Ligament repair method and system

Abstract

Ligament Repair. Some examples are directed to methods and associated systems for calibrating optical instruments for use in computer-guided endoscopic ligament repair, such as anterior cruciate ligament (ACL) repair. Other examples are directed to methods and associated systems for verifying registration between a three-dimensional bone model and bone visible through an endoscope during ligament repair. Yet further examples are directed to intraoperatively modifying tunnel plans for ligament repair.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Application No. 63 / 239,006, entitled "Methods and Systems of Ligament Repair," filed August 31, 2021, and also claims priority to U.S. Provisional Application No. 63 / 239,018, entitled "Video Based Navigation Calibration Apparatus," filed August 31, 2021. Both provisional applications are incorporated herein by reference as if reproduced in full below. [Background technology]

[0002] The anterior cruciate ligament (ACL) serves as the primary mechanical constraint in the knee to resist anterior translation of the tibia relative to the femur. Similarly, the posterior cruciate ligament (PCL) serves as the primary mechanical constraint to resist posterior translation of the tibia relative to the femur. These cruciate ligaments contribute greatly to the stability of the knee, and ACL injuries are extremely common. Most ACL injuries are complete ruptures of the ligament.

[0003] Since ACL injuries are common in young, active patients, reconstruction of the ACL is performed to allow return to activity. The goal is to restore stability to the knee and reduce the likelihood of further damage to the meniscus and articular cartilage leading to osteoarthritis. Reconstruction may consist of placing a substitute graft (e.g., an autograft from the middle third of the patellar tendon or from the hamstring tendon). Both ends of the graft are placed into corresponding tunnels prepared through the femur and tibia, respectively. The ends of the graft may be attached using interference screws or using a suspension fixation device, such as the ENDOBUTTON® brand fixation device manufactured by Smith & Nephew, Inc., Andover, Massachusetts, USA.

[0004] One challenge in ACL reconstruction is where to place the tunnel. The native ACL is composed of two major bundles: the anteromedial (AM) bundle and the posterolateral (PL) bundle. In many cases, the goal of surgery is to place the reconstruction in an anatomical location, for example, a single tunnel within the footprint of the attachment site of the native ACL. In other cases, the reconstruction may involve creating two tunnels in both the femur and the tibia in an attempt to reconstruct two native bundles.

[0005] Considerable variability exists in tunnel placement relative to the planned tunnel location. Errors in actual tunnel location relative to the planned tunnel location have been shown to be between 8.3 millimeters (mm) and 13.9 mm. Furthermore, failure rates in ACL reconstruction range from 10% to 15%, with 61% of failures attributable to technical error. Approximately 80% of technical failures are due to femoral tunnel malpositioning and 37% are due to tibial tunnel malpositioning. Summary of the Invention

[0006] One example is a method for calibrating an endoscopic optical system that includes placing an endoscope in a calibration assembly that holds the endoscope in a fixed relationship to a calibration target on an inner surface of the calibration assembly, capturing, by a surgical controller, a plurality of images of the calibration target, where each image is captured with a unique rotational relationship between a camera head and the endoscope, the unique rotational relationship being relative to a central longitudinal axis of the endoscope, and creating, by the surgical controller, a characterization function that characterizes optical distortion between the calibration target and the capture array of the camera head.

[0007] In an exemplary method for calibrating an endoscope, placing the endoscope in the calibration assembly may further include placing the endoscope in the calibration assembly such that a line of sight of the distal end of the endoscope is perpendicular to the calibration target. In an exemplary method for calibrating an endoscope, placing the endoscope in the calibration assembly may further include placing the endoscope in the calibration assembly such that a line of sight of the distal end of the endoscope is non-perpendicular to the calibration target. In an exemplary method for calibrating an endoscope, placing the endoscope in the calibration assembly may further include placing the endoscope in the calibration assembly such that a central longitudinal axis of the endoscope intersects a center of the calibration target and such that a line of sight of the distal end of the endoscope is perpendicular to the calibration target.

[0008] An exemplary method for calibrating an endoscope may further include placing water within an interior volume of the calibration assembly such that the interior volume between the calibration target and the distal end of the endoscope is filled with water or saline.

[0009] In an exemplary method for calibrating an endoscope, capturing the multiple images may further include capturing a first image of the calibration target at a first rotational orientation between the endoscope and the camera head, followed by capturing a second image of the calibration target at a second rotational orientation between the endoscope and the camera head, and then capturing a third image of the calibration target at a third rotational orientation between the endoscope and the camera head.

[0010] In an exemplary method for calibrating an endoscope, capturing the multiple images may further include capturing multiple images of a calibration target in a fixed relationship between the endoscope and the calibration assembly.

[0011] In an exemplary method for calibrating an endoscope, creating a characterization function may further include creating a characterization function that includes calibration for determining an orientation of a fiducial marker by an endoscope having a single optical path through the endoscope.

[0012] Yet another example is a calibration assembly for calibrating an endoscopic optical system, the calibration assembly including: a container defining an interior volume, the interior volume defining a calibration surface; a calibration target disposed on the calibration surface; a wall of the container defining an opening into the container, the opening defining a central axis that intersects with the calibration target; an axial support surface defined by the wall associated with the opening, the axial support surface located a predetermined distance from the calibration target measured along the central axis of the opening; and a rotational support surface associated with the wall.

[0013] In the exemplary calibration assembly, the rotational support surface may further include a ridge disposed within the countersunk hole defined by the wall, the rotational support surface being defined by a wall opposite the ridge, and the ridge may be parallel to the central axis of the opening.

[0014] In the exemplary calibration assembly, the wall may further include a notch defining a channel, the channel having a closed bottom forming the axial support surface, two sides forming the rotational support surfaces, and an open top. The channel of the notch may be perpendicular to the central axis of the opening.

[0015] In the exemplary calibration assembly, the rotating holding surface may further include a clip configured to hold an optical post of an endoscope.

[0016] In an exemplary calibration assembly, the calibration surface may be planar. In an exemplary calibration assembly, the calibration surface may define a first portion defining a first plane and a second portion defining a second plane, where the first plane and the second plane are non-planar.

[0017] In an exemplary calibration assembly, the wall of the container associated with the opening may further include a tube defining an internal passageway, the tube protruding from the container, the internal passageway defining an opening through the wall of the container.

[0018] In the exemplary calibration assembly, the central axis of the aperture may intersect with the center of the calibration target. In the exemplary calibration assembly, the central axis of the aperture may form an acute angle with a vector normal to the calibration surface, the acute angle being non-zero.

[0019] Yet another example is a system for calibrating an endoscopic optical system, the system including an endoscope system including an endoscope and a camera head coupled to the endoscope, the endoscope defining a central longitudinal axis and a light post, and a calibration assembly. The calibration assembly may include a container defining an interior volume, a calibration surface defined on an interior surface of the container, a calibration target disposed on the calibration surface, and an opening through a wall of the container, the endoscope being fitted through the opening with the central longitudinal axis intersecting the calibration target. The calibration assembly may be configured to hold a distal end of the endoscope a predetermined distance from the calibration target, and the calibration assembly may be configured to hold the endoscope in a fixed rotational orientation relative to the calibration target.

[0020] In an exemplary system for calibrating an endoscopic optical system, the calibration assembly may further include a set of rotational support surfaces defined by ridges disposed within a countersunk hole defined by the walls, the set of rotational support surfaces being defined by walls located on opposite sides of the ridges, the set of rotational support surfaces holding the endoscope in a fixed rotational orientation relative to the calibration target.

[0021] In an exemplary system for calibrating an endoscopic optical system, the calibration assembly may further include a notch defining a channel, the channel having a closed bottom and an open top, the optical post being disposed within the notch, the notch holding the distal end of the endoscope a predetermined distance from the calibration target, and the notch holding the endoscope in a fixed rotational orientation relative to the calibration target.

[0022] In an exemplary system for calibrating an endoscopic optical system, the calibration assembly may further include a clip coupled to the optical post, the clip holding the endoscope in a fixed rotational orientation relative to the calibration target.

[0023] An exemplary system for calibrating an endoscopic optical system may further include water within the interior volume between the distal end of the endoscope and the calibration target. The water may be saline.

[0024] In an exemplary system for calibrating an endoscopic optical system, the calibration surface may be planar. In an exemplary system for calibrating an endoscopic optical system, the calibration surface may define a first portion defining a first plane and a second portion defining a second plane, where the first plane and the second plane are non-planar.

[0025] In an exemplary system for calibrating an endoscopic optical system, the calibration assembly may further include a tube defining an internal passage, the tube protruding from the container, and the endoscope being fitted through the internal passage such that a distal end of the endoscope is located within the interior volume of the container.

[0026] In an exemplary system for calibrating an endoscopic optical system, a central longitudinal axis of the endoscope may intersect with a center of the calibration target. In an exemplary system for calibrating an endoscopic optical system, a central longitudinal axis of the endoscope may form an acute angle with a vector normal to the calibration surface, the acute angle being non-zero.

[0027] Yet another example is an intraoperative method including receiving, by a surgical controller, a three-dimensional bone model of a bone; receiving, by the surgical controller, an image of the bone viewed by an endoscope and an attached camera head during a surgical procedure, the image of the bone including images of reference points coupled to the bone; receiving, by the surgical controller, a plurality of positions relative to an outer surface of the bone shown in the image of the bone; registering, by the surgical controller, the three-dimensional bone model to the bone using the plurality of positions; displaying, by the surgical controller, a representation of the three-dimensional bone model superimposed onto the image of the bone on a display device; and receiving, by the surgical controller, an indication indicating that the three-dimensional bone model has been properly registered to the bone in the image of the bone.

