System and method for monitoring offset during navigation-assisted surgery - Patents.com

Abstract

A surgical system and method for tracking a physical object near a target site during a surgical procedure is provided. The surgical system employs a navigation system and a surgical instrument. An instrument tracker is provided on the surgical instrument and a patient tracker is provided on the target tissue of the patient. The system and method detect error conditions that impair the accuracy of the navigation guidance and track and monitor tool-to-bone offset.

Description

[Technical field]

[0001] The present disclosure relates generally to computer-assisted surgery. More specifically, systems and techniques for determining the offset of a monitor position of a surgical device relative to a patient are disclosed. The techniques can be implemented as a method, a non-transitory medium of a computer program, a computing device, and a system for computer-assisted surgery.

[0002] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims priority to and the entire benefit of U.S. Provisional Patent Application No. 63 / 054,811, filed July 22, 2020, and U.S. Provisional Patent Application No. 62 / 960,218, filed January 13, 2020, the entire contents of which are incorporated herein by reference. [Background technology]

[0003] Navigation-assisted surgery is often based on a patient's anatomy imaged preoperatively using one or more of magnetic resonance imaging (MRI), computed tomography (CT), x-ray, or other imaging techniques. Data generated through these techniques can be highly accurate and provide the basis for generating a virtual three-dimensional (3D) model of the target anatomy stored in a memory in or in communication with the navigation system. During navigation-assisted surgery, a patient tracker can be associated with the patient's anatomy and a tool tracker can be associated with the surgical tools. The navigation system can locate and track the anatomy and surgical tools based on the associated trackers in the navigation system's virtual space to provide important information to the surgeon or other medical professional during surgery.

[0004] Surgical navigation systems are used in industrial, aerospace, and medical applications to precisely locate and track physical objects in space and orientation. In the medical field in particular, navigation systems can assist surgeons or other medical professionals in precisely positioning surgical instruments relative to a target site on a patient, for example, during a surgical procedure. The target site typically requires some form of therapy or treatment, such as tissue removal. Conventional navigation systems employ localizers that include one or more sensors that cooperate with trackers to provide position and / or orientation data associated with surgical information and the target site, e.g., a volume of tissue requiring treatment. These trackers allow the surgeon to see the position and / or orientation of a surgical tool overlaid on a monitor in conjunction with a virtual representation of the tool and anatomy based on pre-operative or intra-operative imaging of the patient. These trackers also allow the navigation system to monitor the relative positioning of the tool and the anatomy and to alert the user if the tool approaches or enters an undesirable position relative to the anatomy. For example, a user may be alerted that the tool is approaching or contacting patient tissue that is not intended to be contacted by the tool.

[0005] The localizer is typically positioned such that it has the field of view of the tracker. That is, the localizer is positioned such that the target site of the patient is within the target space of the localizer. The tracker includes an identifiable array of fiducials or markers that are fixed to at least one of the surgical instrument or the patient and move with the surgical instrument or the patient, respectively. The surgical navigation system can determine the position and orientation of the surgical instrument or the patient from the detected positions of the tracker and monitor changes in the determined position and orientation over time. The term position refers to the 3D coordinate values ​​of the object's coordinate system relative to a reference coordinate system used by the surgical navigation system. The term orientation refers to the pitch, roll, and yaw of the object's coordinate system relative to the reference coordinate system. The position and the specific pitch, roll, and yaw values ​​for a given orientation can be collectively referred to as the pose of the object in the reference coordinate system. Once both the position and orientation (i.e., pose) are determined, the object is recognized by the surgical navigation system and can be tracked by the surgical navigation system (i.e., registered (registered, registered) by the surgical navigation system).

[0006] The tracker attached to the patient and the tracker attached to the tool are rigidly fixed to the bone and the tool applying the treatment, thereby maintaining a fixed relationship to the target site and tool due to the rigidity of the bone or tool, the rigid structure of the tracker, and the fixation between them. In another form known in the art, the tracker can be deformable and attached to soft tissue such as skin. The tracker is constructed of a pattern or array of markings, markers, or fiducials according to known deformations that provide similar information as a rigid tracker. By using separate trackers on the surgical tool and the patient, the treating end of the surgical instrument can be precisely positioned at the target site by the surgeon aided by the navigation system.

[0007] During the early stages of surgery, an object, whether it is a surgical tool or the patient's anatomy, needs to be calibrated or registered to the surgical navigation system. The process of calibration or registration refers to defining the relationship between a physical object and its tracker as a virtual representation of the object and tracker as data in the surgical navigation system, i.e., as virtual object data and virtual tracker data, respectively. The virtual data may or may not be a model of the object, whether the object or the tracker. Rather, the virtual data may include enough information to identify or designate specific points of interest and may further include other information regarding the dimensional characteristics of the object. The virtual data may be established pre-operatively or intra-operatively. The virtual data may be based on existing modeling or object specification data, or may be based on imaging of the object in situ. The virtual data may be generated from imaging data through a process of segmentation. For example, pre-operative imaging of the patient's anatomy may be used to generate a 3D model of that anatomy as virtual object data in the memory of the surgical navigation system and in the virtual environment. Similarly, a surgical tool can be manufactured according to a known geometry and structure. This geometry and structure can be represented in the 3D model of the tool as virtual object data in the memory of the surgical navigation system and in the virtual environment. To perform the calibration, an additional reference pointer or frame with an additional tracker reference array may be required to touch off a reference point according to the alignment or calibration system. Alternatively, the calibration may be established using optical processes, using projected light patterns, optical recognition, or other conventional methods.

[0008] A localizer typically includes multiple sensing technologies that are variously adapted for beneficial use in a particular surgical aspect. In one example, a localizer may include one or more sensors suitable for navigation. The one or more navigation sensors may be adapted for navigation by operating high frequency sensing cycles to accurately track small movements over small time increments, i.e., by providing high resolution tracking data.

[0009] The localizer may further comprise sensors suitable for machine vision or other applications beneficial to surgery. For example, the localizer may comprise one or more optical cameras to provide video recording of the surgical procedure. The localizer may include multiple sets of individual sensors performing different functions, i.e., sensing different physical properties or light, electromagnetic energy, or other properties. Data representative of the localizer's sensor output can be processed to derive important information regarding the surgical site within the field of view or range of the localizer.

[0010] Conventional surgical navigation systems may be adapted for use with a robotic arm or manipulator that supports the surgical tools used during a medical procedure. Incorporating a robotic arm manipulator into the navigation system provides a higher degree of control, allowing the movement of the surgical tools to be accomplished by or with the assistance of the robotic arm, allowing proper placement of the tools relative to the anatomy. Joint encoders or other sensing technology may be incorporated into the robotic arm to provide additional data to determine the position of the tool while it is being tracked by the navigation system. This information may be compared, and if a discrepancy occurs, the operator may be alerted and the surgical procedure may be halted until the error can be diagnosed and corrected. Summary of the Invention [Problem to be solved by the invention]

[0011] There is a need for improved surgical navigation systems adapted for use without the assistance of a robotic manipulator. Removing the closed loop of data provided by the robotic system introduces additional uncertainty and leaves the navigation system at risk of losing calibration or alignment to the tool tracker or anatomy tracker without the ability to detect such loss of calibration or alignment and to alert the user. This can lead to improper placement of tools relative to the anatomy during surgery. Thus, there is a need in the art for systems and methods that address the shortcomings of conventional navigation systems and provide efficient techniques for monitoring offsets during navigation-assisted surgery. [Means for solving the problem]

[0012] A method of navigating a surgical instrument having a variable speed motor relative to a bone is provided. The method includes using a navigation system including a localizer having a localizer coordinate system. An instrument tracker is coupled to the surgical instrument. A patient tracker is coupled to the bone. A controller is in communication with the navigation system. The controller controls the surgical instrument.

[0013] The method includes registering a patient tracker to a localizer coordinate system with a localizer, the registration defining a location of the bone relative to the localizer coordinate system, and the method includes registering an instrument tracker to the localizer coordinate system with a localizer, the registration defining a location of an instrument tool tip relative to the localizer coordinate system.

[0014] The method includes defining motor operation of the instrument when the instrument tool tip is not in contact with bone. The method includes monitoring motor operation of the instrument during the medical procedure with a controller and monitoring a position of the instrument tool tip relative to the bone with a navigation system to determine when the instrument tool tip contacts the bone in a localizer coordinate system.

[0015] The method includes comparing the motor motion to a monitored position of the instrument tool tip and determining an error condition when the monitored position of the instrument tool tip is in contact with the bone in a localizer coordinate system and the monitored motor motion is equal to a defined motor motion of the instrument when the instrument tool tip is not in contact with the bone. The method includes triggering an action when the error condition is determined.

[0016] In the method, defining the motor operation of the instrument when the tool tip is not in contact with bone may include defining a threshold of power, voltage, current, or a combination thereof when the instrument motor operates while the instrument tool tip is not in contact with bone. Defining the motor operation may include storing data representing the motor operation in a memory of one or more of the controller, the navigation system, the surgical instrument, or a combination thereof.

[0017] The method may also include defining a second motor motion of the instrument when the instrument tool tip is in contact with the bone. Defining the second motor motion, the method may further include determining a second error condition when the monitored position of the instrument tool tip is not in contact with the bone in the localizer coordinate system and the monitored motor motion is equal to the second defined motor motion of the instrument when the instrument tool tip is in contact with the bone. The method may also include triggering a second action when the second error condition is determined.

[0018] In the method, the step of triggering one of the action or the second action includes one of sounding an audible alert, displaying a visual alert, activating a tactile alert, cutting power to the surgical instrument, or a combination thereof.

[0019] A method is provided for navigating a surgical instrument having a variable speed motor relative to a bone and monitoring tool-to-bone offset. The method includes using a navigation system including a localizer having a localizer coordinate system. An instrument tracker is coupled to the surgical instrument. A patient tracker is coupled to the bone. A controller is in communication with the navigation system and controls the surgical instrument.

[0020] The method includes registering a patient tracker to a localizer coordinate system with a localizer, the registration defining a location of the bone relative to the localizer coordinate system, and the method includes registering an instrument tracker to the localizer coordinate system with a localizer, the registration defining a location of an instrument tool tip relative to the localizer coordinate system.

[0021] The method includes defining a first motor motion of a surgical instrument that operates while not in contact with a bone. The method includes monitoring the motor motion of the surgical instrument during the medical procedure with a controller and monitoring a position of the instrument tool tip relative to the bone in a localizer coordinate system with a navigation system.

[0022] The method includes comparing the monitored motor motion to a defined motor motion and determining a time of contact (or a time point of contact) between the instrument tool tip and the bone when the monitored motor motion deviates from a first defined motor motion. The method includes determining, at the time point of contact, a tool-bone offset using a navigation system as a distance between the instrument tool tip and a surface of the bone in a localizer coordinate system. Although described herein as a tool-bone offset, it is understood that the reference to "bone" is not intended to be limiting and such use of "bone" may be understood as any type of biological structure on which a surgical procedure is performed, including non-bone type tissues such as skin, muscle, connective tissue, nerve tissue, etc. The method includes triggering an action when the tool-bone offset exceeds a predetermined magnitude.

[0023] In the method, the step of triggering an action may include one of sounding an audible alert, displaying a visual alert, activating a tactile alert, cutting off power to the surgical instrument, or a combination thereof. In the method, the predetermined magnitude may be equal to 0.5 millimeters. The step of triggering an action may include prompting a user to update the model of the bone, and the method may include updating the model of the bone. Updating the model includes contacting a resection surface of the bone with an instrument tool tip while power from the controller to the surgical instrument is disabled.

[0024] The method may further include displaying the determined tool-bone offsets on a display device. The method may include displaying the series of tool-bone offsets as a chart of offset values ​​over time.

[0025] In the method, the step of monitoring the position of the instrument tool tip relative to the bone may include tracking the location of the instrument tool tip and the location of the bone during the medical procedure and may further include detecting, using a navigation system, each occurrence during the operation of the monitored location of the instrument tool tip in contact with a surface of the bone and recording a series of tool-to-bone offset values ​​determined during the medical procedure at each occurrence. The method may further include displaying the series of tool-to-bone offsets as continuously updated values ​​on a display device.

[0026] The method may further include defining a first level magnitude and a second level magnitude. In the method, the step of displaying the determined tool-bone offset may include displaying the offset in a first color if the offset is less than the first level magnitude, displaying the offset in a second color different from the first color if the offset is between the first level and second level magnitudes, and displaying the offset in a third color different from the first and second colors if the offset is greater than the second level magnitude. The predetermined magnitude for triggering an action may be equal to the second level magnitude. The predetermined magnitude for triggering an action may be greater than the second level magnitude. The method may further include defining a third level magnitude, the method also including disabling power from the controller to the surgical instrument if the tool-bone offset is greater than the third level magnitude. The method may include prompting a user to input a value for the predetermined magnitude, the first level magnitude, the second level magnitude, the third level magnitude, or a combination thereof. The method may include disabling power from the controller to the surgical instrument if the tool-bone offset is greater than a predetermined value.

