to determine the acetabular rim. The navigation system 100 has one or more processors that receive data and determine the relative positions of those (or other) anatomical landmarks from those points. The data can be generated by a plurality of inertial sensors or by other types of sensors, as discussed throughout this specification. Preferably, the sensors are small enough to be mounted in or within a portable housing, or small enough to be embedded in an instrument. The navigation system 100 also preferably has a recording device to store at least temporarily the position or appropriate orientation data of those points.

[0044] Figure 3 shows further details of the recording jig 104 and further embodiments of the method of navigating the artificial hip joint. The proximal end of the pin 132 is connected to or positioned above the platform 136. The platform 136 is configured to connect to the alignment assembly 108 and / or the landmark acquisition assembly 112. As shown in Figure 1, the platform 136 can be connected to both the alignment assembly 108 and the landmark acquisition assembly 112 simultaneously. In the illustrated embodiment, the platform 136 includes a rigid bar fixed to the proximal end of the pin 132 and / or the cannula 124. The platform 136 includes a plurality of mounting features 140A and 140B, for example, mounting features at each of the two lateral ends 144A and 144B of the platform. Mounting feature 140A is configured to allow non-rotating mounting to the alignment assembly 108.

[0045] Figure 3 illustrates that the recording jig 104 is configured for use in left and right hip surgery, for example, having a dedicated mounting feature 140A for each hip joint. Preferably, the mounting feature 140A provides a post spaced away from the hip joint to be treated, thereby allowing the alignment assembly 108 to be mounted as far away from the hip joint as possible. Figure 5 shows the alignment assembly 108 on this post and another exposed post. The exposed post is not used during the hip surgery illustrated in Figure 5. However, if the patient's other hip joint is to be treated, the platform 136 will be oriented in the opposite direction, and the exposed post in Figure 5 will be connected to the alignment assembly 108. Alternatively, the longitudinal axis of the platform 136 extends between two mounting posts, and each of the two mounting posts can be dedicated to a hip joint on one side of the patient's medial-lateral midplane.

[0046] Mounting feature 140B allows for rotational mounting of the landmark acquisition assembly 112. For example, mounting feature 140B may include a rotatably mounted fixture 148. The fixture 148 protrudes upward to a free end configured to couple with an orientation detection device, as discussed below. The fixture 148 allows a memory arm, such as an elongated member 224, as discussed below, to be tilted downward so that it contacts multiple landmarks at different heights.

[0047] In one technique, the recording fixture 104 is pre-assembled and driven within a suitable anatomical landmark, for example, the ilium. In another technique, the anchor fixture can be mounted offset from the landmark to be acquired. The ilium will be identified in advance by conventional means, for example, by radiography, or by resection and visual inspection of the pelvis. In one technique, the cannula 124, pin 132, and platform 136 are separable, so that the pin is positioned later and the platform 136 is connected to the pin. The cannula 124 can be connected to other landmarks in various modifications.

[0048] Figure 4 illustrates further stages of various technologies. For example, the alignment assembly 108 can be connected to a mounting feature 140A. In one embodiment, the alignment assembly 108 includes a rigid extension 160, which is adapted to be detachably attached to the mounting feature 140A. The rigid extension 160 has a first end 164 and a second end 168. The second end 168 is detachably attached to a surgical orientation device 172, which detects the orientation and rotation of the surgical orientation device 172 with respect to a reference coordinate system. The surgical orientation device 172 preferably includes at least one sourceless sensor, such as an accelerometer, a gyroscope, or a combination of these sensors and other sensors. In one preferred embodiment, the orientation device includes a three-axis accelerometer for detecting orientation relative to gravity and a plurality of gyroscopes for detecting rotation. Other sensors can be used in various modifications. Specific sensor combinations include, among many, the ADIS 16445 from Analog Devices and the MPU-6050 or MPU-9150 from InvenSense. In other approaches, the orientation device 172 may be disposable, and therefore, the sensor is preferably a less expensive sensor. The sensor on the landmark acquisition assembly 112 is reusable in some structures, and therefore, a more expensive, more robust, or more accurate sensor may be incorporated.

[0049] The first end 164 of the detachable extension provides various functions. The first end 164 has a device for engaging the mounting feature 140A in a secure but detachable manner. The engagement between the rigid extension 160 and the platform 136 minimizes or prevents relative movement between them to avoid any mechanical relative movement during navigation surgery. Thereafter, the movement of the orientation device 172 corresponds to the movement of the hip joint. The first end 164 also has a docking device, which provides a stable and controlled method for positioning the landmark acquisition assembly 112 relative to the orientation device 172, as will be discussed further below.

[0050] Figure 4 also illustrates that the landmark acquisition assembly 112 can be securely coupled to the platform 136, for example, at the mounting feature 140B. In one embodiment, the landmark acquisition assembly 112 includes a gimbal-type fixture 200 and an orientation detection device 204. The gimbal-type fixture 200 includes a coupler 208 for detachably coupling to the mounting feature 140B of the platform 136. The coupler 208 is rotatably connected to a slide support 212. The slide support 212 includes a slot that allows for a slidable extension of an elongated member 224. This slidable extension allows the range of motion of the distal end 228 of the elongated member to facilitate the acquisition of multiple landmarks, which are at different distances from the mounting position of the cannula 124, as will be discussed further below. In other words, the distal end 228 can extend away from the axis of the slide support 212, or it can be retracted to a position close to the axis of the slide support 212.

[0051] Figures 4 and 6 illustrate the mobility of the landmark acquisition assembly 112 relative to the platform 136 between two positions. In Figure 4, the elongated member 224 is swung around an axis that can be parallel to the longitudinal axis of the cannula 124, so that the distal end 228 moves away from the first end 164 of the extension 160. This constitutes the movable structure of the gimbal-type fixture 200. In addition to the rotation made possible by the pivot connection between the coupler 208 and the slide support 212, a rotatably mounted joint 148 allows the elongated member 224 to rotate around an axis that is not parallel to the axis of the cannula 124. The axis of rotation of the joint 148 can be perpendicular to the axis of rotation of the slide support 212. This rotatability allows the distal remainder 228 of the elongated member 224 to rotate downward until it contacts the anatomical landmark, as discussed above. Furthermore, the sliding capability of the elongated member 224 within the sliding member 212, as discussed above, allows the distal end 228 to move to reach anatomical landmarks on the same plane, but to approach or move further away from the distal end of the cannula 124 or pin 132. Figure 6 shows the distal end 228 of the elongated member 224 positioned at a higher height or closer to a platform 136 for referencing multiple landmarks, for example, on the lateral surface of the femur.

[0052] Figure 4 also shows that the distal end 228 includes an inclined length, which allows the elongated member 224 to avoid small irregularities at a height adjacent to recorded anatomical landmarks. Such irregularities may be normal anatomical structures, or they may be osteophytes or various types of irregular bone growth.

[0053] Figure 5 illustrates the stopping structure 260 of the landmark acquisition assembly 112. In particular, a portion of the elongated member 224 is moved into a latch 262 located at the first end 164 of the upright extension 160. The stopping structure 260 allows the navigation system 100 to manage errors that may be mixed in several inertial sensors. For example, in one embodiment, the gyroscope sensors in the orientation device 172 and the orientation detection device 204 can be synchronized when a stable, well-known orientation is detected. Then, one or more gyroscopes, for example, the gyroscope of the orientation detection device 204, can be set to zero after the condition is met. Further techniques employed in the stopping structure 260 will be discussed further below. As will be discussed further below in relation to system 450, some fixtures have recording points adjacent to the distal end of the anchor fixture or the bone connection site. System 450 allows for accurate acquisition of landmarks based solely on the accelerometer operating in the orientation detection device 204 in one mode. In such a mode, the recording features can, for example, provide a function similar to a stop structure to improve the accuracy of the detection device in the system.

[0054] Other examples of the stopping structure of system 100 can be provided. For example, the stopping structure advantageously includes the ability to stably position and hold the orientation device 172 and orientation detection device 204, as there is substantially no relative movement. In one approach, the orientation detection device 204 is mounted on the rigid extension 160. Other arrangement configurations may include mounting posts on the platform 136 adjacent to the rigid extension 160.

[0055] When error control is not an issue, the stopping structure 260 can still be useful in preventing unwanted shaking or other movements in the field of surgical procedures.

[0056] In one basic method, the fixture described above is connected to the pelvic bone, the system 100 becomes a stop structure 260, and the sensors are initialized. Initialization may include synchronizing at least two sensors. In some cases, initialization may include setting one or more sensors to zero. In this context, “setting to zero” is a broad term that includes methods for eliminating accumulated errors in the system, methods including any form of sensor reset, and / or methods for ensuring that data from other devices is reliable for at least a certain period of time in one device.

[0057] Figure 6 illustrates an arbitrary stage of acquiring femoral landmarks in connection with hip replacement surgery. The hip joint is positioned in a neutral flexion / abduction position. The landmark acquisition assembly 112 is a retractable structure 266 in which an elongated member 224 is moved by sliding a sliding support 212 to adapt to a relatively short distance from, for example, the platform 136 and the proximal femoral landmark. In one technique, the tip of the distal end 228 is in contact with a portion of the greater trochanter or other portion on the proximal femur. After the landmark has been found and / or contacted, the clinician may mark the femur with a bovie mark, pen mark, suture, or other durable marking. When the tip of the distal end 228 is in contact with the desired landmark, the navigation system 100 processes data from one or more sensors and stores the orientation of one or more centers in the orientation detection device 204. Furthermore, in some embodiments, the elongated member 224 is provided with a scale 226 indicating the position of the tip of the elongated member 224, for example, relative to a cannula 124, or to some other suitable fixation feature of the patient or system 100. By providing a scale 226 to be read by a clinician, the system is simplified and cost-effective.

[0058] After any of the steps illustrated in Figure 6, the proximal thigh can be excised to remove the original ball.

[0059] Figure 7 illustrates, in one advantageous technique, that the user returns the system 100 to the stop structure 260. This step may optionally depend on the timing of femoral resection and the sensors. At this position, the sensors in orientation detection devices 172 and 204 can be initialized again, for example, set to zero. As discussed above, this is one technique to minimize the accumulation of errors in some inertial sensors. By providing this optional step, inexpensive sensors can be used, thereby enabling the system 100 to achieve highly accurate hip replacement while generally helping to manage costs for patients, healthcare institutions, and healthcare management systems.

[0060] Figure 8 illustrates a first extension structure 264 provided in the stage where a second anatomical landmark is acquired or referenced after proximal femoral resection. In particular, an elongated member 224 can be extended and rotated by a fixture 148 to make contact with the appropriate landmark. In one technique, contact is made between the distal end 228 and the ischium. To provide maximum accuracy, this contact may be made within a short period of time, for example, during 20 seconds after being released from the stop structure 260. Once contact is made, the system 100 is configured to store the orientation of the sensing device 204. In one configuration, the orientation is stored after a button on the orientation device 172 or other direct means is pressed. In addition to acquiring the orientation, position values ​​are input into the system. For example, a scale 226 on the elongated member 224 can be read by the user, and the value of that scale is input into the system. In one technique in which the scale 226 is read and input by the user, the orientation device 172 has a user interface having an input device for inputting such variables. As can be seen in the drawings, the scale 226 can actually be two different scales, the two scales of which are used for the retractable structure 266 and the extended structure, respectively. Alternatively, the scale 226 can extend along the entire length of the elongated member 224 to provide a wider range of positions that can be read by a clinician or system, as shown in Figures 13 and 14.

[0061] The extended structure 264 is configured such that the distal end 228 of the elongated member 224 contacts an anatomical landmark located between the medial cranial-caudal plane of the patient and the acetabular fossa of the pelvis.

[0062] Depending on the sensors used and the timing of the landmark acquisition stage in Figure 8, the user can return the system 100 to the stop structure 260, or initialize the system 100 again, or set it to zero.

[0063] Figure 9 illustrates a second extension structure 272 provided after proximal femoral resection, at a stage in which a third anatomical landmark is acquired or referenced. In some techniques, the third anatomical landmark can be acquired before the second anatomical landmark. In the second extension structure, the distal end 228 of the elongated member 224 is moved to contact a landmark such as the pubic bone. To provide maximum accuracy, this contact may be provided within a short period of time, for example, during 20 seconds after being released from the stop structure 260. Once contact is made, the system 100 can store the orientation of the sensing device 204. The orientation can be stored by pressing a button or other user interface device. In some techniques, the orientation and position are input into the system. For example, a scale 226 on the elongated member 224 can be read by a user, and the value of the scale is input into the system. In one technique in which the scale 226 is read and input by a user, the orientation device 172 has an input device, such as a user interface, for inputting such variables.

[0064] The extended structure 272 is configured such that the distal end 228 of the elongated member 224 contacts an anatomical landmark located on the anterior side of the acetabular fossa.

[0065] Once multiple landmarks are acquired, system 100 can determine the bearing of three landmarks, including the bearing of the mounting position of the cannula 124, if the pin is attached to the appropriate landmark. The system can calculate the orientation of the orientation device 172 with respect to a plane containing those three landmarks (or, in other ways, three or more landmarks from other groups). From this, various post-processing can be performed. For example, the orientation (anterior tilt and / or abduction) can be adjusted based on means of knowing the orientation of a plane containing those three landmarks (or, if used, three or more other landmarks) from an anatomical reference plane of the pelvis.

[0066] One variation of system 100 allows the user to select from among several sets of landmarks for use in the above calculation. The method discussed above utilizes the use of three points from the acetabular rim. These points are less affected by localized protrusions on the acetabular rim that may result from disease or deformity. Therefore, they have a low probability of requiring unplanned work during surgery. On the other hand, other sets of landmarks can be selected so that the acetabular rim is freed from deformity. This may be confirmed before surgery. For example, two or three points can be selected on the acetabular rim for landmark acquisition. Landmarks on the acetabular rim are advantageous in that they are easier to access through small excisions. For example, points on the acetabular rim may include the center of the posterior insertion of the transverse acetabular ligament, the center of the anterior insertion of the transverse acetabular ligament, and the uppermost point on the acetabular rim. A group of anatomical landmarks including one or more landmarks other than the acetabulum may include the ilium (in which recording fixture 104 or other anchor members may be inserted), the lowest point of the ischium in the acetabular groove, and the process of the superior pelvic ramus.

[0067] Some techniques involve referring to a fourth point. The fourth point can be used in connection with several forms of patient-specific records. The fourth point may be located elsewhere than the acetabulum, or it may be located on the acetabular rim. An example of an anatomical landmark is the acetabular notch. Other landmarks are discussed in this specification, for example, in relation to Figures 34 and 35.

[0068] The posterior approach system is advantageously configured to allow for intraoperative selection between points on and outside the acetabular rim. For example, the acetabular rim may appear deformed preoperatively but show a different condition when exposed, allowing the surgeon to select a set of landmarks other than the acetabular rim.

[0069] Various techniques can be employed to improve the accuracy of the relationship between multiple detected landmarks and the locations of calculated anatomical features, such as the anterior pelvic plane or the angle of the acetabular fossa. For example, user input indicating whether the hip joint to be treated is on the patient's left or right side, and whether the patient is male or female, can be collected. More accurate estimations of the model can be provided based on the characterization of the research group. For example, the hip joints of a group of patients aged 30 and older can be studied to confirm the correspondence between features that can be accessed by one approach and more surgically relevant anatomical features that cannot be accessed. The target group can be studied for multiple demographic features, such as sex, age, weight, height, or other variable in the people concerned. For those subgroups, correlations or transformations can occur between measured parameters and parameters that cannot be measured but are desirable to know. Once such correlations or transformations are established, the transformation of measured features into useful but unmeasurable features can be achieved by manipulating software on the processor. This software can be programmed to calculate tilt and anterior tilt based on one or two angles, for example, a recorded pelvic plane such as a surrogate acetabular plane. Such a system can be used to generate in real time the angle of a freehand instrument relative to the anatomical structure, for example, the acetabulum, when positioning the hip socket components.

[0070] Furthermore, data from preoperative imaging or positioning (discussed below) can be used to improve the accuracy of those calculations. Therefore, the posterior approach system is preferably configured to allow the user to input data directly by activating a button on the orientation device 172, by connecting an auxiliary data storage device such as a flash memory device to the system, or by other means of communication with the system, including Wi-Fi® connection, Bluetooth®, and Internet connection.

[0071] In some techniques, the posterior approach system described herein is adapted to determine, monitor, and verify appropriate leg length and joint offset results in hip replacement. For example, system 100 can calculate and store components of a leg length criterion, e.g., a vector along the superior-inferior axis (leg length) and / or a vector along the medial-lateral axis (offset). In one approach, device 172 has a display indicating when the femur is in the same position before and after surgery. For example, it can display "zero (0)," meaning there is no displacement that would cause a change in leg length. "Zero (0)" indicates that there is no movement of the femur further away from the cranial-caudal midplane of the patient before and after surgery. For improved accuracy, multiple points, e.g., three points, can be acquired and / or marked on the femur. These points can be spaced apart by an amount sufficient to provide increased accuracy. These points can be used to verify the proper placement of the femur in abduction, rotation, and flexion.

[0072] One improvement involves referencing the femoral neck to ensure that the femur rotates and positions correctly after hip transplantation. For example, it may be desirable to ensure that femoral features such as the greater trochanter are in the same rotational orientation with respect to an axis extending through the center of rotation of the femoral head and perpendicular to the plane of the acetabular fossa. To ensure substantially unchanged rotational orientation after transplantation, system 100 can record one or more points on the femoral neck before and after transplantation, for example, three points. (Discussed below in relation to Figures 18-24B) Three points that are easy to use from either a posterior or anterior approach are the greater trochanter, the lesser trochanter, and the insertion of the obturator externus muscle.

[0073] The aforementioned steps are several steps that can be used to determine and memorize various parameters that are beneficial in a navigated hip replacement surgery. After some or all of those steps have been performed, in one embodiment, the acetabular fossa can be prepared to receive the cup. For example, the acetabular fossa can be widened in a conventional manner. In some embodiments, the reamer can be coupled with an orientation device including an inertial sensor to guide the reaming process. This is discussed in some detail in US2010 / 0076505, issued on March 25, 2010. For this purpose and for all disclosures contained herein, this application is incorporated by reference to its entirety.

[0074] Figure 10 shows that after reaming, the impactor 300 can be used to position the cup of the artificial hip joint. The impactor handle 304 can be positioned in an approximate, precise orientation. For example, the longitudinal direction of the impactor is positioned perpendicular to the plane navigated above or a plane determined based on the navigated plane. Figure 10 shows that the initial positioning is performed when the system 100 is set to the stop structure 260. The impactor 300 can be substantially aligned at this point based on visual inspection. As part of the steps illustrated in Figure 10, or immediately thereafter, the sensor can be initialized, for example, set to zero, as discussed above.

[0075] Figure 11 shows that in a later stage, the orientation detection device 204 can be detached from the proximal end 230 of the elongated member 224 and then connected to the impactor 300. Preferably, this step is performed while the impactor 300 is positioned on the hip joint in proximity to proper alignment. In other embodiments, a third detection device similar to the orientation detection device 204 can be connected to the impactor and, for example, pre-mounted on the impactor, and the data collected above is transferred to the third device. The impactor 300 and the detection device 204 comprise a cup orientation navigation system. Preferably, the impactor 300 has a cylindrical shell 312, the cylindrical shell 312 is movable relative to the internal shaft 316 of the handle 304. The shell has a docking device 320, the docking device 320 can receive the docking device of the detection device 204. The mobility of the shell helps to isolate the detection device from the force transmitted through the impactor 300. These forces are applied by a mallet or other device for forcibly moving the cup into place. By providing at least some force isolation between the shell 312 and the sensing device, the impact on the sensor in the sensing device 204 can be reduced. Excessive force applied to the sensing device 204 can cause it to become inoperable, for example, until it is synchronized with device 172.

[0076] Figure 11A illustrates a further embodiment of the impactor 300A. In this further embodiment, the movement of the shell 312A is mitigated by a plurality of spring members 340, 344, which are configured to absorb at least some of the impact shock of the impactor 300A. The impactor 300A is also configured to be modified to suit any of a plurality of hip prostheses. For example, a plurality of end-effectors 348 can be provided in a kit in which each end-effector is attachable to and detachable from the distal end of the shaft 316A of the impactor 300A.

[0077] Figures 11B and 11C show detailed distal features of the impactor 300A. In particular, the tip component 348 is detachable from the shaft 316A of the impactor 300A. Figure 11C shows that the tip component 348 may have a recess 352 formed on its proximal side and an engagement device 356 formed on its distal side. The recess 352 may comprise a plurality of flat sections 350A corresponding to a plurality of flat sections 350B on the distal end of the shaft 316A. The plurality of flat sections allow the recess 352 to slide proximal-distal on the distal end of the shaft 316A. Preferably, a retaining device or other mechanism is provided between the tip component 348 and the shaft 316A so as not to fall off the shaft. These flat sections prevent the tip component 348 from rotating relative to the shaft 316A. The engaging device 356 is equipped with threads in one embodiment, thereby allowing the cup 360 of the prosthesis to be screwed onto the distal end of the tip component 348. The sliding engagement of the tip component 348 on the shaft 316A is important because the impactor 300A is intended to be used with prosthesis hips from various manufacturers. In many cases, the cup 360 will have a pattern of holes for securing the cup to a prepared acetabular fossa. This prepared acetabular fossa is manufacturer-specific and required by anatomical structure. Their flat surfaces allow for many individual, alternate relative angular positions of the tip component 348 (and therefore the cup 360) relative to the shaft 316A. Multiple grooves or long axial ridges 346 on the outer surface of the tip component 348 allow the user to securely grasp the tip component for mounting and removing it from the shaft 316A.

[0078] Figure 12 shows the cup orientation placement navigation assembly of Figures 11A-11C adjacent to an anatomical structure. This drawing also illustrates a freehand navigation structure 274. In this navigation 274 structure, at least orientation devices 172 and 204 allow for a 6-degree movement relative to each other. Any of the modifications of Figures 11A-11C may be used instead in the illustration. In particular, the handle 304 is oriented as desired. In one embodiment, the system 100 displays the angle of the cup relative to the navigated plane in real time, which is obtained as discussed above. The angles that can be displayed include, for example, one or more of anterior tilt and abduction. Preferably, the clinician can confirm the position of the cup within a short period of time, for example, within about 20 seconds. In one embodiment, the displayed angle can be adjusted by about 40 degrees of abduction and about 20 degrees of anterior tilt. The angles are not critical and they relate to the range of leg movement. It is preferable to be close to those angles, as the movement in abduction and anterior tilt extends to either side of those angles. The system discussed in this application is thought to be able to increase the proportion of patients in the “safe zone” close to those angles, which is typically described as within 10 degrees of those angles. In contrast, studies show that conventional techniques have an impact on approximately 50% of multiple patients outside the “safe zone.”

[0079] Depending on the timing of the sensor and the cup placement step in Figure 12, the user can reattach the detection device 204 to the elongated member 224, return the system 100 to the stop structure 260, and initialize or set the system 100 to zero.

[0080] System 100 can be configured to provide pre- and / or post-operative angle estimates for the angle of the operating table. In a posterior approach, the patient is positioned to one side. In this approach, there are more opportunities for the patient's position to shift during surgery. In one embodiment, an alignment rod can be connected to a sensing device 204 and aligned with the plane of the operating table. When aligned in this manner, the orientation of the sensing device 204 is recorded in the system. Later in the surgery, one or more angles are calculated based on the assumption that the pelvis does not move and are displayed to the user. At such a later stage, the orientation of the sensing device 204 can be checked against the surgery again to provide information on whether the patient has moved. If significant movement occurs that breaks the assumption that there is no movement, some or all of the landmark acquisition stages can be repeated. Alternatively, pelvic movement can be tracked and corrected by the sensing device. Methods for incorporating the orientation of the operating table by landmark acquisition are discussed in more detail below.

[0081] The user can position the artificial joint ball of the replacement hip in the proximal thigh, and then position the ball within the cup, which is then properly oriented using the techniques discussed above.