[0028] In an exemplary intraoperative method, receiving the image of the bone may further include receiving at least one selected from the group consisting of an image of an intercondylar recess of the femur and an image of an intercondylar ridge of the tibia. In an exemplary intraoperative method, receiving the three-dimensional bone model may further include receiving a three-dimensional bone model constructed by segmentation of a pre-operative image of the bone.

[0029] In an exemplary intra-operative method, receiving a plurality of locations relative to the outer surface of the bone may further include tracking, by the surgical controller, a position of a distal tip of the touch probe as the touch probe abuts against the bone at the plurality of locations. Tracking the position of the distal tip of the touch probe may further include at least one selected from the group consisting of: tracking fiducials disposed on the outer surface of the touch probe, the fiducials being visible in an image of the bone as viewed by the endoscope and an attached camera head, and tracking an array of fiducials coupled to the touch probe as viewed by a stereoscopic camera.

[0030] In an exemplary intraoperative method, displaying a representation of the three-dimensional bone model may further include overlaying a mesh model representing the three-dimensional bone model onto the image of the bone shown on the display device.

[0031] Another example is a surgical controller including a processor configured to be coupled to a display device and a memory coupled to the processor that stores instructions that, when executed by the processor, cause the processor to receive a three-dimensional bone model of a bone, receive an image of the bone viewed by an endoscope and an attached camera head during a surgical procedure, the image of the bone including an image of a reference point coupled to the bone, receive a plurality of positions relative to an outer surface of the bone shown in the image of the bone, register the three-dimensional bone model to the bone using the plurality of positions, display a representation of the three-dimensional bone model superimposed onto the image of the bone, and receive an indication that the three-dimensional bone model is properly registered to the bone in the image of the bone.

[0032] In the exemplary surgical controller, when the surgical controller receives an image of the bone, the instructions may further cause the processor to receive at least one selected from the group consisting of an image of an intercondylar recess of the femur and an image of an intercondylar ridge of the tibia. In the exemplary surgical controller, when the surgical controller receives a three-dimensional bone model, the instructions may further cause the processor to receive a three-dimensional bone model constructed by segmenting a pre-operative image of the bone. In the exemplary surgical controller, when the surgical controller receives a plurality of positions relative to an outer surface of the bone, the instructions may further cause the processor to track a position of a distal tip of the touch probe when the touch probe abuts against the bone at a plurality of positions. In the exemplary surgical controller, when the surgical controller tracks a position of a distal tip of the touch probe, the instructions may further cause the processor to perform at least one selected from the group consisting of tracking fiducials located on the outer surface of the touch probe, the fiducials being visible in an image of the bone as viewed by the endoscope and the attached camera head, and tracking an array of fiducials coupled to the touch probe as viewed by the stereoscopic camera.

[0033] In an exemplary surgical controller, when the surgical controller displays a representation of the three-dimensional bone model, the instructions may further cause the processor to overlay a mesh model representing the three-dimensional bone model onto the image of the bone.

[0034] Yet another example is an intraoperative method including displaying, by a surgical controller, on a display device a planned tunnel path for a ligament repair, the planned tunnel path being indicated relative to at least a portion of a bone, the planned tunnel path being selected preoperatively; receiving, by the surgical controller, a revised tunnel entry location during the surgical procedure; calculating, by the surgical controller, a revised tunnel path through the bone during the surgical procedure and displaying, by the surgical controller, the revised tunnel path on the display device; tracking, by the surgical controller, an axial alignment of a drill axis of a drill wire relative to a central longitudinal axis of the revised tunnel path prior to drilling; and displaying, by the surgical controller, a graphic on the display device indicating the relative position of the drill axis and the central longitudinal axis of the revised tunnel path.

[0035] In an intraoperative method, the planned tunnel path may be for anterior cruciate ligament (ACL) repair.

[0036] In the intraoperative method, after calculating the revised tunnel path, the method may further include determining, by the surgical controller, a value indicative of an overlap between the planned tunnel path and the revised tunnel path, and displaying, by the surgical controller, on a display device, a visual representation of the value indicative of the overlap between the planned tunnel path and the revised tunnel path.

[0037] The intraoperative method may further include calculating, by the surgical controller, an entrance position offset between a planned tunnel entrance of the planned tunnel path and a corrected tunnel entrance of the corrected tunnel path, calculating, by the surgical controller, an exit position offset between a planned tunnel exit of the planned tunnel path and a corrected tunnel exit of the corrected tunnel path, and displaying, by the surgical controller, a visual representation of the entrance position offset and the exit position offset on a display device.

[0038] The intra-operative method may further include ascertaining, by the surgical controller, a value indicative of a posterior wall burst likelihood for the modified tunnel path, and displaying, by the surgical controller, a visual representation of the value indicative of the posterior wall burst likelihood on the display device. In the intra-operative method, ascertaining the value indicative of the posterior wall burst likelihood may further include measuring a distance between the modified tunnel path and an outer surface of the three-dimensional bone model. Measuring the distance between the modified tunnel path and an outer surface of the three-dimensional bone model may further include measuring a shortest distance between the modified tunnel path and an outer surface of the three-dimensional bone model.

[0039] In the intraoperative method, displaying the planned tunnel path may further include displaying at least one selected from the group consisting of a planned tunnel path through the femur and a planned tunnel path through the tibia.

[0040] In the intraoperative method, receiving the modified tunnel entry location may further include receiving, by the surgical controller, the modified tunnel entry location located within at least one selected from the group consisting of an intercondylar recess of the femur and an intercondylar ridge of the tibia.

[0041] In the intraoperative method, receiving the revised tunnel entrance position may further include receiving based on a position of a distal tip of the sight as viewed within the surgical site by the endoscope and attached camera head.

[0042] In the intraoperative method, tracking the axial alignment may further include tracking the axial alignment of a sight through which the drill wire fits.

[0043] In the intraoperative method, tracking the axial alignment of the sight may further include receiving, by the surgical controller, images from the endoscope and attached camera head, the images including reference points disposed on an outer surface of the sight, and calculating, by the surgical controller, based on the images, an axial alignment of the sight relative to a three-dimensional model of the outer surface of the bone.

[0044] The intraoperative method may further include tracking, by the surgical controller, the drill axis of the drill wire during drilling to form a through hole having a central axis, and displaying, by the surgical controller, on the display device, a value indicative of an offset between the central axis of the through hole and a central longitudinal axis of the modified tunnel path.

[0045] In the intraoperative method, displaying a graphic indicating the relative position of the drill axis and the central longitudinal axis of the corrected tunnel path may further include displaying a tunnel path target indicating the central longitudinal axis of the corrected tunnel path, displaying a distal end target indicating the position of a distal end of the drill wire relative to the central longitudinal axis of the corrected tunnel path, and displaying a proximal end target indicating the position of a proximal end of the drill wire in axial alignment relative to the central longitudinal axis of the corrected tunnel path.

[0046] Yet another example is a surgical controller including a processor configured to be coupled to a display device and a memory coupled to the processor, the memory storing instructions that, when executed by the processor, cause the processor to receive images of a leg bone viewed by an endoscope and an attached camera head during a surgical procedure, display on the display device a planned tunnel path for an anterior cruciate ligament (ACL) repair, illustrating the planned tunnel path relative to at least a portion of the leg bone, receive a corrected tunnel entry location, calculate a corrected tunnel path through the leg bone, the corrected tunnel path having a central longitudinal axis, display the corrected tunnel path on the display device, track an axial alignment of a drill axis of a drill wire relative to the central longitudinal axis, and display on the display device a graphic indicating a relative position of the drill axis and the central longitudinal axis of the corrected tunnel path.

[0047] In an exemplary surgical controller, after the processor calculates the revised tunnel path, the instructions may further cause the processor to determine a value indicative of an overlap between the planned tunnel path and the revised tunnel path, and display, on a display device, a visual representation of the value indicative of the overlap between the planned tunnel path and the revised tunnel path.

[0048] In an exemplary surgical controller, the instructions may further cause the processor to calculate an entrance position offset between a planned tunnel entrance of the planned tunnel path and a corrected tunnel entrance of the corrected tunnel path, calculate an exit position offset between a planned tunnel exit of the planned tunnel path and a corrected tunnel exit of the corrected tunnel path, and display a visual representation of the entrance position offset and the exit position offset on a display device.

[0049] In an exemplary surgical controller, the instructions may further cause the processor to ascertain a value indicative of a posterior wall breach probability for the modified tunnel path and display a visual representation of the value indicative of the posterior wall breach probability on a display device. In an exemplary surgical controller, when the processor ascertains a value indicative of a posterior wall breach probability, the instructions may further cause the processor to measure a distance between the modified tunnel path and an outer surface of the three-dimensional bone model. In an exemplary surgical controller, when the processor measures a distance between the modified tunnel path and an outer surface of the three-dimensional bone model, the instructions may further cause the processor to measure a minimum distance between the modified tunnel path and the outer surface of the three-dimensional bone model.

[0050] In an exemplary surgical controller, when the processor displays the planned tunnel path, the instructions may cause the processor to display at least one selected from the group consisting of a planned tunnel path through the femur and a planned tunnel path through the tibia.

[0051] In an exemplary surgical controller, when the processor receives the modified tunnel entry location, the instructions may cause the processor to receive the modified tunnel entry location located within at least one selected from the group consisting of an intercondylar recess of the femur and an intercondylar ridge of the tibia.

[0052] In an exemplary surgical controller, when the processor receives a revised tunnel entrance position, the instructions may further cause the processor to receive based on the position of the distal tip of the sight visible in an image of the bone viewed by the endoscope and attached camera head.