[0027] A surgical system is provided that includes a surgical instrument having a variable speed motor or actuator and a tool tip. The surgical system includes a controller that provides power to the surgical instrument, the controller operable to monitor motor or actuator operation of the instrument, the controller including a processor and a memory, the memory operable to store information including information representative of instrument operation. The system includes an instrument tracker coupled to the instrument and a patient tracker coupled to a bone.

[0028] The system includes a navigation system including a localizer. The navigation system is operable to store information representative of a surgical instrument and information representative of a bone in a virtual space. The navigation system is operable to track a location of the instrument and the bone in the virtual space during a motion based on information collected by the localizer. The localizer is operable to align a location of the instrument tracker and a location of the patient tracker relative to a localizer coordinate system and cooperate with the instrument tracker and the patient tracker, respectively, to collect information regarding the location of the instrument and the bone. The controller and the navigation system are in electronic communication and configured to cooperate. The controller and the navigation system determine a time of contact between the tool tip and the bone based on the change in motion. The controller and the navigation system determine a tool-to-bone offset as a distance between the tracked location of the tool tip and the tracked location of the bone at the time of contact. The system also includes an alert device, the controller and the navigation system further configured to trigger an action if the tool-to-bone offset is greater than a predetermined magnitude.

[0029] A method is provided for operating a surgical navigation system during a surgical procedure to verify tracking alignment. The surgical navigation system includes a localizer having a localizer coordinate system. An instrument tracker is coupled to a surgical instrument. The surgical instrument includes a tool tip. A patient tracker is coupled to the patient's anatomy. A control console is in communication with the localizer. The control console is in communication with data representative of the surgical instrument and data representative of the patient's anatomy.

[0030] The method includes tracking a surgical instrument and an anatomical structure with a navigation system and storing, with a control console, first data representative of the tracked surgical instrument and second data representative of the tracked anatomy in a common coordinate system. The method includes determining that a tool tip is within a predetermined proximity range relative to the tracked anatomy based on the tracked surgical instrument and the tracked anatomy. The method includes determining that the tool tip does not leave the predetermined proximity range by more than a predetermined magnitude for a predetermined duration. The method includes determining an offset distance based on the first data representative of the tracked surgical instrument and the second data representative of the tracked anatomy. The method includes comparing the offset distance to a predetermined threshold and triggering an action of the navigation system if the offset distance is greater than the predetermined threshold.

[0031] Optionally, the method includes prompting the user to verify the tracking alignment by one of displaying a prompt on a display, sounding an audible alert, generating a haptic sensation, or a combination thereof.

[0032] In this method, the step of determining that the tool tip is within a predetermined proximity range relative to the anatomical structure may include defining a surface area of ​​the anatomical structure that is not to be resected, and determining that the tool tip is within a predetermined proximity range relative to the defined surface area.

[0033] In this method, the offset distance may be defined as the magnitude of the minimum separation between the tool tip and the tracked anatomical structure in a common coordinate system, or as the magnitude of the maximum overlap between the tool tip and the tracked anatomical structure in a common coordinate system.

[0034] In the method, determining that the tool tip is within a predetermined proximity range relative to the tracked anatomy may include the surgical instrument being positioned at a first orientation relative to the tracked anatomy, the surgical instrument may define a first proximal point of the tool tip, and determining the offset distance may include determining a first offset distance. The method further includes determining that the tool tip is within a predetermined proximity range relative to the tracked anatomy, the surgical instrument may be positioned at a second orientation relative to the tracked anatomy, the surgical instrument may define a second proximal point of the tool tip, and determining the offset distance may include determining a second offset distance.

[0035] Comparing the offset distance to a predefined threshold may include comparing the first offset distance to a predefined threshold and comparing the second offset distance to a predefined threshold, such that initiating an action may include initiating an action if the first offset distance, the second offset distance, or both the first offset distance and the second offset distance are greater than the predefined threshold.

[0036] The surgical instrument may include an elongated surface terminating in a tool tip, the elongated surface defining a longitudinal axis extending substantially parallel to the elongated surface, the second proximal point being at least 90 degrees from the first proximal point relative to rotation about the centerline. The surgical instrument may include a tool tip having a spherical surface defining a center point, the second proximal point being at least 90 degrees away from the first proximal point relative to rotation about the center point.

[0037] Determining that the tool tip is within a predetermined proximity range relative to the tracked anatomy may include positioning the surgical instrument at a third pose relative to the tracked anatomy. The surgical instrument may define a third proximal point, the third proximal point being different from the first proximal point and the second proximal point. Determining an offset distance may include determining a third offset distance.

[0038] Comparing the offset distances to predetermined thresholds may include comparing the first offset distance to a predetermined threshold, comparing the second offset distance to a predetermined threshold, and comparing the third offset distance to a predetermined threshold. Initiating an action may include initiating an action if the first offset distance, the second offset distance, the third offset distance, or a combination thereof is greater than the predetermined threshold.

[0039] Triggering the action may include sounding an audible alert, displaying a visual alert, activating a tactile alert, cutting power to the surgical instrument, or one of a combination thereof.

[0040] The predetermined threshold may include a first predetermined threshold and a second predetermined threshold. Triggering an action of the navigation system may include triggering a first action if the offset distance is greater than the first predetermined threshold but less than the second predetermined threshold, and triggering a second action if the offset distance is greater than the second predetermined threshold. The action may include one of sounding an audible alert, displaying a visual alert, activating a tactile alert, cutting power to the surgical instrument, or a combination thereof.

[0041] A surgical system is provided that includes a navigation system that includes a control console and a localizer. The navigation system is in communication with first data representative of a surgical instrument and second data representative of a patient's anatomy. The surgical instrument includes a tool tip.

[0042] The navigation system is operable to track the surgical instrument and the anatomy in the virtual space during operation based on information collected by the localizer from an instrument tracker coupled to the surgical instrument and a patient tracker coupled to the anatomy. The navigation system is configured to track the surgical instrument and the anatomy and to store data representing the tracked poses of the surgical instrument and the anatomy in a common coordinate system.

[0043] The navigation system is configured to determine that the tool tip is within a predetermined proximity range relative to the anatomy based on a pose of the tracked surgical instrument and a pose of the tracked anatomy. The navigation system is further configured to determine that the tool tip does not leave the predetermined proximity range by more than a predetermined magnitude for a predetermined duration. The navigation system is further configured to determine an offset distance based on the tracked surgical instrument and the tracked anatomy in a common coordinate system. The navigation system is further configured to compare the offset distance to a predetermined threshold.

[0044] The navigation system may include an alert device, and the navigation system may be further configured to trigger an action if the offset distance is greater than a predetermined threshold. The alert device may be a foot switch, the foot switch operable to generate a vibration.

[0045] A method of providing navigational guidance for a surgical procedure is provided. The method includes registering a patient's anatomy to a common coordinate system. The patient's anatomy includes at least a first bone and a second bone. The method includes registering a surgical instrument to the common coordinate system. The method includes tracking the patient's anatomy and the surgical instrument with a navigation system during movement of the surgical instrument on the first bone of the patient's anatomy. The method includes determining an offset distance according to the methods disclosed herein relative to the second bone, and tracking the patient's anatomy and the surgical instrument with the navigation system during movement of the surgical instrument on the second bone of the patient's anatomy.

[0046] A method of performing a surgical procedure is provided. The method includes coupling a patient tracker to a patient's anatomy and coupling an instrument tracker to a surgical instrument, the surgical instrument including a tool tip. The method includes operating a navigation system to align the instrument tracker and the patient tracker to a common coordinate system and track the surgical instrument and the patient's anatomy. The method includes pausing the tool tip in contact with the patient's anatomy for a predetermined duration to initiate an alignment verification. The navigation system is configured to determine an offset distance based on the tracked surgical instrument and the tracked patient's anatomy. The method includes evaluating the offset distance against a predetermined threshold.

[0047] The navigation system may be configured to trigger an action if the evaluation of the offset distance determines that the offset distance is greater than a predetermined threshold, and the action may include one of sounding an audible alert, displaying a visual alert, activating a tactile alert, cutting power to the surgical instrument, or a combination thereof. The method may also include providing an input to the navigation system to terminate the triggered action.

[0048] The step of resting the tool tip in contact with the anatomy may include resting the tool tip in contact with a first anatomy contact point at a first time. The surgical instrument may be in a first orientation at the first time and a first proximal point of the tool tip may contact the first anatomy contact point. The method may further include resting the tool tip in contact with a second anatomy contact point at a second time. The surgical instrument may be in a second orientation at the second time and a second proximal point of the tool tip may contact the first anatomy contact point. The navigation system may be configured to determine a first offset distance based on the first anatomy contact point and the first proximal point and to determine a second offset distance based on the second anatomy contact point and the second proximal point.

[0049] The step of evaluating the offset distance may include one of evaluating the first offset distance against a predetermined threshold, evaluating the second offset distance against a predetermined threshold, or a combination thereof.

[0050] The patient's anatomy may include a first bone and a second bone, and the method may further include applying and operating a surgical instrument to the first bone and applying and operating the surgical instrument to the second bone. The step of pausing the tool and initiating the alignment verification may occur in contact with the second bone after applying and operating the surgical instrument to the first bone and prior to applying and operating the surgical instrument to the second bone.

[0051] Other objects, features and advantages of the present disclosure will be readily appreciated as the same becomes better understood after reading the subsequent description in conjunction with the accompanying drawings.

[0052] Other advantages will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings. [Brief description of the drawings]

[0053] [Figure 1]FIG. 1 is an illustration of a surgical system including a set of surgical tools for use in performing navigation-assisted surgery. [Diagram 2] FIG. 1 is a perspective view of a navigation system used in conjunction with surgical tools in performing navigation-assisted surgery. [Diagram 3] FIG. 2 illustrates a localizer coordinate system and a tracker coordinate system of a tracker connected to a surgical instrument. [Figure 4A] FIG. 1 illustrates a surgical instrument and a bone in a first relationship. [Figure 4B] FIG. 4B illustrates a navigation display representation of the relationship shown in FIG. 4A in a first error state. [Figure 5A] FIG. 13 illustrates a surgical instrument and a bone in a second relationship. [Figure 5B] FIG. 5B illustrates a navigation display representation of the relationship shown in FIG. 5A in a second error condition. [Figure 6] FIG. 13 shows a chart of actuator operation over time for a cutting operation. [Figure 7] 1 is a flow chart illustrating a first method of navigating a surgical instrument relative to a bone. [Figure 8] 13 is a flow chart showing a second method of navigating a surgical instrument relative to a bone and determining a tool-bone offset. [Figure 9] 13 is a flow chart illustrating a method for performing tracking registration verification. [Figure 10] 11 is a flow chart illustrating a second method for performing tracking registration verification. [Figure 11] 13 is a flow chart illustrating additional steps for performing tracking registration verification. [Figure 12] FIG. 1 illustrates a surgical instrument having an elongated surface for contacting bone. [Figure 13] FIG. 1 illustrates a surgical instrument having a spherical surface that contacts the bone. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] FIG. 1 illustrates a surgical system 10 with a set of surgical tools for use in performing navigation-assisted surgery on a patient. The version illustrated in FIG. 1 includes a surgical navigation system 20. The surgical navigation system 20 is configured to track the movement of various objects within an operating room, including, for example, surgical tools and the patient's anatomy. The surgical navigation system 20 tracks these objects to indicate the relative positions and orientations of these objects to the surgeon, and in some cases to alert the surgeon to certain events or occurrences related to the operation of the surgical tools. For example, a virtual cutting boundary may be associated with the patient's anatomy, and the system 10 may alert the surgeon when the surgical tool approaches the cutting boundary or may stop the tool if the surgical tool exceeds the cutting boundary.

[0055] The navigation system 20 may include a computer cart assembly 24 that houses a navigation computer 26. A navigation interface is in operative communication with the navigation computer 26. The navigation interface may include a first display 28 located outside the sterile field of the surgical procedure and a second display 29 located inside the sterile field. The displays 28, 29 are adjustably mounted to the computer cart assembly 24. One or more input devices (not shown), such as a keyboard, mouse, trackball, etc., may also be provided for inputting information into the navigation computer 26 or for selecting or controlling certain aspects of the operation of the navigation computer 26. Additionally, other hardware may be provided to facilitate alternative forms of input. For example, sensors may be provided in one or more displays to allow input by gesture control, or a microphone may be provided for voice command control.