[0082] Figure 1 shows that the user can then optionally verify the orientation and / or leg length using the system 100. The leg with the assembled prosthetic hip is positioned in a neutral flexed and / or abducted and / or rotated position. The acquisition assembly 112 can be positioned in the retractable structure 266. The distal end 228 of the elongated member 224 can be brought into contact with a landmark which may be the same landmark acquired in Figure 6. Once contact with this landmark (e.g., Bobby Mark) is made, the orientation of the sensing device 204 is determined by the system 100. The distance indicated by the scale 226 of the elongated member 224 is also input into the system in one of the methods discussed above (e.g., manually or by sensing). The system 100 can then calculate the components of the vector along the SI axis (leg length) or the ML axis (offset).

[0083] Once leg length and offset are determined postoperatively, they can be compared to preoperative measurements (Figure 6) to inform the surgeon whether adjustments should be made before completing the hip replacement surgery.

[0084] Figures 13 and 14 show other embodiments of the hip navigation system 400 that can include any of the features discussed above. Furthermore, the system 400 includes a freehand sensor mount 404 which can be used to mount a freehand orientation device 204A in one structure. The freehand orientation device 204A preferably includes an inertial sensor similar to the inertial sensors previously described in this specification. The orientation device 204A also preferably includes a camera 412. The field of view is illustrated by a cone projected downward from the base of the freehand orientation device 204A. Figure 14 shows that the field of view includes a window 418 in the slide support 420. The window 418 allows the scale 225 to be viewed through the window 418.

[0085] Because hip replacement surgery involves an open surgical field with a substantial amount of exposed tissue and a substantial amount of blood, the camera 412's field of view relative to the scale may be obstructed. In one embodiment, a hood is provided above the window 418. The hood keeps most of the blood and tissue outside the space in which the camera views the scale. Furthermore, scrubber components, such as thin rubber members, may be provided above the scales 226 and 226A (as discussed below) to prevent tissue or fluid from entering the field of view from the side.

[0086] One advantage of system 400 is that the camera 412 can automatically process the image captured through the window 418, thereby determining the position of the elongated member 224 relative to the slide support 420. A further advantage of this is the elimination of a step from the navigation process, for example, the elimination of the need to input length dimensions into system 400. Eliminating this step can reduce time and / or the number of people in the operating room. Furthermore, the camera 412 can be configured to read at a much higher resolution than that read by a clinician. This can provide higher accuracy in the system as a whole. Not only that, the camera can be configured to make slight errors or no errors at all when reading the position. This can improve the overall results. For example, the miniature camera can produce data in JPEG format or other image formats, which can be processed so that a processor in one or both of the orientation devices 172 and 204A extracts the linear position of the elongated member 224.

[0087] Further modified embodiments are shown in Figure 15. This embodiment shows a curved scale 226A that can be positioned in a structure beneath an elongated member 224, for example, a curved scale 226A that can be positioned in a structure beneath an orientation device 204A that is rotatably fixed with respect to an axis extending outward from the page. Figure 16 shows one structure having this arrangement configuration. A pivot 440 allows the slide support 420 to rotate with respect to an axis extending upward from the page. Although the pivot 440 is fixed to this upward-extending axis, it can rotate with respect to the pivot 440. A window 418A in the elongated member 224 allows a camera to view through the support to see the scale 226A positioned on the curved or disc-shaped feature of the pivot 440. The scale 226A can be read by camera 412 or a second camera to provide precise measurement of the rotational position of the elongated member 224. This makes it possible to exclude or disable one of the multiple sensors in the orientation device 204A. In other embodiments, camera data obtained from the scale 226A can be used to verify data from the multiple sensors in the orientation device 204A. Preferably, the scale 226A has markings over a range of about 15 degrees to about 90 degrees, for example, over a range of about 30 degrees to about 60 degrees, for example, over a range of about 40 degrees to about 50 degrees.

[0088] [2. Rear approach system adapted for accelerometer sensitivity] Figures 17 to 17C2 illustrate further embodiments. System 450 is adapted for navigating hip replacement surgery from a posterior approach. This system 450 includes an anchor fixture 454, a positioning system 458, and a landmark acquisition assembly 462. These components may be similar to those discussed above, and their descriptions are incorporated into this embodiment where there is no contradiction.

[0089] The anchor fixture 454 includes a hollow fixing member 466 and a platform 468 for connecting multiple devices to the pelvis. The platform 468 has a substantially T-shaped structure, which includes a first portion 468A connected to the proximal end of the hollow fixing member 466 and a second portion 468B positioned transversely to the first portion 468A. The first portion 468A further provides support for the cradle 476 discussed below. The second portion 468B may include multiple docking devices 469 for direct or indirect connection with the orientation device 172. The T-shaped structure offers the advantage that the docking devices 469 can be positioned further away from the surgical site than if the system 100 were present. This reduces any intrusion of the orientation device 172 into the working field of view.

[0090] In some cases, the fixing member 466 provides sufficient stability when fixing the system 450 to the pelvis. In other situations, the anchor fixture 454 can be connected to the pelvis from the second portion 468B. For example, a slot 470 can be formed in the second portion 468B on one or both sides of the position where the first portion 468A extends from the second portion 468B. The slot 470 can extend from the lateral edge of the second portion 468B toward the position where the first portion 468A extends from the second portion 468B. The slot 470 may include a plurality of channels 471, which are configured to receive a plurality of fixing pins (e.g., Steinmann pins) that can be advanced into the pelvis. The plurality of channels 471 extend substantially parallel to the fixing member 466. The plurality of fixing pins can be securely fixed to the second portion 468B in the plurality of channels 471 by a clamping device 472. The clamping device may include a screw, which is configured to pull the second portion 468B toward each other on both sides of the slot 470, and thus to generate a large frictional force on the pins in multiple slots 471.

[0091] The slots 470 are preferably aligned such that a plane extends along both of the multiple slots 470 along their length. Because the multiple slots 470 are long and narrow, this plane can be easily visualized in the X-ray image. The anchor fixture 454 is preferably aligned with the pelvis such that the plane extending along the multiple slots 470 (e.g., the intersection of the medial-lateral plane and the patient's transverse central plane) is perpendicular to the patient's axis. This feature provides a convenient way to visually confirm the proper positioning of the anchor fixture 454 in one embodiment.

[0092] The fixing member 466 includes a recording feature 473, a foot portion 474 adjacent to its distal end, and a connecting portion 475 adjacent to its proximal end for connection to the platform 468. The foot portion 474 includes a plurality of spaced-apart spikes extending from its distal end. These spikes can prevent or limit the rotation of the anchor fixture 454 when the fixing portion 466 is connected to the pelvis. Figure 17 shows that fixing the fixture 462 to the pelvis may include positioning a pin or other bone engagement device through the fixing member 466. The pin and the plurality of spikes extending from the foot portion 474 can provide three or more contact points that contact the pelvis, providing secure attachment of the fixture 462.

[0093] The coupling portion 475 typically secures the platform 468 to the fixing member 466. In some embodiments, the coupling portion 475 has rotational capability, which allows the platform to be positioned at a selective position with respect to the longitudinal axis of the pin 466, for example, allowing the platform 468 to be initially positioned in the correct orientation, or allowing it to be moved during or after surgery to create space for other surgical instruments. One arrangement configuration provides matching splines extending parallel to the longitudinal axis of the fixing member 466. This arrangement configuration would allow the splines on the upper part of the coupling portion 475 to be disengaged from the splines on the lower part of the coupling portion 475. When disengaged, the upper part of the platform 468 and the coupling portion 475 can rotate relative to the lower part of the coupling portion 475. The splines can then be re-engaged.

[0094] The fixture 454 includes a cradle 476 which can be used to hold the probe arm 477. The cradle 476 includes a U-shaped recess which has a width between two upright members that is approximately equal to the width of the arm 477 of the landmark acquisition system 462. Figure 17 shows the probe arm 477 in the stopping structure as discussed above. When the sensor 204 operates with components that are prone to accumulating errors, the stopping structure can be used to eliminate such errors. As discussed above, the system 450 can be configured so that the position and / or orientation of the sensor 204 relative to the orientation device 172 is known. Therefore, when the arm 477 is in the cradle 476, accumulating errors of the components of the sensor 204 can be eliminated.

[0095] Even if the detection device in sensor 204 is affected by accumulated error sources, the cradle 476 can provide other useful functions. As discussed throughout this specification, it may be desirable at some points in the surgery to use the probe arm 477 and sensor 204 to estimate the plane of the operating table on which the patient lies, in order to verify the accuracy of the system or to provide a simplified reference coordinate system that does not require landmark acquisition. As discussed above, when the fixture 454 is attached to the pelvis, if the plane intersecting the slot 470 is oriented perpendicular to the patient's axis, the cradle will be parallel to the patient's axis. When the fixing member 466 is oriented perpendicularly, the arm 477 will be parallel to the plane of the operating table when it is inside the cradle 476. The system 450 can therefore use the plane of the operating table as a reference coordinate system to guide the placement of the cup without recording landmarks. Alternatively, the plane of the operating table can be used in combination with recording the anatomical structure of the acetabular rim, as discussed above, to increase the accuracy of navigating the cup.

[0096] The cradle 476 also provides a convenient fixed position for keeping the arm 477 stationary and out of the way of other surgical instruments. Figure 17A illustrates the probe arm 477 as it is extended from the cradle 476 and moves freely to make contact with a landmark.

[0097] The fixture 454 also includes a horizontally positioned rotating feature 478. Figure 17B shows that the rotating feature 478 includes two horizontal holes 480. One of the two horizontal holes 480 is formed in the same structure that forms the cradle 476, but at a height below the cradle 476. The other hole 480 is formed between the cradle 476 and the projection of the fixed member 466. Figure 17A shows that the probe arm 477 is connected to the rotating feature 478 by a shaft 482 extending through the hole. A moving device is provided between the shaft 482 and the arm 477, thereby allowing the distal end of the arm to rotate about a vertical axis and move linearly relative to the fixed fixture 454. One axis of rotation A of the moving device is positioned parallel to the platform 468 and at a height above the platform 468. The other axis of rotation B is positioned substantially perpendicular to axis A. The sliding of arm 477 within housing C is enabled by a snug fit of the arm, or by a sliding fit of the arm. By orienting the rotation axis A in this manner, the sensitivity of the accelerometer in sensor 204 to small angular motion reference points with respect to the acetabular fossa is increased or maximized. This enables the acquisition of landmarks by the accelerometer-based system 450. This is advantageous because it is not affected by accumulated errors and simplifies the landmark acquisition process.

[0098] The recording feature 473 is a convenient method for improving the accuracy of the sensor 204. In particular, in one variation of the method discussed above, the distal tip of the probe arm 477 is in contact with the recording feature 473. In one embodiment, the recording feature 473 is a notch configured to receive and temporarily hold the tip. The user can then interact with the orientation device 172 to initialize the accelerometer in the sensor 204. Subsequently, multiple points to be acquired can be brought into contact, and the orientation and position of the sensor 204 can be recorded in the system 450. Since the accelerometer is initialized in close proximity to the multiple points to be acquired, angular errors arising from errors in the accelerometer's scale factor are minimized due to the small arc from the recording feature, and therefore the accuracy of the reading is improved. For example, the fixture 454 is configured to allow the landmark acquisition assembly 458 to reach all points to be recorded by moving less than about 45 degrees from an initial or fixed position in some embodiments. In another embodiment, the jig 454 is configured to allow the landmark acquisition assembly 458 to reach all points to be recorded by moving less than approximately 25 degrees from its initial position. In another embodiment, the jig 454 is configured to allow the landmark acquisition assembly 458 to reach all points to be recorded by moving less than approximately 15 degrees from its initial position.

[0099] The jig 454 is also configured to interact well with the soft tissues positioned around the surgical site in a posterior approach. In this approach, the excision is made in the soft tissues so that the excision remains as small as possible. In one approach, the fixation member 466 is positioned at the end of the excision. When the excision is made to be as small as possible, the jig 454 can also function as a retractor. The T-shaped structure is particularly well suited to this function, as the first part 468A of the platform 468 can be received between the middle and ring fingers of the user with the second part 468B in the palm. With the foot 474 gripping the pelvis, the jig 454 can be tilted away from the platform 468 to retract the tissue away from the hip joint.

[0100] Figures 17C-1 and 17C-2 illustrate further embodiments of a posterior approach jig 454A having a mounting device 488 positioned adjacent to the distal end of the fixation member 466A. In those drawings, otherwise, it is the same as the fixation member 466. The fixation member 466A includes a tubular body 490 connected to the fixation member 466A. In this embodiment, the tubular body 490 acts as a first fixation member. The tubular body 490 extends along a lumen inclined with respect to the lumen of the fixation member 466A. The lumen of the tubular body 490 is configured to receive a fixation pin 492 which can be driven into the bone at a 90-degree angle, as shown in Figure 17C-2. The fixation pin 492 complements the fixation provided by the fixation member 466A. The fixation pin 492 can be used, for example, in the ilium, or in conjunction with an optional longer pin extending through a channel 471 as an alternative for this optional setting. The fixation pin 492 has the advantage of not requiring an additional hole in the skin, as it is located within the main excision formed to access the joint during surgery. In one embodiment, the fixation pin 492 can be threaded to engage with bone. In some embodiments, a locking device 494 can be provided to secure the fixation pin 492 within the lumen of the tubular body 490. A set screw is an example of a locking device 494 that can be used. The locking device 494 allows the fixation pin 492 to be headless. This avoids the problem of thread wear in the hole in the bone into which the fixation pin 492 is inserted.

[0101] [3. Backward Approach: Workflow Consideration] As mentioned above, the workflow problem arises in typical hip replacement surgery, specifically because readily accessible anatomical features are unavailable in the traditional posterior approach for joint surgery.

[0102] By performing numerous CT-based studies on the human pelvis, the assignee of this application can calculate a population-based average relationship between a plurality of planes (each plane, “acetabular plane”) generated by various points in the acetabular fossa, various points on the acetabular fossa, or various points around the acetabular fossa that are accessible during posterior approach hip replacement surgery, and an anterior pelvic plane. One of several important features of posterior hip navigation for some embodiments disclosed in this specification is the capability of modules, for example, software incorporated into a processor which may be a computer, or software incorporated into one or both of the orientation device 172 and sensor 204 to calculate transformations from one reference coordinate system to another. As described in detail throughout this specification, the various points are referenced in the acetabular fossa, on the acetabular fossa, or around the acetabular fossa, and from these points the proxy acetabular plane is calculated.

[0103] Next, in one embodiment described herein, a module operable to process an algorithm can calculate a transformation from a surrogate acetabular plane to anterior pelvic plane by running software in one or both of, for example, the orientation device 172 and the sensor 204, either alone or in conjunction with a separate computer. The approach indirectly records the anterior pelvic plane without requiring direct supine recording and subsequent patient movement, as well as the need for re-draping in standard navigation. The module in one embodiment described herein can then provide the user with real-time navigation data of the orientation of a hip joint surgical instrument (e.g., impactor 300, 300A) relative to the anterior pelvic plane.

[0104] A further advantage of some of the systems described in this specification is that these systems can implement a plane transformation algorithm for calculating the anterior pelvic plane from one of several surrogate acetabular planes selected by the surgeon to record. This allows the surgeon to have greater adaptability in the selection of landmarks for the acetabular plane to take into account the nature or accessibility of certain landmarks. For example, in cases of minimal deformity around the acetabular rim, the surgeon may choose to record several landmarks around the acetabular rim, which are easily accessible. In cases of significant deformity or the presence of high osteophytes on the acetabular rim, the surgeon may instead choose to record an acetabular plane based on non-acetabular landmarks (or, as described in this specification as "non-rim") outside the rim that are not altered by disease or previous hip replacement surgery.

[0105] Examples of anatomical landmarks that can be used to generate a surrogate acetabular plane are shown in Figure 2, but are not limited to the following:

[0106] Landmarks other than the acetabulum (ischium / ilium / pubis) (A) The lowest point of the acetabular groove of the ischium (B) Process of the suprapubic ramus (G) The confluence of the anterior inferior iliac spine (AIIS) and the lateral boundary of the acetabular rim.

[0107] Landmarks on the acetabular rim (E) Center of anterior insertion of the transverse acetabular ligament (F) Center of posterior insertion of the transverse acetabular ligament • (H) The uppermost point of the acetabular rim

[0108] Additional points can be combined with any of the group of points listed above. For example, in one embodiment, point "D" is used. Point D is defined as the midpoint of the inferior edge of the acetabular notch. As will be discussed below in relation to Figure 36, point D corresponds to the bottom landmark 380B used to form line 382. Point D is used in its approach to provide patient-specific improvement points for positioning.

[0109] A further important advantage of one embodiment discussed in this specification is that the aforementioned plane conversion capability increases the accuracy of the conversion between a recorded surrogate acetabular plane and an anterior pelvic plane on average data for a general population, by allowing the user to input certain patient-specific information, such as gender.

[0110] Furthermore, a given embodiment of the system including one or more orientation devices 172, sensors 204, or a separate computer may have a module that can be operated, for example by processing software, to allow a user to input an angular or planar relationship between a surrogate acetabular plane and an anterior pelvic plane measured by the surgeon based on preoperative imaging, thereby enabling partial or whole planar transformations based on patient-specific data rather than population data. As an example, the surgeon may choose to preoperatively measure angles formed by (a) several landmarks that can be viewed in both A / P pelvic X-rays and can be referenced during posterior hip replacement surgery, and (b) several landmarks that can be viewed in both A / P pelvic X-rays and are directly related to inclination measurements in the anterior pelvic plane. When this angular relationship is input to a module of the system including one or more orientation devices 172, sensors 204, or a separate computer, the module may be operated by computational processing software, the surgeon may record the landmarks described in (a), and the inclination navigation will be based on patient-specific data rather than population averages. The landmarks (D) and (H) listed above are examples of landmarks that can be seen on A / P pelvic X-rays and can be referenced to form a surrogate acetabular plane in posterior hip replacement surgery.

[0111] Those embodiments of the system adapted for posterior approach hip replacement surgery can greatly improve both workflow and precision in such surgery.

[0112] [4. Rear approach: Further systems using orientation detection devices and cameras] Figure 18 shows a hip joint navigation system 600 adapted to navigate hip joint surgery by reference to anatomical landmarks. Figure 18 shows the system 600 attached to the pelvis in a posterior approach. Figure 18 shows the early stages of surgery after the system 600 has been attached to the pelvis, before the joint is dislocated. The system 600 can be adapted to various techniques. As will be further discussed below, such modifications include recording the femur before and after the joint is replaced in order to confirm the relative position and / or orientation of the femur, e.g., leg length, joint offset, and rotational orientation of the femoral neck. The system 600 may include any components described in this specification. The system 600 can be used in any technique or method described in this specification.

[0113] System 600 may include a fixed base 602, a first assembly 604, and a second assembly 606. The first assembly 604 is rigidly connected to the hip joint in the illustrated structure, so that hip joint movement causes corresponding movement of a sensor in the first assembly 604, as discussed below. Detecting this movement allows System 600 to eliminate patient movement as a source of navigation errors. The second assembly 606 provides a sensor capable of tracking movement and a maximum range of controlled movement, in cooperation with the sensor in the first assembly 604. Further details of the system, apparatus, sensors, and methods are described in U.S. Patent No. 8,118,815, U.S. Patent Application Publication No. 2010 / 0076505, and U.S. Patent No. 8,057,479, all of which are incorporated into this specification by reference as a whole for all purposes. The sensors in assemblies 604 and 606 preferably transfer data between them, and in some cases wirelessly transfer data to external devices and monitors using Bluetooth®, Wi-Fi®, or other standard wireless telemetry protocols.

[0114] The system 600 may include one or more fixing pins. In the illustrated embodiment, a first fixing pin 610 and a second fixing pin 612 are shown. Other configurations are conceivable (e.g., one fixing pin, three fixing pins, four fixing pins, etc.). The fixing pins 610, 612 may be elongated in shape. Figure 19 shows a fixing pin 610. In some embodiments, the fixing pins 610, 612 are identical or substantially similar. In some embodiments, the fixing pins 610, 612 may be different and adapted to be inserted into different anatomical locations.

[0115] The fixing pin 610 may be substantially cylindrical, as shown in Figure 19. The fixing pin 610 may have a distal end 614 that can be advanced into the pelvic bone at an anatomical location or landmark or other selected location. In the illustrated embodiment, the distal end 614 is threaded. The distal end 614 may include a sharp tip designed to perforate bone. The fixing pin 610 may have a proximal end 616. The proximal end 616 may include mounting features for connecting the fixing pin 610 to a driver. In the illustrated embodiment, the proximal end 616 includes a tri-flat shape designed to connect to a tri-flat socket. The fixing pin 610 may include one or more markings along its length. The markings may indicate the orientation of the fixing base 602 relative to the fixing pin 610.

[0116] Referring back to Figure 18, each fixation pin 610, 612 can be driven into the ilium on the pelvis. Each fixation pin 610, 612 can be connected to other bones in other techniques, as will be discussed further below. For example, one of the fixation pins 610, 612 can be connected to the ischium or pubis. In some techniques, one of the fixation pins 610, 612 is attached to the pelvic bone rather than a landmark. One of the fixation pins 610, 612 can be connected at a point above the uppermost point on the acetabular rim. In some techniques, one of the fixation pins 610, 612 is approximately 10 mm above the uppermost point on the acetabular rim. In some techniques, three or more anatomical landmarks located around the acetabular fossa can be acquired, as will be discussed below. If one of the fixation pins 610, 612 is connected to a landmark, only two additional landmarks are acquired in some embodiments, as will be discussed below. One reason for mounting the fixation pins 610 and 612 away from the landmark is that the landmark may not be visible or accessible before dislocating the hip joint. If the clinician wishes to use system 600 to reference the femur, as discussed below, it may be necessary to mount the fixation pins 610 and 612 away from the landmark.

[0117] The system 600 may include a fixing base 602, as shown in Figures 20A to 20H. The fixing base 602 can function as a clamp with one or more fixing pins 610, 612. Figure 20A shows an exploded view of the fixing base 602. Figures 20B to 20D show other views of the fixing base 602. The fixing base 602 may include a platform 620 and a support 622. The platform 620 can interact with the support 622 to function as a clamp. In the illustrated embodiment, the fixing base 602 may include one or more fixing devices 624. In the illustrated embodiment, two fixing devices are shown, but other structures (e.g., one, three, four, etc.) are contemplated. The fixing device 624 may include one or more threaded parts. In the illustrated embodiment, the fixing device 624 is a screw having a head and a threaded shank. The platform 620 may include one or more holes. The support portion 622 may include one or more holes. The fixing device 624 can pass through or engage with one or more holes in the support portion 622. In some embodiments, each hole in the support portion 622 is threaded. The fixing device 624 can pass through or engage with one or more holes in the platform 620. In some embodiments, each hole in the platform 620 is threaded. Rotation of the fixing device 624 can move the support portion 622 toward the platform 620 and / or move the platform 620 toward the support portion 622.

[0118] The platform 620 and the support 622 form one or more channels between them, as shown in Figure 20C. The number of channels may correspond to the number of fixing pins. In the illustrated embodiment, a first channel 626 and a second channel 628 are shown. The channels extend from the top surface of the platform 620 and / or the support 622 to the bottom surface of the platform 620 and / or the support 622. The channels 626, 628 extend in a direction transverse to the direction of the fixing device 624 when the fixing device 624 is engaged with the platform 620 and the support 622. The first channel 626 is sized to receive a first fixing pin 610, and the second channel 628 is sized to receive a second fixing pin 612. Rotation of the fixing device 624 can move the support 622 toward the platform 620. The diameters of the channels 626, 628 may decrease with rotation of the fixing device 624. When the fixing device 624 rotates, each fixing pin 610, 612 is held between the platform 620 and the support 622. The fixing base 602 may include a divot 630. The divot 630 may be associated with a stop structure or fixed position as described in this specification. The divot 630 is an example of a recording feature placed in the system 600.