[0053] In an exemplary surgical controller, when the processor tracks axial alignment, the instructions may further cause the processor to track axial alignment of a sight through which the drill wire fits and that is visible in an image of the bone viewed by the endoscope and associated camera head. In an exemplary surgical controller, when the processor receives an image of the bone viewed by the endoscope and associated camera head, the instructions may further cause the processor to receive the image including reference points disposed on an exterior surface of the sight, and when the processor tracks axial alignment of the sight, the instructions may further cause the processor to calculate the axial alignment of the sight relative to a three-dimensional model of the exterior surface of the bone based on an orientation of the reference points.

[0054] In an exemplary surgical controller, the instructions may further cause the processor to track the drill axis of the drill wire during drilling to form a through hole having a central axis, and display on the display device a value indicative of an offset between the central axis of the through hole and the central longitudinal axis of the modified tunnel path.

[0055] In an exemplary surgical controller, when the processor displays a graphic indicating the relative position of the drill axis and the central longitudinal axis of the modified tunnel path, the instructions may further cause the processor to: display a tunnel path target indicating the central longitudinal axis of the modified tunnel path; display a distal end target indicating the position of the distal end of the drill wire relative to the central longitudinal axis of the modified tunnel path; and display a proximal end target indicating the position of the proximal end of the drill wire in axial alignment relative to the central longitudinal axis of the modified tunnel path. [Brief description of the drawings]

[0056] For a detailed description of the exemplary embodiments, reference is now made to the accompanying drawings.

[0057] [Figure 1] FIG. 1 shows an anterior or frontal view of the right knee with the patella removed.

[0058] [Diagram 2] FIG. 2 shows a posterior or rear view of the right knee.

[0059] [Diagram 3] FIG. 3 shows a view of the femur from below, looking into the intercondylar recess.

[0060] [Figure 4] FIG. 4 illustrates a surgical system according to at least some embodiments.

[0061] [Diagram 5] FIG. 5 illustrates a conceptual diagram of a surgical site with various objects being tracked within the surgical site, according to at least some embodiments.

[0062] [Figure 6] FIG. 6 illustrates an exploded perspective view of a calibration assembly according to at least some embodiments.

[0063] [Figure 7] FIG. 7 illustrates a top view of an example calibration assembly according to at least some embodiments.

[0064] [Figure 8] FIG. 8 illustrates a cross-sectional view of a calibration assembly and an arthroscope, according to at least some embodiments.

[0065] [Figure 9A] FIG. 9A illustrates a perspective view of a calibration assembly according to at least some embodiments.

[0066] [Figure 9B] FIG. 9B illustrates a perspective view of a calibration assembly according to at least some embodiments.

[0067] [Figure 9C] FIG. 9C illustrates a cross-sectional view of the calibration assembly and arthroscope, according to at least some embodiments.

[0068] [Figure 9D] FIG. 9D illustrates a perspective cutaway view of a portion of a calibration assembly in accordance with at least some embodiments.

[0069] [Figure 10] FIG. 10 is an exemplary video display showing a portion of a femur with bone reference points visible therein, according to at least some embodiments.

[0070] [Figure 11] FIG. 11 is an exemplary video display showing a portion of the femur and bone reference points during a registration procedure, according to at least some embodiments.

[0071] [Figure 12] FIG. 12 illustrates an exemplary video display during a registration procedure showing a portion of a femur, bone reference points, and an overlaid three-dimensional bone model, according to at least some embodiments.

[0072] [Figure 13] FIG. 13 is an exemplary video display illustrating intraoperative changes to the tunnel path, according to at least some embodiments.

[0073] [Figure 14] FIG. 14 is an exemplary video display illustrating intraoperative changes to the tunnel path, according to at least some embodiments.

[0074] [Figure 15] FIG. 15 is an exemplary video display showing computer guidance for placement of pilot tunnels, according to at least some embodiments.

[0075] [Figure 16] FIG. 16 is an exemplary video display illustrating intraoperative analysis of a pilot tunnel path versus a corrected tunnel path, according to at least some embodiments.

[0076] [Figure 17] FIG. 17 illustrates a method for calibrating an endoscope optical system, according to at least some embodiments.

[0077] [Figure 18] FIG. 18 illustrates a method for intraoperative verification of registration of three-dimensional bone models, according to at least some embodiments.

[0078] [Figure 19] FIG. 19 illustrates a method for implementing intraoperative tunnel rerouting, according to at least some embodiments.

[0079] [Figure 20] FIG. 20 illustrates a computer system according to at least some embodiments. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0080] definition Various terms are used to refer to particular system components. Although different companies may refer to a component by different names, this document does not intend to distinguish between components that differ in name but not function. In the following discussion and claims, the terms "including" and "comprises" are used in an open-ended manner and should be interpreted to mean "including, but not limited to." Additionally, the terms "couple" or "couples" are intended to mean either an indirect or direct connection. Thus, when a first device is coupled to a second device, the connection may be by a direct connection or an indirect connection via another device or other connection.

[0081] "Receiving a position" shall mean receiving data indicating a position on a bone within a coordinate space (e.g., the coordinate space of an endoscope's field of view). Thus, example systems and methods may "receive a corrected tunnel entry position," which is data indicating a proposed position of a tunnel entry point within a three-dimensional coordinate space. Other example systems and methods may "receive a plurality of positions on a bone," which is data indicating the location of an outer surface of the bone, as part of registering the bone to a three-dimensional bone model.

[0082] An endoscope having a "single optical path" through it is intended to mean that the endoscope is not a stereoscopic endoscope having two separate optical paths separated by the interocular distance at the focusing end of the endoscope. The fact that an endoscope has two or more optical elements (e.g., glass rods, optical fibers) forming a single optical path does not negate its status as a single optical path.

[0083] "Through-hole" is intended to mean an opening or passageway through the underlying device. However, the term "through-hole" should not be construed as implying any method of formation. Thus, through-holes may be formed in any suitable manner, such as drilling, punching, laser drilling, casting, etc.

[0084] "Counterbored hole" is intended to mean an opening or passageway into an underlying device. Where the counterbored hole intersects with another opening (e.g., a through hole), the counterbored hole may thereby define an internal shoulder. However, the term "counterbored hole" should not be construed as implying any method of formation. Counterbored holes may be formed in any suitable manner, such as drilling, punching, laser drilling, casting, etc.

[0085] The following discussion is directed to various embodiments of the present invention. Although one or more of these embodiments may be preferred, the disclosed embodiments should not be interpreted as limiting the scope of the present disclosure, including the claims, and should not be used in other ways. In addition, those skilled in the art will understand that the following description has a broad range of applications, and that the discussion of any embodiment is meant to be merely an example of that embodiment, and is not intended to imply that the scope of the present disclosure, including the claims, is limited to that embodiment.

[0086] Various examples are directed to methods and systems related to ligament reconstruction and repair. Ligament repair (e.g., anterior cruciate ligament (ACL) repair) may be arthroscopic or computer-assisted. Some examples include methods and systems for calibrating an endoscopic optical system including an arthroscope and an attached camera head. The calibration is to account for optical distortions present in the optical path so that images produced by the arthroscope and the attached camera head may be used in arthroscopic repair, such as to register a bone model to the bones seen through the arthroscope, such as to track the positions of various objects in the surgical site with respect to the bone model, and / or to update the position of a tunnel intraoperatively. Another example includes verifying the registration of a three-dimensional bone model to the bones seen through the arthroscope. Yet another example includes intraoperatively modifying a tunnel path for ligament repair and then forming a tunnel along the modified tunnel path.

[0087] Various examples have been developed in the context of ACL repair, and thus the following discussion is based on the developed context. However, the technology is applicable to many types of ligament repair, such as medial collateral ligament repair, lateral collateral ligament repair, and posterior cruciate ligament repair. Moreover, various exemplary methods and systems can also be used to plan and place anchors for reattaching soft tissues, such as hip labrum, shoulder, or meniscal root reattachment. Thus, the present specification and the developed context should not be interpreted as limiting the applicability of the present teachings. To orient the reader, the present specification first describes the knee.

[0088] FIG. 1 shows an anterior or frontal view of a right knee with the patella removed. In particular, visible in FIG. 1 is an inferior portion of a femur 100, including a lateral or lateral condyle 102 and a medial or medial condyle 104. The femur 100 and condyles 102, 104 are in operative relationship with a tibia 106, including a tibial tuberosity 108 and a Gördi tubercle 110. Disposed between the femoral condyles 102, 104 and the tibia 106 are a lateral meniscus 112 and a medial meniscus 114. Also visible in the illustration of FIG. 1 are several ligaments, such as an ACL 116, which extends from the lateral side of the femoral recess to the medial side of the tibia 106. Conversely, a posterior cruciate ligament 118 extends from the medial side of the femoral recess to the tibia 106. Also visible is a fibula 120, as well as several additional ligaments not specifically labeled.

[0089] FIG. 2 shows a posterior or rear view of the right knee. In particular, visible in FIG. 2 is the lower portion of the femur 100, including the lateral condyle 102 and medial condyle 104. The femur 100 and femoral condyles 102, 104 are again in operative relationship with the tibia 106, with the lateral meniscus 112 and medial meniscus 114 disposed between the femoral condyles 102, 104 and the tibia 106. FIG. 2 also shows the ACL 116 extending from the lateral side of the femoral recess to the medial side of the tibia 106, although its attachment point to the tibia 106 is not visible. The posterior cruciate ligament 118 extends from the medial side of the femoral recess to the tibia 106, although its attachment point to the femur 100 is not visible. Again, several additional ligaments are shown, not specifically labeled.