[0056] The localizer 34 communicates with the navigation computer 26. In the illustrated example, the localizer 34 is an optical localizer and includes a camera unit 36. The camera unit 36 ​​has an outer casing 38 that houses one or more optical sensors 40. The optical sensors 40 can be rigidly mounted to a common support structure. The outer casing can provide a common support structure for the optical sensors 40. Alternatively, the rigid support structure common to the optical sensors can be covered by a separate outer casing 38. As shown in FIG. 1, the optical sensors 40 are disposed at both ends of the elongated camera unit 36, such that the optical sensors 40 are stereoscopically positioned relative to the surgical site.

[0057] Although described in the context of optical localizers including camera technology for locating and tracking objects based on sensing electromagnetic energy in the visible or near-visible spectrum, other locating and tracking technologies may be used. For example, electromagnetic energy in the microwave or radio spectrum may be used instead or in addition. Similarly, sonic or ultrasonic energy may be another alternative technology for locating and tracking objects. A common feature of these technologies useful for tracking and locating objects is that energy can be generated or reflected off the object being tracked and sensed by a navigation system to determine the object's location.

[0058] In some alternatives, such as that shown in Figure 1, two optical sensors 40 are employed. In other alternatives, additional optical sensors may be provided apart from the first set of optical sensors 40 to avoid obscuring the view of the surgical site and the tracker present therein. The optical sensors 40 may variably attenuate radiant energy, e.g., light, into a signal as a small burst of electrical current that may be communicated as information between electronic devices.

[0059] Camera unit 36 ​​may also, or alternatively, include a video camera 41 or other additional sensing devices (not shown). Video camera 41 may include similar or different light sensing technology than that employed by optical sensor 40. For example, optical sensor 40 may be configured to sense energy in the infrared or near-infrared spectrum, and video camera 41 may be configured to transmit light in the visible spectrum.

[0060] The optical sensor 40 may be a separate charge-coupled device (CCD). In some alternatives, two two-dimensional CCDs are employed. In some cases, the optical sensor 40 is positioned for stereoscopic operation. In other alternatives, the optical sensor 40 may be a single camera combined with a depth sensor, laser range finder, or the like. It should be appreciated that in other alternatives, multiple separate camera units 36, each having a separate CCD or two or more CCDs, may be positioned around the operating room. The additional optical sensor helps ensure that the navigation system 20 maintains an unobstructed view of the surgical site through one or more of the optical sensors 40 throughout the surgical procedure. The optical sensor 40 may include a CCD capable of detecting infrared (IR) radiant energy. The optical sensor may employ other sensing technologies, including, but not limited to, complementary metal-oxide semiconductor (CMOS) active pixel sensors, and the like.

[0061] The camera unit 36 ​​may be mounted on an adjustable arm or other articulating support structure of the cart assembly 24 to selectively position the localizer 34 with a preferably unobstructed view of a target space including the patient's anatomy and the surgical site where the tracker will be positioned (as described below). In some cases, the camera unit 36 ​​is adjustable in at least one degree of freedom by rotating about a rotational joint. In other alternatives, the camera unit 36 ​​is adjustable for two or more degrees of freedom. When multiple camera units 36 are employed, each may be individually mounted for selective positioning about the surgical environment. Alternatively, the cart structure 24 may support multiple adjustable arms to support multiple camera units 36.

[0062] The camera unit 36 ​​further includes a camera controller 42 that communicates with and receives signals from the optical sensor 40. The camera controller 42 communicates with the navigation computer 26 through either a wired or wireless connection (not shown). One such connection may be an IEEE 1394 interface, which is a serial bus interface standard for high speed communication and isochronous real-time data transfer. Other suitable connection types include Ethernet, Thunderbolt, USB interface, PCI Express, DisplayPort, etc. The connection may also use company-specific or proprietary protocols. In another alternative, the optical sensor may communicate directly with the navigation computer 26, such that the navigation computer incorporates the functionality of the camera controller 42 and thus operates as the camera controller 42. Processing of the signals from the optical sensor may occur in the camera controller 42. Alternatively, the camera controller 42 may communicate the signals to the navigation computer 26 for processing. In communicating the signals to the navigation computer 26 for processing, the camera controller 42 may perform some pre-processing conditioning, reformatting, conversion, etc.

[0063] The navigation computer 26 may be a personal computer or a laptop computer. The navigation computer 26 communicates with the displays 28, 29 and includes a central processing unit (CPU), other processors, memory units, data storage units, and combinations thereof. The navigation computer includes software as described below. The software converts signals received from the camera unit 36, camera controller 42, or optical sensor 40 into data representative of the position and orientation of the object being tracked. The position and orientation signals, or data derived therefrom, are used by the navigation computer 26 to track the object. The cart assembly 24, display 28, and camera unit 36 ​​may be similar to those described in U.S. Patent No. 7,725,162, entitled "Surgery System," issued May 25, 2010 to Malackowski et al., which is incorporated herein by reference.

[0064] The surgical system 10, including the navigation system 20, can be configured to operate with a variety of surgical tool systems. While Figure 1 illustrates representative available tool systems, it should be understood that other options are available or may become available in the future without departing from the scope of this disclosure.

[0065] The surgical system 10 can be used in connection with a cordless power tool. The cordless power tool can include a sagittal saw, a reciprocating saw, a rotary drill, a sternal saw, and the like. In the example of FIG. 1, the cordless power tool is shown as a cordless power driver 60. It should be understood that corded power tools can also be used. An example of such a cordless power driver 60 tool is the System 8 Cordless Driver sold by Stryker. The driver 60 includes a battery unit 61 that provides power to the driver 60. The battery unit 61 can include a rechargeable battery pack. The battery unit 61 can be a smart battery pack that includes a data module 62 having electronics and programming to facilitate communication between the driver 60 and the navigation computer 26.

[0066] The driver 60 may include a driver controller 64 in operative communication with the data module 62. Alternatively, a single computer module may be provided that provides the functionality of both the driver controller 64 and the data module 62. The driver controller 64 controls the operation of the driver 60 and communicates with input controls such as triggers 63, 65, the driver motor 68, and other sensors or instrumentation contained within the driver 60. In one example, a temperature sensor is included to detect overheating of the driver motor 68 and disable operation of the driver 60 by the driver controller 64.

[0067] The driver 60 is provided with a tracker 70. The tracker 70 may be an active or passive tracker. An active tracker requires a power source and has an array of markers 72 (also referred to as tracking elements or fiducials) that actively generate and emit radiation at wavelengths detectable by the optical sensor 40. The markers 72 of an active tracker may be light emitting diodes (LEDs), including, for example, infrared LEDs. The array of active markers may be in an "always on" state, or may be operable "on" to selectively emit (i.e., emit radiation) in response to a command from the surgical navigation system 20. In such a selectively emitting active tracker, the tracker may communicate with the navigation computer 26 of the surgical navigation system 20 by a wired or wireless connection. The active tracker may be powered by an internal battery or may have leads that receive power from an externally connected power source.

[0068] Alternatively, tracker 70 can be a passive tracker, i.e., an array of markers 72 can reflect ambient radiant energy or radiant energy emitted into a target space. For example, camera unit 36 ​​may include one or more infrared LEDs to emit infrared energy that is reflected by markers 72 and then sensed by optical sensor 40. Passive trackers typically do not require a power source.

[0069] Although described with reference to optical technology including light reflective or light emitting markers, other trackers consistent with the sensing technology of the localizer may be used. For example, the localizer may include an electromagnetic field generator and the tracker may employ a coil or coil array. An example of the use of this technology can be seen in the disclosure of U.S. Patent No. 8,249,689, entitled "Coil Arrangement for Electromagnetic Tracking Method and System," the entirety of which is incorporated herein by reference.

[0070] The surgical system 10 can also be used with a generic integrated console or tool platform. The generic platform 80 includes a console 82, a foot switch 4, and a powered surgical tool 86. The console 82 controls and powers the connected tool 86. The tool 86 can be a miniature bone orthopedic saw or drill, a high speed drill (e.g., for neuro or spinal applications), an ENT shaver, a joint shaver, a bone mill, etc. One example of such a generic platform is the Core 2 Console power tool driver and associated tools sold by Stryker and described in International Patent Publication No. WO 2015 / 021216, entitled "System And Method For Driving An Ultrasonic Handpiece As A Function Of The Mechanical Impedance Of The Handpiece," which is incorporated herein by reference in its entirety. The console 82 includes a data module 88 that facilitates communication between the console and the navigation computer 26.

[0071] Similar to the driver 60 described above, the instrument 86 is provided with a tracker 90. The instrument tracker 90 is similar to the driver tracker 70 and includes an array of markers 72. The markers 72 may be active or passive and are sensed by the camera unit 36 ​​to track and monitor the position and orientation of the instrument 86.

[0072] The surgical system 10 may also be used with an ultrasonic aspirator system 100. The ultrasonic aspirator system 100 includes a console 102, a foot switch 104, and an aspirator tool 106. The console 102 controls and powers the connected aspirator tool 106. An example of such an ultrasonic aspirator system is the SONOPET iO Ultrasonic Aspirator sold by Stryker. The console 102 includes a data module 108 that facilitates communication between the console and the navigation computer 26.

[0073] The tool 106 is provided with a tracker 110 similar to the instrument tracker 90 and the driver tracker 70. The tool tracker 110 includes an array of markers 72, which may be active or passive as described above, that are sensed by the camera unit 36 ​​to track and monitor the position and orientation of the tool 106. As can be seen from FIG. 1, the driver tracker 70, the instrument tracker 90, and the tool tracker 110 are distinguishable based on the array of markers 72. The descriptions provided herein and names such as "tool tracker" or "instrument tracker" are not intended to be limiting, but are merely used to distinguish surgical articles available for use with the present disclosure. The trackers may be attached in a manner shown in U.S. Patent No. 7,725,162, entitled "Surgery System," issued May 25, 2010 to Malackowski et al., the disclosure of which is incorporated herein by reference. Alternatively, the trackers may be mounted as shown in U.S. Patent No. 9,566,120, entitled "Navigation Systems and Method for Indicating and Reducing Line-of-Sight Errors," issued Feb. 14, 2017 to Malackowski et al., the disclosure of which is incorporated herein by reference. In yet another alternative, the trackers may be mounted in other manners conventional in the art.

[0074] Although shown as a separate structure mounted on and extending from the surgical object, the tracker may alternatively be integrated into the structure of the article itself. For example, the marker 72 may be formed directly within the structure of the tool or instrument to be tracked. In yet another alternative, a structure or feature of the article itself may be used as the tracker, eliminating the need for a dedicated marker. In such a case, the surface or edge of the article may be visible to the navigation system and used to track the position and orientation of the article. Additionally, markings or patterns may be included on the surface of the article to be used as trackers. For example, a linear barcode, or a 2D barcode (also known as a QR code) may be featured on the surface of the article that remains visible to the camera unit 36 ​​throughout the procedure to track the article.

[0075] 2, the surgical system 10 is shown in an exemplary surgical environment for use with a universal tool platform 80 including a console 82, foot switches 84, and instruments 86. The surgical site is also provided with a C-arm computed tomography (CT) system 120 for providing intraoperative imaging of the patient's anatomy. Although illustrated with a CT system 120, other imaging techniques including MRI, X-ray, or videography may be employed for intraoperative imaging. Generally, regardless of the technique selected, the imager communicates with the navigation computer 26. Information from the imager is used to prepare a virtual representation of the patient's anatomy, such as a 3D model of the tissue to be treated in the surgery. The process of preparing the virtual representation can be through segmentation of the image data. Segmentation may be an automated process, for example, by machine learning. Exemplary processes are disclosed in U.S. Pat. No. 1,0198,662, entitled "Image Analysis," issued Feb. 5, 2019, and U.S. Pat. No. 8,867,809, entitled "Image Processing Method," issued Oct. 21, 2014. Using information from the imager, by fixing an additional tracker, the patient tracker 130, on the tissue to be treated, a model of the tissue can be displayed within the navigation system 20 and tracked during the surgical procedure.

[0076] Initially, objects to be located and tracked during surgery are observed and identified by optical sensors. The objects to be tracked may be selected and identified by using an input device connected to the navigation computer 26. The navigation computer 26 may store detailed information about a large number of objects in memory or data storage on the navigation computer 26, and a user may manually select an object to be tracked from a database of objects.

[0077] Additionally or alternatively, the navigation computer 26 may identify objects to be tracked based on a pre-operative surgical plan. In this case, the navigation computer 26 may have a preset list of workflow objects that may be used in a pre-described surgical workflow. The navigation computer 26 may actively search for and locate workflow objects using software. For example, pixel groups associated with different sizes and shapes of various objects may be stored in the navigation computer 26. By selecting or identifying an object to be located and tracked, the software identifies corresponding pixel groups, and the software then operates to detect similar pixel groups using conventional pattern recognition techniques.