[0119] The fixed base 602 may include a first coupler 632. The first coupler 632 can be coupled to one or more components of the system 600. In some embodiments, the first coupler 632 is a general-purpose coupler. The first coupler 632 may include an elongated post 635. In some embodiments, the first coupler 632 may have a regular shape (e.g., cylindrical). In some embodiments, the first coupler 632 may have an irregular shape (e.g., triangular, teardrop-shaped, elliptical, rectangular). An irregular shape may facilitate alignment between the platform 620 of the fixed base 602 and other components of the system 600. In the illustrated embodiment, other components of the system 600 can be coupled to the first coupler 632 in a single orientation.

[0120] The first coupler 632 may include a slot 634. The slot 634 may be transverse to the longitudinal axis of the first coupler 632. The slot 634 may form an angle with the axis transverse to the longitudinal axis. This angle may be approximately 10°, 5° to 15°, 0° to 20°, etc. The slot 634 may be designed to interact with a retaining element of other components of the system 600, as described in this specification. The first coupler 632 may include a tapered surface 636. The tapered surface 636 may facilitate the entry of the first coupler 632 into other components of the system 600. The tapered surface 636 may move a retaining element of other components of the system 600 when the first coupler 632 is an inserter in the other components. As shown in Figure 20A, the first coupler 632 may include an elongated post 635 connected to a hole in the upper surface of the platform 620. As shown in Figure 20E, in an alternative embodiment, the first coupler 632A is integrally formed with the platform 620. The post 632B can be inserted from the bottom of the platform 620 to support the first coupler 632A.

[0121] System 600 may include a first assembly 604 shown in Figures 21A to 21G. The first assembly 604 may include a pelvic bracket 638. In the illustrated embodiment, the pelvic bracket 638 may be substantially vertical, as shown in Figure 18. The first assembly 604 may be designed to connect to a first coupler 632 of a fixed base 602. The first assembly 604 may include a locking lever 640. The locking lever 640 may be connected to the pelvic bracket 638 using a pivot pin. The locking lever 640 may be pivotable relative to the pelvic bracket 638. In some embodiments, a tapered surface 636 of the first coupler 632 causes the locking lever 640 to rotate. In some embodiments, a surgeon causes the locking lever 640 to rotate. The locking lever 640 may include a retainer 642. The retainer 642 is sized and molded to be received in a slot 634. The engagement of the retaining element 642 and the slot 634 allows the first assembly 604 to be firmly connected to the fixed base 602.

[0122] The first assembly 604 may include an extension 644. The extension 644 may be connected to a pelvic bracket 638. The extension 644 may include a mounting portion 646 designed to connect to a surgical orientation device 172. In the illustrated embodiment, the mounting portion 646 includes a lock and release lever that can rotate relative to the extension 644. The surgical orientation device 172 may include features for coupling with the lock and release lever (not shown). Other structures are contemplated. The surgical orientation device 172 is firmly connected to the extension 644 when engaged with the mounting portion 646. The surgical orientation device 172 may be tilted when connected to the first assembly 604, as shown in Figure 18. The surgical orientation device 172 may be tilted approximately 35° from the horizontal axis. Other angles from the horizontal axis are considered (e.g., 5°, 10°, 15°, 20°, 25°, 30°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, or 85°, 30°-40°, 25°-45°). In some embodiments, the angle of the surgical orientation device 172 improves visibility. This angle is a compromise between tilting the surgical orientation device 172 upward toward the surgeon and still allowing another surgeon or surgical assistant opposite the patient to view the display. One reason for tilting the surgical orientation device 172 is that in anterior approaches, the surgeon is often positioned facing the patient's feet while pushing in the acetabular implant, making it difficult to view a horizontal display.

[0123] The surgical orientation device 172 detects the orientation and rotation of the device 172 relative to a reference coordinate system. The surgical orientation device 172 preferably comprises at least one sourceless sensor, such as an accelerometer, a gyroscope, or a combination of these sensors and other sensors. In some embodiments, the surgical orientation device 172 includes a three-axis accelerometer for detecting orientation relative to gravity and multiple gyroscopes for detecting rotation. Other sensors can be used in various modifications. Specific sensor combinations include, among many, the ADIS16445 from Analog Devices and the MPU-6050 or MPU-9150 from InvenSense. In some approaches, the surgical orientation device 172 may be disposable, and therefore, the sensors are preferably less expensive. In some embodiments, the surgical orientation device 172 is disposable.

[0124] The extension 644 may include a second coupler 648. In some embodiments, the second coupler 648 is a general-purpose coupler. The second coupler 648 may be substantially similar to the first coupler 632 described herein. The second coupler 648 may be designed to connect to a second assembly 606. Couplers 632, 648 are designed to be secured to other components of the system 600 in a secure but detachable manner. The engagement between coupler 632 and the first assembly 604 minimizes or prevents relative movement between them to avoid any mechanical relative movement during navigation surgery, thereby ensuring that the movement of the surgical orientation device 172 corresponds to the movement of the hip joint. The second coupler 648 provides a stable method for positioning the second assembly 606 relative to the first assembly 604.

[0125] System 600 may include a second assembly 606, as shown in Figures 22A–22F. The second assembly 606 may include a probe bracket 652. In the illustrated embodiment, the probe bracket 652 may be substantially tilted relative to the pelvic bracket 638 during use, as shown in Figure 18. The second assembly 606 may be designed to connect to a second coupler 648 of the first assembly 604. The second assembly 606 may include a locking lever 654. The locking lever 654 may be connected to the probe bracket 652 using a pivot pin. The locking lever 654 may be pivotable relative to the probe bracket 652. In some embodiments, the tapered surface of the second coupler 648 causes the locking lever 654 to rotate. In some embodiments, the surgeon causes the locking lever 654 to rotate. The locking lever 654 may include a retaining clip 656. The retaining arm 656 is sized and molded to be received in a slot in the second coupler 648. The engagement of the retaining arm 656 and the slot allows the second assembly 606 to be firmly connected to the first assembly 604.

[0126] In the illustrated embodiment, the second assembly 606 includes a mounting portion 658. The mounting portion 658 is connected to the probe bracket 652 to allow relative movement between them. The mounting portion 658 can be received within an opening in the probe bracket 652. The mounting portion 658 can be rotated around its longitudinal axis relative to the probe bracket 652.

[0127] The second assembly 606 may include a dock 662. The dock 662 is connected to the mounting portion 658 to allow relative movement between them. The dock 662 may be connected to the mounting portion 658 using one or more pivot pins 660. The dock 662 may have two degrees of freedom relative to the probe bracket 652 (e.g., rotational motion and pivotal motion). The dock 662 may include a sliding support having a through-lumen 664. The through-lumen 664 is sized to receive a probe 678. The probe 678 has a distal end 680 designed to contact multiple positions as described in this specification. The distal end 680 may be straight, as shown in Figure 22A. In other embodiments, the distal end 680 may be sloped or curved, as shown, for example, in Figures 4 and 17.

[0128] The through-lumen 664 of the dock 662 allows for the sliding extension of the probe 678. The dock 662 is movable relative to the probe bracket 652 (for example, via rotation of the mounting portion 658 and rotation of the pivot pin 660). The dock 662 can be rotated around the longitudinal axis of the mounting portion 658 to different rotational positions relative to the mounting positions of the fixed pins 610, 612. This may require movement of the mounting portion 658 in the method of rotation relative to the probe bracket 652. The dock 662 can be rotated around the longitudinal axis of the pivot pin 660 to different positions relative to the mounting positions of the fixed pins 610, 612. This may require movement of the dock 662 in the method of rotation relative to the mounting portion 658.

[0129] The probe 678 can be connected to a dock 662, thereby making the probe 678 movable relative to the probe bracket 652 (e.g., via rotation of the mounting portion 658 and rotation of the pivot pin 660). This operability allows the distal end 680 of the probe 678 to rotate or rotate to contact anatomical landmarks, as discussed in this specification. The probe 678 can be slid relative to the dock 662 to different translational positions with respect to the mounting positions of the fixing pins 610, 612. The sliding capability of the probe 678 within the dock 662 allows the distal end 680 to move to reach anatomical landmarks that are coplanar with the probe 678 but closer to or further away from the distal end 680.

[0130] The second assembly 606 allows for a range of motion of the distal end 680 of the probe 678, which facilitates the acquisition of multiple landmarks at different distances from the mounting positions of the fixing pins 610, 612, as will be discussed further below. In other words, the distal end 680 of the probe 678 can extend away from the axis of the slide support of the dock 662, or can be retracted to a position closer to the axis of the slide support of the dock 662.

[0131] The dock 662 may include a third coupler 668. In some embodiments, the third coupler 668 is a general-purpose coupler. In some embodiments, the third coupler 668 is identical or substantially similar to the second coupler 648. This allows the orientation detection device 204 to be coupled to either the second coupler 648 or the third coupler 668, as described in this specification. In some embodiments, the third coupler 668 may be substantially similar to the first coupler 632 as described in this specification. The third coupler 668 may be designed to be coupled to the orientation detection device 204. Figures 23A to 23C illustrate embodiments of the orientation detection device 204. The second assembly 606 may include an extension 670. The extension 670 can be coupled to the third coupler 668 of the dock 662. The engagement between the third coupler 668 and the extension 670 minimizes or prevents relative movement between them to avoid any mechanical relative movement during navigation surgery. The extension 670 may include a mounting portion 672 designed to connect with an orientation detection device 204. In the illustrated embodiment, the mounting portion 672 includes a lock and release lever that can rotate relative to the extension 670. The orientation detection device 204 may include features for coupling with the lock and release lever. Other structures are contemplated. When the orientation detection device 204 engages with the mounting portion 672, it is firmly coupled to the extension 670.

[0132] The orientation detection device 204 can be tilted when connected to the second assembly 606, as shown in Figure 18. The orientation detection device 204 can be tilted approximately 35° from the horizontal axis. Other angles from the horizontal axis (e.g., 5°, 10°, 15°, 20°, 25°, 30°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, or 85°, 30° to 40°, 25° to 45°) are intended. In some embodiments, the angle of the orientation detection device 204 improves visibility.

[0133] The orientation detection device 204 detects the orientation and rotation of the probe 678 as described in this specification. The orientation detection device 204 preferably comprises at least one sourceless sensor, such as an accelerometer, a gyroscope, or a combination of these sensors and other sensors. In some embodiments, the orientation detection device 204 includes a three-axis accelerometer for detecting orientation relative to gravity and a plurality of gyroscopes for detecting rotation. Other sensors can be used in various modifications. In some embodiments, the orientation detection device 204 is reusable.

[0134] Referring back to Figures 22A and 22C, the probe 678 may include a marking 682. The marking 682 may indicate the length or extension of the probe 678 relative to the dock 662. The marking 682 may include a scale. In some embodiments, the marking 682 may span a range such as approximately 8 inches, 10 inches, 12 inches, or approximately 8–12 inches. The marking 682 may be printed on the probe 678. In some embodiments, the marking 682 may be on a separate component such as a probe inlay 676. The probe inlay 676 may be received within a portion of the probe 678. In some embodiments, the probe inlay 676 is located at a distance from the distal end 680 of the probe 678.

[0135] Referring to Figure 23C, the system 600 may include a camera 684. The camera 684 can capture an image of the marking 682. In some embodiments, the camera 684 and / or the orientation detection device 204 may include a light for illuminating the marking 682. In some embodiments, this light is an LED. In some embodiments, the dock 662 includes a window to allow the camera 684 to capture an image. In other embodiments, the camera 684 captures an image of the marking 682 extending beyond the dock 662. The camera 684 reads the marking 682 to provide a precise determination of the translational position of the probe 678 relative to the dock 662. This may allow one of the sensors in the orientation detection device 204 to be removed or disabled. In another embodiment, the camera data obtained from the marking 682 may be used to verify data from the sensors in the orientation detection device 204.

[0136] In some embodiments, the camera 684 is integrally formed with the orientation detection device 204. In some embodiments, the camera 684 is a separate component from the orientation detection device 204. The camera 684 can be held in a fixed position relative to the dock 662. The marking 682 can be positioned directly below the camera 684 on the probe 678 when the probe 678 is positioned within the through-lumen 664. The camera 684 can be positioned directly above the marking 682. The camera 684 can be fixed relative to the through-lumen 664 of the dock 662. The dock 662, camera 684, and orientation detection device 204 can move together to allow the positioning of the probe 678. One advantage of oriented the orientation detection device 204 as shown in system 600 is improved visibility. The thinner the structure, the less likely it is to obstruct the user's field of view. One advantage of orienting the orientation detection device 204 as shown in system 600 is ease of manufacture. The camera 684 can be embedded on a circuit board. A corresponding transparent window (not shown) within the housing of the orientation detection device 204, which allows the camera 684 to capture an image, is oriented in the mold tension direction. Also, the shorter the distance to the marking 682, the better it is possible to adapt an available camera having a short focal length. In some embodiments, the camera 684 captures an image through a lumen (not shown) in a dock 662. One advantage of having the camera 684 read the marking 682 through a lumen is that this protects the camera 684 from external light sources. Light such as OR light may interfere with camera functions, such as the ability to capture an image of the marking 682. In other embodiments, the camera 684 may incorporate a shroud feature to block ambient light. In some embodiments, the camera 684 is directed downward from the rear of the orientation detection device 204. In some embodiments, the orientation detection device 204 protects the camera 684 from light.

[0137] System 600 may include a femoral tracker 686, as shown in Figures 24A and 24B. The femoral tracker 686 may be connected to the femur, as shown in Figure 18. The femoral tracker 686 may be used to track the position of the femur during surgery. The femoral tracker 686 may include one or more fixation structures. In the illustrated embodiment, the fixation structure is a hole 688. The hole 688 is sized to allow fasteners (e.g., screws, pins, K-wires, etc.) to pass through it. The femoral tracker 686 may include one or more points 690. The points 690 may include points A, B, and C as described in this specification and shown in Figure 24A. The femoral tracker 686 may include three points 690 (e.g., one point, two points, four points, five points, etc.). Other structures are contemplated. The points 690 may include divots, as shown in Figure 24A. Point 690 may include markings. The femoral tracker 686 can provide more consistent and repeatable results than a marked femur. The femoral tracker 686 can provide points 690 fixed to the femur. The femoral tracker 686 can provide multiple points 690. One advantage of recording multiple points on the femur is that the software in the surgical orientation device 172 can then compensate for changes in the femoral angle relative to the pelvis between baseline and subsequent measurements. Baseline measurements may be preoperative measurements. Subsequent measurements may be after the shell has been positioned in the acetabular fossa. In some embodiments, point 690 is located on the femoral tracker 686. In some embodiments, one or more points are marks located directly on the femur Fm, and one or more points are located on the femoral tracker 686. In some embodiments, one or more points are marks located directly on the femur Fm. One advantage of using the femoral tracker 686 is that marks are easy to find in the case of repeated recordings.One advantage of using the femoral tracker 686 is that by spacing the points 690 at a known distance from each other, it allows a software check to verify that the correct points 690 are recorded in the correct order. Another advantage of using the femoral tracker 686 is that by spacing the points 690 at a known distance from each other, it allows a software check to verify that the femur and pelvis have not moved during point recording. One advantage of using marks that are directly located on the femur Fm is that the components are not fixed to the femur. The marks do not require any drilled holes or fasteners. This can prevent future bruising or damage to the proximal end of the femur. The femoral tracker 686 can be a single-piece structure. The femoral tracker 686 can be a low-profile component. The femoral tracker 686 can be connected to the femur throughout the surgery. The femoral tracker 686 can form a smooth surface that prevents it from catching on soft tissue. The femoral tracker 686 can form a smooth surface that prevents it from loosening within the bone.

[0138] Figure 18 illustrates the stopping structure or fixed position of the probe 678. In some embodiments, a portion of the distal end 680 is moved into engagement with the platform 620. In some techniques, the distal end 680 of the probe 678 engages with a divot 630 of the platform 620. The stopping structure allows the navigation system 600 to manage errors that may be mixed in several inertial sensors. For example, the stopping structure advantageously includes the ability to position the devices 172, 204 so that there is substantially no relative movement and to maintain their stability. Also, the relative positions of the sensors in the devices 172, 204 when coupled with the first and second assemblies 604, 606 can be determined from the geometric arrangement of the first assembly 604 and the second assembly 606. For example, in one embodiment, the gyroscope sensors in the surgical orientation device 172 and the orientation detection device 204 can be synchronized when a stable, known orientation is detected, and one or more of the gyroscopes, for example, the gyroscope in the orientation detection device 204, can be set to zero after the conditions are met. Further techniques using a stop structure are discussed below.

[0139] At the surgeon's discretion, system 600 can be used to navigate the state of the femur before hip replacement. The orientation detection device 204 can be initialized or set to zero by positioning it to return to a stop structure on platform 620, as shown in Figure 18. The distal end 680 of probe 678 can then be brought into contact with point 690. The orientation detection device 204 can be set to stationary relative to dock 662. The surgical orientation device 172 can be set to stationary relative to the pelvis. The surgical orientation device 172 can transmit a signal to record the orientation of orientation detection device 204. Camera 684 can record the extension of probe 678 relative to dock 662. The distance from camera 684 to the distal end 680 of probe 678, or the distance from system 600 to the recorded anatomical structure, can then be recorded by the surgical orientation device 172. This position can be based on the camera 684 reading of marking 682. This distance can be automatically captured by the camera 684. In another embodiment, the user reads the measurement from the marking 682 and inputs this distance into the surgical orientation device 172.

[0140] System 600 may include features that offer significant advantages to surgeons. System 600 may include modular equipment. In some embodiments, the fixation base 602 may include a low-profile platform 620 and a low-profile support 622. The low-profile fixation base 602 can prevent interference with the surgical field. The fixation base 602 can be easily removed when not in use. The clamping action between the platform 620 and the support 622 allows the fixation base 602 to be easily removed from the fixation pins 610, 612. In the illustrated embodiment, rotation of the fixation device 624 can move the support 622 away from the platform 620. The channels 626, 628 may have increased diameters. The platform 620 and support 622 can be separated from the fixation pins 610, 612.

[0141] One or more fixation pins 610, 612 can be spaced apart from each other. This allows the fixation pins 610, 612 to be driven into different locations in the patient's anatomical structure. In the illustrated embodiment, two fixation pins 610, 612 are provided. The use of two or more fixation pins may provide further stability to the fixation base 602. The fixation pins 610, 612 allow the surgeon greater flexibility when fixing the system 600. The surgeon has flexibility in the position and / or depth of placement. The surgeon can optimize the penetration angle. In some techniques, the surgeon can enter the bone more vertically. The fixation pins 610, 612 can be positioned to avoid vulnerable anatomical structures.

[0142] System 600 may include one or more couplers. System 600 may include a first coupler 632 connected to a platform 620 of a fixed base 602. The first coupler 632 can connect the fixed base 602 to a first assembly 604, as shown in Figure 18. The first coupler 632 can connect the fixed base 602 to any other component of System 600. System 600 may include a second coupler 648 connected to the first assembly 604. The second coupler 648 can connect the first assembly 604 to a second assembly 606, as shown in Figure 18. The second coupler 648 can connect the first assembly 604 to an extension 670, as described in this specification. The second coupler 648 can connect the first assembly 604 to any other component of System 600. The system 600 may include a third coupler 668 connected to a dock 662 of the second assembly 606. The third coupler 668 can connect the dock 662 to the extension 670, as shown in Figure 18. The third coupler 668 can connect the second assembly 606 to any other component of the system 600.

[0143] Other tools or assemblies, such as those described in this specification, may include one or more couplers. Couplers allow components to be tightly connected. In some embodiments where the coupler has an irregular shape, the coupler can connect components in a single orientation. Slots in a coupler, such as slot 634 of the first coupler 632, can be inclined with respect to the horizontal axis. This prevents unintended detachment of components from the coupler.

[0144] System 600 may include a camera 684. The camera 684 may be a component of the orientation detection device 204. The orientation detection device 204 may be connected to the dock 662 using a third coupler 668. The camera 684 may be in a fixed position relative to the probe 678. The camera 684 may remain fixed in place when the probe 678 is moved. The camera 684 may be oriented so that it faces the marking 682. In addition, the orientation detection device 204 may be in a fixed position relative to the probe 678. The orientation detection device 204 may remain fixed in place when the probe 678 is moved. The orientation detection device 204 may be oriented so that its flat back surface faces the marking 682.

[0145] Camera 684 can capture an image of the marking 682. This image can be matched to the distance of probe 678. The distance changes as probe 678 slides through the through-lumen 664 of dock 662. In some embodiments, camera 684 can read the binary code of the marking 682. In some embodiments, camera 684 can read a scale or other marking. Camera 684 can be positioned directly above the marking 682.

[0146] The distance associated with the extension of the probe 678 can be used in conjunction with orientation and position data from the orientation detection device 204. The surgical orientation device 172 can determine the position of the distal end 680 of the probe 678 using length measurements from the camera 684 and data from the orientation detection device 204.

[0147] Figures 25A–25C show a hip navigation system 600A adapted to navigate hip surgery by referencing anatomical landmarks. Figures 25A–25C show system 600A mounted to the pelvis via a posterior approach. System 600A may include any of the features described above with respect to system 600 and any components described in this specification. System 600A may be used in any technical or method step described in this specification. For example, system 600A may include a surgical orientation device 172 as described in this specification. For another example, system 600A may include an orientation detection device 204 as described in this specification. For yet another example, system 600A may include a camera 684 as described in this specification.

[0148] System 600A may include a fixed base 602A, a first assembly 604A, and a second assembly 606A. The first assembly 604A is rigidly connected to the hip joint in the illustrated configuration, as discussed below, such that hip joint movement triggers corresponding movement of a sensor within the first assembly 604A. Detecting this movement allows System 600A to eliminate patient movement as a cause of navigation errors. The second assembly 606A provides a sensor capable of tracking movement over a maximum range of controlled motion, in cooperation with the sensor in the first assembly 604A.

[0149] System 600A may include a fixing base 602A, as shown in Figures 26A-26C. The fixing base may include a platform 620A. The platform 620A may include one or more holes 611A. The holes 611A may be sized to receive fasteners 613A for fixing the fixing base 602A to bone, as shown in Figure 25B. The platform 620A may include one or more spikes 615A. The spikes 615A can fix the fixing base 602A to bone. The fixing base 602A may include a divot 630A. The divot 630A may be associated with a stop structure or fixed position, as shown in Figure 25B. The divot 630A may be a recording feature of System 600.

[0150] Referring to Figure 25B, each fastener 613A can be driven into the ilium on the pelvis. Each fastener 613A can be connected to other bones in other techniques, as will be discussed further below. For example, one of the fasteners 613A can be connected to the ischium or pubis. In some techniques, one of the fasteners 613A is attached to the pelvic bone rather than a landmark. One of the fasteners 613A can be connected at a point above the uppermost point on the acetabular rim. In some techniques, one of the fasteners 613A is approximately 10 mm above the uppermost point on the acetabular rim. In some techniques, three or more anatomical landmarks located around the acetabular fossa can be acquired, as will be discussed below. If one of the fasteners 613A is connected to a landmark, only two additional landmarks are acquired in some embodiments, as will be discussed below. One reason for mounting the fastener 613A away from the landmark is that the landmark may not be visible or accessible before dislocating the hip joint. If a clinician wishes to use system 600A to reference the femur, as discussed below, it may be necessary to mount the fastener 613A away from the landmark.

[0151] The fixed base 602A may include a first coupler 632. The first coupler 632 may be connected to one or more components of system 600A. System 600A may include a first assembly 604A, as shown in Figures 25A and 25B. The first assembly 604A may include a pelvic bracket 638A. In the illustrated embodiment, the pelvic bracket 638A may be positioned substantially vertically in use, as shown in Figure 25A. The first assembly 604A may be designed to connect to the first coupler 632 of the fixed base 602A. The pelvic bracket 638A of system 600A may be longer than the pelvic bracket 638 of system 600.

[0152] System 600A may include a second assembly 606A, as shown in Figure 25A. The distal end 680A of probe 678A can rotate or swivel to contact an anatomical landmark, similar to probe 678A as described in this specification. The distal end 680 can be inclined, sloped, or curved. The curvature of the distal end 680A of probe 678A can facilitate the acquisition of a landmark or other point as described in this specification. Probe 678A can be slid to different translational positions relative to the mounting position of the fixed base 602A. The second assembly 606A allows for a range of motion of the distal end 680A of probe 678A that facilitates the acquisition of multiple landmarks at positions different from the mounting position of the fixed base 602A.