[0090] The most common ACL injury is a complete rupture of the ligament. The procedure involves reconstructing the ACL by placing a substitute graft (e.g., an autograft from either the patellar tendon, the quadriceps tendon, or the hamstrings tendon). The graft is placed inside a tunnel prepared in the femur 100 and in the tibia 106. The current standard of care for ACL repair is to place the tunnel so that the tunnel entry point for the graft is at the anatomical attachment point of the natural ACL. This tunnel placement at the attachment point of the natural ACL attempts to replicate the kinematic characteristics of the natural knee. In arthroscopic surgery, the location of the tunnel through the tibia 106 is relatively easy to reach, especially when the knee is bent or flexed. However, the tunnel through the femur 100 is located inside the intercondylar recess. Depending on the patient's size and how the surgeon selects the location of the percutaneous port through which various instruments are inserted into the knee, it can be difficult to reach the attachment location of the native ACL to the femur 100.

[0091] FIG. 3 illustrates a view of the femur from below, looking into the intercondylar recess. Specifically visible in FIG. 3 are the lateral condyle 102 and the medial condyle 104. Defined between the femoral condyles 102, 104 is a femoral recess 200. The femoral tunnel may define a medial opening 202 in the femoral recess 200 that is proximal to the lateral condyle 102 and displaced toward a posterior portion of the femoral recess 200. The femoral tunnel extends through the femur 100 and forms an outer opening on the outer or lateral surface of the femur 100 (the outer opening is not visible in FIG. 3). FIG. 3 illustrates an exemplary drill wire 204 that may be used to form an initial tunnel or pilot hole. After the surgeon is satisfied that the pilot hole is precisely aligned with the planned tunnel path, the femoral tunnel is created by drilling or reaming with another instrument (e.g., a reamer) that may use the drill wire 204 as a guide. Optionally, a socket or counterbore may be created on the intercondylar recess side to accommodate the width of the graft that extends into the bone, and the counterbore may be created with another instrument (e.g., a reamer) that may also use the drill wire 204 as a guide.

[0092] The tunnel may be drilled from either direction. Considering the femoral tunnel again as an example, the tunnel may be drilled from the outside or lateral portion of the femur 100 toward and into the femoral recess 200, which is referred to as an "outside-in" procedure. Conversely, the exemplary femoral tunnel may be drilled from the interior of the femoral recess 200 toward and into the lateral portion of the femur 100, which is referred to as an "inside-out" procedure. The various examples described below are equally applicable to both outside-in and inside-out. In an outside-in procedure, additional devices may be used to hold the drill wire on the outside portion and physically indicate the expected tunnel location of the internal opening inside the knee. However, devices for the outside-in procedure are difficult to use in an arthroscopic procedure, so an inside-out procedure is used in many arthroscopic repairs. Thus, although the further examples described below are based on an inside-out procedure, this should not be construed as limiting.The present specification now turns to a description of an exemplary surgical system.

[0093] 4 illustrates a surgical system (not to scale) according to at least some embodiments. In particular, the exemplary surgical system 400 includes a tower or device cart 402, an exemplary mechanical ablation instrument 404, an exemplary plasma-based ablation instrument (hereafter simply ablation instrument 406), and an exemplary configuration of an endoscope consisting of an arthroscope 408 and an attached camera head 410. The endoscope 408 defines an optical interface or light post 420 through which light is provided and transmitted into the interior of the endoscope 408 to illuminate a surgical field at the distal end of the endoscope 408. The device cart 402 may include a camera 412 (illustratively shown as a stereoscopic camera), a display device 414, a resection controller 416, and a camera control unit (CCU), along with an endoscope light source and video controller 418. In the exemplary case, the CCU and video controller 418 provides light to the light post 420 of the arthroscope 408 and displays images received from the camera head 410. In an exemplary case, the CCU and video controller 418 also implements various additional aspects, such as calibration of the arthroscope and camera head, displaying the planned tunnel path on the display device 414, receiving the corrected tunnel entry position, calculating the corrected tunnel path, and calculating and displaying various parameters indicative of the relationship between the corrected tunnel path and the planned tunnel path. Thus, hereinafter the CCU and video controller are referred to as the surgical controller 418. However, in other cases, the CCU and video controller may be separate systems that are separate from the controller that handles aspects of intraoperative changes, although the separate devices would still be operatively coupled.

[0094] The exemplary device cart 402 further includes a pump controller 422 (e.g., a single or dual peristaltic pump). Fluid connections between the mechanical ablation instrument 404 and the ablation instrument 406 are not shown to avoid overcomplicating the drawing. Similarly, fluid connections between the pump controller 422 and the patient are not shown to avoid overcomplicating the drawing. In the exemplary system, both the mechanical ablation instrument 404 and the ablation instrument 406 are coupled to an ablation controller 416, which is a dual function controller. However, in other cases, a separate mechanical ablation controller may be provided that is separate from the ablation controller. The exemplary devices and controllers associated with the device cart 402 are merely illustrative; other examples include vacuum pumps, patient positioning systems, robotic arms that hold various instruments, ultrasonic cutting devices and associated controllers, patient positioning controllers, and robotic surgical systems.

[0095] FIG. 4 further illustrates additional instruments that may be present during an exemplary ACL repair. In particular, FIG. 4 illustrates an exemplary guide wire or drill wire 424 and a sight 426. The drill wire 424 may be used to form an initial or pilot tunnel through the bone. In some cases, the diameter of the drill wire may be approximately 2.4 millimeters (mm), although larger or smaller diameters may be used for the drill wire 424. The exemplary drill wire 424 is illustrated with enlarged portions at both ends, one enlarged portion showing a cutting member on the distal end of the drill wire 242 and another enlarged portion showing a connector for coupling to a chuck of a drill. After the surgeon drills the pilot tunnel, the surgeon and / or surgery controller 418 (described further below) may evaluate whether the pilot tunnel is consistent or approximately consistent with the planned tunnel path. If the pilot tunnel is deemed sufficient, the drill wire 424 may be used as a guide to create a full diameter through hole for the tunnel and, in some cases, may also be used as a guide to create a counterbore hole associated with the intercondylar recess to accommodate the graft. In some cases, the drill wire may be used alone when creating the pilot tunnel, while in still other cases, the surgeon may use the sight 426 to help guide and position the drill wire 424 into the designed tunnel entry location.

[0096] 4 also illustrates that the exemplary system may include a calibration assembly 428. As described in more detail below, the calibration assembly 428 may be used to detect optical distortions in images received by the surgical controller 418 via the arthroscope 408 and attached camera head 410. There will be additional tools and instruments, such as drills for drilling with the drill wire 424, various reamers for forming the through hole and counterbored aspects of the tunnel, and various tools for suturing and anchoring the graft in place. These additional tools and instruments are not shown so as not to further complicate the drawing.

[0097] The present specification now turns to a description of an exemplary workflow for ACL repair. The workflow may be conceptually categorized into pre-operative planning and intra-operative repair. The intra-operative repair workflow may be conceptually further categorized into optical system calibration, model registration, intra-operative tunnel path planning, intra-operative tunnel formation, and intra-operative tunnel placement analysis. Each will be addressed in turn.

[0098] plan

[0099] According to various examples, ACL repair begins with imaging (e.g., x-ray imaging, computed tomography (CT), magnetic resonance imaging (MRI)) of the patient's knee, including relevant anatomical structures such as the lower portion of the femur, the upper portion of the tibia, and articular cartilage. In the following description, MRI is assumed, although again, many different types of imaging may be used. The MRI imaging may be segmented from image slices to create a volumetric or three-dimensional model of the anatomical structures. Any suitable segmentation technique, currently available or later developed, may be used to create the three-dimensional model. More specifically with respect to the example of ACL repair, and particularly with respect to the selection of a tunnel path through the femur, a three-dimensional bone model of the lower portion of the femur, including the femoral condyles, is created.

[0100] Using the three-dimensional bone model, a surgical plan is created that includes selecting a planned tunnel path through the femur, including the location of the bone opening that defines the end of the tunnel. For an exemplary inside-out repair, the opening in the femoral recess is the entry location for the drill hole, and the opening on the side of the femur is the exit. For an outside-in repair, the entry and exit locations for the drill hole are swapped. Nevertheless, assuming an inside-out repair, the entry location may be selected to be the same or close to the attachment location of the natural ACL to the femur in the femoral recess. In some cases, the selection of the entry location in the femoral recess may include using Bernard & Hertel quadrants or grids placed on a fluoroscopic image, or may include placing Bernard & Hertel quadrants on a simulated fluoroscopic image created from the three-dimensional bone model. Based on the use of the Bernard & Hertel quadrants, the entry location of the tunnel is selected. In the case of an inside-out repair, the choice of exit location is less limited, not only because the portion of the tunnel proximal to the exit location is used for placement of the graft anchor, but also because the exit location is approximately in the center of the femur (considered anterior to posterior), making bone wall thickness issues at the exit location less of a concern. Optionally, a three-dimensional bone model of the proximal end of the tibia is also created, and the surgeon may select the planned tunnel path(s) through the tibia as well.

[0101] The results of the planning may include a three-dimensional bone model for the distal end of the femur, a three-dimensional bone model for the proximal end of the tibia, entry and exit locations through the femur and thus the planned tunnel path in the femur, and entry and exit locations through the tibia and thus the planned tunnel path in the tibia. Other surgical parameters such as tunnel through hole diameter, tunnel counterbore hole diameter and depth, desired post-restoration curvature, and the like, may also be selected during planning, although these additional surgical parameters have been omitted so as not to overly complicate the specification.

[0102] Intraoperative repair

[0103] The present specification now turns to a description of intraoperative aspects. Intraoperative aspects include steps and procedures for setting up the surgical system to perform various repairs. However, it should be noted that some of the intraoperative aspects (e.g., calibration of the optical system) may be performed before any ports or incisions are made through the patient's skin, and in fact, before the patient is brought into the operating room. Nevertheless, such steps and procedures may be considered intraoperative, since they are performed using the surgical instruments and tools that are used to perform the actual repairs in the surgical setting.