[0078] Additionally or alternatively, the objects to be located and tracked can be identified by using an interface where one of the users outlines or selects the object to be tracked on one or more of the displays 28, 29. For example, an image of the surgical site taken by the optical sensor 40 or video camera 41 may be displayed on one or more of the displays 28, 29. The user then traces the object to be located or tracked on the display 28 or 29 using a mouse, digital pen, or the like. The software stores the pixels associated with the traced object in its memory. The user can identify each object by a unique identifier, such as by naming the object using the software, so that the saved pixel groups can be associated with the unique identifier. Multiple objects can be stored in this manner. The navigation computer 26 later detects these objects using conventional pattern recognition and associated software. The navigation system 20 can detect the movement of these objects by continuously taking images, reviewing the images, and detecting the movement of the pixel groups associated with the object.

[0079] In a conventional surgical navigation system, the object to be tracked is first aligned using a navigation pointer P. For example, the navigation pointer P may have an integrated tracker PT. The navigation computer 26 can store initial data corresponding to the location of the tip of the pointer P relative to the pointer tracker PT, which allows the navigation system 20 to identify and track the location of the tip of the pointer P in the localizer coordinate system LCLZ. Thus, before the start of a surgical procedure, once all objects are located in their desired locations, one of the users can touch all objects with the pointer P while identifying the objects in the navigation system 20 using one of the input devices mentioned above. Thus, for example, if the user touches an instrument 86 with the tip of the pointer P, the user can simultaneously trigger (via another input device such as a foot pedal) the collection of that point in the localizer coordinate system LCLZ. Once the point is collected, the user can also input the object's identification into the navigation software (via typing, pull-down selection from a list of objects, etc.).

[0080] As shown, camera unit 36 ​​receives optical signals from markers 72 of trackers 70, 90, 110 and outputs signals to navigation computer 26 regarding the positions of the trackers relative to localizer 34. Based on the received signals, navigation computer 26 generates data indicative of the relative positions and orientations of trackers 70, 90, 110 with respect to localizer 34.

[0081] Prior to the start of a surgical procedure, additional data is loaded into navigation computer 26. Based on the positions and orientations of trackers 70, 90, 110 and previously loaded data, such as virtual object data representing the geometry of the object to which the trackers are attached, navigation computer 26 determines the location of the working end of the surgical object (e.g., drill point, aspirator tip, etc.) and the orientation of the object relative to the tissue against which the working end will be applied.

[0082] The navigation computer also generates information indicative of the relative position of the working end of the surgical instrument with respect to the tissue. This information can be rendered into a usable image and applied to the displays 28, 29. Based on the display, the user can see the relative position of the working end of the surgical instrument with respect to the tissue at the surgical site. The displays 28, 29 may include a touch screen 30 or other input / output device to allow for the entry of commands, as described above.

[0083] Referring now to FIG. 3, tracking of objects at the surgical site is generally performed with reference to a localizer coordinate system LCLZ. The localizer coordinate system has an origin and an orientation that defines relative x-, y-, and z-axes. It is preferable to maintain the localizer in a stationary position during the surgical procedure. An accelerometer (not shown) mounted on the camera unit can be used to track sudden or unexpected movements of the localizer coordinate system LCLZ, such as may occur when the camera unit 36 ​​is inadvertently moved by the surgical personnel.

[0084] Each tracker 70, 90, 110 associated with a surgical object or patient anatomy has its own coordinate system separate from the localizer coordinate system LCLZ. As shown in Figure 3, the coordinate system associated with the tool tracker 90 has its own origin and orientation defining relative x-, y-, and z-axes. The navigation system 20, through the localizer 34, monitors the position and orientation of the surgical object and patient anatomy by calculating the relative changes in tracker origin and orientation with respect to the localizer coordinate system.

[0085] During the initial stages of the surgical procedure, the tracker is fixed to the article (if not provided at manufacture) and the anatomical structure to be tracked. The pose of each such item must be mapped to the coordinate system of the tracker relative to that item. This alignment or calibration step creates a fixed relationship between a virtual representation of the tracked article's geometry and the coordinate system of the associated tracker. In this way, the sensed movements of the tracker can be virtually represented with corresponding movements of the tracked article by the navigation computer 26 relative to other tracked articles, for example in a common coordinate system of the localizer LCLZ.

[0086] While navigation systems have been used with robotically controlled surgical systems, there is a need for improved methods for providing navigational guidance for manual surgery using powered surgical tools.In accordance with the present disclosure, an improved method of navigating a surgical instrument is provided to verify the position of the instrument tool tip relative to the patient's anatomy.

[0087] In a first exemplary case, the surgical instrument includes a variable speed motor, such as a driver motor 68. The variable speed motor is controlled by a controller. For example, in the case of a powered driver 60, the variable speed motor may receive control signals from a driver controller 64. In another example, in the case of a universal tool platform 80, control signals that control the variable speed motor in the instrument 86 may be received from a universal console 82. The following description may be described in the context of a particular tool or tool type. This is not intended to be limiting, and the methods and systems may be practiced with other currently known or future developed surgical tools, tool systems, and the like. Additionally, the steps of a method may be practiced in the context of any other method, and features of a disclosed system may be practiced with any other features without departing from the scope of the present disclosure.

[0088] Although the control signals for a variable speed motor are described in the previous paragraph, this is not limiting and other alternative actuators are contemplated within the scope of this disclosure. For example, in the case of an ultrasonic aspirator, a variable speed motor may not be employed, but rather a control signal from the aspirator console 102 may control the operation of the aspirator tool 106. The aspirator tool 106 includes a hollow tip that vibrates longitudinally along its axis, driven, for example, by a piezoelectric transducer as the actuator of the tool. The vibration occurs at a frequency corresponding to ultrasound. The longitudinal vibration of the tip disrupts cell membranes by its hammering effect. A protective sheath carries fluid to irrigate the tip as heat is generated by the high frequency vibration. The irrigation strength can be varied as needed to regulate the application of heat from the tip to the tissue. If the irrigation is small, the heat generated by ultrasonic aspiration can be used for cutting or coagulation purposes. Suction can be applied via the aspirator tool 106 to remove fragmented tissue, and irrigation can also be applied through the tip. By monitoring the operating characteristics of the control signal, the system can detect when the tool tip is operating in free space or in contact with tissue.

[0089] Regardless of the type of surgical article, operating the article while it is in free space may have different characteristics than operating the article while it is in contact with a patient's anatomy, including soft tissue such as bone or skin. In the case of a powered driver 60, or other article with a variable speed motor, the power supplied to the motor results in a certain rotational speed when operating in free space. If there is resistance applied to the rotation of the motor, such as when a drill, burr, or other tool type is in contact with tissue for material removal, the rotational speed may decrease unless the power supplied to the motor is adjusted. For example, the current or voltage may be increased during cutting to maintain a constant rotational speed versus when the tool is not in contact with any tissue. Similarly, tools employing other actuators and not driven by a motor may operate under a first condition when not in contact with tissue and under a second condition different from the first condition when in contact with tissue. Such non-motor driven tools are similarly contemplated to be practiced with the described methods and systems disclosed herein.

[0090] A controller that drives a surgical article communicates with sensors on the article to provide control signals for operating the article and also monitors operating conditions. For example, in powered driver 60, driver controller 64 may receive signals indicative of the instantaneous rotational speed of driver motor 68, applied power, voltage, current, temperature, etc. The signals may be received by the controller as frequently as several times per second. For example, the frequency may be about 60 Hz, about 100 Hz, about 1000 Hz, or other suitable frequencies. In other examples that do not employ a motor, such as ultrasonic aspirator system 100, the controller, in this case aspirator console 102, may receive one or more signals indicative of the operating conditions of the article, i.e., aspirator tool 106. In particular, aspirator console 102 may monitor the temperature at the tool tip, the flow rate of irrigation through the tool tip, the vacuum applied to the aspirator, etc.

[0091] The controller may include or be in communication with a memory or data storage, so that the operating conditions can be recorded for a recording time. The controller may begin recording the operating conditions when the surgical object begins to operate and may continue to do so throughout the duration of the operation. The controller may analyze the monitored operating conditions to determine a first characteristic operating condition when the surgical object is operating without contacting the patient's anatomy, and may further determine a second characteristic operating condition when the surgical object is operating while in contact with the patient's anatomy. The monitored operating conditions may be defined according to the particular tool. In the case of a motor-driven tool, the operating conditions may be applied power, current, voltage, rotational speed, etc.

[0092] As described above, the navigation system 20 tracks and monitors the position of the surgical object and the patient's anatomy throughout the surgical procedure. The navigation system 20 communicates through a navigation computer 26 with one or more controllers that control the surgical object employed in the surgical procedure. The monitored motion status of the surgical object can be used to verify the tracked position of the surgical object and, if necessary, to determine error conditions.

[0093] The navigation system 20 maintains a virtual representation of the surgical object and the patient's anatomy and illustrates and visually renders their relative positions on the displays 28, 29. However, during surgery, the tracker may be displaced. Tool wear or tissue removal from the patient may change the fidelity of the virtual model to its physical counterpart. Thus, the accuracy and reliability of the virtual representation in the navigation system 20 for a surgical procedure may be adversely affected. Comparing the virtual representation in the navigation system 20 to the operating conditions may provide an important validation of the system accuracy. Specifically, if the navigation system 20 indicates that the virtual model of the surgical object is in contact with the patient's anatomy, but the operating conditions indicate that there is no contact between the object and the anatomy, an error condition may be determined and appropriate corrective action may be taken.

[0094] FIG. 4A illustrates a surgical object and a patient's anatomy in a first relationship where there is no contact between the surgical object and the anatomy. In the illustrated example, the surgical object is an instrument 86, specifically the portion of the instrument 86 that includes a tool tip 87. The patient's anatomy shown in FIG. 4A that is the target of the surgical procedure is a bone (vertebra V). The instrument 86 can be energized by a general purpose console 82, which also monitors parameters of the operation of the instrument 86, including the power, voltage, current, and / or rotational speed of the instrument 86. As shown in FIG. 4, the instrument 86 has a first motion that can be characterized by the console 82 according to monitored parameters for operation in free space, i.e., space not in contact with the bone (vertebra V).

[0095] 6 shows an example graph 160 of motor activity over time. In a first phase 162, the instrument is unpowered and therefore motor activity is at its lowest level and stationary. At some later point T1, the instrument is powered up and rotated to a first operating state 164, and then comes into contact with the patient's anatomy at T2. While in contact with the patient's anatomy during the surgical procedure, motor activity is at a higher level 166. The instrument is released from contact with the anatomy after the procedure (168) and can then return to an unpowered state (170).

[0096] 4B illustrates an exemplary user interface 140 displayed by the navigation system 20. The navigation system 20 determines the relationship between the instrument 86 and the bone (vertebra V) to be contacted. The user interface 140 is divided into several sections on the display, each of which may display different information. In a first section 142 of the user interface 140, a virtual representation of the surgical object and the patient's anatomy is shown based on (1) models of those items, which may be stored in the memory of the navigation system 26, and (2) the relative positions of the surgical object and the patient's anatomy, which are determined based on data detected by the optical sensor 40 reading the instrument tracker 90 and the patient tracker 130.

[0097] The navigation system 20 can compare the determined contact or non-contact relationship of the surgical object to the patient's anatomy with the monitored motion parameters to verify the accuracy of the navigation guidance. In the example illustrated in Figures 4A and 4B, an error condition exists and the navigation system 20 determines that the tool tip 87 of the instrument 86 is in contact with the vertebra V, but the monitored motion parameters correspond to the instrument 86 being in a relationship as shown in Figure 4A with no contact between the tool tip 87 and the vertebra V.

[0098] The navigation system 20 or console 82 may trigger an action in response to determining an error condition. For example, a visual alert 144 may be activated in a toolbar area 146 of the user interface 140. The visual alert 144 may be a flashing or blinking indicator light on the display 28, 29. Other visual alerts may alternatively or in combination include indicator lights on the console 82, on the computer cart assembly 24, on the camera unit 36, or elsewhere. Other visual alerts may take the form of prompts for user action, informational displays, or other shapes, forms, pictures, etc.

[0099] Other actions may also be triggered in response to the determination of an error condition. The triggered actions may include displaying specific information about the error condition, suggesting corrective actions to correct the error condition, or a combination thereof. In FIG. 4B, the error information 148 may be displayed in an area of ​​the user interface 140 separate from the first section 142. The error information 148 may indicate that an error has been detected. The error information 148 may indicate the nature of the error, in this case the navigation system 20 has determined that the instrument 86 is in contact with the bone, i.e., vertebra V, but the motor action indicates that there is no contact between the tool and the bone. The error information 148 may alternatively or in combination indicate that a corrective action is recommended and further indicate what a preferred corrective action may include for a particular condition. If the navigation system determines that there is contact between the bone and the tool, but the motor action does not indicate that contact has occurred, the corrective action may require updating the bone model to reflect that tissue has been removed from the bone and that the actual bone surface is no longer reflected in the virtual model.