[0153] System 600A may include a femoral tracker 686A, as shown in Figure 25C. The femoral tracker 686A may be connected to a femoral base 687A, as shown in Figure 25C. The femoral tracker 686A may be used to track the position of the femur during surgery. The femoral base 687A may include one or more fixation structures. In the illustrated embodiment, the fixation structure is a hole 688A, as shown in Figure 28C. The hole 688A is sized to allow fasteners (e.g., screws, pins, K-wires, etc.) to pass through it. The femoral base 687A may include a spike 685A, as shown in Figures 28A-28B. The spike 685A can fix the femoral base 687A to the femur.

[0154] The femoral tracker 686A and / or femoral base 687A may include one or more points 690. The points 690 may include points A, B, C as described in this specification. The femoral tracker 686A and / or femoral base 687A may include three points 690. In the illustrated embodiment, the femoral base 687A includes one point 690, and the femoral tracker 686A includes two points 690. Other structures are intended (e.g., one point on the femoral base 687A, two points on the femoral base 687A, three points on the femoral base 687A, four points on the femoral base 687A, five points on the femoral base 687A, one point on the femoral tracker 686A, two points on the femoral tracker 686A, three points on the femoral tracker 686A, four points on the femoral tracker 686A, five points on the femoral tracker 686A, etc.). Point 690 may include a divot. Point 690 may include a marking. The femoral tracker 686A and the femoral base 687A may be separate components. In other embodiments, the femoral tracker 686A and the femoral base 687A may be an integrated structure.

[0155] The femoral tracker 686A may include a bracket 689A, as shown in Figures 27A to 27C. In the illustrated embodiment, the bracket 689A may be positioned approximately vertically during use, as shown in Figure 25C. The femoral tracker 686A may include a locking lever 691A. The locking lever 691A may be connected to the bracket 689A using a pivot pin. The locking lever 691A may be rotatable relative to the bracket 689A. The femoral tracker 686A may include an extension 693A. The extension 693A may include a point 690.

[0156] The femoral base 687A may include a fifth coupler 695A, as shown in Figures 28A-28C. The femoral tracker 686A may be designed to connect to the fifth coupler 695A of the femoral base 687A. In some embodiments, the tapered surface of the fifth coupler 695A causes the locking lever 691A to rotate. In some embodiments, the surgeon causes the locking lever 691A to rotate. The locking lever 691A may include a retainer that is sized and molded to be received in a slot 697A. The engagement of the retainer and slot 697A allows the femoral tracker 686A to be firmly connected to the femoral base 687A.

[0157] Figure 25B illustrates the stopping structure or fixed position of probe 678A. In some embodiments, a portion of the distal end 680A is moved into engagement with platform 620A. In some techniques, the distal end 680A of probe 678A engages with the divot 630A of platform 620A. At the discretion of the surgeon, system 600A can be used to navigate the condition of the femur before hip replacement.

[0158] System 600A may include features that offer significant advantages to the surgeon. System 600A may include modular equipment. In some embodiments, the fixed base 602A may include a low-profile platform 620A. The low-profile fixed base 602A can prevent interference with the surgical field. The first assembly 604A can be easily removed when not in use. The distal end 680A of the probe 678A may be inclined, bent, or curved to facilitate the acquisition of one or more landmarks or points. The distal end 680A of the probe 678A may be bent or curved to reach a fixed position. The femoral tracker 686A may be releasably connected to the femoral base 687A. The femoral tracker 686A can be easily removed when not in use. The femoral tracker 686A and / or the femoral base 687A may provide points on multiple planes.

[0159] [5. Rear approach: Method using orientation detection device and camera] Figures 18 and 25A illustrate the steps of a navigated hip joint transplant surgery, which will be discussed in detail below. Some of the preceding steps include removing the joint to be replaced, navigating the hip joint, preparing the implantation site for the prosthesis, and positioning the joint, as will be discussed in detail below. As will be discussed further below, Figures 18 and 25B illustrate techniques for ensuring that these steps are performed correctly.

[0160] Referring back to Figure 2, points A–H are anatomical locations that may be relevant to the various methods and systems described in this specification. In some embodiments, navigation systems 600, 600A are configured to determine appropriate anatomical features to assist in the proper placement of the artificial hip joint. In some methods, preoperative imaging techniques are used. In some methods of use, the surgeon can use standing or supine anterior-posterior (AP) pelvic radiography. Figure 29 shows standing AP radiography taken in a patient standing in a neutral rotational position with feet shoulder-width apart. The distance from the X-ray tube to the film is 120 cm, and the crosshairs are centered at the midpoint between the upper edge of the pubic symphysis and the line connecting the anterior superior iliac spine (ASIS). The coccyx is centrally positioned in alignment with the pubic symphysis, and the iliac wings, obturator foramen, and radiograph should be symmetrical in appearance. For proper pelvic tilt, a gap of 1–3 cm should be visible between the tip of the coccyx and the upper edge of the pubic symphysis. This positioning can be considered important for measuring the patient's unique rim teardrop (RT) angle.

[0161] To obtain a patient-specific marginal teardrop (RT) angle from AP pelvic X-rays, the surgeon may complete one or more of the following steps: The surgeon may draw a line on the X-ray connecting the bases of the teardrops. The surgeon may draw a line from the outermost point on the margin of the acetabular fossa (R) on the surgical side, through the base of the teardrop (T), to a horizontal interteardrop line. If bone spurs are present on the margin (R), the surgeon may draw a line through the outermost bone spurs. The surgeon may measure the angle between the interteardrop line and the RT line just drawn. This patient-specific RT inclination angle may be the input value for systems 600 and 600A.

[0162] Figure 30 shows patient positioning for a posterior hip approach. In a posterior hip approach, the patient must be positioned in a lateral decubitus position. When positioning the patient before surgery, the surgeon must carefully align the anterior pelvic landmarks (both the ASIS and pubic tuberosity) in a vertical plane parallel to the long side of the operating table. The surgeon must ensure that the pelvis is securely held in place by an appropriate positioning device, such as a pegboard or a vice-type patient positioner.

[0163] The surgical orientation device 172 and orientation detection device 204 must be turned on. If different programs exist, the surgeon must select the hip surgery program. If different programs exist, the surgeon must select the posterior hip approach. The surgeon can verify that the patient is positioned in the standard lateral decubitus position. The surgical orientation device 172 may include a display screen. The display screen can confirm communication between the surgical orientation device 172 and the orientation detection device 204.

[0164] Systems 600 and 600A can be partially assembled for calibration, as shown in Figure 31. The pelvic bracket 638 can be connected to the extension 644 if it is a separate component. The surgical orientation device 172 can be connected to the mounting portion 646. In some techniques, the extension 670 can be connected to a second coupler 648. The orientation detection device 204 can be connected to the mounting portion 672. The surgical orientation device 172 and the orientation detection device 204 generally form a V-shaped structure. The orientation detection device 204 can be fixed in place relative to the surgical orientation device 172.

[0165] The surgical orientation device 172 and orientation detection device 204 can be calibrated. Assemblies 604, 606, or 604A, 606A can be tilted forward so that the back of the surgical orientation device 172 is on a flat surface. The surgeon can hold the assemblies 604, 606, or 604A, 606A in a stable position until the surgical orientation device 172 indicates completion. Assemblies 604, 606, or 604A, 606A can be tilted backward so that the back of the orientation detection device 204 is on a flat surface. The surgeon can hold the assemblies 604, 606, or 604A, 606A in a stable position until the surgical orientation device 172 indicates completion. Assemblies 604, 606, or 604A, 606A can be placed to the left so that the left side of the surgical orientation device 172 is on a flat surface. The surgeon can keep assemblies 604, 606, or 604A, 606A stable until the surgical orientation device 172 indicates completion. The assemblies 604, 606, or 604A, 606A can be tilted forward so that the back of the surgical orientation device 172 is flat to verify the calibration. The surgeon can keep assemblies 604, 606, or 604A, 606A stable until the surgical orientation device 172 indicates completion. In some embodiments, the displayed angle should be less than 2°, less than 1°, approximately 0°, etc., to verify the calibration.

[0166] The extension 670 can be separated from the second coupler 648. The second assemblies 606, 606A can be assembled as shown in Figures 22B and 25A. The mounting portion 658 can be connected to the probe bracket 652. The mounting portion 658 can rotate relative to the probe bracket 652. The mounting portion 658 can be connected to the dock 662. The dock 662 can rotate around one or more pivot pins 660 relative to the mounting portion 658. The extension 670 can be connected to the third coupler 668 of the dock 662. The orientation detection device 204 can be connected to the mounting portion 672. The probe bracket 652 can be connected to the second coupler 648. The first assemblies 604, 604A can be connected to the second assemblies 606, 606A, as shown in Figures 18 and 25A.

[0167] The probe 678 can be inserted into the through-lumen 664 of the dock 662. The marking 682 can be positioned directly below the camera 684. The surgeon can verify that the camera 684 is capturing measurements of the marking 682 by sliding the probe 678 to different positions. The surgical orientation device 172 can display the different positions of the probe 678 as the probe 678 is moved. The probe 678A can be similarly positioned within the second assembly 606A, as shown in Figure 25A.

[0168] Systems 600 and 600A can be attached to the pelvis. Fixation pins 610 and 612 can be inserted into the bone. In some techniques, one or more of the fixation pins 610 and 612 are positioned approximately 10 mm above the uppermost point on the acetabular rim. The fixation pins 610 and 612 can be perpendicular to the patient's long axis. The fixation pins 610 and 612 can be inserted using a screwdriver. In other embodiments, the fixation pins 610 and 612 are driven into the bone with a mallet until their distal ends are fully embedded within the bone.

[0169] Fixing pins 610 and 612 can be inserted into channels 626 and 628 before or after the fixing pins 610 and 612 are driven into the bone. Support portion 622 can be brought closer to platform 620, thereby reducing the diameter of channels 626 and 628. Fixing pins 610 and 612 can be fixed to fixing base 602. First assembly 604 can be coupled to first coupler 632. Surgical orientation device 172 can be coupled to first assembly 604. Second assembly 606 can be coupled to second coupler 648. Orientation detection device 204 can be coupled to second assembly 606. System 600 can be positioned as shown in Figure 18. Fixing base 202A can be fixed using fastener 613A as shown in Figure 25B. System 600A can be positioned as shown in Figure 25B.

[0170] The femoral trackers 686 and 686A can be connected to the femur. The femoral tracker 686 can be positioned on the greater trochanter. The curved end of the femoral tracker 686 can point toward the patient's head. One or more fixation devices can be positioned through each of the holes 688 of the femoral tracker 686 to fix the femoral tracker 686 to the femur. The femoral tracker 686 can be positioned as shown in Figure 18. The femoral base 687A can be positioned on the greater trochanter. The femoral tracker 686A can be assembled as shown in Figure 25C. The femoral tracker 686A can be connected to the femoral base 687A as described in this specification.

[0171] If different programs exist, the surgeon must select which hip joint will be operated on (e.g., right or left hip). The surgeon can verify that the patient is positioned in the standard lateral decubitus position. If different programs exist, the surgeon must select the gender of the patient to be operated on (e.g., male or female). If different programs exist, the surgeon must select the target cup tilt angle. This angle can be selected based on the radiographic tilt angle. If different programs exist, the surgeon must select the target cup anterior tilt angle. This angle can be selected based on the radiographic anterior tilt angle. If different programs exist, the surgeon must select the RT tilt angle. This angle can be selected based on the radiographic RT tilt angle, such as from an A / P pelvic X-ray.

[0172] The surgeon can record the stopping structure or fixed position. In some techniques, the distal ends 680, 680A of probes 678, 678A can be engaged with points on platforms 620, 620A. Platforms 620, 620A can include divots 630, 630A. Divots 630, 630A can be sized to receive the distal ends 680, 680A of probes 678, 678A. This position is shown in Figures 18 and 25B. Probes 678, 678A can be tilted relative to the vertical in a fixed position. Dock 662 can be tilted relative to the vertical in a fixed position. Orientation detection device 204 connected to dock 662 can be tilted relative to the vertical in a fixed position. Surgical orientation device 172 can also be tilted relative to the vertical in a fixed position.

[0173] The orientation detection device 204 can record the operating table, in other words, perform table recording. The patient can be positioned so that the sagittal plane of the pelvis is flat. The surgeon can align probes 678, 678A with the horizontal line. Probes 678, 678A can be parallel to the frontal plane. Systems 600, 600A can calculate the cup angle based on the assumption that the patient's pelvis is accurately positioned during table recording.

[0174] The femur can be positioned in a neutral reference position with respect to flexion, abduction, and rotation. This neutral position can represent the patient's standing position. The femur must be maintained in this position during the initial recording of points 690, such as points A, B, and C, as shown in Figures 24A and 25C. The surgeon can ensure that the orientation detection device 204 is connected to the dock 662. The surgeon can position the distal end 680, 680A of the probe at point A of points 690. In some cases, the distal end 680, 680A is positioned in a divot at point A on the femoral tracker 686, femoral base 687A. The surgeon can input a value to record point A (e.g., by pressing a button on the surgical orientation device 172). The surgical orientation device 172 can indicate that point A has been recorded. The surgeon can position the distal end 680, 680A of the probe at point B of points 690. In some cases, the distal ends 680, 680A are positioned within a divot at point B on the femoral trackers 686, 686A. The surgeon can input a value to record point B (e.g., by pressing a button on the surgical orientation device 172). The surgical orientation device 172 can indicate that point B has been recorded. The surgeon can position the distal ends 680, 680A of the probe at point C of point 690. In some cases, the distal ends 680, 680A are positioned within a divot at point C on the femoral trackers 686, 686A. The surgeon can input a value to record point C (e.g., by pressing a button on the surgical orientation device 172). The surgical orientation device 172 can indicate that point C has been recorded.

[0175] The surgeon can position the distal ends 680, 680A of probes 678, 678A to various anatomical landmarks. Figure 32 illustrates four landmarks that can be used in several techniques. In one technique, point 1 is the uppermost point of the margin. The surgeon should not remove any bone spurs from this landmark before recording point 1. The landmark on which point 1 is recorded should coincide with an anatomical structure identified on preoperative radiography. In several methods, the distal ends 680, 680A of probes 678, 678A are positioned at point 1. The surgeon can input a value to record point 1 (e.g., by pressing a button on the surgical orientation device 172). The surgical orientation device 172 can indicate that point 1 has been recorded.

[0176] Point 2 can be defined as the lowest point of the acetabular notch. The surgeon should not remove any bone spurs from this landmark before recording point 2. The landmark where point 2 is recorded should coincide with an anatomical structure identified on preoperative X-ray. The transverse acetabular ligament (TAL) spans the lower limit of the bony acetabular fossa. It is a strong weight-bearing structure and, in a normal hip joint, works with the labrum to provide part of the weight-bearing surface for the femoral head. In some cases, the distal ends 680, 680A of probes 678, 678A are positioned at point 2. The surgeon can input a value to record point 2 (e.g., by pressing a button on the surgical orientation device 172). The surgical orientation device 172 can indicate that point 2 has been recorded.

[0177] Point 3 can be the posterior insertion of the transverse acetabular ligament (TAL). The surgeon should remove any osteophytes from this landmark before recording point 3. This reveals or reproduces the original anatomical structure of the landmark. In some cases, the distal ends 680, 680A of probes 678, 678A are positioned at point 3. The surgeon can input values ​​to record point 3 (e.g., by pressing a button on the surgical orientation device 172). The surgical orientation device 172 can indicate that point 3 has been recorded.

[0178] Point 4 is, in one embodiment, the anterior insertion of the transverse acetabular ligament (TAL). The surgeon should remove any osteophytes from this landmark before recording point 4. This reveals or reproduces the original anatomical structure of the landmark. In some methods, the distal ends 680, 680A of probes 678, 678A are placed at point 4. The surgeon can input values ​​to record point 4 (e.g., by pressing a button on the surgical orientation device 172). The surgical orientation device 172 can indicate that point 4 has been recorded.

[0179] When recording an anatomical point or a point 690 on the femoral tracker 686, camera 684 captures an image of the marking 682. Camera 684 reads the marking 682 to provide a precise determination of the translational position of probe 678 relative to dock 662. Camera 684 can be positioned directly above the marking 682. In some cases, camera 684 can read the binary code of the marking 682.

[0180] In some cases, the orientation detection device 204 converts the image from the camera 684 into an extension measurement of the probe 678. In some embodiments, the surgical orientation device 172 converts the image from the camera 684 into an extension measurement of the probe 678. The distance associated with the extension of the probe 678 can be used in conjunction with orientation and position data from the orientation detection device 204. The surgical orientation device 172 can determine the position of the distal end 680 of the probe 678 using the length measurement from the camera 684 and the data from the orientation detection device 204. In some embodiments, the surgeon inputs an input value (e.g., by pressing a button) to collect data from the orientation detection device 204. In some cases, the surgeon inputs an input value (e.g., by pressing a button) to collect data from the camera 684. In some embodiments, the surgeon inputs an input value (e.g., by pressing a button) to collect data from both the orientation detection device 204 and the camera 684 simultaneously. In some cases, the orientation detection device 204 and / or camera 684 transmit data to the surgical orientation device 172 only when the orientation detection device 204 is stable or not moving. Point 690 may include a divot to stabilize the distal ends 680, 680A of probes 678, 678A when point 690 is being recorded.

[0181] The surgeon can set the angle of the cup. Later in the surgery, the surgeon can check the cup angle after it has been set. The surgeon can detach the second assemblies 606, 606A from the first assemblies 604, 604A. The surgeon can detach the extension 670 from the third coupler 668. The surgeon can connect the extension 670 to the impactor 300B as shown in Figures 56A to 56F. The impactor 300B may have a fourth coupler 338B. In some embodiments, the fourth coupler 338B is a general-purpose coupler. In some embodiments, the fourth coupler 338B is identical or substantially similar to the second coupler 648 and the third coupler 668. This allows the orientation detection device 204 to be connected to either the second coupler 648, the third coupler 668, or the fourth coupler 338B as described in this specification. The fourth coupler 338B may be the same as the first coupler 632 described in this specification. The fourth coupler 338B may extend from the side of the impactor 300B. The fourth coupler 338B may extend perpendicular to the longitudinal axis of the impactor 300B. The extension 670 may be connected to the fourth coupler 338B. The mounting portion 672 may be connected to the orientation detection device 204. The acetabular shell may be screwed into the shell adapter as in Figure 11C. The shell adapter may be fastened to the end of the impactor 300B as in Figure 11B.

[0182] The acetabular shell is inserted into the acetabular fossa and can be positioned at a desired angle. The surgical orientation device 172 can guide the surgeon to set the appropriate cup angle. The surgical orientation device 172 can display a diagram when the orientation detection device 204 is positioned at a previously entered tilt and anterior tilt angle. The surgical orientation device 172 can display the tilt and anterior tilt angles as the orientation detection device 204 is moved. The surgeon can input values ​​to set the desired angle (for example, by pressing a button on the surgical orientation device 172). The surgical orientation device 172 can output all tilt and anterior tilt angles according to the radial specifications. Anterior tilt (radial anterior tilt) is the angle between the acetabular axis and the frontal plane. Tilt (radial tilt) is the frontal projection of the angle between the acetabular axis and the longitudinal axis of the body. When the orientation detection device 204 is connected to the impactor 300B, the surgical orientation device 172 can display the radial tilt and the anterior tilt angle of the impactor 300B relative to the anterior pelvic plane.

[0183] The inclination and anterior tilt cup angles can be displayed statically. The anatomical angle is calculated by system 600 based on pelvic landmark recording. The table angle is calculated by system 600 based on the initial position of the pelvis during table recording. In some embodiments, the orientation detection device 204 can record the operating table by aligning probes 678, 678A with the horizontal line. In some embodiments, only the direction of protrusion of probes 678, 678A onto the horizontal plane is used. Probes 678, 678A can be at countless angles from the horizontal line, and it yields the same software result. This is convenient due to the mechanical constraints imposed by the rotational structure of system 600. The displayed angle can be the average between the anatomical reference point and the table reference point. The inclination angle is calculated based on the average between the anatomical reference point and the table reference point. The anterior tilt angle is calculated based on the table reference point. The surgeon can check the cup angle after the angles have been set.

[0184] The surgeon can record the center of the hip joint. The surgeon can connect the second assemblies 606, 606A to the first assemblies 604, 604A, as shown in Figures 18 and 25A. The mounting part 672 can be connected to the orientation detection device 204. The mounting part 646 can be connected to the surgical orientation device 172. The surgeon can ensure that the components of the systems 600, 600A are securely connected. The surgeon can select a first set of points on the edge of the shell 360 to be recorded, as shown in Figure 33. In the illustrated method, the first set of points is selected on the edge of the shell. The surgeon can position the distal ends 680, 680A of the probes 678, 678A to each of the first set of points shown in Figure 33. In some ways, the surgeon can select a second set of points on the edge of the shell to be recorded. In the illustrated method, the second set of points are selected on the edge of the shell. The surgeon can position the distal ends 680 and 680A of probes 678 and 678A on each of the points in the second set. In some methods, the surgeon must select a third set of points on the edge of the shell to be recorded. In the illustrated method, the third set of points are selected on the edge of the shell. The surgeon must position the distal ends 680 and 680A of probes 678 and 678A on each of the points in the third set. In some methods, the minimum separation distance allowed between points is 25 mm. In some methods, the maximum separation distance allowed between points is 65 mm.

[0185] The shell's inclination and anterior tilt angles are displayed on the surgical orientation device 172. These angles are based on a plane determined by three points recorded on the edge. The surgeon can input the liner offset to be used. The offset is the distance from the center of the shell's front to the center of the femoral head. If the shell is hemispherical and the femoral head and shell are cocentered, the surgeon can input zero. In some cases, the offset is between 0 mm and 10 mm. If the liner offset is changed later in the surgery, the surgeon can repeat this step. The surgical orientation device 172 can calculate the center of rotation (COR) of the hip joint using a set of points on the edge of the shell.

[0186] The surgeon can record the leg length and offset after implantation of the acetabular shell. The surgeon can connect the second assemblies 606, 606A to the first assemblies 604, 604A, as shown in Figures 18 and 25A. The attachment 672 can be connected to the orientation detection device 204. The attachment 646 can be connected to the surgical orientation device 172. The surgeon can ensure that the components of systems 600, 600A are securely connected. The femur can be flexed and repositioned within + / - 20° from its preoperative position. The femur can be abducted and repositioned within + / - 15° from its preoperative position. The femur can be rotated and repositioned within + / - 20° from its preoperative position.

[0187] In several methods, the distal ends 680, 680A of probes 678, 678A are positioned within the divot at point A of point 690. The surgeon can input a value to record point A (e.g., by pressing a button on the surgical orientation device 172). The surgeon can position the distal ends 680, 680A of the probes at point B of point 690. The surgeon can input a value to record point B (e.g., by pressing a button on the surgical orientation device 172). The surgeon can position the distal ends 680, 680A of the probes at point C of point 690. The surgeon can input a value to record point C (e.g., by pressing a button on the surgical orientation device 172). The surgical orientation device 172 can indicate that points A, B, and C have been recorded. Using points A, B, and C, the surgical orientation device 172 can calculate the change in the angle between the pelvis and the femur since the initial recording before dislocation. The surgical orientation device 172 can mechanically rotate points A, B, and C on the femur around the center of rotation (COR) of the hip joint to align the femur to its initial position. The new positions of the centers of gravity of points A, B, and C on the femur are compared to the initial positions. Points A, B, and C on the femur can be positioned on femoral trackers 686, 686A, or femoral base 687.