[0104] The exemplary ACL repair is arthroscopic and computer-assisted in the sense that a surgical controller 418 is used to navigate the arthroscope within the surgical site. More specifically, in the exemplary system, the surgical controller 418 provides computer assistance during ligament repair by tracking the positions of various objects within the surgical site, such as the positions of bones within the three-dimensional coordinate space of the arthroscope's field of view, and the positions of various instruments (e.g., drill wire 424, sight 426) within the three-dimensional coordinate space of the arthroscope's field of view. This specification turns to a brief description of such tracking techniques.

[0105] Figure 5 is a conceptual diagram of a surgical site within which various objects reside. Specifically visible in Figure 5 are the distal end of an arthroscope 408, a portion of a bone 500 (e.g., the femur), a bone reference point 502 within the surgical site, a touch probe 504, and a probe reference point 506. Each will be addressed in turn.

[0106] The distal end of the arthroscope 408 is designed and constructed to illuminate the surgical site with visible light received via light post 420 (FIG. 4). In the example of FIG. 5, the illumination is illustrated by arrow 508. Illumination provided to the surgical site is reflected by various objects and tissues within the surgical site, and the reflected light returning to the distal end enters the arthroscope 408 and propagates along optical channels within the arthroscope 408 and ultimately onto a capture array within the camera head 410 (FIG. 4). Images detected by the capture array within the camera head 410 are electronically transmitted to the surgical controller 418 (FIG. 4) and displayed on the display device 414 (FIG. 4). According to the exemplary system, the arthroscope 408 has a single optical path through the arthroscope for capturing images of the surgical site, although the single optical path may be constructed from two or more optical members (e.g., glass rods, optical fibers). That is, in the exemplary system and method, the computer-assisted steering provided by the arthroscope 408, camera head 410, and surgical controller 418 provides an arthroscope 408 that is not a stereoscopic endoscope with two separate optical paths separated by the interocular distance at the distal endoscope.

[0107] During a surgical procedure, the surgeon selects an arthroscope that has a viewing direction that is useful for the planned surgical procedure. The viewing direction refers to a line centered on the angle formed by the outer or peripheral edge of the endoscope's field of view. The viewing direction for some arthroscopes is aligned with the longitudinal central axis of the arthroscope, and such arthroscopes are referred to as "0 degree" arthroscopes (e.g., the angle between the viewing direction and the longitudinal central axis of the arthroscope is 0 degrees). The viewing direction for other arthroscopes forms a non-zero angle with the longitudinal central axis of the arthroscope. For example, with a 30° arthroscope, the viewing direction forms a 30° angle with the longitudinal central axis of the arthroscope, and this angle is measured as an obtuse angle beyond the distal end of the arthroscope. In many cases in ACL repair, the surgeon selects a 30° or 45° arthroscope based on the location of the port that will be created through the patient's skin. In the example of FIG. 5, the viewing angle 510 of the arthroscope 408 forms a non-zero angle with respect to a central longitudinal axis 512 of the arthroscope 408 .

[0108] Still referring to FIG. 5, a portion of a bone 500 is present within the field of view of the arthroscope 408 along with bone reference points 502, a touch probe 504, and a probe reference point 506. Although the bone reference points 502 are shown as planar members with a pattern disposed on the top surface, other shapes for the bone reference points 502 may be used (e.g., a square block with a pattern on each face of the block). The bone reference points 502 may be attached to the bone 500 in any suitable manner (e.g., fasteners such as screws). The pattern of the bone reference points is designed to provide information regarding the orientation of the bone reference points 502 within the three-dimensional coordinate space in the field of view of the arthroscope 408. More specifically, the pattern is selected such that the orientation of the bone reference points 502, and therefore the orientation of the underlying bone 500, may be determined from images captured by the arthroscope 408 and attached camera head 410 (FIG. 4).

[0109] The probe reference point 506 is shown as a planar member attached to the touch probe 504. As described further below, the touch probe 504 may be used to "paint" the faces of the bone 500 as part of the registration of the bone 500 to the three-dimensional bone model, and the touch probe 504 may also be used to indicate a modified tunnel entry location if the tunnel path is modified intraoperatively. Although the probe reference point 506 is shown as a planar member having a pattern disposed on its top surface, other shapes for the probe reference point 506 may be used (e.g., a square block surrounding the touch probe 504 and having a pattern on each face of the block). The pattern of the probe reference point 506 is designed to provide information regarding the orientation of the probe reference point 506 in three-dimensional coordinate space in the field of view of the arthroscope 408. More specifically, the pattern is selected such that the orientation of the probe reference point 506, and therefore the location of the point of the touch probe 504, can be determined from images captured by the arthroscope 408 and attached camera head 410 (FIG. 4).

[0110] Other instruments, such as drill wire 424 (FIG. 4) and sight 426 (FIG. 4), located within the field of view of arthroscope 408 may also have reference points, although the additional instruments are not shown so as not to overly complicate the drawing. Moreover, in addition to or instead of tracking the position based on the field of view of arthroscope 408, the position of the distal end of one or more instruments may be tracked by other methods and systems. For example, in the case of a device that extends rigidly from the surgical site (e.g., sight 426 (FIG. 4)), the position may be tracked by an optical array coupled to the sight and viewed by camera 412 (FIG. 4), such as a stereo camera. The position of camera 412 in the three-dimensional coordinate space is then transformed to the three-dimensional coordinate space of the field of view of the exemplary arthroscope, thereby determining the position of the distal end within the surgical site.

[0111] The images captured by the arthroscope 408 and attached camera head 410 are subject to optical distortion in various forms. For example, the field of view between the distal end of the arthroscope 408 and the bone 500 in the surgical site is filled with liquids, such as bodily fluids and saline used to distend the joint. Many arthroscopes have one or more lenses at the distal end that widen the field of view, which, when widened, creates a "fish-eye" effect in the captured image. Additionally, the optical elements (e.g., rod lenses) in the arthroscope may have optical aberrations inherent to the manufacturing and / or assembly process. Still further, the camera head 410 may have various optical elements for focusing the received images onto the capture array, which may have aberrations inherent to the manufacturing and / or assembly process.

[0112] -Calibration of optical systems

[0113] In an exemplary system, prior to use in each surgical procedure, the endoscopic optical system is calibrated to account for various optical distortions. In particular, various embodiments include a system for calibrating an endoscopic optical system. Referring again to FIG. 4 , the exemplary system includes a surgical controller 418, an arthroscope 408, a camera head 410, and a calibration assembly 428. In particular, the calibration may include placing the arthroscope 408 in the calibration assembly 428. The calibration assembly 428 holds the arthroscope 408 in a fixed relationship to a calibration target on an inner surface of the calibration assembly 428. After the distal end of the arthroscope 408 is placed in the calibration assembly 428, the exemplary method includes capturing multiple images of the calibration target, each image captured at a unique rotational relationship between the camera head 410 and the arthroscope 408, the unique rotational relationship being relative to a central longitudinal axis of the arthroscope 408. Using the multiple images, the example surgical controller 418 creates a characterization function that characterizes the optical distortion between the calibration target and the capture array in the camera head 410. The characterization function may include calibration to determine the orientation of fiducial markers (e.g., bone fiducials 502, probe fiducials 506) that are visible within the surgical site by the arthroscope 408 and attached camera head 410. The specification now turns to a more detailed description of the example calibration assembly 428.

[0114] FIG. 6 illustrates an exploded perspective view of an exemplary calibration assembly. In particular, FIG. 6 illustrates an arthroscope 408 (without a camera head) and an exemplary calibration assembly 600. The calibration assembly 600 includes an upper housing 602 and a lower housing 604. From the bottom up of the calibration assembly 600, the lower housing 604 defines a calibration surface 606. Thus, when the lower housing 604 is coupled to the upper housing 602, the calibration surface 606 is disposed on an inner surface of an internal volume defined by the calibration assembly. A calibration target 608 is disposed on the calibration surface 606. In the example of FIG. 6, the calibration target 608 is shown as a checkerboard pattern, although any suitable pattern having distinctive features may be used as the calibration target 608.

[0115] When assembled, the lower housing 604 is coupled to the upper housing 602, such as by fasteners 610. In use for calibrating an arthroscope 408, the interior volume of the calibration assembly 600 is filled with water, such as saline. An exemplary O-ring 612 is disposed between the upper and lower housings 602, 604 to form a water-tight seal. However, in other cases, the O-ring may be omitted and the connection between the upper and lower housings 602, 604 may be sealed by other techniques (e.g., friction fit, friction welding). In still other cases, the upper and lower housings 602, 604 may be a unitary piece, and thus no fasteners or O-rings are used.

[0116] The exemplary upper housing 602 defines an enclosure or vessel 614 and a cylinder or tube 616. The vessel 614 together with the lower housing 604 defines an interior volume within which the calibration surface 606 and the calibration target 608 reside. The tube 616 has a proximal end 618 coupled to the vessel 614 and a distal end 620. As shown, the tube 616 protrudes from the vessel 614. The tube 616 defines a throughbore extending from the distal end 620 to the proximal end 618. The throughbore is fluidly coupled to the interior volume of the vessel 614, thereby defining an opening into the vessel 614. The throughbore further defines a central longitudinal axis 624. The distal end 620 of the tube defines a flange 622. The flange 622 defines features that perform several functions. First, the flange 622 defines a feature that holds the distal end of the arthroscope 408 at a predetermined distance from a calibration target 608 defined on an inner surface of the calibration assembly 600 when the arthroscope 408 is fitted into the tube 616 along a central longitudinal axis 624. Additionally, the exemplary flange 622 defines a feature that holds the arthroscope 408 in a fixed rotational orientation relative to the calibration assembly 600 and the calibration target 608. Various exemplary features for performing the functions of holding the arthroscope 408 at a predetermined distance from the calibration target 608 and for performing the functions of holding the arthroscope 408 in a fixed rotational orientation relative to the calibration assembly 600 are described in more detail below.