[0100] Actions triggered upon detection of an error condition may include other actions in addition to or in the alternative to a visual alert. Triggered actions may include one or more of sounding an audible alert, activating a haptic alert, cutting off power to the surgical instrument, or combinations thereof. Sounding an audible alert may include any type of voice alarm, beep, buzzer, etc. Displaying a visual alert may include displaying a prompt on one or more of the displays 28, 29 of the navigation system 20 indicating the nature of the determined error condition. Activating a haptic alert may include energizing a vibration feature on the instrument or foot switch, or both. The vibrations may be characterized as a pattern of vibrations associated with a type of error such that a user can distinguish between different types of errors based solely on the type of vibration.

[0101] Another situation is shown in Figures 5A and 5B. In Figure 5A, the tool tip 87 of the instrument 86 is in contact with the bone (vertebra V). In this situation, the motor motion is at a higher level 166 of the monitored motor motion shown in Figure 6. At time T2, the console 82 records that the motor motion is no longer in the first motion state 164, which corresponds to motion in free space, i.e., the tool tip 87 of the instrument 86 is not in contact with the bone. The console communicates with the navigation computer 26 and can evaluate the determined positions of the tool tip and bone based on optical sensor data corresponding to the tool tracker 90 and the patient tracker 130 to determine the tool-bone offset D. At time T2, the navigation system measures the distance D between the determined position of the tool tip 87 and the nearest surface of the bone (vertebra V) in the longitudinal direction along the length of the instrument 86. This distance is the tool-bone offset value. This value can be displayed as a numerical measurement 150 in the area of ​​the displays 28, 29. The system may be operative to measure the tool-bone offset whenever the monitored motor motion is no longer a first level of magnitude corresponding to motion of the instrument in free space, i.e., not in contact with bone, which may include, for example, the motor motion changing from a first level of magnitude to a second level of magnitude corresponding to motor motion every time the tool is in contact with bone, as shown, for example, at time T2 in FIG.

[0102] Because the value of the tool-bone offset may change over time as the surgical procedure progresses, the numeric measurement 150 may be a continuously updated value that changes based on the latest evaluation of the tool-bone offset. Additionally, by recording and displaying historical data, a user may track and monitor trends in the tool-bone offset and recognize that corrective action may be required when its magnitude increases to a level where navigational guidance cannot be trusted with a high degree of accuracy. For example, as shown in FIG. 5B, a portion of the user interface 140 includes a graph 152 of tool-bone offset values ​​that tracks and displays changing values ​​over time. The graph 152 shows the current value on the right side of the graph, with a trendline 154 of past values ​​scrolling toward the left side of the display. The illustration is not intended to be limiting, and other graphic formats are contemplated without departing from the scope of the present disclosure.

[0103] Monitoring and displaying the tool-to-bone offset can provide a variety of ways to communicate the status of the system to the user. For example, the numeric measurements 150 can be displayed in different colors depending on the magnitude. The visual alerts 144 can light up in different colors or flash at different frequencies to alert the user to a change in condition. The system may be programmed or prompt the user to enter thresholds for the tool-to-bone offset to trigger different types of actions.

[0104] In one example, the tool-bone offset may be maintained below 0.50 millimeters or may trigger a response action such as powering down the instrument. It may be desirable to alert the user to a change in condition before the change in condition reaches that threshold. The numerical measurement 150 may be displayed in a first color for values ​​between 0.00 millimeters and 0.25 millimeters. The numerical measurement 150 may be displayed in a second color, different from the first color, for values ​​between 0.25 millimeters and 0.4 millimeters. The numerical measurement 150 may be displayed in a third color, different from the first or second color, for values ​​greater than 0.4 millimeters. Similarly, trendlines may be displayed in different colors as the values ​​change. The first color may be green, the second color may be yellow, and the third color may be red. These illustrations are provided by way of example and are not intended to be limiting.

[0105] In either of the conditions of Figures 4A and 4B or 5A and 5B, the system can alert the user to the error condition and advise potential corrective action. The preferred corrective action may depend on the particular error encountered. In one example, if the error condition is caused by a broken or worn tool, the corrective action would be to replace the tool. In another example, if the error condition is caused by a tracker being displaced from its relationship to an associated tracked object, or if the navigation cart assembly is rocked or bumped, realigning the tracker with respect to the object in the localizer coordinate system may be an appropriate corrective action. These examples are by way of example only and are not intended to be limiting.

[0106] 7 shows a first method 400 of navigating a surgical instrument having a variable speed motor relative to a bone. The method includes using a navigation system 20, which includes a localizer having a localizer coordinate system, an instrument tracker connected to the surgical instrument, and a patient tracker connected to the bone, as described above. The method uses a controller in communication with the navigation system to control the surgical instrument.

[0107] In a first step 402 of the method 400 shown in Figure 4, a user aligns a patient tracker to a bone. Aligning the patient tracker relates the patient tracker coordinate system to the localizer coordinate system. This step also determines the location and orientation of the bone relative to the patient tracker, so that the navigation system can track and monitor the position and orientation of the bone based on the detected movement of the patient tracker and update the virtual representation of the bone in the navigation system.

[0108] In a second step 404, the user aligns the instrument tracker to the surgical instrument. Aligning the instrument tracker relates the instrument tracker coordinate system to the localizer coordinate system. This step also defines the location and orientation of the instrument tool tip relative to the instrument tracker, thereby enabling the navigation system to track and monitor the position and orientation of the instrument tool tip based on the detected movement of the instrument tracker and update the virtual representation of the instrument in the navigation system.

[0109] The method includes, at step 406, defining the operation of the motor of the surgical instrument or article when the tool tip is not in contact with bone. This defining step may include evaluating at least one of the power, voltage, current, rotational speed, or other operating parameter, or combination of parameters, that characterize the operation of the motor. Data representing the operating parameters may be stored in a memory of a controller that controls the operation of the surgical instrument. Alternatively or additionally, the data may be sent from the controller to a navigation system. As a further alternative or addition, the data may be stored in a memory built into the surgical instrument itself or in another device in communication with the instrument or console.

[0110] During a surgical procedure, and after the operating parameters have been analyzed to define motor motion in free space, the method includes the controller monitoring motor motion of the instrument at step 408. This monitoring may include periodically receiving a signal indicative of motor motion and recording the signal as data representative of the motor motion at the time the signal was received. In this manner, the controller may create a record of motor motion over time during a surgical procedure.

[0111] Concurrent with monitoring the motor operation, the method includes monitoring the position of the tool tip of the instrument relative to the patient's bone using the navigation system in step 410. Trackers attached to the instrument and bone, respectively, are sensed by the navigation system, and based on the previous alignment, the relative positions of the tool tip and bone can be determined by the navigation system and, if desired, virtually represented on a display. As part of monitoring the positions of the tool tip and bone, the navigation system can determine when contact is made between the instrument and bone in the localizer coordinate system.

[0112] Once it is determined that contact between the instrument and bone has been made, the method includes comparing the motor motion to a monitored position of a tool tip of the instrument at step 412. A navigation system in communication with the instrument controller may evaluate the motor motion of the instrument, including whether the motor motion matches a defined motor motion of the instrument when the tool tip of the instrument is not in contact with bone.

[0113] If the navigation system determines that the instrument is in contact with the bone based on the tracked positions, but the motor operation indicates that the instrument is not currently in contact with the bone, the method includes determining an error condition in step 414. This determination reflects that some disturbance or anomaly has been introduced into the system. If the tracked positions in the navigation system do not reflect the true physical positions of the instrument or bone, the accuracy and reliability of the navigation system cannot be trusted.

[0114] If an error condition is determined, the method includes, at step 416, triggering an action in response to the determination of the error condition so that appropriate corrective action can be taken.

[0115] In one alternative, the method optionally includes defining a second motor operation of the instrument when the tool tip of the instrument is in contact with bone. Similar to the first motor operation of the instrument when the tool tip of the instrument is not in contact with bone, the data representative of the operating parameters of the second motor operation may include at least one of power, voltage, current, rotational speed, or other operating parameter, or combination of parameters, that characterize the operation of the motor while in contact with bone. This data representative of the second motor operation may be stored in a memory of a controller that controls the operation of the surgical instrument. Alternatively or additionally, the data may be communicated by the controller to a navigation system. As a further alternative or addition, the data may be stored in a memory incorporated in the surgical instrument itself.

[0116] Defining a second motor motion when the surgical instrument is in contact with bone, the method can include determining a second error condition when a monitored position of a tool tip of the instrument is not in contact with bone in the localizer coordinate system but the motor motion is equal to the second defined motor motion, which is the motor motion when the tool tip of the instrument is in contact with bone. Upon determining that the second error condition exists, the method can include triggering a second action such that appropriate corrective action can be taken.

[0117] With respect to any of the error conditions described above, the resulting action may include one or more of sounding an audible alert, displaying a visual alert, activating a haptic alert, cutting off power to the surgical instrument, or a combination thereof. Sounding an audible alert may include any type of voice alarm, beep, buzzer, etc. Displaying a visual alert may include displaying a prompt on one or more of the displays of the navigation system indicating the nature of the determined error condition. The visual alert may also include illuminating a light, such as an LED light, on the surgical instrument itself. The visual alert may include any other visual type indication that an error condition has been determined. Activating a haptic alert may include energizing a vibration feature on the instrument or foot switch. The vibration may be characterized as a pattern of vibration associated with a type of error such that a user can distinguish between different types of errors based solely on the type of vibration.

[0118] FIG. 5 illustrates a second method 500 for navigating a surgical instrument having a variable speed motor relative to a bone and determining a tool-to-bone offset. The second method 500 is similar in some respects to the first method 400 described above. The steps of the second method 500 may be defined with respect to the steps of the first method 400 where such similarities exist. In particular, the second method 500 employs a navigation system, surgical instrument, instrument tracker, and patient tracker similar to method 400. Similarly, a controller communicates with the navigation system and provides power to the surgical instrument.

[0119] The second method 500 begins with step 502 of aligning a patient tracker to a bone and step 504 of aligning an instrument tracker to a surgical instrument, similar to steps 402 and 404. The second method 500 also includes step 506 of defining a first motor motion of the surgical instrument while the instrument is not in contact with the bone, which is the same as step 406 described above. Further similar to the first method 400, the second method 500 includes step 508 of monitoring the motor motion with a controller, as in steps 408 and 410, and step 510 of monitoring the position of a tool tip of the instrument relative to the bone with a navigation system.

[0120] Unlike the first method 400, the second method 500 includes comparing the monitored motor motion to a first predefined motor motion at step 512. This comparison can be repeated over time in successive cycles at a fixed frequency during surgery. The second method 500 also includes determining, at step 514, a contact time (or a contact point) between the tool tip of the instrument and the bone when, as a result of the comparison at step 512, the monitored motor motion is no longer the first predefined motor motion. When the continuously monitored characteristic of the motor motion changes from the first predefined motor motion, which represents the motor motion when the instrument is not in contact with the bone, a contact point between the instrument and the bone can be determined.

[0121] Once the time of contact between the instrument and the bone is determined in step 514, the second method 500 includes determining, with the navigation system, a tool-to-bone offset as the distance between a tool tip of the instrument and the surface of the bone in the localizer coordinate system at the time of contact in step 516. The navigation system, which monitors the position of the tool tip of the instrument and the bone, may receive a signal from the instrument controller indicative of contact between the tool tip and the bone based on a determination by the controller that the monitored motor motion is no longer a first motor motion defined when the instrument is not in contact with the bone.

[0122] Given the contact time, the navigation system evaluates the tracked positions of the tool tip and the bone, and when the navigation system determines that the tool tip has left the bone, it calculates the distance between the closest point of the tool tip in the localizer coordinate system and the bone surface. In another case, the navigation system may determine that the tool tip has entered the bone a certain distance given the contact time based on the controller's determination of a deviation from a defined motor motion. In this case, the navigation system calculates the perpendicular distance of the maximum penetration depth of any point of the tool tip relative to the bone surface. In either case, the calculated distance is the tool-to-bone offset. In other words, the tool-to-bone offset is a measure of the margin of accuracy between the true physical position of the tool relative to the bone and the virtual representation of the tool's position relative to the bone.

[0123] As mentioned above, there are multiple factors that can introduce or increase the tool-bone offset. If the tracker is displaced or deformed after being aligned, this can lead to reduced navigation accuracy. Similarly, if the navigation cart assembly is shaken or bumped during surgery causing the camera unit to shift, this can also lead to reduced navigation accuracy. Other factors can include tool wear, tool deformation, or gross removal of tissue from the bone. To maintain consistent and highly accurate navigation, it is preferable to keep the tool-bone offset small.