[0188] Leg length and offset are displayed on the surgical orientation device 172. Changes in leg length are in the proximal-distal direction. Joint offset is in the medial-lateral direction. If the angle between the femur and pelvis changes significantly beyond the hardcoded limits in any axis, the surgical orientation device 172 may display an error message. The hardcoded limits can be 15°, 10-20°, 5-25°, etc. The surgical orientation device 172 may display guidance on repositioning the femur (e.g., abducting the femur, flexing the femur, etc.). The surgeon may replace or reposition the shell to adjust the leg length and offset. The surgeon may replace or reposition the shell based on a target from a preoperative template or image. Where desired and possible, leg length and offset may be adjusted according to the surgeon's standard surgical procedures.

[0189] The surgeon can record the fixed position. The surgeon can connect the second assemblies 606, 606A to the first assemblies 604, 604A, as shown in Figures 18 and 25A. The mounting part 672 can be connected to the orientation detection device 204. The mounting part 646 can be connected to the surgical orientation device 172. The surgeon can verify that the components of the system 600, 600A are securely connected. The surgeon can verify the stop structure or fixed position. The distal ends 680, 680A of the probes 678, 678A can engage with points on the platform 620, 620A. The platform 620, 620A may include divots 630, 630A. The divots 630, 630A can be sized to receive the distal ends 680, 680A of the probes 678, 678A. This position is shown in Figures 18 and 25B. Changes in the fixed position are displayed on the surgical orientation device 172. The numbers may not be zero due to mechanical play and / or sensor noise. If the displayed number is greater than 3 mm, the surgeon may wish to verify the secure connections between the components of systems 600 and 600A.

[0190] [B. Navigation using fixtures and inertial sensors for referencing anatomical landmarks via an anterior approach] [1. Forward approach: A system using an orientation detection device connected to the probe] Figures 34–38 illustrate a hip joint navigation system 500 adapted for navigating hip replacement surgery from an anterior approach. An anterior approach to hip replacement surgery can be advantageously less invasive than a posterior approach. In particular, an anterior approach allows for smaller resections, less incision in soft tissue, and a shorter recovery period for the patient. The system 500 includes an anchoring system 504, a positioning assembly 508, and a landmark acquisition assembly 512.

[0191] Figure 34 shows the anchor system 504 in more detail. This anchor system 504 is configured to securely connect the navigation system 500 to the hip joint. This minimizes or eliminates movement between the system and the hip joint. The anchor system 504 includes a cannula 516, which has a distal end 520, a proximal end 524, and a lumen 502 extending between the distal and proximal ends. The proximal end 524 of the cannula 516 is connected to a platform 536, for example, adjacent to one of the lateral ends of the platform. The platform 536 is similar to the platform described above and has a number of docking devices 538, 538A located away from the location where the proximal end 524 and the platform 536 are connected.

[0192] The docking device 538 securely connects the sensor to the anchor system 504, but is configured to connect to a detachable mounting device that temporarily connects the sensor to the anchor system 504. The two docking devices 538 on the upper surface of platform 536 allow the anchor system 504 to be used for either left-side hip surgery or right-side hip surgery. As shown in Figure 34, the docking device 538 on the side of platform 536 closest to the patient's medial plane is preferably used for docking. The upper docking feature not used in Figure 34 would actually be used when performing surgery from the other side of the patient. The docking device 538A on the side of platform 536 is provided for temporary mounting of the sensor to platform 536 during surgery. As will be further discussed below, this temporary mounting provides a known orientation and / or position of the two sensors relative to each other during surgery. This allows system 500 to control the source of errors by certain types of sensors.

[0193] The platform 536 may also have a channel 540 positioned away from the cannula 516. The channel 540 may have a lumen positioned along an axis substantially parallel to the lumen 532 of the cannula 516. In one embodiment, the anchoring system 504 is configured to securely connect the platform 536 to the hip joint by the arrangement of two spaced-apart pins 544A, 544B. Figure 34 shows that pin 544A is advanced through the cannula 516 so that its distal end can contact and perforate a bony prominence of the pelvis. In one technique, pin 544A is positioned at the anterior superior iliac spine (ASIS) of the pelvis, or as close as possible to the anterior superior iliac spine (ASIS) of the pelvis. Pin 544B is advanced into the pelvis through the channel 540 at a position offset from the anterior superior iliac spine (ASIS). The distance between pin 544A and pin 544B and the exact position of pin 544B are not important, but are determined by the position of the connection of the cannula 520 to the platform 536 and the position of the channel 540.

[0194] The pins 544A and 544B can take any suitable shape, but preferably have the same cross-sectional contour as the lumen in the cannula 520 and the lumen in the channel 540. For example, they can have a circular cross-section. The pins 544A and 544B can be improved Steinman pins, for example, pins configured to extend at least about 5 cm on the platform 536 and having a diameter of about 4 mm.

[0195] The anchor device 504 also has a locking device 556 for fixing the platform 536 to pins 544A, 544B. In one embodiment, the portion of the platform disposed around the pins includes an inner portion 560M and an outer portion 560L, and the inner portion 560M and the outer portion 560L can move away from each other to release the pins 544A, 544B, or can move toward each other to frictionally engage the pins. For example, a pair of hex drive screws can engage the inner portion 560M and the outer portion 560L to translate them toward each other or away from each other, respectively. The locking device 556 is preferably removed quickly and easily from the pins, whereby other instruments such as an X-ray diagnostic device or other diagnostic device can reach near the surgical field during surgery. Preferably, the pins 544A, 544B have markings along their lengths. Thereby, when the platform 536 is removed for imaging or other reasons, it can be quickly repositioned at the same height.

[0196] The cannula 520 also has a foot 568 adjacent to or at the distal end portion 528 to minimize or exclude errors that may occur due to the non-uniform penetration depth of the anchor system 504 when comparing with the position of the distal probe of the landmark acquisition system 512 when a landmark is acquired. The foot 568 can include an annular protrusion disposed outside the cannula 520. Preferably, the foot 568 extends laterally from the outer surface of the cannula 520 by a distance equal to or greater than the wall thickness of the cannula 520. In some embodiments, the surface area under the foot is equal to or greater than the surface area of the cannula when viewed in a cross-section at a position where the foot 568 is not located, for example, at a height with respect to the foot 568.

[0197] The alignment assembly 508 is similar to the assemblies described above. The alignment assembly 508 can have a rigid extension 570 configured to removably secure the orientation device 172 to the docking device 538.

[0198] The landmark acquisition assembly 512 is similar to the assemblies described above but is configured to not be blocked during use by the soft tissue anterior to the patient's pelvis. In one embodiment, the extension 578 is provided with a pivot slide mechanism 582 that elevates. The pivot slide mechanism allows the probe arm 584 to slide towards the position of the landmark to be acquired away from the extension 578. The pivot slide mechanism 582 can be similar to any of the mechanisms discussed above. The distal end (lower end) of the extension 578 can be connected to the platform 536 in any suitable manner. For example, the distal end can include a pin-like protrusion that is received within an opening 578A having the same shape, e.g., friction fit within the opening 578A. A detent or other locking feature can be provided to securely connect the extension to the platform 536 at the opening 578A. FIG. 35 shows that the opening 578A can be formed in a portion of the platform 536 that is elevated compared to a portion of the platform 536 through which the pin "544A" extends. This portion is elevated to provide sufficient support engagement to minimize play. It also has slots substantially parallel to the upper surface of the platform 536, and these slots function to engage a ball detent at the lower end of the extension 578.

[0199] The probe arm 584 can be configured as an elongated member having multiple markings, as discussed below. The distal end of the probe arm 584 may include an inclined tip 586, which in some techniques assists in examining precise anatomical structures, for example, examining the portion of the femur for confirmation of leg length and femoral head positioning. In a posterior approach, the inclined tip 586 is used to make direct contact with anatomical structures.

[0200] In the forward approach, the inclined tip 586 is connected to a probe extension 590 configured to contact a selected anatomical structure. The probe extension 590 has an upright member 592, which is configured to extend downward in the forward approach, between the heights of the probe 584, toward the height of the tissue to be examined. A foot 594 on the distal end (lower end) of the upright member 592 is configured to engage with the tissue in a manner that minimizes errors caused by uneven tissue compression between the mounting point of the pin 544A and the mounting point of the foot 594. For example, the foot 594 may have a cross structure that spreads the force or pressure applied by the landmark acquisition system 512 during use. The proximal end of the extension 590 includes a connector 596, which connects the distal end of the probe arm 584 to the upright member 592. Preferably, the connector 596 is easily operable by the user to correct the connection to the probe arm 584. The connecting portion may include an L-shaped member having a hole configured to receive the tip 586 of the probe arm 584. A set screw can be driven through the L-shaped portion to secure the probe arm 584 in place. The L-shaped portion is configured to connect to the probe arm 584, thereby resting the tip of the inclined tip 586 on a projection of the longitudinal axis of the upright member 592.

[0201] [2. Forward approach: Method using an orientation detection device connected to the probe] The system 500 can be used to navigate from a forward approach in the following ways: The orientation device 172 and the sensor 204 can be paired to communicate wirelessly with each other. This allows one or the other of the orientation device 172 and the sensor 204 to control the other, store data from the other, and / or display information based on the signals from the other. In one way, the orientation device 172 has a display that allows the surgeon to confirm a predetermined angle based on data detected by the sensor 204. The paired orientation devices 172 and the sensor 204 can include linking them together and comparing sensor outputs between the two devices in multiple orientations, for example, horizontal, vertical, and 30-degree angles. Some of these positions can be repeated in multiple orientations, for example, a vertical orientation with the left side up, a vertical orientation with the right side up, and a vertical orientation with the top side up.

[0202] As described above, the components discussed in this specification can be provided as a kit that allows a surgeon to select between different surgical approaches, for example, between a posterior approach and an anterior approach. The orientation device 172 and sensor 204 can be operated differently in those different approaches. Therefore, in one way, the user will enter into one or both of the orientation device 172 and sensor 204 in which the approach being used will be. This will execute a software module in the orientation device 172 corresponding to the selected approach (or, in the sensor 204, a processor that executes the software is located therein).

[0203] In various embodiments suitable for forward approaches, both the orientation device 172 and the sensor 204 may have multiple power-free sensors. These components may, in some embodiments, include accelerometers and gyroscopes. Some gyroscopes are affected by accumulated errors that may be significant in the time frame in relation to their methods. Accordingly, various methods are provided to prevent such errors from affecting the accuracy and reliability of the angles displayed to the surgeon by the system 500. Some approaches can be performed by accelerometers alone. For example, a variation of the forward approach can be performed by an accelerometer with somewhat lower accuracy, although the accuracy when using only an accelerometer is acceptable. The reduction in accelerometer accuracy is balanced by the benefit of excluding accumulated errors caused by some gyroscopes. The resolution of the accelerometer is sufficient because the navigated points are relatively far apart.

[0204] The calculations performed by System 500 are specific to the hip joint being treated in some embodiments, and the system accepts input of the hip joint being treated.

[0205] The foot portion 568 is positioned at a selected anatomical location, for example, on the anterior superior iliac spine as discussed above. When the cannula 520 is oriented approximately vertically, the platform 536 is fixed to the hip joint. Fixing the platform 536 to the hip joint can be done in any suitable way, such as with two spaced Steinmann pins. The orientation device 172 and sensor 204 are then attached to the platform 536 in the manner shown in Figure 36A. Depending on the nature of the dispersed sensing devices in sensor 204, it may be advantageous to initialize the sensor at a point in this surgery. As discussed above, certain inertial sensors (e.g., some gyroscopes) are affected by accumulated errors. One technique for managing the cause of this error is to periodically initialize, or zero, this error. Some techniques involve initializing at a point in time.

[0206] In some embodiments, a coordinate system based on the plane of the operating table can be input into the system 500. The operating table coordinate system can be a secondary coordinate system. In one technique, the sensor 204 is moved from the platform docking position in Figure 36A to a navigation position on the probe arm 584 as shown in Figure 34. The probe arm 584 is consequently rotated by the mechanism 582. Thereafter, the arm is oriented parallel to the medial-lateral central plane of the patient, and the inclined tip 586 is oriented upward (generally towards the patient's head). The probe arm 584 is also held substantially parallel to the plane of the operating table. This orientation and orientation allow the user to interact with the user interface on the orientation device 172 to send a signal to the orientation system 508 to capture the orientation of the sensor 204. This orientation provides an estimate of the orientation of the anterior pelvic plane. This estimate can be tracked in the system 500 and can alone provide an improvement over prior art in unnavigated hip replacement surgery, including individual operations guided by the naked eye.

[0207] At the surgeon's discretion, system 500 can be used to navigate the condition of the femur before hip replacement surgery. A mark Fm can be formed on the proximal part of the femur. The sensor 204 can then be initialized or set to zero by positioning it back to a docking position on the platform, for example (as shown in Figure 36A). The probe tip 586 can then be brought into contact with the femoral mark Fm and fixed in place in such contact. See Figure 37. The sensor 204 can be moved to the proximal end of the probe 584, and the orientation device 172 can send a signal to record the orientation of the sensor 204. The distance from the attachment point of the cannula 520 to the anterior superior iliac spine relative to the marked position on the femur can then be recorded by the orientation device 172. This position can be based on reading the memorized mark on the probe 584, or it can be automatically captured by a camera system or a sensor incorporated within system 500. In one embodiment, the memory mark is read by the upright edge 598 within the curved portion of the sliding part of the rotating slide mechanism 582.

[0208] Figure 36A illustrates a further step in navigating the anterior pelvic plane. As shown, the sensor 204 is docked to the platform 204. At this position, any accumulated errors associated with several sensors can be eliminated. In the aforementioned step, the extension 590 is coupled to the distal portion of the probe 584. The foot portion 594 is in contact with the contralateral anterior superior iliac spine (ASIS). The sensor 204 can then be attached to the proximal end of the probe 284, as shown in Figure 34. The landmark acquisition system 512 can be fixed in place, and the orientation of the sensor 204 can be recorded in the memory of the orientation device 172. Furthermore, the distance that the probe 584 extends to contact the contralateral anterior superior iliac spine can be recorded in the orientation device 172. As described above, that distance can be read from the scale of the probe 584 at the upright edge 598.

[0209] The step of recording the contralateral anterior superior iliac spine can be repeated for one or more further points. Sensor 204 can be docked to a platform as shown in Figure 36A to eliminate the source of accumulated errors. Probe 584 can then be moved to bring the foot portion 594 into contact with the pubic tubercle. Probe 584 can be fixed, and the sensor can be coupled to its proximal end as shown in Figure 36B. Subsequently, data indicating the orientation of sensor 204 and the distance to the pubic tubercle are recorded in the orientation device 172 in one of the methods discussed above.

[0210] Once the aforementioned points on the pelvis are navigated and the data is recorded in the orientation device 172, the anterior pelvic plane can be calculated from the data indicating the navigated points. The orientation of the anterior pelvic plane is the baseline for the placement of the cup portion of the artificial hip joint.

[0211] Sensor 204 and orientation device 172 can be used at this point to guide the placement of cup 360 in a defined orientation. Prior to placement, impactors 300, 300A are provided. For example, impactor 300A can be provided by selecting a suitable tip component 348 for the distal end of shaft 316A. The tip component 348 is connected to cup 360, for example, by a screw. The rotational orientation of cup 360 relative to shaft 316A, which is the most convenient given hole pattern and position of sensor 204, is selected by combining flat sections 350A, 350B as needed. During the process of providing impactor 300, sensor 204 can be docked to platform 536, and the source of accumulated errors can be eliminated just before navigating cup 360 into place in the acetabular fossa.

[0212] In one technique, the cup 360 is inserted into the acetabular fossa and positioned in an approximately correct orientation. The sensor 204 is then connected to a docking device 338 on the impactor, as shown in Figure 11A. The orientation device 172 is activated to display angles indicating the orientation of the cup, such as the inclination angle and anterior tilt angle relative to the anterior pelvic plane. The displayed angles can be directly reflected in the coordinate system of the operating table discussed above. The displayed angles can also directly reflect the coordinate system from the acquisition of landmarks. In some cases, angles that directly reflect both the operating table coordinate system and the landmark coordinate system can be displayed. In other embodiments, the operating table coordinate system is not displayed, but rather the orientation device 172 displays instructions such as directions for reacquiring landmarks due to discrepancies between the angles resulting from the two coordinate systems.

[0213] Either of the aforementioned combinations of the operating table coordinate system and the landmark coordinate system provides redundancy to ensure that the angular information provided to the user is accurate and reliable, thereby ensuring that the surgery being performed is well contained within the "safe zone."

[0214] If the correct angle is achieved, the tool is used to strike the proximal end of the impactor 300 to fit the cup 360 into place at the desired angle. In some techniques, the sensor 204 is removed before striking the proximal end of the impactor 300. The system 500 includes a module that monitors the signal from the sensor 204. If a large deviation occurs in the reading, the module prevents the angle on the orientation device's display from changing. This "freezing" on the display is a precaution for both safety and accuracy, as a large force resulting from the impact can affect the accuracy of the sensor 204.

[0215] If a femoral landmark was acquired during surgery before separating the original hip joint, the same landmark can be acquired after the prosthesis is placed to confirm that the hip replacement has not altered the leg length from the patient's torso, leg offset, or both. For example, sensor 204 can be docked to docking device 538A, as shown in Figure 36A. The source of accumulated errors can be eliminated by initializing sensor 204. The probe arm 538 can then be brought into contact with the same landmark (e.g., Fm) acquired earlier during surgery. See Figure 38. The probe arm 538 can be fixed in place, and then sensor 204 can be connected to the proximal end of probe arm 538. The orientation of the sensor and the distance to probe arm 538 can be input to orientation device 172. These data enable orientation device 172 to output the amount of change in leg length and leg offset.

[0216] In one modification, multiple points, for example, three points in the femur, are obtained before and after joint replacement. This approach allows for further confirmation that the rotational orientation of the femoral neck with respect to an axis extending through the center of the cup 360 perpendicular to the plane of the acetabular fossa has not changed postoperatively.

[0217] Naturally, femoral recording procedures allow for the correction of diagnosed deformities, including excessive leg length offset, joint offset, and poor orientation of the femoral neck in the original hip joint. In other words, a surgeon can initiate surgery with the intention of adding some offset or altering rotational orientation to improve the position and / or orientation of the patient's bone after the operation.

[0218] [3. Forward Approach: System using orientation detection device and camera] FIG. 39 shows a system 600 adapted to navigate hip surgery with reference to anatomical landmarks from a front approach. The system 600 can include an orientation detection device 204 not shown in FIG. 39 as described above. The system 600 can be adapted to either a posterior approach or a front approach as described above.

[0219] FIGS. 40 - 42 show a hip navigation system 600B adapted to navigate hip surgery with reference to anatomical landmarks from a front approach. As described above, in a front approach, the patient is in a supine position. The system 600B can include any of the above features, including those referring to the system 600. The system 600B can be used in any technique or method described in this specification. The system 600B can include a surgical orientation device 172 described in this specification. The system 600B can include an orientation detection device 204 described in this specification. The system 600B can include a camera 684 described in this specification.

[0220] The surgical orientation device 172 and the orientation detection device 204 can be turned on before the surgery begins. If this system can be used in a posterior or front approach, one method can include the surgeon selecting the module corresponding to that approach. For example, the surgeon can select a front hip approach module or a posterior hip approach module in the surgical orientation device 172. In some embodiments, this method can include the step of inputting surgical techniques into the surgical orientation device 172. The surgeon can verify that the patient is positioned in an appropriate position, for example, in a supine position. The surgical orientation device 172 can include a display screen. The display screen can confirm the communication between the surgical orientation device 172 and the orientation detection device 204.

[0221] Systems 600 and 600B can be partially assembled for calibration. In some embodiments, the first assembly 604 can be assembled. The pelvic bracket 638 can be coupled to the extension 644 if it is a separate component. The surgical orientation device 172 can be coupled to the mounting portion 646. In some techniques, the extension 670 can be coupled to the second coupler 648. The orientation detection device 204 can be coupled to the mounting portion 672. The surgical orientation device 172 and the orientation detection device 204 generally form a V-shaped structure, similar to the orientation shown in Figure 31. The orientation detection device 204 can be fixed in place to the surgical orientation device 172.

[0222] The surgical orientation device 172 and orientation detection device 204 can be calibrated. The surgical orientation device 172 can be placed on a flat horizontal surface with the display facing upward. The surgeon can hold the assembly 604, 606 or 604B, 606B in a stable position until the surgical orientation device 172 indicates completion. The surgical orientation device 172 can be placed on a flat vertical surface with the display facing sideways. The surgeon can hold the assembly 604, 606 or 604B, 606B in a stable position until the surgical orientation device 172 indicates completion. The assembly 604, 606 or 604B, 606B can be positioned to the left of the surgical orientation device 172 so that the left side is on a flat surface. The surgeon can hold the assembly 604, 606 or 604B, 606B in a stable position until the surgical orientation device 172 indicates completion. Assembly 604, 606, or 604B, 606B can be tilted forward to verify calibration. The surgeon can keep assembly 604, 606, or 604B, 606B stable until the surgical orientation device 172 indicates completion.

[0223] The extension 670 can be separated from the second coupler 648 as described in this specification. The second assembly 606 can be assembled as shown in Figures 39 and 40. The first assemblies 604, 604B can be coupled to the second assemblies 606, 606B as shown in Figures 39 and 40. The probes 678, 678B can be inserted into the through-lumens of the docks 662, 662B. The marking 682 can be positioned directly below the camera 684. The surgeon can verify that the camera 684 is capturing measurements of the marking 682 by sliding the probes 678, 678B to different positions. An error message may be displayed if the camera 684 is not reading the marking 682.

[0224] Systems 600 and 600B can be attached to the pelvis. Fixation pins 610 and 612 can be inserted into the bone. In some techniques, one or more of the fixation pins 610 and 612 are positioned across the ASIS on the surgical side. In some techniques, one or more of the fixation pins 610 and 612 are positioned at the iliac crest. The fixation pins 610 and 612 can be positioned nearly vertically. The fixation pins 610 and 612 can be inserted using a screwdriver. The fixation bases 602 and 602B can be rotated if necessary to position the fixation pins 610 and 612 within the channels 626 and 628, as shown in Figure 20C. The support 622 can be brought closer to the platform 620, thereby reducing the diameter of the channels 626 and 628. The fixation pins 610 and 612 can be fixed to the fixation bases 602 and 602B.

[0225] The first assemblies 604, 604B can be coupled to the first coupler 632 as described in this specification. The surgical orientation device 172 can be coupled to the first assemblies 604, 604B. The second assemblies 606, 606B can be coupled to the second coupler 648 as described in this specification. The orientation detection device 204 can be coupled to the second assembly 606. The system 600 can be positioned as shown in Figures 39 and 41.

[0226] The surgeon can record a stopping structure or fixed position as shown in Figure 41. In some techniques, the distal ends 680, 680B of probes 678, 678B can be engaged with a point on platform 620 or cannula 621B. Platform 620 or cannula 621B may include a divot 630 as described in this specification. The divot 630 may be sized to receive the distal ends 680, 680B of probes 678, 678B. The distal ends 680, 680B of probes 678, 678B may be curved or bent to facilitate the placement of an anatomical landmark or point as shown in Figures 39 and 40. Probes 678, 678B may be vertical in fixed position. The orientation detection device 204 may be vertical in fixed position.

[0227] The orientation detection device 204 can record the operating table or perform table recording for an anterior approach. The patient can be positioned so that the frontal plane of the pelvis is flat. In some embodiments, the surgeon can align probes 678, 678B with the horizontal line. In some embodiments, only the direction of projection of probes 678, 678A toward the horizontal plane is used. Probes 678, 678A can be at countless angles from the horizontal line, and it will yield the same software result. This is convenient due to the mechanical constraints imposed by the rotational structure of system 600. Probes 678, 678B can be parallel to the sagittal plane. System 600, 600B can calculate the cup angle based on the assumption that the patient's pelvis is precisely positioned during table recording.

[0228] At the surgeon's discretion, systems 600, 600B may be used to navigate the state of the femur before hip replacement. A mark Fm may be created on the proximal femur. The orientation detection device 204 can then be initialized or set to zero by being positioned to return to its fixed position, as described in this specification. Subsequently, the distal ends 680, 680B of probes 678, 678B can be brought into contact with the femoral mark Fm. The surgical orientation device 172 can transmit a signal to record the orientation of the orientation detection device 204. The distance from the mounting points of the fixation pins 610, 612 to the marked position on the femur can then be recorded in the surgical orientation device 172. This position may be based on capturing the marking 682, probes 678, 678B, or probe inlay 676 by camera 684, in conjunction with inertial data from the orientation detection device 204.