[0117] 6 , when the arthroscope 408 is fitted into the exemplary tube 616 for calibration, the volume between the distal end of the arthroscope 408 and the calibration target 608 within the interior volume of the container 614 is filled with water, such as saline, to better represent the use case. To that end, the exemplary container 614 further defines an opening or port 626 formed through a wall of the container 614 and fluidly coupled to the interior volume. Water may be injected through the port 626 for calibration purposes. In some cases, the port 626 is associated with a connector or nipple 628. The nipple 628 is coupled (e.g., press-fit, threaded connection) to the port 626, and may provide a connection (e.g., a luer connection) for supplying water to the interior volume as well as act as a check valve to reduce or prevent water from leaking out of the interior volume. Note that for purposes of calibrating the arthroscope 408 and camera head 410 (FIG. 4), enough water is provided to the interior volume to displace the air in the volume between the distal end of the arthroscope 408 and the calibration target 608. The addition of more water may cause the top level of the water to rise and enter the tube 616, although the entire calibration assembly 600 need not be "filled" with water.

[0118] FIG. 7 illustrates a top view of an exemplary calibration assembly 600. In particular, visible in FIG. 7 are the container 614, the tube 616, and the flange 622 on the distal end 620 of the tube 616. More clearly shown in FIG. 7 are exemplary features for assisting in retention of the arthroscope 408, as defined by the flange 622. In particular, the flange 622 defines a counterbored hole 700 having an exemplary circular cross-sectional shape. As such, the counterbored hole 700 defines an inner diameter that is larger than the inner diameter of the throughbore 702 in the tube 616. In the illustrated example, the central longitudinal axis 624 of the throughbore 702 is coaxial with the central axis of the counterbored hole 700. However, in other cases, the alignment of the central axes may vary depending on the location of each feature on the arthroscope and depending on the cross-sectional shape of the counterbored hole. The difference between the inner diameter dimensions of the counterbore 700 and the through hole 702 creates a shoulder region 704. When the arthroscope 408 (FIG. 6) is fitted into the tube 616, features on the arthroscope 408 abut against the shoulder region 704 to hold the distal end of the arthroscope 408 a predetermined distance from the calibration target 608 (FIG. 6). Thus, the shoulder region 704 may be considered an axial retention surface.

[0119] The exemplary counterbore 700 further defines a ridge 706 on an inner surface of the counterbore 700. The ridge 706 defines a top surface and two side surfaces, the ridge 706 projects inwardly into the counterbore 700, and the ridge 706 extends parallel to the central longitudinal axis 624. The exemplary ridge 706, particularly the two opposing side surfaces, defines a pair of rotational retention surfaces. In particular, the ridges 706 are designed and constructed to fit within corresponding notches in an arthroscope. When the arthroscope 408 (FIG. 6) is fitted into the tube 616, in the exemplary system, the notches in the arthroscope 408 slide over the ridges 706 and the side walls of the notches abut against the rotational retention surfaces. Thus, calibration assembly 600, and in particular the rotational holding surfaces defined by the ridges, holds the arthroscope in a fixed rotational orientation relative to calibration target 608 (FIG. 6).

[0120] The ridges 706 defining the exemplary rotational retention surfaces are designed and constructed to engage corresponding notches in the arthroscope 408 (FIG. 6). However, the rotational retention surfaces may take any suitable form based on the corresponding features of the arthroscope 408. For example, if the arthroscope 408 defines a ridge rather than a notch, the feature corresponding to the counterbore 700 may be a notch into the flange 622, with the sidewalls of the notch forming the rotational retention surface. Other rotational retention features and surfaces, including the functionality of both holding the distal end of the arthroscope at a predetermined distance from the calibration target 608 (FIG. 6) and holding the arthroscope in a fixed rotational orientation relative to the calibration target 608, are presented below.

[0121] FIG. 8 shows a cross-sectional view of an exemplary calibration assembly and an arthroscope fitted into the calibration assembly. In particular, FIG. 8 shows a simplified cross-section of an arthroscope 408, with the internal components of the arthroscope 408 omitted so as not to overly complicate the drawing. Additionally, FIG. 8 shows a cross-section of an exemplary calibration assembly 600, which includes an upper housing 602, a lower housing 604, an O-ring 612, and a single fastener 610 (based on a cut plane to create the cross-section). More clearly shown in FIG. 8 is an interior volume 800 defined by the receptacle 614 and the inner surface (e.g., calibration surface 606) of the lower housing 604. The calibration target 608 (FIG. 6) is not visible in the view of FIG. 8.

[0122] In the illustrated exemplary calibration assembly 600, the calibration surface 606 is a planar surface. Non-planar surfaces may also be used, and if so, the non-planar shape is taken into account during the calibration procedure. In the exemplary system, the central longitudinal axis 624 of the arthroscope 408 intersects the calibration surface 606, and thus the calibration target 608 (FIG. 6). In some cases, the central longitudinal axis 624 forms an acute angle with a vector perpendicular to the calibration surface, but the vector perpendicular to the calibration surface is not shown here to avoid further complicating the drawing. In some cases, the central longitudinal axis 624 intersects the calibration target 608 at the center of the calibration target 608. In other cases, as shown, the intersection of the central longitudinal axis 624 is within the calibration target 608, but is not located at the center of the calibration target. In any case, the arthroscope 408 and the camera head 410 (FIG. 4) can capture an image of the calibration target 608.

[0123] As discussed above, each arthroscope is designed and constructed with a particular viewing direction, which is quantified as an angle relative to the central longitudinal axis 624, the angle being measured beyond the distal end of the arthroscope 408. In FIG. 8, the viewing direction 802 is directed toward the calibration surface 606, and thus toward the calibration target 608 (FIG. 6). In the specific example of FIG. 8, the viewing direction 802 is perpendicular to the calibration surface 606, and thus to the calibration target 608. The relationship of the viewing direction 802 to the calibration surface 606 is set, at least in part, by a cut angle on the distal end of the arthroscope 408 that helps define the viewing direction 802. Because the cut angle on the distal end of the arthroscope 408 has a fixed rotational relationship to the remainder of the arthroscope 408, the orientation of the viewing direction 802 is controlled by the position of the rotational bearing surface defined by the flange 622. In the cross-sectional view of FIG. 8, the rotational retaining surfaces are not visible, but the ridges 706 are visible along with a portion of a corresponding notch 804 in the exemplary arthroscope 408 .

[0124] 8, also visible in the cross-sectional view is a shoulder region 704. When the arthroscope 408 is fitted into the calibration assembly 600 as shown, a corresponding feature of the arthroscope 408 contacts or abuts against the shoulder region 704. The abutment of the corresponding feature of the arthroscope 408 against the shoulder region 704 limits the distance that the arthroscope 408 may be fitted into the calibration assembly 600. Thus, the combination of the features of the arthroscope 408 and the shoulder region 704 holds the distal end of the arthroscope 408 a predetermined distance from the calibration surface 606 and thus the calibration target 608 (FIG. 6). Note that in the example described thus far, the optical post 806 of the arthroscope 408 does not contact the calibration assembly 600.

[0125] FIG. 9A illustrates a perspective view of another exemplary calibration assembly. In particular, the calibration assembly 600 of FIG. 9A includes a lower housing 900 and an upper housing 902. Although not visible in FIG. 9A, the lower housing 900 defines a calibration front having a calibration target. The upper housing 902 defines a container 904 and a tube 906. As above, the container 904 together with the lower housing 900 defines an interior volume. Also as above, the tube 906 defines a through hole fluidly coupled to the interior volume within the container 904. The exemplary calibration assembly 600 of FIG. 9A further defines a flange 908 on a distal end of the tube 906.

[0126] The arrangement of the tube 906 relative to the canister 904 and relative to the lower housing 900 differs from the calibration assembly 600 of FIG. 6. In particular, in the example of FIG. 9A, the central longitudinal axis of the through hole of the tube 906 is designed and constructed to intersect the calibration target (not visible) such that the central longitudinal axis of the tube 906 is perpendicular to the calibration surface and thus to the calibration target. Even more particularly, in the exemplary arrangement of FIG. 9A, the central longitudinal axis of the through hole of the tube 906 intersects the center of the calibration target, although intersections other than at the center are contemplated. Due to the arrangement of the tube 906 and canister 904, the exemplary calibration assembly 600 of FIG. 9A may be designed and constructed to calibrate an arthroscope having a viewing angle of zero degrees.

[0127] 9A further illustrates another mechanism for holding the distal end of the arthroscope at a predetermined distance from the calibration target and for holding the arthroscope in a fixed rotational orientation relative to the calibration target. In particular, the exemplary flange 908 defines features that provide both axial retention (e.g., axial retention along the central longitudinal axis of the arthroscope and / or along the through bore of the tube 906) and a rotational retention surface. In even more detail, the exemplary flange 908 defines a notch 910. The notch 910 defines a channel having a closed bottom wall, an open top wall, and two side walls. The channel formed by the notch 910 traverses the flange 908, and in the illustrated example, the channel line formed in the direction of the notch intersects with the central longitudinal axis of the through bore of the tube 906. In some cases (not specifically illustrated), the channel line is perpendicular to the central longitudinal axis of the through bore of the tube 906.