[0124] If the tool-bone offset becomes too large, the accuracy of the navigation guidance may be compromised and corrective action may be required. As such, the second method 500 includes a step 518 of triggering an action if the tool-bone offset exceeds a predetermined magnitude. In one example, the predetermined magnitude is 0.5 millimeters. That is, if the instrument contacts the bone as determined by a change in motor operation monitored by the controller, the navigation system determines that the tool tip is 0.5 millimeters from the bone surface. Although described with reference to a particular magnitude, this is not intended to be limiting and other limitations are contemplated. Additionally, different limitations may be applicable to different tools or different applications of the same tool. This step 518 of triggering an action is similar to step 416 of triggering an action in response to determining an error condition. The resulting action may include one or more of sounding an audible alert, displaying a visual alert, activating a tactile alert, cutting off power to the surgical instrument, or combinations thereof, as described above.

[0125] To provide information to a user, the second method 500 may further include displaying the value of the tool-bone offset on a display of the navigation system. This allows a user to track and monitor the accuracy of the navigation guidance being provided by the navigation system. When performing the method in a surgical procedure, the step of determining the value of the tool-bone offset may be repeated multiple times throughout the procedure, for example, each time the controller determines the time of contact between the instrument and the bone based on changes in motor motion. Thus, the display of the tool-bone offset may be a value that is continuously updated each time a determination is performed. In addition to a numerical presentation of the value of the tool-bone offset, this information may be displayed as a chart, or line graph, of values ​​over time.

[0126] To further assist the user, the tool-bone offset value may be displayed differently based on its magnitude. For example, if its magnitude is small (indicating a small tool-bone offset and more accurate navigation guidance), it may be displayed in a first color, if its magnitude is large, it may be displayed in a second color different from the first color, and if its magnitude is still large, it may be displayed in a third color different from the first and second colors. Other color combinations or visual representations may be employed as well.

[0127] To facilitate this dynamic display of the tool-bone offset value, the second method 500 may include the step of defining a first level magnitude and a second level magnitude. These first level magnitude and second level magnitude may be predefined within the system as default values. Alternatively, the first level magnitude and second level magnitude may be input by a user at the start of an operation or during a system setup operation. In one example, the first level magnitude may be 0.25 millimeters and the second level magnitude may be 0.4 millimeters.

[0128] In one example, if the tool-bone offset is determined to be less than the first level of magnitude, the displayed value may be presented in green. If the tool-bone offset is determined to be less than the second level of magnitude, the displayed value may be presented in yellow. If the tool-bone offset is greater than the second level of magnitude, the displayed value may be presented in red. These color designations are not intended to be limiting, but merely to provide an example. In another case, the dynamic display of the tool-bone offset may utilize a variable size instead of, or in addition to, changing the color of the displayed value.

[0129] The first level magnitude and the second level magnitude of the tool-bone offset value may also be utilized to trigger one or more of the actions in step 518 of the second method 500. For example, a visual alert may be triggered when the tool-bone offset reaches or exceeds the first level magnitude, and a combination visual and audible alert may be triggered when the tool-bone offset reaches or exceeds the second level magnitude.

[0130] In addition, the third level magnitude may also be defined in the same or different manner as the first level magnitude and the second level magnitude. The third level magnitude may represent a value of the tool-bone offset at which the system determines to disable power from the controller to the surgical instrument. When the tool-bone offset reaches the third level magnitude, the accuracy of the navigation system may be compromised, creating a risk of harm, and the surgical instrument should be disabled until corrective action is taken.

[0131] As described above, the navigation system can alert the user to certain errors or conditions that require corrective action to improve the accuracy of the navigation guidance depending on the determined value of the tool-to-bone offset. Since several different corrective actions are possible, the appropriate correction may vary depending on the particular error encountered. In one example, if the error condition results from a broken or worn tool, the corrective action would be to replace the tool. In another example, if the error condition results from displacing a tracker from its relationship to an associated tracked object, or if the navigation cart assembly is rocked or bumped, realigning the tracker with respect to the object in the localizer coordinate system may be an appropriate corrective action.

[0132] In another example, in a surgical procedure where a large amount of tissue is removed, the virtual representation of the anatomy no longer represents the patient's actual anatomy. To remedy this situation, additional imaging, modeling, and registration may be required to redefine the location of tissue surfaces in the virtual representation of the anatomy. In one example, the surgical instrument is unpowered and can be used as a pointer to touch off multiple points on the resection surface of the anatomy, creating a new point cloud for the navigation system to redefine the surface of the virtual representation of the bone.

[0133] The disclosed methods may be practiced with an improved surgical system as shown in Figures 1 and 2 and described above in various configurations. The surgical system includes a surgical instrument having a variable speed motor and a tool tip. The surgical instrument is in operative communication with a controller that provides power to the surgical instrument. The controller is further operable to monitor motor operation of the instrument and includes a processor and a memory operable to store information including information representative of the monitored motor operation. The system also includes an instrument tracker connected to the instrument and a patient tracker connected to the patient's anatomy.

[0134] The surgical system also includes a navigation system. The navigation system includes a localizer and a navigation computer. The navigation computer includes a processor and a memory that stores information in a virtual space including information representative of a surgical instrument and information representative of a patient's anatomy relative to a localizer coordinate system in the virtual space. The navigation system is operable to track positions of the instrument and bones in the virtual space during surgery based on the information collected by the localizer. The localizer is operable to align a position of the instrument tracker and a position of the patient tracker relative to the localizer coordinate system and to cooperate with the instrument tracker and the patient tracker, respectively, to collect information regarding the positions of the instrument and bones.

[0135] The controller and navigation system are in electronic communication and configured to cooperate with one another. During surgery, the controller and navigation system determine a time of contact between the tool tip and the bone based on changes in motor motion of the instrument. The controller and navigation system also determine a tool-to-bone offset as the distance between the tracked position of the tool tip and the tracked position of the bone at the time of contact.

[0136] The surgical system may further include an alert device. The controller and navigation system further communicate with the alert device and are operable to trigger an action when the tool-bone offset is greater than a predetermined amount. The alert device may include a visual alert device, such as a light or display on the console 82, on the computer cart assembly 24, on the camera unit 36, or elsewhere in the operating environment. Other visual alerts may take the form of prompts for user action, information displays, or other shapes, forms, pictures, etc. The alert device may include an audible alert device, such as a speaker, bell, horn, buzzer, etc. Other audible alerts may include tones, alarms, pre-recorded messages, etc. The alert device may include a tactile alert device that may generate a tactile alert perceivable to the user, such as by vibration.

[0137] In a configuration in which the tracker is properly aligned with the surgical instrument and the patient's anatomy, the user can place an unpowered tool tip of the surgical instrument in contact with the patient's anatomy, and the navigation system will accurately determine that the tool tip is in contact with the patient's anatomy without gaps or overlaps in a common coordinate system. However, the tracker, the surgical instrument, or the anatomy may be deflected or deformed, or the camera unit of the navigation system may be obstructed, causing the alignment to be inaccurate. It is therefore desirable to provide a way for the navigation system to perform an alignment verification operation that does not require the tool to be powered, and therefore does not depend on any parameters of the tool operating in free space or in contact with the patient's anatomy. The user can place the tool tip of the surgical instrument in static unpowered contact with the patient's anatomy, such that the anatomy is not affected by the tool, hold that position, and trigger the navigation system to perform the alignment verification.

[0138] As shown in Figure 9, a method 600 is provided for operating a surgical navigation system during a surgical procedure to verify tracking alignment. In the method 600, the surgical navigation system includes a localizer having a localizer coordinate system, an instrument tracker coupled to a surgical instrument, and a patient tracker coupled to a patient anatomy, e.g., vertebrae, other bones, or soft tissue, as described above. References to a patient anatomy, specific bones, or bone in general should be interpreted broadly to include soft tissue and other non-bone applications. The method 600 uses a controller in communication with the navigation system and to control the surgical instrument.

[0139] In a first step 602 of method 600, a user aligns a patient tracker to a bone. Aligning the patient tracker relates the patient tracker coordinate system to a localizer coordinate system or other common coordinate system. This step also determines the location and orientation of the bone relative to the patient tracker, so that the navigation system can track and monitor the position and orientation, or pose, of the bone based on the detected movement of the patient tracker and update the virtual representation of the anatomy in the navigation system.

[0140] In a second step 604 of method 600, the user aligns the instrument tracker to the surgical instrument. Aligning the instrument tracker relates the instrument tracker coordinate system to the localizer coordinate system or other common coordinate system. This step 604 also defines the position and orientation of the instrument tool tip relative to the instrument tracker, thereby enabling the navigation system to track and monitor the position and orientation, or pose, of the instrument tool tip based on the detected movement of the instrument tracker and update the virtual representation of the instrument in the navigation system.

[0141] The method 600 includes using the navigation system to monitor the pose of the anatomy and the location of the surgical instrument over time, and to track the pose of the anatomy and the instrument using a virtual representation that may be displayed to a user 606, 608. Monitoring the location of the patient's anatomy and the surgical instrument includes monitoring both the position and orientation of the tracked object. The position and orientation are monitored over time in continuous cycles at a fixed frequency during surgery. Using this information, the navigation system can determine velocity, acceleration, and other quantities including magnitude and direction of motion in a common coordinate system relative to other tracked objects.

[0142] The method 600 includes determining that a tool tip of a surgical instrument is statically positioned within a predetermined proximity relative to the patient's anatomy, where the navigation system monitors the position of the tool tip and the anatomy as well as the velocity of the tool tip relative to the anatomy. During surgery, the user places the tool tip in contact with bone while the tool is not powered, prompting the navigation system to verify alignment of the surgical instrument and the tracker on the patient's anatomy.

[0143] Since alignment is subject to error, the navigation system may evaluate alignment verification when the navigation system determines that the tool tip is stationary within a predetermined proximity range with the patient's anatomy. The navigation system may determine that the tool tip is stationary when the tracking position does not change for a predetermined period of time. The predetermined period of time may be preprogrammed into the navigation system to be, for example, 3 seconds, 5 seconds, or other duration. The predetermined proximity range may be, for example, about 3 millimeters, about 1 millimeter, or about 0.5 millimeters. The predetermined proximity range may be some other distance value appropriate to the level of accuracy measurable by the navigation system. During configuration of the navigation system, for example during start-up prior to a surgical procedure, the user may be prompted to select the duration of the predetermined period or the distance of the predetermined proximity range from a list of options, or may be prompted to enter the duration or distance via a touchpad, button selection, touch screen, or other input.

[0144] The navigation system may determine that the tool tip is stationary when the tracked position and tracked orientation of the tool tip are static and do not change during a predefined period of time. Alternatively, the navigation system may determine that the position is stationary when the position and orientation do not change by more than a certain amount. Alternatively, the navigation system may determine that the position is stationary when the position and orientation do not change or do not change by more than a certain amount in a particular direction, such as when the particular direction is toward the anatomy.

[0145] If the navigation system determines that the tool tip is resting in a static position and orientation proximate to the bone, the method 600 includes determining 612 an offset distance. The offset distance is a measure of the inaccuracy in the system. The navigation system receives input from the user indicating that the tool tip is in static contact with the anatomy and evaluates the tracked position of the instrument tool tip and the patient's anatomy. The result of this evaluation based on the tracked position may determine that the tool tip is a certain distance away from the bone or that the tool tip has penetrated the bone a certain distance based on the tracked position and tracked orientation of the virtual representation of the surgical instrument and the patient's anatomy. The magnitude of the determined distance defines a tool-bone offset, which indicates a margin of accuracy between the true physical position of the tool tip relative to the anatomy and the virtual representation of the tool tip relative to the anatomy in the navigation system.

[0146] In calculating the offset distance, the navigation system identifies a first point on the virtual representation of the surgical instrument, the first point being the closest proximal point to the virtual representation of the patient's anatomy or the deepest penetration or overlap point of the virtual representation of the surgical instrument into the virtual representation of the patient's anatomy. If the first identified point of the instrument is outside the anatomy, the offset distance is the shortest distance between the first identified point and a point on the surface of the virtual representation of the anatomy, the offset distance being perpendicular and outward to the surface. If the first identified point of the instrument is inside the virtual representation of the anatomy, the offset distance is the largest distance between the first identified point and a point on the surface of the virtual representation of the anatomy, the offset distance being perpendicular and inward to the surface.

[0147] Once the offset distance is determined, the navigation system of method 600 compares the calculated offset distance to a predefined threshold of acceptable system inaccuracy in step 614. If the offset distance is greater than the predefined threshold, indicating a lower level of accuracy than desired, the navigation system can be configured to trigger an action accordingly. In one example, the predefined threshold is 0.5 millimeters. That is, if the navigation system determines that the tool tip is in static contact with the anatomy based on the tracked position, the navigation system calculates that the virtual representation of the tool tip is 0.5 millimeters from the virtual representation of the anatomy. Although described with reference to a particular magnitude, this is not intended to be limiting and other limitations are contemplated. Additionally, different limitations may be applicable to different tools or different applications of the same tool. The triggered action may include one or more of sounding an audible alert, displaying a visual alert, activating a tactile alert, disabling power to the surgical instrument, or a combination thereof, as described above.