[0229] The femur can be positioned in a neutral reference position with respect to flexion, abduction, and rotation. This neutral position can represent the patient's standing position.

[0230] The surgeon can position the distal ends 680, 680B of probes 678, 678B at various anatomical landmarks. The surgeon can maintain hip joint stability. In some methods, point 1 of the system is the attachment point of one or more fixation pins 610, 612. Referring back to Figure 39, each fixation pin 610, 612 can be driven into the pelvis. In some techniques, one of the fixation pins 610, 612 is attached to the pelvic bone at a landmark. If one of the fixation pins 610, 612 is connected to a landmark, only two additional landmarks are acquired in some embodiments, as discussed below. In some methods, the distal ends 680, 680B of probes 678, 678B are positioned at contralateral ASIS landmarks. The surgeon can input a value to record point 2 (e.g., by pressing a button on the surgical orientation device 172). The surgical orientation device 172 can indicate that point 2 has been recorded. The probes 678 and 678B can be fixed in place, and the orientation of the orientation detection device 204 can be recorded by the surgical orientation device 172. In addition, the distance to which the probes 678 and 678B extend to contact the contralateral ASIS can be captured by the camera 684 and recorded by the orientation device 172.

[0231] The process of recording the contralateral ASIS can be repeated at one or more additional points. In some cases, the distal ends 680, 680B of probes 678, 678B are positioned on the pubic tubercle. The surgeon can input a value to record point 3 (e.g., by pressing a button on the surgical orientation device 172). The surgical orientation device 172 can indicate that point 3 has been recorded. In some cases, either pubic tubercle may be used as a reference. Probes 678, 678B can be fixed in place, and the orientation of the orientation detection device 204 can be recorded by the surgical orientation device 172. In addition, the distance that probes 678, 678B extend to contact the pubic tubercle can be recorded by the orientation device 172, when captured by the camera 684.

[0232] When recording anatomical points, camera 684 captures an image of marking 682. Camera 684 reads marking 682 to provide precise determination of the translational positions of probes 678, 678B relative to dock 662. Camera 684 can be positioned directly above marking 682. In some cases, camera 684 can read the binary code of marking 682.

[0233] In some cases, the orientation detection device 204 converts images from camera 684 into extension measurements of probes 678 and 678B. In some embodiments, the surgical orientation device 172 converts images from camera 684 into extension measurements of probes 678 and 678B. Distances related to the extensions of probes 678 and 678B can be used in conjunction with orientation and position data from the orientation detection device 204. The surgical orientation device 172 can determine the positions of the distal ends 680 and 680B of probes 678 and 678B using length measurements from camera 684 and data from the orientation detection device 204. In some embodiments, the surgeon inputs values ​​(e.g., by pressing a button) to collect data from the orientation detection device 204. In some cases, the surgeon inputs values ​​(e.g., by pressing a button) to collect data from camera 684. In some embodiments, the surgeon inputs values ​​(e.g., by pressing a button) to collect data from both the orientation detection device 204 and camera 684 simultaneously. In some cases, the orientation detection device 204 and / or camera 684 transmit data only when the orientation detection device 204 is stable or not moving.

[0234] Once the aforementioned points on the pelvis are navigated and the data is recorded in the surgical orientation device 172, the anterior pelvic plane can be calculated from the data indicating the navigated points. The orientation of the anterior pelvic plane is the baseline for the placement of the cup portion of the artificial hip joint.

[0235] The orientation detection device 204 and the surgical orientation device 172 can be used at this point to guide the placement of the cup in a predetermined orientation. The surgeon can set the angle of the cup. Later in the surgery, the surgeon can check the cup angle after it has been set. The surgeon can remove the second assembly 606 from the first assembly 604. The surgeon can remove the extension 670 from the third coupler 668. The surgeon can connect the extension 670 to the impactor 300B as shown in Figures 56A to 56F. The impactor 300B may have a fourth coupler 338B, which allows the orientation detection device 204 to connect to the fourth coupler 338B. The acetabular shell can be screwed into the shell adapter, as shown in Figure 11C. The shell adapter can be secured to the end of the impactor 300B, as shown in Figure 11B.

[0236] The acetabular shell is inserted into the acetabular fossa and can be positioned at a desired angle. The surgical orientation device 172 can guide the surgeon to set the appropriate cup angle. The surgical orientation device 172 can display a diagram when the orientation detection device 204 is positioned at the tilt and anterior tilt angles entered by the surgeon. The surgical orientation device 172 can display the tilt and anterior tilt angles as the orientation detection device 204 is moved. The surgeon can enter input values ​​to set the desired angle (for example, by pressing a button on the surgical orientation device 172).

[0237] The inclination and anterior tilt cup angles can be displayed statically. The anatomical angles are calculated by System 600 based on pelvic landmark recordings. The table angles are calculated by System 600 based on the initial position of the pelvis in the table recording. The surgeon can check the cup angles after the angles have been set.

[0238] If a femoral landmark Fm is acquired during surgery before the original joint is separated, the same landmark can be acquired after the prosthesis is placed to confirm that the joint replacement does not alter the leg length from the patient's torso, leg offset, or both. Subsequently, the distal ends 680, 680B of probes 678, 678B can be brought into contact with the same landmark (e.g., Fm) acquired earlier during surgery. The orientation of the orientation detection device 204 and the extension of probes 678, 678B can be input to the surgical orientation device 172. These data enable the surgical orientation device 172 to output the changes in leg length and leg offset.

[0239] In the above modified example and in Figure 24A, connected to systems 600 and 600B, multiple points on the femur, for example, three points, are acquired before and after joint replacement using, for example, a femoral tracker 686. This approach allows for further confirmation that the rotational orientation of the femoral neck with respect to an axis extending through the center of the cup perpendicular to the plane of the acetabular fossa has not changed postoperatively.

[0240] The surgeon can record the fixed position. The surgeon can connect the second assemblies 606, 606B to the first assemblies 604, 604B as shown in Figures 39 and 40. The mounting portion 672 can be connected to the orientation detection device 204 as described in this specification. The mounting portion 646 can be connected to the surgical orientation device 172 as described in this specification. The surgeon can verify that the components of the systems 600, 600B are securely connected. The surgeon can verify the stop structure or fixed position. The distal ends 680, 680B of the probes 678, 678B can engage with a point on the platform 620 or cannula 621B. The platform 620 or cannula 621B may include a divot 630 as described in this specification. The divot 630 can be sized to accommodate the distal ends 680, 680B of probes 678, 678B. Changes in position are indicated by the surgical orientation device 172.

[0241] [C. Preoperative imaging and navigation using patient-specific fixtures] While the aforementioned approaches can improve treatment standards in the current configuration, further increases in accuracy, better outcomes, and simplification of surgery can be achieved if the system is configured to take into account patient-specific anatomical variations.

[0242] [1. Patient-specific fixtures: Navigation using fixing pins that are attached via patient-specific fixtures] Figure 43 shows the placement of the hip joint movement tracking sensor 204 on pin 732 adjacent to the acetabular fossa. While this position is not limited, the hip joint movement tracking sensor 204 can be mounted anywhere on the pelvis. However, the position adjacent to the acetabular fossa is convenient. Pin 732 is positioned using patient-specific preoperative hip joint characterization. In these methods, pin 732 is positioned without the need for intraoperative landmark acquisition.

[0243] In one approach, preoperative three-dimensional characterization of the acetabular fossa is performed using appropriate techniques such as CT scans or MRI. This preoperative procedure can be performed to fully characterize the pelvis and, in some cases, the proximal femur. Subsequently, the shape, position, and orientation of the acetabular fossa are known. Similarly, the bone features around the acetabular fossa are also known. From this data, a custom fixture 700 can be manufactured specifically for the patient. The custom fixture 700 will have features that are not only specific to the anatomical structure of the individual patient, but also recorded features 702 that will be known orientations of the acetabular fossa relative to the plane and the anterior pelvic plane.

[0244] Figure 44 shows an example of a custom fixture 700. The custom fixture 700 has an anterior surface 704 and a posterior surface 708. The posterior surface 708 is formed by an acetabular portion 712 configured to securely bond with at least one feature of the acetabular fossa. For example, the acetabular portion 712 can fit snugly across the acetabular rim with the central portion of the posterior surface 708 positioned within the acetabular fossa. The custom fixture 700 preferably has only one predefined orientation. The surface on the posterior portion of the fixture can define a plane corresponding to a preferred orientation angle of the implanted cup. One or more channels 716 can be formed on the posterior surface 708, and these channels 716 accept local bony prominences of the acetabular rim only when the custom fixture 700 is in the appropriate position and orientation. In another approach, the recording feature 702 of the custom fixture 700 has a surface or hole that is oriented in a desired orientation for the implant shell or cup. Therefore, when the custom fixture 700 is positioned, the sensing device 204 can be positioned relative to a face or surface, and when the pin 732 is connected, the pin can be inserted into the hole. When positioned in this manner, the orientation of the device, the orientation of the acetabular rim, or a substitute thereof, can be recorded by one or both of the devices 172, 294. The hole 702 preferably extends from the anterior surface 704 to the posterior surface 708 of the custom fixture 700. The distance between the anterior surface 704 and the posterior surface 708 provides a depth of the hole 702 that is considered sufficient to guide the pin to a specific anatomical structure along a particular direction.

[0245] Figure 45 shows the initial placement of the custom fixture 700 within the acetabular fossa in an orientation indicated by the fitting of the custom fixture 700 to the anatomical structure. The appearance of the posterior surface 708, including the channel (multiple channels) 716, accommodates the patient-specific acetabular rim, including local bony protrusions and recesses, in and around the acetabular fossa. The opening 702 is located in the periphery projection 720 of the custom fixture 700. The structure of the periphery projection 720 is designed to be positioned over a specific bone or bone region of the hip joint. In this example, the periphery projection 720 is configured to be positioned over the bone superior to the acetabular fossa. Other regions of bone around the acetabular fossa can be used if they are sufficiently thick or strong and conveniently located so as not to interfere with the surgeon's movements during surgery. The precise location of the selected periphery projection 720 can be determined by preoperative imaging and incorporated into the formation of the custom fixture 700.

[0246] Figure 46 shows that after the fixture is positioned, the pin 732 can be positioned through the hole 702. The pin 732 has a length that extends above the anterior surface 704 of the fixture 700, thereby allowing the sensor 204 to be attached to it. Once the sensor 204 is attached to the pin, the sensor can track any movement of the pelvis during surgery. Since the position and orientation of the pin relative to the acetabular fossa and / or anterior pelvic plane are known from preoperative imaging, there is no need to record landmarks in this technique.

[0247] Figure 47 shows that the plug 700 may advantageously include an alignment guide 736 to control the rotational orientation of the sensor 204 on the pin 732. The alignment guide 736 may be a line extending along a specific direction with respect to the recording feature 702. As described above, the sensing device inside the sensor 204 may be sensitive to the direction of gravity. The tilt of the sensor with respect to the pin 732 can alter the reading of the sensing device. To eliminate the source of error associated with this sensitivity, the navigation system incorporating the sensor 204 may be programmed to assume that the sensor will be in a specific rotational position with respect to the longitudinal axis of the pin 732. The sensor 204 may be mechanically or visually aligned with a guide mark 738 to ensure that this assumption is satisfied during use. In one modification, the sensor 204 may have a laser projected onto the fixture 700 and be aligned with the mark 736 to facilitate alignment. Alternatively, pin 732 may be configured to enter only the hole in a specific orientation (e.g., an asymmetric non-circular cross-section) and to allow the sensor to be attached to the pin in a specific orientation (by including an asymmetric connection feature).

[0248] Once the sensor 204 is attached to the pin 732, the fixture 700 can be removed from the surgical area. For example, the fixture 700 can be manufactured from a material that can be cut along line 742 at the lateral edge of the fixture. A saw or bone forceps can be used to cut through the fixture 700. The majority of the body of the fixture 700 can then be removed from the surgical area. Figure 49 shows that the projection 720 remains in place in several ways so as not to disrupt the position and orientation of the sensor 204.

[0249] A second sensor 204 is mounted on a cup impactor, which may be similar to the impactor shown in Figures 11A-11C. The impactor guides the placement of the cup by referring to signals from sensor 204 mounted on pin 732 on the pelvis. Signals from the sensors on the impactor can be corrected if hip joint movement is detected by the sensors on pin 732.

[0250] Figures 50 to 52 illustrate one method of implementing a cannula-type guide supply method. The cannula-type method is advantageous in that, once the guide member is attached, orientation tracking is simplified, and in some cases, orientation tracking may no longer be necessary, as accumulated errors, sensor drift, or other types of misreadings of interest can be excluded.

[0251] The custom fixture 750 is formed by the process discussed above in relation to fixture 700. The custom fixture 750 has many of the same components as fixture 700, including recording features 752 extending between the anterior surface 754 and the posterior surface 758. Guide marks 738 can be provided on the anterior surface 754 to rotatably align the sensor 204 with respect to a pin 732. The custom fixture 750 also has a guide channel 762 located approximately in the center of the custom fixture 750. The guide channel 762 has an anterior opening on the anterior surface 74, a posterior opening on the posterior surface 758, and a wall extending between these openings. The wall is positioned with respect to a central axis A. The position and orientation of the central axis A can be determined based on preoperative characterization of the acetabular fossa. In one embodiment, an MRI or CT scan reveals the optimal axis for feeding the cup of the prosthesis along it. The wall forming the guide channel 762 is formed with respect to axis A, which coincides with the optimal axis when the fixture 750 is positioned in the acetabular fossa of a particular patient.

[0252] Figure 51 shows that the impactor 300A can then be advanced into the guide channel 762 along axis A. The distally facing shoulder 766 on the impactor 300A can be coupled in a predetermined manner to the anterior surface 754 and the inlet to the channel 762, and when coupled in such a manner, the orientation of the sensor 204 on the impactor 300A can be recorded. In this technique, the fixture 750 is a cannula having a channel 762 configured to receive the impactor 300A. When patient movement is permitted, the sensor 204 on the pin 732 can be held in place to track such movement. Otherwise, the sensor 204 on the pin 732 can be removed. The sensor 204 on the impactor 300A will store the orientation of axis A in memory, and the user can be notified of any misalignment of the impactor from this axis. It is preferable to keep sensor 204 on pin 732, since, due to accumulated errors (e.g., drift) in some sensors, such as a relatively inexpensive gyroscope, only the orientation stored by sensor 204 on impactor 300A is accurate for a short period of time.

[0253] In one modified example, when the impactor is positioned within the guide channel 762 and the shoulder 766 is in contact with the anterior surface 754, the impactor 300A has a central channel that coincides with axis A. A guide pin can be advanced into the acetabular fossa through this channel. The guide pin can be embedded in the base of the acetabular fossa. The sensor 204, connected to the pelvis by pin 732, can be removed because the guide pin positioned through the channel of the impactor 300A provides a mechanical way for it to follow the movement of the hip joint. The impactor 300A, having a cup attached thereto, can then slide along the guide pin to its proper position in the acetabular fossa.

[0254] In a further modification, the sensor 204 connected to the impactor 300A can also be removed. In this further modification, the guide pin is configured along the cup to prevent the cup of the artificial joint from tilting relative to axis A. In particular, the joint surface between the guide member and the cup of the artificial hip joint can be formed to have a sufficient length along axis A so that tilting is prevented by this joint surface. In some cases, the cup 360 is connected to the impactors 300, 300A. Modifications of the impactors 300, 300A may be tubular and may have other features to accommodate tracking along the guide pin in the pelvis, for example.

[0255] [2. Patient-specific fixtures: Navigation using inertial sensors attached to the impactor] Figures 53 to 60 show another embodiment of the custom fixture. The system described herein can be used with the patient-specific fixture 1000, as shown in Figure 55. In some embodiments, the system 600, 600A, 600B, or their components can be used with the patient-specific fixture 1000.

[0256] Referring to Figure 53, system 600A may include a fixed base 602A. The fixed base 602A may include a platform 620A. The platform 620A may include one or more holes 611A. The holes 611A may be sized to receive fasteners 613A for fixing the fixed base 602A to the pelvis. The fixed base 602A may include a divot 630A. The divot 630A may be a stopping structure or a recording feature associated with a fixed position. Each fastener 613A may be driven into the ilium on the pelvis. Each fastener 613A may be connected to other bones in other techniques, as will be discussed further below. For example, one of the fasteners 613A may be connected to the ischium or pubis. One of the fasteners 613A may be connected at a point above the uppermost point on the acetabular rim. In some techniques, one of the fasteners 613A is located approximately 10 mm above the uppermost point on the acetabular rim.

[0257] The fixed base 602A may include a first coupler 632. The first coupler 632 may be connected to one or more components of the system 600A. The system 600A may include a first assembly 604A, as shown in Figure 54. The first assembly 604A is firmly connected to the hip joint in the illustrated structure such that hip joint movement causes corresponding movement of sensors within the first assembly 604A, as discussed below. The first assembly 604A may include a pelvic bracket 638A. In the illustrated embodiment, the pelvic bracket 638A may be positioned substantially vertically during use, as shown in Figure 54. The first assembly 604A may be designed to connect to the first coupler 632 of the fixed base 602A.

[0258] The first assembly 604A may include an extension 644A. The extension 644 may be connected to a pelvic bracket 638A. The extension 644A may include a mounting portion (not shown) designed to connect to a surgical orientation device 172. The surgical orientation device 172 may include features (not shown) for coupling with the mounting portion. When the surgical orientation device 172 engages with the mounting portion, it is firmly connected to the extension 644A.

[0259] System 600A may include a second assembly 606A or a portion thereof. The second assembly 606A may include an extension 670. The extension 670 may be coupled to a second coupler 648. The engagement between the second coupler 648 and the extension 670 minimizes or prevents relative movement between them to avoid any mechanical relative movement during navigation surgery. The extension 670 may include a mounting portion 672 designed to couple with an orientation detection device 204. In the illustrated embodiment, the mounting portion 672 includes a lock and release lever that can rotate relative to the extension 670. The orientation detection device 204 may include features for coupling with the lock and release lever. Other structures are contemplated. When the orientation detection device 204 engages with the mounting portion 672, it is firmly coupled to the extension 670. In some methods of use, System 600 or a portion thereof is coupled to the pelvis instead of System 600A.

[0260] The surgeon can select the hip joint (e.g., right or left) using the surgical orientation device 172. The surgeon can input a target cup tilt angle into the surgical orientation device 172. The tilt angle may be a radial tilt as described in this specification. The surgeon can input a target cup anterior tilt angle into the surgical orientation device 172. The anterior tilt angle may be a radial anterior tilt as described in this specification.

[0261] The second assembly 606 includes an extension 670 and a mounting portion 672, as shown in Figure 23A. The orientation detection device 204 can be coupled to the mounting portion 672. The extension 670 can be coupled to the second coupler 648. The orientation detection device 204 and the surgical orientation device 172 can be calibrated as described in this specification. System 600 can be mounted similarly to system 600A shown in Figure 54. The step of coupling the orientation detection device 204 with the second coupler 648 allows the orientation data of the orientation detection device 204 to be associated with the reference coordinate system of the surgical orientation device 172.

[0262] In some embodiments, preoperative three-dimensional characterization of the acetabular fossa is performed using any preferred technique such as a CT scan or MRI. This preoperative act can be performed to fully characterize the pelvis, and in some cases the proximal femur. Subsequently, the shape, position, and orientation of the acetabular fossa are known. Similarly, the bone features around the acetabular fossa are also known. From this data, a patient-specific fixture 1000 can be manufactured to suit the individual patient. The patient-specific fixture 1000 not only has features that are specific to the anatomical structure of the individual patient, but also has recorded features 1002 shown in Figure 55, which would be known orientations of the acetabular fossa relative to the plane and the anterior pelvic plane.

[0263] Figure 55 shows an example of a patient-specific jig 1000. The patient-specific jig 1000 has an anterior surface 1004 and a posterior surface 1008. The posterior surface 1008 is formed in a three-dimensional shape configured to securely bond with at least one feature of the acetabular fossa. For example, with the central portion of the posterior surface 1008 positioned within the acetabular fossa, an acetabular projection 1012 that fits snugly across the acetabular rim can be provided. The patient-specific jig 1000 preferably has only one predefined orientation. The surface on the posterior surface 1008 of the patient-specific jig 1000 can define a plane corresponding to a preferred orientation angle of the implanted cup. One or more channels 1016 can be formed on the posterior surface 1008, and these channels 1016 accept local bony projections of the acetabular rim only when the patient-specific jig 1000 is in the appropriate position and orientation.

[0264] In some embodiments, the recording feature 1002 of the patient-specific fixture 1000 may include recesses, holes, or protrusions. In one method using the illustrated embodiment, an orientation detection device 204, not shown but described herein, is connected to an impactor 300B. The impactor 300B can be inserted into the recording feature 1002. Thus, when the patient-specific fixture 1000 is positioned, the orientation detection device 204 can be positioned in a known orientation relative to the recording feature 1002. When positioned in this manner, the orientation of the acetabular rim or a substitute thereof from the orientation of the orientation detection device 204 can be recorded by one or both of the devices 172, 204. The recording feature 1002 preferably extends from the anterior surface 1004 to the posterior surface 1008 of the patient-specific fixture 1000. The distance between the front surface 1004 and the rear surface 1008 provides a depth for the recording feature 1002 that is considered sufficient to securely connect to the impactor 300B. In other embodiments, the recording feature 1002 extends to the front side of the front surface 1004 of the fixture 1000, for example, as a projection or post.

[0265] Figures 56A to 56F show the impactor 300B. The impactor 300B may be substantially the same as the impactor described in this specification and may include any features of the impactor described in this specification. The shaft 316B may include a plurality of flat sections 350B on the distal end of the shaft 316B, as shown in Figure 56F. The flat sections 350B allow the recording feature 1002 of the patient-specific fixture 1000 to slide proximal-distally across the distal end of the shaft 316B as the feature 1002 moves in and out, as shown in Figure 57. In some embodiments, a retaining device 351B or other locking mechanism is provided between the shaft 316B and the recording feature 1002. This mechanism may prevent unintended release of the patient-specific fixture 1000 from the impactor 300B. The flat sections prevent the shaft 316B from rotating relative to the patient-specific fixture 1000. The flat section 350B can enable many individual, alternate relative angular positions of the patient-specific fixture 1000 relative to the shaft 316B. The number of orientations of the impactor 300B relative to the patient-specific fixture 1000 can depend on the number of flat sections.

[0266] Figures 58A and 58B show the initial placement of the patient-specific fixture 1000 within the acetabular fossa in an orientation indicated by the fitting of the patient-specific fixture 1000 to the anatomical structure. This method may include the step of connecting the patient-specific fixture 1000 to the rim of the acetabular fossa. The appearance of the posterior surface 1008, including the channel (multiple channels) 1016 shown in Figure 55, accommodates the acetabular rim of a particular patient, including local bony protrusions and recesses in and around the acetabular fossa. The acetabular protrusion 1012 may be a periphery protrusion of the patient-specific fixture 1000. The structure of the acetabular protrusion 1012 is designed to be positioned over a specific bone or bone region of the hip joint. In this example, the acetabular protrusion 1012 is configured to be positioned over the bone superior to the acetabular fossa. Other areas of bone around the acetabular fossa can be used if they are sufficiently thick or strong and conveniently located so as not to interfere with the surgeon's movements during surgery. The precise location of the selected acetabular protrusion 1012 can be determined by preoperative imaging and incorporated into the formation of a patient-specific fixture 1000.

[0267] The impactor 300B can be positioned within the recording feature 1002 before or after the patient-specific fixture 1000 is placed in the acetabular fossa. The impactor 300B has a length that extends above the anterior surface 1004 of the patient-specific fixture 1000, thereby allowing the sensor 204 to be attached thereto. Referring back to Figure 54, the orientation detection device 204 can be detached from the second coupler 648. The orientation detection device 204 can then be coupled to the fourth coupler of the impactor 300B. The fourth coupler is shown in Figure 58B.