[0128] In use, arthroscope 408 (FIG. 4) is fitted into tube 906 and optical post 420 (FIG. 4) is placed in notch 910. The side walls of notch 910 hold the arthroscope in a fixed rotational orientation relative to calibration assembly 600. Additionally, the side walls (and bottom wall if the notch is rectangular) hold the distal end of the arthroscope at a predetermined distance from the calibration target. Thus, notch 910 can be considered both an axial and a rotational holding surface.

[0129] Also visible in Figure 9A is a sight gauge 912. To the extent that the material forming the upper housing 902 is opaque except for the sight gauge, the exemplary sight gauge 912 is constructed from a clear or transparent material to allow a user to view the height of the air-water interface within the calibration assembly 600, thereby allowing the user to determine the depth of the water within the calibration assembly 600. The surgeon can use the sight gauge during the set-up procedure to ensure that sufficient water is provided to the reservoir 904, such as to ensure that the water level is above the distal end of the arthroscope.

[0130] Thus, Figure 9A illustrates several alternative configurations, including alternative configurations of tube 906 relative to canister 904 and lower housing 900, alternative configurations of rotational retention features for holding the arthroscope in a fixed rotational orientation, alternative configurations of axial retention features for holding the distal end of the arthroscope at a predetermined distance from the calibration target, and an exemplary sight gauge. However, it should be noted that these features are not limited to the calibration assembly 600 of Figure 9A. With this understanding of the calibration assembly, one skilled in the art will recognize that the various features may be mixed and matched as desired. For example, notch 910, which forms a dual role of axial and rotational retention features, may be used with the tube and canister configurations of Figures 6, 7, and 8. Conversely, flange 622 of the calibration assembly in Figures 6, 7, and 8 may be used as the flange of the calibration assembly in Figure 9A. Similarly, the sight gauge can be implemented in the calibration assembly 600 in Figures 6, 7 and 8, and the filling mechanism can be implemented in the calibration assembly in Figure 9A.

[0131] FIG. 9B illustrates a perspective view of another exemplary calibration assembly. In particular, the calibration assembly 600 of FIG. 9B includes an outer housing 920 and a lower housing, which is not visible in FIG. 9B. As will be further described below, the lower housing defines or supports a calibration surface having a calibration target. The outer housing 920 defines a container 922 and a tube 924. As above, the container 922 together with the lower housing defines an interior volume. As also above, the tube 924 defines a through hole that is fluidly coupled to the interior volume within the container 922. The exemplary calibration assembly 600 of FIG. 9B further defines a snap or clip 926 for a light post disposed at a distal end of the tube 924.

[0132] In the example of Figure 9B, the central longitudinal axis of the through hole of the tube 924 is designed and constructed to intersect with the calibration target (not visible) such that the central longitudinal axis of the tube 924 forms an acute angle with the calibration surface and therefore with the calibration target. Due to the arrangement of the tube 924 and the container 922, the exemplary calibration assembly 600 of Figure 9B may be designed and constructed for calibrating arthroscopes having a non-zero degree viewing angle. Moreover, the calibration assembly 600 of Figure 9B may be more stable, for example, when placed on a table for use or for later reuse.

[0133] 9B further illustrates another mechanism for holding the distal end of the arthroscope at a predetermined distance from the calibration target and for holding the arthroscope in a fixed rotational orientation relative to the calibration target. In particular, the exemplary clip 926 defines features that provide both axial retention (e.g., along the central longitudinal axis of the arthroscope and / or along the throughbore of the tube 924) and a rotational retention surface. In even more detail, the exemplary clip 926 defines a first wall or arm 930 and a second wall or arm 932, although the arms 930, 932 may be integrally formed components. The arms 930, 932 define an inner surface 934 that is complementary to the optical post 420 (FIG. 4). In particular, the inner surface 934 defines a semicircular surface having a central axis 936 that intersects with the central longitudinal axis 624 of the tube 924. In the exemplary case, the central axis 936 is perpendicular to the central longitudinal axis 624. The exemplary arm 930 defines a slide member 938 having an outer surface (not visible in FIG. 9B) that guides the optical post 420 into the volume defined by the inner surface 934. Additionally, the arm 932 defines a slide member / release member 940 having an outer surface 942 that guides the optical post 420 into the volume defined by the inner surface 934. When the arthroscope 408 (FIG. 4) is installed into the calibration assembly 600 of FIG. 9B, the optical post 420 abuts against the outer surface of the slide member 938 and against the outer surface 942 of the slide member / release member 940 as the elongated shaft of the arthroscope 408 is fitted into the tube 924. Further application of pressure can cause the arms 930, 932 to flex slightly open, allowing the optical post 420 to snap or clip into the clip 926. The clip 926 thus holds the arthroscope 408 in a fixed rotational orientation relative to the calibration assembly 600, and further, the clip 926 holds the distal end of the arthroscope 408 at a predetermined distance from the calibration target. The clip 926 can thus be considered an axial and rotational holding surface.

[0134] FIG. 9C illustrates a cross-sectional view of the calibration assembly and arthroscope. In particular, FIG. 9C illustrates the arthroscope 408 in simplified form. Additionally, FIG. 9C illustrates a cross-sectional view of an exemplary calibration assembly 600, which includes an outer housing 920, a lower housing 944 defining a calibration surface 946 and a calibration target 948, and an optional reflective surface 950. The exemplary outer housing 920 defines a container 922 and a tube 924, as well as a stand 952 that may allow the calibration assembly 600 of FIG. 9C to rest on a horizontal surface both during and between uses. In this example, the lower housing 944 is coupled to the outer housing 920 and sealed in any suitable manner, such as by friction welding the lower housing 944 to the outer housing 920 at an interface point 954. Shown more clearly in FIG. 9C is the interior volume 956 defined by the reservoir 922 and the interior surface (e.g., calibration surface 946) of the outer housing 920. The calibration target pattern is not visible in the view of FIG. 9C. In one example, the calibration target 948 is a polymer specifically selected to allow for laser marking to create the calibration pattern, after which the calibration target 948 is placed on the calibration surface 946 and held in place by other structural components. In other cases, the calibration target may be a pre-printed flexible material that is bonded (e.g., glued) to the calibration surface 946 before the lower housing is assembled to the remaining components.

[0135] In the exemplary calibration assembly 600 of FIG. 9C, the calibration surface 946 is a planar surface. Non-planar surfaces can also be used, and if used, the non-planar shape is taken into account during the calibration procedure. In the exemplary system, the central longitudinal axis 624 of the arthroscope 408 intersects the calibration surface 946, and thus the calibration target. In some cases, the central longitudinal axis 624 forms an acute angle with a vector perpendicular to the calibration surface, but the vector perpendicular to the calibration surface is not shown here to avoid further complicating the drawing. In some cases, the central longitudinal axis 624 intersects the calibration target 948 at the center of the calibration target 948. In other cases, as shown, the intersection of the central longitudinal axis 624 is within the calibration target 948, but is not located at the center of the calibration target. In any case, the arthroscope 408 and the camera head 410 (FIG. 4) can capture an image of the calibration target 948.

[0136] As discussed above, each arthroscope is designed and constructed with a particular viewing direction, which is quantified as an angle relative to the central longitudinal axis 624, the angle being measured beyond the distal end of the arthroscope 408. In FIG. 9C, the viewing direction (not specifically shown) is directed toward the calibration surface 948, and thus the calibration target 948. In the specific example of FIG. 9C, the viewing direction may be perpendicular to the calibration surface 946, and thus to the calibration target 948. The relationship of the viewing direction to the calibration surface 946 is set, at least in part, by a cut angle on the distal end of the arthroscope 408 that helps define the viewing direction. Because the cut angle on the distal end of the arthroscope 408 has a fixed rotational relationship to the remainder of the arthroscope 408 (e.g., the optical post 420), the orientation of the viewing direction is controlled by the position of the rotational support surface defined by the clip 926. In the cross-sectional view of FIG. 9C, the rotational support surface is not visible.

[0137] 9C , when the arthroscope 408 is fitted into the calibration assembly 600 of FIG. 9C as shown, the optical post 420 contacts or abuts against an inner surface of the clip 926. The abutment of the optical post 420 against the clip 926 limits the distance the arthroscope 408 is fitted into the calibration assembly 600. Additionally, the rotational retention feature that the clip 926 implements for the optical post 420 keeps the line of sight oriented relative to the calibration target 928. The exemplary calibration assembly 600 further defines a neck or flange 958 at the transition from the tube 924 to the interior volume 956. The flange 958 defines a diameter that forms a snug fit with the outer surface of the arthroscope 408. That is, while most of the inner surface of the tube 924 has an inner diameter larger than the outer diameter of the arthroscope 408 (e.g., 1 mm to 5 mm), the inner diameter at the flange 958 is small enough that the arthroscope 408 can fit through the flange and still hold the distal end of the arthroscope 408 in a fixed position relative to the calibration target 948. In one example, the inner diameter of the flange 958 may be 0.1 mm to 0.5 mm larger than the outer diameter of the portion of the arthroscope that fits through the flange. In order to have a vent path for fluid within the arthroscope-displaced interior volume 956, the exemplary calibration assembly of FIG. 9C also includes a vent opening 960.