[0148] The predetermined threshold may include multiple values ​​indicating different levels of accuracy, and different actions are triggered in response to a comparison of the offset distance to the multiple values. For example, the predetermined threshold may include a first predetermined threshold and a second predetermined threshold. Triggering the action may include triggering a first action if the offset distance is greater than the first predetermined threshold and triggering a second action if the offset distance is greater than the second predetermined threshold. The action may include any action as described above to include an audible alert, a visual alert, a tactile alert, or various combinations thereof.

[0149] The method 600 shown in FIG. 9 can be extended as shown as method 620 in FIG. 10. In one extended form, the navigation system can prompt the user in step 622 to initiate an alignment verification cycle as detailed in method 600 above. The prompt can be presented to the user as a visual prompt, such as by showing a message on a display. Alternatively, the visual prompt can include a flash of light, or the like. The prompt can be presented to the user as an audible prompt, such as a tone, beep, pre-recorded message, or the like. The prompt can be presented to the user as a tactile prompt, such as by a predetermined series of vibrations or a series of vibrations. The prompt can be presented to the user as a combination of visual, auditory, or tactile prompts.

[0150] The method 620 includes a step 624 of determining a first offset with the surgical instrument in a first pose. This step is performed to match the steps of the method 600 shown in FIG. 9, where the static position of the tool tip comprises a first pose (position and orientation) of the surgical instrument. The method 620 includes a step 626 of determining a second offset in a second pose. This requires changing the position, orientation, or both of the surgical instrument to place the tool tip in static contact with the anatomical structure a second time. With the tool tip in static contact with the anatomical structure in the second pose, the navigation system determines a second offset value. Thus, the navigation system can evaluate the tool-bone offset from more than one angle in this manner to ensure the accuracy of the system at multiple angles.

[0151] After determining the first and second offsets from the first and second poses, respectively, in steps 624, 626, the navigation system compares the first and second offsets to a tolerance threshold in step 628. In this step, the navigation system may independently compare the first offset to a tolerance threshold and the second offset to a tolerance threshold, and may trigger an action if one or the other of the first and second offsets exceeds a tolerance threshold. Step 630 of triggering an action may be similar to step 616 of triggering an action.

[0152] Once an action has been triggered in response to the navigation system determining that the offset exceeds a tolerance threshold, the user may have the opportunity to provide input and maintain system operation without taking other corrective action, such as realigning the tracker with the surgical instrument or the patient's anatomy. The navigation system may receive input to override or cancel the action triggered by the offset being greater than the tolerance threshold, step 631. The navigation system may receive input, such as a voice command, gesture input, or other input via a keypad, touch screen, etc. Upon receiving input to override or cancel the triggered action, the navigation system and surgical instrument may return to normal operation.

[0153] 11 illustrates a method 632 as an alternative or addition to step 628 of the method 620 of comparing the first and second offsets to a tolerance threshold. Once the navigation system has determined the first and second offsets in the first and second poses, as in step 634, the navigation system can calculate a three-dimensional offset based on the first and second offsets and the geometric relationship between the first and second poses, or more specifically, the geometric relationship between specific contact points on the surface of the tool tip applied in static contact with the anatomy in the first and second poses. Once the three-dimensional offset value is determined, the navigation system can compare the three-dimensional offset to a tolerance threshold, which may be of the same or different magnitude than the tolerance threshold for comparing the first or second offset.

[0154] As a further alternative, methods 620 and 632 may further include determining a third offset in a third pose. In step 628 of method 620, comparing the first and second offsets to a tolerance threshold may include comparing the third offset to a tolerance threshold. Similarly, in method 632, step 634 may include determining a third offset in a third pose in addition to determining the first and second offsets in the first and second poses. Furthermore, in step 636, the navigation system may calculate a three-dimensional offset based on the first, second, and third offsets and a geometric relationship between the first, second, and third poses or the first, second, and third contact points between the tool tip and the anatomy in the first, second, and third poses.

[0155] The calculation of the three-dimensional offset depends on the geometry of the tool tip. In a first example, as shown in FIG. 12, the tool tip 180 may be substantially cylindrical, tapered, rounded conical, or include an elongated surface 182, such as a drill bit or a router. The elongated surface 182 of the tool tip 180 may define a longitudinal axis L extending through the center and parallel to the elongated surface 182. When placed in static contact with an anatomical structure, such as a vertebra V, to verify alignment and determine offset values, the contact point 184 between the tool tip 180 and the anatomical structure V is along a periphery 186 at the end of the elongated surface 182 at a distance from the longitudinal axis equal to the radius of the elongated surface, for example.

[0156] 13, the tool tip 190 may include a substantially spherical surface 192 having a rounded burr or the like. The spherical surface 192 of the tool tip 190 may define a center point 194 at the center of the spherical surface. When placed in static contact with an anatomical structure, such as a vertebra V, to verify alignment and determine offset values, a contact point 196 between the tool tip 190 and the anatomical structure V is on the surface of the spherical surface 192 at a distance from the center point 194 equal to the radius of the spherical surface 192, for example.

[0157] Determining three-dimensional offsets, such as in step 636 of method 632 shown in Figure 11, involves determining a first offset by the surgical instrument in a first pose relative to the anatomy, a second offset in a second pose, and optionally a third offset in a third pose. By positioning the surgical instrument in multiple different poses, various views of the surgical instrument tracker are presented to the camera unit of the localizer. The multiple views allow any alignment errors to be identified by the navigation system and not obscured by a particular view of the instrument.

[0158] To ensure sufficient differentiation in the view of the surgical instrument by the navigation system, sufficient rotation of the surgical instrument from one pose to the next is necessary. For example, upon establishing a first offset distance in a first pose, the surgical instrument may be rotated such that the contact point on the tool tip is approximately 90 degrees away in the second pose from the contact point on the tool tip in the first pose. As shown in FIG. 12, if the tool tip 180 has an elongated surface 182, the second contact point 188 may be approximately 90 degrees from the first contact point 184 by rotation about the longitudinal axis L of the tool tip 180. As shown in FIG. 13, if the tool tip 190 has a spherical surface 192, the second contact point 198 may be approximately 90 degrees from the first contact point 196 by rotation about a center point 194 in any plane. When a third offset distance is determined, the third contact points 189, 199 in the third pose may be approximately 90 degrees away from the first contact points 184, 196 and the second contact points 188, 198 in the first and second poses, respectively.

[0159] During the course of a surgical procedure, a surgical instrument may be applied in contact with two or more bones, such as multiple vertebrae along the spine. In the early stages of a surgical procedure, the tracker may be aligned with each of the individual bones affected by the surgery. When transitioning from surgery on one bone to surgery on a second bone, the user may verify the alignment of the tracker on the second bone following completion of the surgical intervention on the first bone. The user may trigger the navigation system to verify the tracking alignment process by positioning the tool tip in static contact with the second bone. Alternatively, the navigation system may prompt the user upon completion of the stage of the surgical plan applied to the first bone to verify the alignment before commencing the surgical intervention according to the surgical plan on the second bone.

[0160] The navigation system can designate portions of bone in contact with the tool tip for alignment verification. The portions of bone designated for alignment verification may nevertheless be exposed portions of bone that are not targeted for resection according to the surgical plan. Selecting portions that are not targeted for surgical intervention increases the likelihood that the bone surface will match the virtual representation of the patient's anatomy, providing an accurate basis for verifying the tracker alignment. The navigation system can display a graphical representation of the patient's anatomy with certain portions highlighted, flagged, and indicated with arrows, outlines, or other symbols to identify portions of the anatomy to the user.

[0161] The above description has been provided by way of example. It is to be understood that the terminology used is intended to be in the nature of words of description rather than of limitation. Many modifications and variations are possible in light of the above teaching. Thus, within the scope of the appended claims, features or implementations may be practiced other than as specifically described.