[0268] The patient-specific jig 1000 may include an alignment guide 1038 to control the rotational orientation of the orientation detection device 204 on the impactor 300B. The alignment guide 1038 may be a line extending along a specific direction with respect to the recording feature 1002. As described above, the orientation detection device 204 may be sensitive to the direction of gravity. Rotation of the orientation detection device 204 around the impactor 300B can alter the readings of those detection devices. To eliminate the source of error associated with this sensitivity, the navigation system incorporating the orientation detection device 204 may be programmed to assume that the orientation detection device 204 will be in a specific rotational position relative to the longitudinal axis of the impactor 300B. The alignment guide 1038 can correspond to the desired rotational position of the orientation detection device 204.

[0269] In the illustrated embodiment, the fourth coupler 338B may be mechanically or visually aligned with the alignment guide 1038 to ensure that this assumption is satisfied during use. In the illustrated embodiment, the alignment guide 1038 is an elongated arrow. The elongated arrow can be aligned with the longitudinal axis of the fourth coupler 338B. The surgeon can look down on the impactor 300B from the proximal end to the distal end. The surgeon can verify the alignment of the alignment guide 1038 and the fourth coupler 338B. The alignment of the alignment guide 1038 and the fourth coupler 338B constrains the orientation detection device 204 in a third degree of freedom. The surgical orientation device 172 can be programmed at this well-known angle of the orientation detection device 204 when the impactor 300B is coupled to the patient-specific fixture 1000. In some embodiments, the surgeon inputs an input value (e.g., by pressing a button) when the patient-specific fixture 1000 is installed together with the impactor 300B and the orientation detection device 204 connected thereto. The surgical orientation device 172 can calculate its orientation relative to the pelvis once the input value is entered. This step may be replaced by recording pelvic landmarks using a probe, as discussed in this specification.

[0270] In some embodiments, the orientation detection device 204 has a laser that can be projected onto the patient-specific fixture 1000 and aligned with an alignment guide 1038 to facilitate alignment. Alternatively, the impactor 300B may be configured to enter only the recording feature 1002 in a specific orientation (e.g., an asymmetric non-circular cross-section) and to allow the orientation detection device 204 to be attached to the patient-specific fixture 1000 in a specific orientation (by including an asymmetric linked feature).

[0271] Once the orientation detection device 204 is attached to the impactor 300B, the surgeon can keep the orientation detection device 204 in a stable state. In some embodiments, the surgeon inputs an input value (e.g., by pressing a button) to collect data from the orientation detection device 204. The data may include the impactor angle. The impactor angle may be fixed during this process so that this angle can be known to the system or in the way of directing the positioning of the hip joint implant components. In some embodiments, the impactor angle may be 10° tilt, 20° tilt, 30° tilt, 40° tilt, 50° tilt, 60° tilt, 70° tilt, 80° tilt, 90° tilt, 30° to 70° tilt, 40° to 60° tilt, etc. In some embodiments, the impactor angle can be 10° forward tilt, 20° forward tilt, 30° forward tilt, 40° forward tilt, 50° forward tilt, 60° forward tilt, 70° forward tilt, 80° forward tilt, 90° forward tilt, 0° to 40° forward tilt, 10° to 30° forward tilt, etc. In the illustrated embodiment, the impactor angle is 50° tilt and 20° forward tilt. The impactor angle can be based on the orientation of the recorded feature 1002 for the patient-specific fixture 1000. The impactor angle can be set during the manufacture of the patient-specific fixture 1000. In some embodiments, the impactor angle must be known by the software of the surgical orientation device 172. In some embodiments, the impactor angle is constant for all fixtures and is hardcoded into the surgical orientation device 172. In some embodiments, the impactor angle can be entered by the user during surgery. The surgeon can input the impactor angle into the surgical orientation device 172 using a user interface such as that described in this specification.

[0272] The orientation detection device 204 can transmit orientation and position data to the surgical orientation device 172. The surgical orientation device 172 can record the guide angle when the orientation detection device 204 is connected to the patient-specific fixture 1000. In some methods, the surgical orientation device 172 can perform a bias removal step. The surgical orientation device 172 can track pelvic movement and generate an output that excludes errors caused by pelvic movement. The surgical orientation device 172 may include a display that provides a user interface. This method may include the step of recording a surrogate orientation of the acetabular rim plane using the orientation detection device 204 connected to the patient-specific fixture 1000.

[0273] The orientation detection device 204 can track any movement of the pelvis during surgery. Since the position and orientation of the impactor 300B and / or orientation detection device 204 relative to the acetabular fossa and / or anterior pelvic plane are known from preoperative imaging, landmark recording is not required in this technique. From the known orientation of the orientation detection device 204 relative to the pelvis, the system can calculate the orientation of the surgical orientation device 172 relative to the pelvis.

[0274] The surgeon can remove the patient-specific guide 1000 from the patient, as shown in Figure 59. The surgeon can remove the impactor 300B from the patient-specific guide 1000. The surgeon can prepare the acetabular fossa. In some embodiments, the surgeon can ream the acetabular fossa. The impactor 300B can be used to position the shell within the acetabular fossa. The shaft 316B may include a plurality of flat portions 350B on the distal end of the shaft 316A, as shown in Figure 56F. Referring to Figures 11B and C and Figure 60, the impactor described herein may be connected to a tip component 348. Figure 11C shows that the tip component 348 may have a recess 352 formed on its proximal side. The recess 352 may include a plurality of flat portions 350B corresponding to a plurality of flat portions 350B on the distal end of the shaft 316B. The flat section 350B allows the recess 352 to slide proximal-distally over the distal end of the shaft 316B. Preferably, a retaining device or other mechanism is provided between the tip component 348 and the shaft 316B to prevent the tip component 348 from detaching. The flat section 350B prevents the tip component 348 from rotating relative to the shaft 316B. In one embodiment, the engagement device 356 includes a screw so that the cup of the prosthesis can be screwed onto the distal end of the tip component 348. The flat section allows for many individual, alternating relative angular positions of the tip component 348 (and therefore the cup) relative to the shaft 316B. Multiple grooves or elongated axial ridges 364 on the outer surface of the tip component 348 allow the user to securely grasp the tip component for mounting and removing it from the shaft 316B. The surgeon can position the cup in the acetabular fossa. The surgeon can keep the impactor 300B in a stable position.

[0275] During orientation, inertial data from the orientation detection device 204 can be used to confirm the correct orientation of the acetabular cup. The surgical orientation device 172 can record the guide angle when the cup is positioned in the acetabular fossa. In some embodiments, the surgeon inputs an input value (e.g., by pressing a button) to collect data from the orientation detection device 204. The surgical orientation device 172 can display the cup angle. The surgeon can move the cup to change the tilt angle. The surgeon can move the cup to change the anterior tilt angle. The surgeon can move the shell until the tilt angle and anterior tilt angle match the preoperative angles. This method may include a step of changing the orientation of the impactor 300B in response to an output that reflects inertial data generated by the orientation detection device 204. In the illustrated embodiment, the preoperative impactor angles may be 50° tilt and 20° anterior tilt. In some methods, the surgical orientation device 172 can perform a bias removal step. In some methods, the surgical orientation device 172 can perform a gyro preparation step. Examples of the bias removal step and the gyro preparation step are discussed in U.S. Patent Application No. 13 / 011815, filed on January 21, 2011, which is incorporated herein by reference for this purpose and all other purposes. The surgical orientation device 172 and / or orientation detection device 204 may include any of the software algorithms described herein.

[0276] The surgeon can use the impactor 300B to position the cup in the acetabular fossa. The surgical orientation device 172 can remain connected to the first assembly 604. The orientation detection device 204 can be connected to the fourth coupler 338B on the impactor 300B, as shown in Figure 60.

[0277] In some embodiments, the surgeon inputs an input value (e.g., by pressing a button) to collect data from the orientation detection device. The data may include the impactor angle. The impactor angle may be known. In this step, the impactor angle may be 50° tilt and 20° forward tilt. The impactor angle may be based on the orientation of the recording feature 1002 relative to the patient-specific fixture 1000. The impactor angle may be set during the manufacturing of the patient-specific fixture 1000. In some embodiments, the impactor 300B may be rotated to a predetermined number of positions within the recording feature 1002. The impactor 300B may be rotated by the surgeon to align the features of the impactor 300B with the alignment guide 1038. The fourth coupler 338B may be aligned with the alignment guide 1038. The impactor 300B may be positioned so that the fourth coupler 338B can face upward. In another embodiment, the impactor 300B has a single orientation within the recording feature 1002. Therefore, when the orientation detection device 204 is connected to the impactor 300B, the position of the orientation detection device 204 can be made known to the patient-specific fixture 1000. The surgical orientation device 172 can calculate and record the orientation of the surgical orientation device 172 relative to the pelvis.

[0278] The impactor 300B may be driven in to set the graft. In some embodiments, the orientation detection device 204 remains on the impactor 300B because the impactor 300B is driven in. Referring to Figure 60, the impactor 300B has a shell 312B that is movable relative to the shaft 316B. The shell 312B may include a fourth coupler 338B that can be connected to the orientation detection device 204. The mobility of the shell 312B helps to isolate the orientation detection device 204 from forces transmitted through the impactor 300B. These forces are applied by other devices for forcing the mallet or cup into place. By providing at least some force isolation between the shell 312 and the orientation detection device 204, the impact on the sensor in the orientation detection device 204 can be reduced. Excessive force applied to the orientation detection device 204 can cause it to become inoperable, for example, until it is synchronized with the surgical orientation device 172. The movement of the shell 312B is mitigated by a plurality of spring members 340B, 344B configured to absorb at least some of the impact force of the impact on the impactor 300B.

[0279] [3. Custom Fixture: Navigation using fixing pins that are mounted through a custom fixture] Figures 61–63 show examples of custom fixtures 1100. The fixture 1100 has an anterior surface 1104 and a posterior surface 1108. The posterior surface 1108 is formed by an acetabular portion 1112 configured to securely bond to at least one feature of the acetabular fossa. The fixture 1100 preferably has only one predefined orientation. In some embodiments, the recording feature 1102 of the fixture 1100 has multiple, for example, two, holes. The recording feature 1102 can be located on the acetabular portion 1112 or any other part on the custom fixture 1100. The holes are sized to receive the fixing pins 610, 612 of the system 600. In the modifications shown in Figures 44–52, the patient-specific guide may have a recording feature including a single hole. The hole can receive the fixing pin 610 in a single orientation to the patient or to the custom fixture 1100. This method may include the step of inserting at least the fixing pin 610 through a patient-specific fixture 700 or fixture 1100 along an axis positioned at a predetermined angle corresponding to the reference coordinate system of the surgical orientation device 172.

[0280] The first hole 1105 of the recording feature 1102 can receive a fixing pin 610, and the second hole 1107 can receive a fixing pin 612. The system 600 can be positioned in a single orientation relative to the custom fixture 1100. Thus, once the fixture 1100 is positioned, the surgical orientation device 172 and / or orientation detection device 204 can be positioned in a known orientation. In some embodiments, when positioned in this manner, the orientation of the acetabular rim or its substitute from the orientation of the system 600 can be recorded by one or both of the devices 172 and 204. In some embodiments, the reference coordinate system can be directly based on a more general pelvic landmark, such as the anterior pelvic plane. The acetabular rim or its substitute can be used as an intermediate step to obtain a reference coordinate system directly based on a more general pelvic landmark. The recording feature 1102 preferably extends from the anterior surface 1104 to the posterior surface 1108 of the fixture 1100. The distance between the anterior surface 1104 and the posterior surface 1108 provides a depth for holes 1105, 1107 that is considered sufficient to guide the fixation pins 610, 612 along a specific direction to a specific anatomical structure. This method may include the step of inserting at least two fixation pins 610, 612 through a patient-specific fixture 1100 along axes positioned at a predetermined angle corresponding to the reference coordinate system of the surgical orientation device 172.

[0281] Once devices 172 and 204 are attached to system 600, the sensors can track any movement of the pelvis during surgery. Since the position and orientation of the fixation pins 610 and 612 relative to the acetabular fossa and / or anterior pelvic plane are known from preoperative imaging, landmark recording is not required in this technique.

[0282] [4. Navigation using inertial sensors and preoperative imaging] In other techniques using less comprehensive imaging, correspondences between one or more length dimensions and angles can be used to improve accuracy. For example, a clinician may use an X-ray or other standard radiographic imaging device to provide an image of the anterior pelvic plane. This image can be read to derive the position and dimensions of anatomical structures in the anterior pelvic plane. For example, angles between upper and lower landmarks around the acetabular fossa (further described below) and the transverse ischial line or other anatomical medial-lateral reference lines can be considered useful patient-specific variables to minimize patient-to-patient variation in at least one relevant angle, such as the abduction angle.

[0283] Patient-specific data can be provided for use by surgeons based on the best medical judgment. For example, any of the systems described herein can be used in a mode based on broad population studies. Such studies can define a patient distribution with sufficient clarity and detail to enable significant improvements to current standards of care. In one mode, dimensions obtained from radiographs or CT scans can be used to inform surgeons whether patient-specific adjustments should be considered. Alternatively, patient-specific adjustments can be coded within the systems described herein so that they are obvious to physicians. Such adjustments can be downloaded to one or both of the devices 172, 204, or to a separate monitor or control device communicating wirelessly with the devices 172, 204. Thus, the systems described herein can fully implement patient-specific adjustments, such as anterior tilt, abduction, leg length, joint offset, or other parameters, or enable surgeons to determine whether such adjustments should be made.

[0284] Figure 68 illustrates an example of preoperative imaging that may be used in one technique. Line 380 is used during surgery and is directed to a landmark visible in the anterior pelvic radiograph. The upper landmark 380A is approximately 1 cm above the uppermost point of the acetabular fossa. In other approaches, the upper landmark 380A may be the uppermost point on the acetabular rim. The bottom landmark 380B is adjacent to or located on the acetabular notch (teardrop shape). The angle between line 382 and line 384 is the patient-specific abduction of the line formed by the landmark, and this angle may be entered into the interface of system 100 (or other systems of this specification) during surgery to provide a patient-specific coordinate system. Line 384 may be the anatomical medial-lateral reference line. Examples include the ischial transverse line and the line transverse the inferior lateral edge of the obturator foramen (shown in Figure 68).

[0285] [5. Navigation using drift-insensitive inertial sensors] In one modification, one or both of the devices 172 and 204 may be equipped with only an accelerometer and may be configured as an inclinometer, or the devices may be configured so that the accelerometer data is the most reliable mode, or otherwise so as to be insensitive to accumulated errors resulting from the integration of data. When the patient is in a reproducible and stable position, patient movement and misalignment can be ruled out. This allows several methods to be performed without using velocity sensor data. In one modification of this inclinometer approach, one or both of the sensors 172 and 204 may be configured to inform the surgeon whether a condition is detected that suggests a landmark acquisition approach which would result in upward alignment. This method can be advantageously used for surgeries that do not require complex movements such as freehand movements. When freehand movements are involved, it would be beneficial to combine several head orientation indicators (gyroscope, magnetometer, or other head orientation indicators).

[0286] [6. Navigation using inertial sensors to track movement in order to define a patient-specific safety zone.] In other techniques illustrated in Figure 64, a patient-specific "safe zone" is defined by recording the original range of motion of one or more joints in the patient. For example, when hip replacement surgery is performed, the patient's range of motion can be recorded before the surgery. If the hip to be replaced is not severely inflamed, the range of motion can be determined for the hip to be replaced. If the range of motion of the hip to be replaced is unnatural due to a diseased condition, the opposite hip can be characterized.

[0287] In a hip replacement technique, the sensor S is connected to the femur. The sensor can be connected above the knee to prevent knee movement from affecting the measurement. The sensor S can be connected below the knee if the knee is fixed. The sensor S can be initialized, or otherwise prepared to record accurate readings. Subsequently, one or more movements of the hip can be performed based on the recorded and processed sensor output. These movements may include, for example, forward and backward (AP) movement within the maximum range of motion, and medial and lateral (ML) movement within the maximum range of motion. These movements define the patient's natural range of motion in those planes.

[0288] The conical motion CM can be defined based on the range of motion in the anterior-posterior and medial-lateral directions. This conical motion CM can be defined to begin at a point defined as the center of rotation of the femoral head and to extend laterally from the acetabular fossa to a circular base located at a distance from the center of rotation equal to the distance to the sensor mounting point. The circular base can be defined to have a radius equal to the average range of motion in the anterior-posterior and medial-lateral directions. In Figure 64, the conical motion is shown on the opposite side for clarity. As described above, the data collected to estimate the conical motion can be based on the leg to be treated or the opposite leg.

[0289] The placement of the cup in a prosthetic hip is influenced by several metrics of the center within the conical motion. For example, the cup can be centered such that an axis extending perpendicular to the plane of the cup's inlet traverses the circular base of the precise conical motion at the center of the cone. In some systems, the orientation of the cup is controlled so that the point of transcendence of the thus protruding axis is closer to the center of the circular base than to the periphery of the circular base. In other systems, the orientation of the cup is controlled so that the point of transcendence of the thus protruding axis is within a distance from the center point that is less than 25% of the radius of the circular base.

[0290] In a patient class, hip joint movement is not symmetrical in the anterior-posterior and medial-lateral directions. The conical movement itself can have a more complex geometric shape. For example, the conical movement may begin at the center of rotation of the femoral head and extend to an elliptical base, where the ellipse may be shorter in the medial direction but larger in the lateral, anterior, and / or posterior directions. Various "safety zone" measurements can be defined based on these irregularly shaped cones. For example, the geometric center of a complex base shape can be calculated, and the cup of the artificial hip joint may be centered such that an axis extending perpendicular to the plane of the cup's inlet crosses the irregularly shaped base of the conical movement at or within the maximum distance of the cone's center of gravity.

[0291] Any suitable set of motion can be used to obtain the center of rotation of the femoral head and / or the boundary of the base of the conical motion. An example of a method for determining the center of rotation of the femoral head using an inertial sensor is discussed in U.S. Patent No. 8,118,815, which is incorporated by reference into this specification for this purpose or all other purposes. The more complete periphery of the base of the conical motion can be recorded directly using a sensor that allows tracking of both position and orientation. For example, various other points between the anterior-posterior and medial-lateral directions can be employed so that 6, 8, 10, 12, or more points are recorded. In other embodiments, precise motion along all or part of the base of the conical motion can be followed and recorded. Since various degrees of freedom of the sensor S are constrained, the sensor can operate on an accelerometer alone in some approaches. This can be achieved by simplifying the sensor S, making it disposable, and inexpensive. Such approaches may be most accurate when rotation with respect to the vertical axis is minimized or excluded.

[0292] In one embodiment, the surgery illustrated in Figure 64 generates an origin and direction that can be input into a cup placement system. The origin may be the rotational center of the femoral head and the corresponding rotational center of the socket of the artificial joint. The direction may be a line connecting the origin and the point that intersects the base of the conical motion. This data is converted into a cup placement system, such as one of the placement systems described above. For example, the impactor 300A may include a sensor 204 on which this data is stored. The movement of the impactor 300A can then be tracked with reference to this origin and direction to ensure proper placement of the cup. Such placement may use, for example, a sensor that tracks the movement of a patient pinned to the pelvis.

[0293] In other embodiments, a cannula-type system can be used to minimize the number of steps while the inertial sensor is in use. For example, once the origin and direction of the axis connected to the intersection of the center of rotation and the base of the conical motion are determined, a guide member can be positioned via a cannula-type impactor (or other cannula). The guide member can be docked with a cup attached to the impactor. The cup can slide on the guide member to a position within the acetabular fossa. The directional and origin information collected in the steps illustrated in Figure 64 is stored by the guide member and by tilt-preventing features on the guide member and / or the cup of the prosthesis.

[0294] When a patient's joints are affected by a widespread disease, conical motion can be established by a combination of data collected from movements similar to those discussed above in relation to Figure 64, and data from preoperative imaging. For example, X-rays can be obtained when the femoral neck moves close to the acetabular rim to supplement some of the data points that define conical motion. Thus, conical motion can be partially established by inertial detection and partially established by imaging to characterize the original anatomical structure.

[0295] [D. Applicable systems for forward or backward approach] The systems described in this specification can be adapted for use in anterior approaches, posterior approaches, or both anterior and posterior approaches. For example, in this specification, System 600 is shown in Figure 18 for posterior approaches, in Figure 39 for anterior approaches, and in Figure 63 in combination with a patient-specific fixture.

[0296] Figures 69–72 illustrate System 900 for navigating hip replacement surgery. System 900 can be adapted for use in both anterior and posterior approaches. System 900 can be considered similar to some of the systems discussed above. However, while some of the aforementioned systems are specialized for specific approaches, System 900 includes a first subsystem 900A adapted for posterior approaches and a second subsystem 900B adapted for anterior approaches. As will be further discussed below, both subsystems 900A and 900B are configured to allow navigation to be performed without the need for gyroscopes or other sensors that are affected by accumulated errors (drift). This improvement makes the system simpler for implementation and use in a wider range of settings for more patients.

[0297] Subsystem 900A includes fixture 904A adapted for hip joint navigation from a posterior approach. Fixture 904A is analogous to fixture 454 in several embodiments, and a consistent description thereof is incorporated into this specification. Fixture 904A includes a platform 908, a cannula coupling device 912, and a recording fixture mounting feature 914. The platform 908 can have any shape, but in some embodiments it may be elongated, for example, having a first end 916 and a second end 920. The elongated shape allows at least one portion of fixture 904A to be low profile in one direction, and allows the fixture to provide multiple positions along its length for the coupling device. When the navigation fixture is applied to a patient, the first end 916 is configured to be oriented downward, and the second end 920 is configured to be oriented upward. The medial-lateral dimensions or range can be minimized so as not to obstruct the surgical field or the surgeon.

[0298] The cannula connector 912 is positioned adjacent to the first end 916 and is configured to allow the cannula 924 to be held adjacent to the bottom surface of the platform 908. The cannula 924 may have an upper surface connected to the bottom surface of the platform 908. The connection between these components may be secured by a device positioned above or below the platform 908. In one embodiment, the proximal structure of the cannula connector 924 may be received in a bottom recess of the platform 908 and held in the recess by a compression device such as a set screw S. Details of various modifications of the cannula connector 912 are discussed below in reference to Figures 73 to 75B. The connection to the bone adjacent to the hip joint is made through the cannula 924. For example, a pin 928 may be positioned in the bone through the platform 908 and the cannula 924.

[0299] The anterior approach cannula 926 is shown in Figures 71 and 72 and is analogous to cannula 516. This description is incorporated into the present specification. The description of the cannula coupling device 912 applies equally to the posterior approach cannula 924 and the anterior approach cannula 926.

[0300] The recording jig mounting feature 914 is positioned on the upper surface 932 of the platform 908 adjacent to the first end 916. In one embodiment, the mounting feature 914 includes a raised portion of the platform. The mounting feature may include one or more recesses, for example two recesses, into which pins can be received. In one embodiment, the raised portion includes a window, for example a through-hole, for viewing such pins to confirm correct placement. In one modification, as shown in Figure 73, a circular recess may be provided for a first pin, and a U-shaped slot may be provided for other pins or members.

[0301] The hip joint navigation fixture 904A also includes a recording fixture 940. This recording fixture 940 may have several features similar to the recording fixtures discussed above. The recording fixture 940 includes an upright member 942, a rotatable member 948, and a probe 952. The upright member 942 is configured to be detachably connected to the platform 908 by a recording fixture mounting feature 914. For example, several pins (e.g., two pins) may protrude from the lower surface of the upright member 942, and these pins are configured to be received in corresponding recesses in the recording fixture mounting feature 914. One of such pins is visible through a window in the recording fixture mounting feature 914, as shown in Figure 70. The upright member 942 includes a first portion 944 and a second portion 946 positioned above the first portion 944. When the recording fixture 940 is attached to the recording fixture mounting feature 914, the first portion 944 is substantially vertical, increasing the height of the second portion 946. The second portion 946 is inclined away from the vertical longitudinal axis of the first portion 944. The inclination of the second portion 946 offers several advantages. As will be discussed below, it allows the upright member 942 to be located so as not to obstruct the range of motion of the probe 952. This is important because the probe 952 must be able to easily and quickly reach multiple anatomical features.