[0162] item I. A method of navigating a surgical instrument having a variable speed motor relative to a bone, the method comprising using a navigation system including a localizer having a localizer coordinate system, an instrument tracker coupled to the surgical instrument, a patient tracker coupled to a bone, and a controller in communication with the navigation system, the controller controlling the surgical instrument, the method comprising: using the localizer to register the patient tracker to the localizer coordinate system and define a bone location of the bone relative to the localizer coordinate system; using the localizer to register the instrument tracker to the localizer coordinate system and define an instrument location of an instrument tool tip relative to the localizer coordinate system; defining motor operation of the instrument when the instrument tool tip is not in contact with the bone; monitoring motor operation of the instrument during a medical procedure with the controller; using the navigation system to monitor a position of the instrument tool tip relative to the bone to determine when the instrument tool tip contacts the bone in the localizer coordinate system; comparing the motor motion to the monitored position of the instrument tool tip; determining an error condition when the monitored position of the instrument tool tip is in contact with the bone in the localizer coordinate system and the monitored motor motion is equal to the defined motor motion of the instrument when the instrument tool tip is not in contact with the bone; triggering an action when an error condition is determined; A method comprising: II. The method of claim 1, wherein defining the motor operation of the instrument when the tool tip is not in contact with the bone includes defining a threshold value of power, voltage, current, or a combination thereof when the motor operates while the instrument tool tip is not in contact with bone. III. The method of any one of items I and II, wherein defining the motor motion includes storing data representing the motor motion in a memory of one or more of the controller, the navigation system, the surgical instrument, or a combination thereof. IV. The method of any one of items I to III, further comprising defining a second motor motion of the instrument when the instrument tool tip is in contact with the bone. V. The method of claim IV, further comprising determining a second error condition when the monitored position of the instrument tool tip is not in contact with the bone in the localizer coordinate system and the monitored motor motion is equal to the second defined motor motion of the instrument when the instrument tool tip is in contact with the bone, and triggering a second action when the second error condition is determined. VI. The method of any one of items I-V, wherein triggering one of the action or the second action includes one of sounding an audible alert, displaying a visual alert, activating a tactile alert, cutting off power to the surgical instrument, or a combination thereof. VII. A method of navigating a surgical instrument having a variable speed motor using a navigation system including a localizer having a localizer coordinate system, an instrument tracker coupled to a surgical instrument, a patient tracker coupled to a bone, and a controller in communication with the navigation system and providing power to the surgical instrument, the method comprising: using the localizer to register the patient tracker to the localizer coordinate system and define a bone location of the bone relative to the localizer coordinate system; using the localizer to register the instrument tracker to the localizer coordinate system and define an instrument location of an instrument tool tip relative to the localizer coordinate system; defining a first motor motion of the surgical instrument that operates while not in contact with the bone; monitoring motor operation of the surgical instrument during a medical procedure with the controller; monitoring a position of the instrument tool tip relative to the bone in the localizer coordinate system using the navigation system; comparing the monitored motor motion with the defined motor motion; determining a time point of contact between the instrument tool tip and the bone when the monitored motor motion deviates from the defined first motor motion; determining, using the navigation system, a tool-to-bone offset as a distance between the instrument tool tip and a surface of the bone in the localizer coordinate system at the time of contact; triggering an action if the tool-bone offset exceeds a predetermined magnitude; A method comprising: VIII. The method of claim VII, wherein triggering an action includes one of sounding an audible alert, displaying a visual alert, activating a tactile alert, cutting power to the surgical instrument, or a combination thereof. IX. The method of claim VII, wherein the predetermined size is 0.5 millimeters. X. The method of claim VII, further comprising displaying the determined tool-bone offset on a display device. XI. The method according to item VIII, wherein monitoring the position of the instrument tool tip relative to the bone includes tracking the instrument location of the instrument tool tip and the bone location of the bone during the medical procedure, the method further including detecting, using the navigation system, each occurrence during the movement of the monitored position of the instrument tool tip in contact with the surface of the bone, and recording a series of tool-bone offset values ​​determined during the medical procedure at each occurrence. XII. The method of claim VII, further comprising displaying the set of tool-bone offsets as successively updated values ​​on a display device. XIII. The method according to item XII, further comprising defining a first level magnitude and a second level magnitude, and wherein the step of displaying the determined tool-bone offset comprises displaying the offset in a first color if the offset is smaller than the first level magnitude, displaying the offset in a second color different from the first color if the offset is between the first and second level magnitudes, and displaying the offset in a third color different from the first and second colors if the offset is larger than the second level magnitude. XIV. The method according to item XIII, wherein the predetermined magnitude for triggering an action is equal to the second level magnitude. XV. The method according to item XIII, wherein the predetermined magnitude for triggering an action is greater than the second level magnitude. XVI. The method of claim XIII, further comprising defining a third level magnitude, the method further comprising disabling power from the controller to the surgical instrument if the tool-bone offset is greater than the third level magnitude. XVII. The method of claim VII, further comprising prompting a user to input a value for the predetermined magnitude. XVIII. The method of claim XVII, further comprising disabling power from the controller to the surgical instrument if the tool-bone offset is greater than the predetermined value. XIX. The method of claim XII, further comprising displaying the series of tool-bone offsets as a chart of offset values ​​over time. XX. The method of claim VII, wherein triggering an action includes prompting a user to update the model of the bone. XXI. The method of claim XX, wherein updating the model of the bone includes contacting a resection surface of the bone with the instrument tool tip while power from the controller to the surgical instrument is disabled. XXII. A method of operating a surgical system during a surgical procedure to verify tracking alignment, the surgical system including a navigation system including a localizer having a localizer coordinate system, an instrument tracker coupled to a surgical instrument, the surgical instrument including a tool tip, a patient tracker coupled to a patient's anatomy, and a control console in communication with the localizer, the control console in communication with data representative of the surgical instrument and data representative of the patient's anatomy, the method comprising: tracking the surgical instrument and the anatomical structure using the navigation system and storing, using the control console, first data representative of the tracked surgical instrument and second data representative of the tracked anatomical structure in a common coordinate system; determining, based on the first data representative of the tracked surgical tool and the second data representative of the tracked anatomical structure, that the tool tip is within a predetermined proximity range relative to the tracked anatomical structure; determining that the tool tip does not leave the predetermined proximity range by more than a predetermined magnitude for a predetermined duration; determining an offset distance based on the first data representative of the tracked surgical instrument and the second data representative of the tracked anatomy; comparing the offset distance to a predetermined threshold; triggering an action if the offset distance is greater than the predetermined threshold; A method comprising: XXIII. The method of claim XXII, further comprising prompting the user to verify the tracking alignment by one of displaying a prompt on the display, sounding an audible alert, generating a tactile sensation, or a combination thereof. XXIV. The method of claim XXII, wherein determining that the tool tip is within a predetermined proximity range relative to the anatomical structure includes defining a surface area of ​​the anatomical structure that is not to be ablated, and determining that the tool tip is within a predetermined proximity range relative to the defined surface area. XXV. The method according to claim XXII, wherein the offset distance is defined as a minimum separation between the tool tip and the tracked anatomical structure in the common coordinate system or as a maximum overlap between the tool tip and the tracked anatomical structure in the common coordinate system. XXVI. Determining that the tool tip is within a predetermined proximity range relative to the tracked anatomy includes positioning the surgical instrument at a first orientation relative to the tracked anatomy, the surgical instrument defining a first proximal point of the tool tip, and determining the offset distance includes determining a first offset distance; XXII. The method of claim XXII, further comprising determining that the tool tip is within a predetermined proximity range relative to the tracked anatomy, the method including positioning the surgical instrument at a second pose relative to the tracked anatomy defining a second proximal point of the tool tip, and determining the offset distance includes determining a second offset distance. XXVII. The method of claim XXVI, wherein comparing the offset distance to a predetermined threshold includes comparing the first offset distance to the predetermined threshold and comparing the second offset distance to the predetermined threshold, and initiating an action includes initiating an action if the first offset distance, the second offset distance, or both the first offset distance and the second offset distance are greater than the predetermined threshold. XXVIII. The method of claim XXVI, wherein the surgical instrument includes an elongated surface terminating in the tool tip, the elongated surface defining a longitudinal axis extending substantially parallel to the elongated surface, and the second proximal point is at least 90 degrees from the first proximal point relative to rotation about a centerline. XXIX. The method of claim XXVI, wherein the surgical instrument includes the tool tip having a spherical surface defining a central point, and the second proximal point is at least 90 degrees away from the first proximal point relative to rotation about the central point. XXX. The method of claim XXVI, wherein determining that the tool tip is within a predetermined proximity range relative to the tracked anatomy includes positioning the surgical instrument in a third orientation relative to the tracked anatomy, the surgical instrument defining a third proximal point, the third proximal point being different from the first proximal point and the second proximal point, and determining the offset distance further includes determining a third offset distance. XXXI. The method of claim XXX, wherein comparing the offset distance to a predetermined threshold includes comparing the first offset distance to the predetermined threshold, comparing the second offset distance to the predetermined threshold, and comparing the third offset distance to the predetermined threshold, and initiating an action includes initiating an action if the first offset distance, the second offset distance, the third offset distance, or a combination thereof is greater than the predetermined threshold. XXXII. The method of claim XXX, wherein the surgical instrument includes an elongated surface terminating at the tool tip, the elongated surface defining a longitudinal axis extending substantially parallel to the elongated surface, the second proximal point being at least 90 degrees from the first proximal point relative to rotation about the longitudinal axis, and the third proximal point being at least 90 degrees away from the first proximal point and the second proximal point relative to rotation about the longitudinal axis. XXXIII. The method of claim XXX, wherein the surgical instrument includes a tool top having a spherical surface defining a center point, the second proximal point being at least 90 degrees away from the first proximal point relative to rotation about the center point, and the third proximal point being at least 90 degrees away from the first proximal point and the second proximal point relative to rotation about the center point. XXXIV. The method of any one of the preceding paragraphs XXII-XXXIII, wherein triggering an action includes sounding an audible alert, displaying a visual alert, activating a tactile alert, cutting off power to the surgical instrument, or any combination thereof. XXXV. The method of any one of the preceding items XXII to XXXIV, wherein the predetermined thresholds include a first predetermined threshold and a second predetermined threshold, and triggering an action of the navigation system includes triggering a first action if the offset distance is greater than the first predetermined threshold but less than the second predetermined threshold and triggering a second action if the offset distance is greater than the second predetermined threshold, the first action includes one of sounding a first audible alert, displaying a first visual alert, activating a first tactile alert, or a combination thereof, and the second action includes one of sounding a second audible alert, displaying a second visual alert, activating a second tactile alert, or a combination thereof. XXXVI. A method of providing navigational guidance for a surgical procedure, the method comprising: registering a patient's anatomy to a common coordinate system, the patient's anatomy including at least a first bone and a second bone; aligning a surgical instrument to the common coordinate system; tracking the patient's anatomy and the surgical instrument with the navigation system during movement of the surgical instrument on the first bone of the patient's anatomy; Determining an offset distance according to claim 1 for the second bone; tracking the patient's anatomy and the surgical instrument with the navigation system during movement of the surgical instrument on the second bone of the patient's anatomy; A method comprising: XXXVII. A method of performing a surgical procedure, said method comprising: coupling a patient tracker to a patient's anatomy; coupling an instrument tracker to a surgical instrument, the surgical instrument including a tool tip; operating a navigation system to align the instrument tracker and the patient tracker to a common coordinate system and track the surgical instrument and the patient's anatomy; initiating an alignment verification by dwelling the tool tip in contact with the anatomy for a predetermined duration; the navigation system is configured to determine an offset distance based on the tracked surgical instrument and the tracked patient anatomy; evaluating the offset distance against a predetermined threshold; A method comprising: XXXVIII. The method of claim XXXVII, wherein the navigation system is configured to trigger an action if the offset distance is greater than the predetermined threshold, the action including one of sounding an audible alert, displaying a visual alert, activating a tactile alert, cutting power to the surgical instrument, or a combination thereof. XXXIX. The method of claim XXXVIII, further comprising providing an input to the navigation system to complete the triggered action. XXXX. Resting the tool tip in contact with the anatomy includes resting the tool tip in contact with a first anatomy contact point at a first time, the surgical instrument being in a first position and a first proximal point of the tool tip in contact with the first anatomy contact point, the method further including resting the tool tip in contact with a second anatomy contact point at a second time, the surgical instrument being in a second position and a second proximal point of the tool tip in contact with the first anatomy contact point; Item XXXVII. The method of item XXXVII, wherein the navigation system is configured to determine a first offset distance based on the first anatomical contact point and the first proximal point, and to determine a second offset distance based on the second anatomical contact point and the second proximal point. XXXXI. The method of claim XXXX, wherein evaluating the offset distance includes one of evaluating the first offset distance against the predetermined threshold, evaluating the second offset distance against the predetermined threshold, or a combination thereof. XXXXII. The method of item XXXX, further comprising calculating a three-dimensional offset value based on the first offset distance and the second offset distance and a geometric relationship between the first proximal point and the second proximal point on the tool tip, wherein evaluating the offset distance comprises comparing the three-dimensional offset value to a predetermined three-dimensional offset threshold. XXXXIII. The patient's anatomy includes a first bone and a second bone, and the method includes: applying and operating the surgical instrument to the first bone; applying and operating the surgical instrument to the second bone; Further comprising: 36. The method of claim XXXVII, wherein pausing the tool and initiating alignment verification occurs in contact with the second bone after operating the surgical instrument on the first bone and before operating the surgical instrument on the second bone.

Claims

1. a surgical instrument having a variable speed motor and a tool tip; a controller that provides power to the surgical tool and monitors operation of a motor of the tool, the controller comprising a processor and a memory that stores information including information representative of operation of the motor of the tool; an instrument tracker connected to the instrument; a patient tracker connected to the bone; A navigation system having a localizer; Equipped with the navigation system stores information representing the surgical instrument and information representing the bone in a virtual space; the localizer aligns a position of the instrument tracker and a position of the patient tracker with respect to a localizer coordinate system and collects information about the positions of the instrument and the bone together with the instrument tracker and the patient tracker, respectively; the navigation system tracks the position of the instrument and the position of the bone in the virtual space based on the information collected by the localizer; The controller and the navigation system are in electronic communication and together determining a contact time between the tool tip and the bone based on the change in motor operation; determining a tool-to-bone offset, which is the distance between the tracked position of the tool tip and the tracked position of the bone, at the contact time; To carry out Surgical systems.

2. monitoring the operation of the motor includes monitoring a power level, a voltage level, a current level, or any combination thereof; the operation of the motors includes an operation of a first motor when operated while the tool tip is not in contact with a bone, and an operation of a second motor different from the operation of the first motor when the tool tip is in contact with a bone. The surgical system of claim 1 .

3. The surgical system of claim 1 , further comprising an alert device, wherein the controller and the navigation system are further configured to trigger an action if the tool-bone offset exceeds a predetermined amount.

4. The surgical system of claim 3 , wherein the alert device is a foot switch, the foot switch configured to generate a vibration, and the action is the vibration of the foot switch.

5. 4. The surgical system of claim 3, wherein the action includes sounding an audible alert, displaying a visual alert, activating a tactile alert, cutting power to the surgical instrument, or any combination thereof.

6. 4. The surgical system of claim 3, wherein the action includes prompting a user to update the bone model by contacting the tool tip with a resection surface of the bone when power is removed from the controller to the surgical instrument.

7. The surgical system of any one of claims 3 to 6, wherein the predetermined size is 0.5 millimeters.

8. The controller and the navigation system trigger a first action when the tool-to-bone offset reaches or exceeds a first predetermined size, and trigger a second action different from the first action when the tool-to-bone offset reaches or exceeds a second predetermined size different from the first predetermined size. A surgical system according to any one of claims 1 to 6.

9. The controller and the navigation system together determining the occurrence of each change in operation of the motor during the medical procedure; determining a contact time between the tool tip and the bone for each occurrence of a change in the motion of the motor; determining a tool-to-bone offset for each contact time; recording the set of determined tool-to-bone offsets; The surgical system according to any one of claims 1 to 6, further comprising:

10. 10. The surgical system of claim 9, wherein any of the controller, the navigation system, or the combination of the controller and the navigation system is further configured to cause a display device to display the determined set of tool-bone offsets as sequentially updated values.

11. a display device in electronic communication with either the controller, the navigation system, or a combination of the controller and the navigation system; Either the controller, the navigation system, or a combination of the controller and the navigation system is further configured to cause the determined tool-bone offset to be displayed on the display device. A surgical system according to any one of claims 1 to 6.

12. 12. The surgical system of claim 11, wherein the tool-to-bone offset is displayed in a first color when the tool-to-bone offset is below a predetermined amount and is displayed in a second color different from the first color when the tool-to-bone offset is above the predetermined amount.

13. a surgical instrument having an actuator and a tool tip; a controller that provides power to the surgical instrument and monitors operation of an actuator of the instrument, the controller comprising a processor and a memory that stores information including information representative of operation of the actuator of the instrument; an instrument tracker connected to the instrument; a patient tracker connected to the tissue; A navigation system having a localizer; Equipped with the navigation system stores information representing the surgical instrument and information representing the tissue in a virtual space; the localizer aligns a position of the instrument tracker and a position of the patient tracker with respect to a localizer coordinate system and collects information regarding the positions of the instrument and the tissue with the instrument tracker and the patient tracker, respectively; the navigation system tracks a position of the instrument and a position of the tissue in the virtual space during surgery based on information collected by the localizer; The controller and the navigation system are in electronic communication and together determining a contact time between the tool tip and the tissue based on the change in actuator movement; determining a tool-to-bone offset, which is the distance between the tracked position of the tool tip and the tracked position of the tissue at the contact time; To carry out Surgical systems.

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