[0302] The inclination of the second portion 946 also provides a simple method for inclining the rotation angle of the rotatable member 948 with respect to the vertical axis. The rotatable member 948 is connected to the upright member 942 for rotation about axis A, which is not vertical when the fixture is attached to a bone adjacent to the hip joint and the upright member is positioned substantially vertically. This configuration is one way that allows a navigation system employing an inertial sensor to eliminate the need to manage sensor drift. As described above, certain sensors, such as gyroscopes, are highly susceptible to accumulated errors (drift). The orientation of axis A allows the fixture 904 to be used in a system that includes an accelerometer and other sensors that are sufficiently sensitive when actuated and moved around a non-vertical axis.

[0303] Other degrees of freedom of rotation and position, as described above for the recording fixture, can be provided for the recording fixture 940, and such a description is incorporated into the present specification.

[0304] The probe 952 has a tip 956 for engaging with anatomical structures. The anatomical structure engaging tip 956 is located at the distal end of an elongated body 960 connected to a rotatable member for rotation around an axis. The orientation and position of the elongated member 960 of the probe can be adjusted during landmark acquisition procedures so that the anatomical structure engaging tip is in contact with multiple anatomical landmarks. Such adjustments can be made by sliding through slide supports similar to those described above.

[0305] The upright member 942 may include a cradle 954, which allows the elongated body 964 of the probe 952 to be held in place when not in use during surgery. The cradle 954 can be used to latch the sensor 204, as described above. In various embodiments, however, the system 900 does not require a zero-setting step, as the sensor is configured to be substantially insensitive to drift. Eliminating sensitivity to drift can be achieved by configuring the sensor 204 as an inclinometer and / or by using an inertial sensor of a type that will not incorporate excessive errors due to drift during surgery. Even sensors with drift can be used, as long as the accumulation of those errors during surgery does not reach a sufficient level. The cradle 954 can be used to zero out errors if the surgery is unexpectedly prolonged or if the sensor is affected by some drift. In one advantageous embodiment, the sensor 204 can operate solely on a signal from an accelerometer, which is insensitive to drift.

[0306] Figures 69 to 72 show that systems 900A and 900B may include one or more sensors for detecting the orientation of probe 952. The sensors may take any form and may include, for example, the surgical orientation device 172 and sensor 204 as described above. Thus, fixture 904 may include a sensor mounting feature 962 positioned on platform 908. If the platform is elongated, the sensor mounting feature 962 may be positioned on a second end 920. Another advantage of fixtures 904A and 904B is that they are symmetrical and can be used for both hip joints. Fixtures 904A and 904B may therefore have a single sensor mounting feature positioned in a symmetrical plane. If platform 908 is elongated, the sensor mounting feature 962 may be positioned in the vertical central plane of the platform. In this application, “vertical” refers to the orientation of fixtures 904A and 904B when applied to the hip joint in a posterior or anterior approach.

[0307] The recording jig 940 may include a sensor mounting feature 964 positioned on it for movement with the probe 952. For example, the sensor mounting feature 964 may be located at the proximal end of the elongated body 960. This position, with the sensor 204 positioned at the proximal end, is one of its advantages. However, the sensor mounting feature 964 and the sensor 204 may also be located on the side of the elongated body 960.

[0308] As discussed herein, the orientation of the axis of rotation A of the rotatable member 948 allows the change in orientation of the sensor 204 to be in a plane other than the horizontal. This is achieved by orienting axis A in a direction other than the vertical. This configuration makes it possible to configure sensor 204 as an inclinometer by using an accelerometer primarily, or solely, to output a signal indicating the orientation of a component, for example, a signal indicating the orientation of probe 952. Examples or ranges of angles of axis A that can be provided include angles of about 20 degrees from the horizontal, about 30 degrees from the horizontal, about 45 degrees from the horizontal, and less than about 60 degrees from the horizontal.

[0309] Figure 70 shows further features of system 900A, including fixture 904A and cannula 924. Cannula 924 is adapted for a posterior approach and is similar to or identical to the hollow fixation member 466. The upper or first end of cannula 924 is configured to connect to the cannula coupling device 912 by, for example, a set screw as described above. The second end of cannula 924 is configured to connect to a bone adjacent to the hip joint. The bone can be any of those discussed above for connecting to the fixation member 466 or other similar structures discussed in any of the above embodiments. The home point feature 968 is positioned adjacent to the second (lower) end of cannula 924. The home point feature 968 is in a predefined, well-known position and can receive the anatomical structure engaging tip 956 of the probe 952. When those structures make contact, they are in a predefined position and orientation. The home point feature 968 may be similar to the recording feature 473 discussed above.

[0310] Since the system 900 can be adapted for a posterior or anterior approach (discussed below), the cannula 924 should be removed from the platform 908 in the operating room, or removed on a back table for the surgeon's preparation. For example, the connection between the cannula 924 and the platform 908 can be oriented in a specific way. This reduces a potential source of surgeon error. That is, the home point feature 968 always faces toward the surgical field from the pelvic attachment position, for example, facing downward when the fixture 904 is attached to an upper position in the surgical field. For example, the projection in the proximal portion of the cannula 924 and the corresponding projection in the recess on the lower surface of the platform 908 can specify only one rotational orientation of the cannula relative to the platform to which their components can be connected.

[0311] As discussed above, the cannula 926 is provided in system 900 to allow the surgeon to switch to an anterior approach. The anterior approach is discussed in great detail above in relation to Figures 34–42. This description is also incorporated into the present specification. System 900B differs from system 500 in that the orientation of the axis of rotation A in system 900B is not perpendicular, as discussed above. For example, the number of sensors can be greatly simplified compared to system 500. The cannula 926 has a home point feature 968B. The home point feature 968B is in a predetermined known position and can receive the anatomical structure engaging tip 956 of the probe 952. When those structures make contact, they are in a predetermined position and orientation. The home point feature 968B can be similar to the recording feature 473 discussed above. The cannula 926 and platform 908 can be configured for a limited rotation position of mounting, for example, only one rotation position. This ensures that the jig 904B will be properly assembled when it is assembled in the operating room or on a back table.

[0312] In one method to maximize the accuracy of landmark acquisition, the fixture 904B is connected to the patient in an anterior approach. The tip 956 comes into contact with the home point feature 968B. User input can then be applied to the surgical orientation device 172A to indicate that the tip 956 is the home point feature 968B. The system then records movement and landmark acquisition in the manner discussed above. This data provides a basis for guiding the placement of the prosthesis cup, as discussed above.

[0313] The placement of the cup of an artificial joint using a device such as the Impactor 300A can be an operation that benefits from multiple inertial sensors, which may include one or more drift-sensitive sensors, such as a gyroscope. System 900 provides a calibration mount 998 for linking the sensor 204 to the surgical orientation device 172A in a well-known and constant position and orientation. The calibration mount 998 is a docking device that positions the sensor 204 immediately before a step to eliminate potential sources of accumulated error, for example, a step to set the drift-sensitive sensors to zero. Figures 69 to 70 show that the system 900A may include two sensors 204, and that one sensor is mounted on the recording fixture 940 and the other sensor is mounted on the calibration mount 998. The two sensors 204 may be identical or dedicated for their particular functions. Figures 71 and 72 show only one sensor 204. In this system, a single sensor 204 is used to position the acetabular implant, to collect landmark data, or to work in conjunction with the impactor 300A.

[0314] Figures 73 to 75B illustrate various features for clamping multiple structures on the platform 908. In particular, these drawings show a fixed pin fixing device 970 incorporated within the platform 908. The fixed pin fixing device 970 can have a low profile so as not to interfere with other tools in the surgical field. Figures 73 to 73A show one embodiment of the pin fixing device 970 including a compression member 972. The cannula coupling device 912 may include a similar mechanism for clamping a pin positioned through a cannula 924. The platform 908 includes one or more slots formed on its surface, for example, the top surface. The slot 974 is larger than the compression member 972 in at least one direction. This allows the compression member to fit into the slot and move over a large range within it. The compression member 972 has a tapered channel 976. Vertical movement of the tapered member 978 in the tapered channel 976 causes the compression member 972 to move in order to narrow the gap G between the compression member 972 and the rigid features of the platform. This gap G can be the space between the curved side surface of the compression member 972 and the curved surface of the platform 908.

[0315] In one method, a pin or other fixation member is advanced into the bone through the gap G. A platform 908 is positioned on the fixation member at an appropriate height, and a pin fixation device 970 is fixed to the fixation member. The fixation member may be a Steinman pin or other similar device. In one technique, a tapered member 978 is a threaded elongated body, which is advanced along a female thread formed in the platform 908 until its tapered surface acts on a tapered surface 976, causing a compression member 972 to move laterally to narrow the gap G. Further advancement of the tapered member 978 causes the compression member 972 to move further to enhance the fixation of the fixation member. The method can be repeated for a second pin when one pin extends through a cannula 924, and the first pin extends parallel to the cannula 924 but is offset upward from there in the patient.

[0316] Figures 74 to 74B illustrate another approach to the fixed pin fixing device 970A. This fixed pin fixing device 970A includes a compression member 972A rotatably mounted on the platform 908. Figure 74A shows two compression members 972A. Each of these compression members 972A is mounted to rotate with respect to a pin or shaft 980. The fixing device 970A on the left in Figure 74A corresponds to a structure in which the fixing member can freely pass through the gap G in this mechanism. The fixing device 970A on the right in Figure 74A corresponds to a structure in which the gap G is narrowed and the fixing member placed in the gap G is firmly clamped and cannot move relative to the platform 908. A rigid surface of the platform 908 opposite the compression member 972, which rotates with the compression member, holds the fixing member in place.

[0317] In one method, a pin or other fixing member is positioned within the fixing pin fixing device 970A and the cannula coupling device 912. In the illustrated embodiment, these devices may employ a similar clamping mechanism. The screw 982 is then advanced to rotate the compression member 972 with respect to the pin or shaft 980 from a first position where the gap G between the clamping surface of the compression member 972A and the rigid surface of the platform 908 is larger, to a second position where the gap G is smaller. The second position is the clamping position for the fixing member, which will hold the platform 908 in place until the screw 982 enlarges and retracts the gap G.

[0318] Figures 75 to 75B illustrate an alternative approach to a fixed pin fastening device 970B, in which the fixed pin fastening device comprises a compression member 972B configured to clamp multiple sections of the outer surface of the fastening member. The platform 908 includes a plurality of projections 984 extending upward from the top surface of the platform. The plurality of projections are threaded. Each projection includes a collet 986 or similar device positioned therein, having an internal lumen sized to receive the fastening member. A plurality of slots extend downward from the top surface of the collet 986, and the angled surface 988 is positioned between the upper ends of each member defined between a pair of such slots. A corresponding angled surface 990 is provided inside a cup 992. The cup 992 has internal threads, which act on the threads of the projections 984 to advance the angled surface 990 on the angled surface 988. Further progression involves crushing the slots in the collet 986, causing compression with respect to the outer surface of the fixing member. Figure 75 shows that this approach can be used for the fixing pin fixing device 970B and / or for the cannula coupling device 912.

[0319] Although the system discussed above is considered highly suitable for a particular approach, system 900 can be adapted for a posterior or anterior approach. This provides surgeons with greater flexibility, adding only minimal additional components to the general-purpose kit. The orientation of axis A of rotation (seen in Figures 70 and 72) enhances the sensitivity of the system, incorporating accelerometers and other sensor drift-insensitive components. Home point features 968A and 968B allow surgeons to achieve maximum accuracy by enabling the acquisition of positional and orientational data for multiple anatomical landmarks in the vicinity of the home point location. This allows the system to initialize sensors adjacent to the points being acquired for increased accuracy.

[0320] [II. Navigation using optical components] Many of the aforementioned systems advantageously utilize inertial sensors to assist in surgical navigation. The specific embodiments discussed herein may advantageously use optical technology, either alone or in combination with the inertial sensor systems discussed herein, to provide additional features and advantages.

[0321] [A. Optical tracking of system components] Figure 65 illustrates one embodiment of system 800, which includes near-range optical tracking capability. In this context, the term “near-range” is a broad term meaning the direct surgical field on the pelvis, within the boundaries of the operating table, and adjacent to the patient, such as the surgical field below the surgeon’s head. This term is intended to exclude systems where the camera is outside the surgical field. Near-range tracking greatly reduces or eliminates the “line of sight” problem that plagues traditional optical navigation.

[0322] In the illustrated embodiment, the fixture system 804 is provided for connection to the patient's bone. The fixture system 804 may include any of the features of any of the fixture systems discussed in this specification. For simplicity, the fixture system is illustrated using the system in Figure 1 and includes, for example, a cannula 124 and a platform 136. The surgical orientation device 172A is mounted on the platform 136. The orientation device 172A may be similar to those described above in this specification but may also include one or more cameras 812. Preferably, the orientation device 172A includes two cameras 812 that enable the capture of binocular data. The cameras are preferably small cameras, for example, the Aptina MT9T111 discussed on the webpage http: / / www.aptina.com / products / soc / mt9t111d00stc / . The conical shape projected from below the orientation device 172A schematically represents the direction of the field of view of the camera 182.

[0323] This data can be used at least to determine the orientation of the stylus 816 and, in some cases, to determine the six degrees of freedom of the stylus 816. The stylus has a far end 828 configured to contact a landmark as part of the landmark acquisition process, as described above. The proximal portion 832 (or other portion) of the stylus 816 has an array of trackers 836. This array of trackers 836 can be tracked by the camera 812 to provide orientation, position, orientation, posture, or other combinations of specific characterization of the connected stylus 816 or a portion of an anatomical structure.

[0324] Camera 812 can operate without any additional sensors, such as an inertial sensor. In some embodiments, camera 812 is used in conjunction with an inertial sensor to verify or improve the accuracy of the sensor. For example, drift in a velocity sensor, such as accumulated error, can be monitored by comparing the position as seen from the camera with the output of the velocity sensor. The system can intervene if the sensor outputs too much drift, for example, by informing the user to reset the velocity sensor.

[0325] Other optical devices, such as a laser emitter or infrared emitter 814, may be provided with the orientation device 172A. Infrared emitters can be useful for illuminating fiduciaries under intense light conditions in the surgical field, as they are easily detachable by the camera.

[0326] [B. Optical components for femoral tracking] Figures 76–78 illustrate embodiments of the system 600 including an optical component 674. In this context, the term optical component is broad. The surgical orientation device 172 may include an optical component 674 that can be located on the upper, bottom, or side walls of the surgical orientation device 172. The optical component 674 may include a transparent window integrated into the surgical orientation device 172. The window may allow visible light (e.g., laser light) to be emitted from the optical component 674 of the surgical orientation device 172. The optical component 674 may provide a visual guide to reproduce the original position of the femur relative to the pelvis.

[0327] Continuing with reference to Figure 76, the optical component 674 may comprise one or more lasers that can be configured to project laser light through the above-mentioned window. For example, the optical component 674 may comprise a forward laser. The laser light can be used to project points, planes, and / or crosshairs onto a target that includes, but is not limited to, anatomical features or landmarks.

[0328] The optical component 674 can provide the surgeon with alternative or additional orientation information regarding the orientation of the surgical orientation device 172. For example, a laser beam can be used to project a plane onto a portion of bone to indicate a resection line, and a crosshair laser pattern can be used to ensure alignment along two perpendicular axes. In certain embodiments, the optical component 674 can be used to determine the alignment of an anatomical feature or landmark. For example, the optical component 674 can project a laser beam onto a target such as an anatomical feature. The surgeon can mark one or more points along the projection line of the optical component 674. The surgeon can complete any of the steps described herein. The surgeon can then verify that one or more points are along the projection line of the optical component 674.

[0329] In the illustrated embodiment, the optical component 674 is a component of the surgical orientation device 172. Other structures are conceivable. The optical component 674 may be a component of the fixed base 602. The optical component 674 may be a component of one or more fixed pins 610, 612. The optical component 674 may be an integral feature of any component of the system 600. The optical component 674 may be a component separate from any component of the system 600. The optical component 674 may be a standalone device attached to the pelvis.

[0330] System 600 can be modified to accommodate optical components 674. The fixed base 602C may include a platform 620C, as shown in Figures 79 and 80. The platform 620C may include a head 609C. The head 609C can be connected to a platform 611C and a support 613C. The platform 611C and support 613C can function as clamps for the head 609C. Figure 80 shows an exploded view of the fixed base 602C.

[0331] In the illustrated embodiments, the fixed base 602C may include one or more fixing devices 615C. In the illustrated embodiments, one fixing device 615C is shown, but other structures (e.g., two, three, four, etc.) are contemplated. The fixing device 615C may include one or more threaded portions. In the illustrated embodiments, the fixing device 615C is a screw having a head and a threaded shank. The platform 611C may include one or more holes. The support portion 613C may include one or more holes. The fixing device 615C may pass through or engage with one or more holes in the support portion 613C. In some embodiments, each hole in the support portion 613C is threaded. The fixing device 615C may pass through or engage with one or more holes in the platform 611C. In some embodiments, each hole in the platform 611C is threaded. Rotation of the fixing device 615C can move the support 613C toward the platform 611C and / or move the platform 611C toward the support 613C. The platform 611C and the support 613C form a channel 617C. The channel 617C can be sized to receive the head 609C. When the platform 611C and the support 613C are separated, the head 609C can have rotational or multi-axis motion. When the platform 611C and the support 613C are coupled by the fixing device 615C, the head 609C can be fixed in place.

[0332] Platform 611C may include a first coupler 632 as described in this specification. The first coupler 632 may be coupled to a first assembly 604 as described in this specification. In Figure 18, the first coupler 632 may be parallel to pins 610, 612. In Figure 76, the first coupler 632 may be inclined relative to pins 610, 612. In a forward approach, pins 610, 612 may be offset from the vertical. A probe 678 (not shown) may be bent or curved as described in this specification. The shape of the probe 678 may facilitate contact with a point or anatomical landmark in a forward approach.

[0333] The assembly shown in Figure 76 can allow the surgical orientation device to be moved relative to the patient's anatomical structure. The clamping of the platform 611C and support 613C can fix the position of the surgical orientation device 172 during surgery. The display of the surgical orientation device 172 can indicate whether the optical component 674 is on or off. The display of the surgical orientation device 172 may include instructions related to how to use the optical component 674.

[0334] In a preferred configuration, the surgical orientation device 172 can be positioned and / or moved until the optical component 674 projects a beam onto a portion of an anatomical structure. To achieve this centralization, the optical component 674 can emit a laser beam centrifugally from the surgical orientation device 172. This laser beam can illuminate a portion of the femur. This laser beam can illuminate a portion of the knee joint. This laser beam can illuminate a portion of the tibia. This laser beam can illuminate a portion of the ankle. This laser beam can illuminate a portion of the foot. This laser beam can illuminate a portion of the foot constrained within a positioning boot. The surgical orientation device 172 can be moved until the laser beam is aligned with at least one anatomical region. In some ways, the laser beam is aligned with at least one anatomical region having a small amount of soft tissue. The soft tissue may move relative to the underlying bone. The surgeon may select a position to mark where the skin is close to the underlying bone.

[0335] Optical component 674 can be used in conjunction with the anterior and posterior approaches described herein. When measuring changes in leg length and lateral joint offset, the apparent change is sensitive to changes in the orientation of the femur relative to the pelvis. This change is particularly sensitive to the abduction angle. This change is moderately sensitive to rotation of the femur around its mechanical axis. Two methods may be available to the surgeon. The first method is to reposition the femur before measuring the change so that the orientation of the femur relative to the pelvis is the same as when the preoperative baseline measurement was made. The surgeon attempts to use the first method, but this method is not very accurate. This method is not accurate mainly because the patient's pelvis is obscured by soft tissue and surgical drapes, giving the surgeon poor visibility of the patient's pelvis.

[0336] The second method involves measuring the orientation of the femur relative to the pelvis during and after the preoperative baseline, and then correcting for changes in orientation by performing a virtual rotation of the femur around the postoperative center of rotation. The second method is described in this specification with respect to posterior and anterior approaches. The second method may require obtaining three points on the femur, such as point 690 shown in Figures 24A and 25C. The second method may require calculating the center of rotation (COR) of the hip joint using a set of points on the edge of the shell, as shown in Figure 33. The second method is typically used in a navigation system, but with additional steps. In the case of the posterior approach described above, for example, three points on the femur 690, femoral tracker 686, 686A, or femoral base 687A must be recorded preoperatively and then postoperatively whenever leg length is measured to determine femoral orientation. The center of rotation must also be determined, which is done by recording three points on the acetabular cup after it has been inserted.

[0337] The optical component 674 can reduce the number of records. ...

Claims

1. A first fixation pin and a second fixation pin configured to be inserted into the bone of the patient, An orientation detection device equipped with an inertial sensor configured to be sensitive to the direction of gravity, A fixing base comprising a first channel configured to receive a first fixing pin and a second channel configured to receive a second fixing pin, wherein the fixing base is configured to function as a clamp together with the first and second fixing pins, and the fixing base comprises a fixing device comprising one or more threaded portions, wherein the first and second channels decrease in diameter with rotation of the fixing device to hold the first and second fixing pins, Equipped with, A hip joint navigation system in which, when an acetabular cup is fitted into the acetabulum using an impactor, the orientation data of the inertial sensor of the orientation detection device is configured to be used to confirm the orientation of the acetabular cup when the orientation detection device is connected to the impactor.

2. Further comprising the fixed base coupler configured to be connected to the components of the hip joint navigation system, The hip joint navigation system according to claim 1, wherein the coupler has an irregular shape.

3. Further comprising the fixed base coupler configured to be connected to the components of the hip joint navigation system, The hip joint navigation system according to claim 1, wherein the coupler is provided with a slot.

4. Further comprising the fixed base coupler configured to be connected to the components of the hip joint navigation system, The hip joint navigation system according to claim 1, wherein the coupler has a cylindrical shape.

5. Further comprising the fixed base coupler configured to be connected to the components of the hip joint navigation system, The hip joint navigation system according to claim 1, wherein the coupler has a tapered surface.

6. Further comprising the fixed base coupler configured to be connected to the components of the hip joint navigation system, The hip joint navigation system according to claim 1, wherein the coupler comprises an elongated post.

7. Further comprising a coupler of the fixed base configured to be connected to a component of the hip joint navigation system, The hip joint navigation system according to claim 1, wherein the coupler is integrally formed with the fixed base.

8. Further comprising an additional coupler of the impactor, The hip joint navigation system according to claim 1, wherein the additional coupler has an irregular shape.

9. Further comprising an additional coupler to the impactor, The hip navigation system according to claim 1, wherein the additional coupler comprises a slot.

10. The hip joint navigation system according to claim 1, wherein the orientation detection device comprises an accelerometer.

11. The hip joint navigation system according to claim 1, wherein the orientation detection device comprises a gyroscope.

12. The hip joint navigation system according to claim 1, wherein the orientation detection device comprises a three-axis accelerometer for detecting orientation relative to gravity.

13. The hip joint navigation system according to claim 1, wherein the orientation detection device comprises a plurality of gyroscopes for detecting rotation.

14. The hip joint navigation system according to claim 1, wherein the first fixing pin and the second fixing pin are configured to be positioned on the iliac crest.

15. The hip joint navigation system according to claim 1, wherein the first fixing pin and the second fixing pin are configured to be driven into the ilium on the pelvis.

16. The hip joint navigation system according to claim 1, wherein the orientation detection device is software incorporated within the processor.

17. The hip joint navigation system according to claim 1, wherein the orientation detection device is configured to calculate a transformation from one reference coordinate system to another.

18. The hip joint navigation system according to claim 1, wherein the orientation detection device is configured to process an algorithm.

19. The hip joint navigation system according to claim 1, wherein the fixing device crosses the first fixing pin and the second fixing pin.

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