[0138] Thus, Figures 9A, 9B, and 9C show several alternative configurations, including alternative configurations for the tube relative to the container and lower housing, and alternative configurations for axial and rotational retention features for holding the arthroscope in a fixed rotational orientation. However, it should be noted that these features are not limited to the calibration assembly 600 in Figures 9A, 9B, and 9C. With this understanding of the calibration assemblies, one skilled in the art will recognize that the various features may be mixed and matched as desired. For example, clip 926 may be used with the calibration assemblies in Figures 6, 7, 8, and 9A. Conversely, flange 622 of the calibration assemblies in Figures 6, 7, and 8 may be used as the flange of the calibration assemblies in Figures 9B and 9C. Similarly, the sight gauge in FIG. 9A can be implemented in the calibration assembly 600 in FIG. 6, FIG. 7, and FIG. 8 or in the calibration assembly in FIG. 9B and FIG. 9C, and the filling mechanism in FIG. 6, FIG. 7, and FIG. 8 can be implemented in the calibration assembly in FIG. 9A, FIG. 9B, and FIG. 9C.

[0139] The calibration targets in Figures 6, 7, 8, 9A, 9B, and 9C are all shown as planar. However, in other cases, the calibration target need not be planar, so long as the shape of the calibration target is known in advance. Figure 9D shows a perspective cutaway view of a portion of an exemplary calibration assembly 600. In particular, visible in Figure 9D is a lower housing 944 and a container 922 cut away to show the portion of an exemplary calibration target 948. However, in this case, the calibration target 948 defines a first portion 962 that defines a first plane and a second portion 964 that defines a second plane, the first and second planes forming an acute angle on the surface of the calibration target (e.g., V-shaped). Although the actual calibration pattern is not shown in Figure 9D, the actual calibration pattern may take any suitable shape or any suitable series of shapes. The view of FIG. 9D more clearly shows that the outer housing 920 can define a shoulder region 966 that holds the exemplary calibration target 948 in place. Additionally, FIG. 9D illustrates an example in which the reflective surface (e.g., reflective surface 950 of FIG. 9C) is omitted from the interior surface of the container 922. Although the calibration target 948 of FIG. 9D shows two planes that define an acute angle between them in the plane of the calibration target, in other cases the calibration target can have a first portion that defines a first plane and a second portion that defines a second plane, where the first and second planes form an obtuse angle in the plane of the calibration target (e.g., an inverted V-shape). In still further cases, the calibration target can include three or more planes in any suitable arrangement.

[0140] Before proceeding to a description of the use of the calibration assembly, a few points are addressed in order. Although Figures 6, 7, 8, 9A, 9B, 9C, and 9D show some examples, any container (e.g., a box, pouch, or bag) that can hold water and contain a calibration target may be used as a calibration assembly. The specification now moves to a description of an exemplary use of the calibration assembly as part of a calibration procedure.

[0141] Returning to FIG. 4 , in operation as part of a calibration procedure, a camera head 410 is attached to the arthroscope 408. The camera head 410 is communicatively coupled to a surgical controller 418, with an optical post of the arthroscope 408 optically coupled to an optical output port of the surgical controller 418. The arthroscope 408 is fitted into a calibration assembly 428. Water is placed into the interior volume of the calibration assembly 428 to displace the air between the calibration target and the distal end of the arthroscope 408. The surgeon may then initiate the calibration procedure, such as by interacting with the surgical controller 418 (e.g., via a tablet-type portable electronic device communicatively coupled to the surgical controller 418). After the calibration procedure is initiated, an exemplary calibration may include capturing multiple images of the calibration target, where each image is captured at a unique rotational relationship between the camera head 410 and the arthroscope 408, with the unique rotational relationship relative to a central longitudinal axis of the arthroscope 408. More specifically, capturing the multiple images may include capturing a first image of the calibration target by the surgical controller 418 via the capture array of the camera head 410 at a first rotational orientation between the arthroscope 408 and the camera head 410, then capturing a second image of the calibration target at a second rotational orientation between the arthroscope 408 and the camera head 410, such as by rotationally driving the camera head 410 relative to the arthroscope 408 while the arthroscope 408 remains at a fixed rotational orientation with respect to the calibration assembly, and then capturing a third image of the calibration target at a third rotational orientation between the arthroscope 408 and the camera head 410, such as by again rotationally driving the camera head 410 relative to the arthroscope 408. In one example, when three images are used, the camera head 410 may be rotationally driven through 120 degrees between each image capture. If more images are to be captured, the amount of rotational drive of camera head 410 between each image capture will be correspondingly reduced.

[0142] Based on the captured images, the surgical controller 418 may calculate a characterization function that characterizes the optical distortion between the calibration target and the capture array of the camera head 410. The distortions include not only distortions introduced in the optics of the camera head 410 (e.g., the focusing assembly), but also any optical distortions associated with the optical path through the arthroscope 408, and even any optical distortions introduced by water (e.g., again mimicking the conditions within the surgical site). Still further, the surgical controller 418 may create a characterization function using the captured images as a calibration for determining the orientation of the fiducial markers via the arthroscope 408, in this case with a single optical path through the arthroscope. The present specification now turns to a description of the registration of the bone models and the human-in-the-arthroscope verification of the registration.

[0143] - Model registration and human-in-the-loop registration verification

[0144] The next exemplary step in the intraoperative procedure is the registration of the bone model(s). That is, during the planning stage, imaging (e.g., MRI) of the knee is performed, including relevant anatomical structures such as the lower portion of the femur, the upper portion of the tibia, and the articular cartilage. The images can be segmented so that a volumetric or three-dimensional model of the anatomical structures is created. More specifically with respect to the example of ACL repair, and in particular with respect to the selection of a tunnel path through the femur, at the time of planning, a three-dimensional bone model of the lower portion of the femur is created.

[0145] During intraoperative repair, the three-dimensional bone model is provided to the surgery controller 418. Again using the example of ACL repair, specifically using computer-assisted navigation for a tunnel path through the femur, a three-dimensional bone model of the lower portion of the femur is provided to the surgery controller 418. Thus, while the surgery controller 418 receives the three-dimensional bone model, and assuming that an arthroscope 408 has been inserted into the knee via a port through the patient's skin, the surgery controller 418 also receives a video image of the femur. To associate the three-dimensional bone model with the images received via the arthroscope 408 and camera head 410, the surgery controller 418 registers the three-dimensional bone model to the images of the femur received via the arthroscope 408 and camera head 410.

[0146] According to an exemplary method, a fiducial marker or bone reference point (e.g., bone reference point 502 in FIG. 5) is attached to the femur. The placement of the bone reference point is such that it is within the field of view of the arthroscope 408, but is located away from the anticipated tunnel entry / exit through the lateral condyle. More specifically, in the exemplary case, the bone reference point is placed in the intercondylar recess above or superior to the anticipated location of the tunnel through the lateral condyle.

[0147] FIG. 10 is an exemplary video display showing a portion of a femur and a bone reference point. The display may be shown on a display device 414 (FIG. 4), such as in association with the device cart 402 (FIG. 4) or in any other suitable location. In particular, visible in FIG. 10 is a femoral or intercondylar recess 1000, a portion of a lateral condyle 1002, a portion of a medial condyle 1004, and an exemplary bone reference point 1006. The bone reference point 1006 is taken as a reference point that includes a cuboid member. Of the six outer surfaces of the cuboid member, the bottom surface is associated with an attachment feature (e.g., a screw). The bottom surface is adjacent or abuts against the bone when the bone reference point 1006 is fixed in place, thereby making it invisible in the field of view of the arthroscope 408 (FIG. 4). The outer surface opposite the bottom surface includes alignment features that are used to hold the bone reference point 1006 prior to alignment and to attach the bone reference point 1006 to the underlying bone. With respect to the remaining four outer surfaces of the cubical member (only two of the remaining surfaces are visible), each of these four outer surfaces has a machine-readable pattern on the top surface, and in some cases each machine-readable pattern is unique. After alignment, the bone reference point 1006 represents a fixed location on the outer surface of the bone within the field of view of the arthroscope 408, even if the position of the arthroscope 408 is moved and changed relative to the bone reference point 1006. Initially, the location of the bone reference point 1006 relative to the three-dimensional bone model is unknown to the surgical controller 418, and therefore registration of the three-dimensional bone model is required.

[0148] For purposes of relating or registering the bone visible in the video image to the three-dimensional bone model, multiple locations on the outer surface of the bone are provided to and received by the surgical controller 418 (FIG. 4). For example, the surgeon may use a touch probe 504 (FIG. 5) to touch the multiple locations. As described above, the touch probe 504 includes a probe reference point 506 (FIG. 5) that is visible in the video image captured by the arthroscope 408 (FIG. 4) and camera head 410 (FIG. 4). Because the physical relationship between the distal end of the touch probe 504 and the probe reference point 506 is known by the surgical controller 418, as the surgeon touches each of the multiple locations on the outer surface of the bone, the surgical controller 418 obtains additional "known" locations on the outer surface of the bone relative to the bone reference point 1006. Given that the touch probe 504 is a relatively rigid and inflexible instrument, in another example, tracking of the touch probe 504 may be by optical tracking (e.g., tracking by camera 412 (FIG. 4)) of an optically reflective array located outside the surgical site and attached to a portion of the touch probe 504 inside the surgical site.

[0149] In some cases, especially when a portion of the bone's exterior surface is exposed to view, receiving multiple positions on the bone's exterior surface may involve the surgeon "painting" the bone's exterior surface. "Painting" is a term of art that does not involve the application of color or pigment, but instead refers to the movement of the touch probe 504 when the distal end of the touch probe 504 touches against the bone.

[0150] FIG. 11 is an exemplary video display showing a portion of a femur and bone fiducials during a registration procedure. The display may be shown on a display device 414 (FIG. 4), such as in association with the device cart 402 (FIG. 4) or in any other suitable location. In particular, visible in the main portion of the display of FIG. 11 are an intercondylar recess 1000, a portion of a lateral condyle 1002, a portion of a medial condyle 1004, and exemplary bone fiducials 1006. Shown in the upper right corner of the exemplary display is a representation of the bone, which may be a rendering 1100 of the bone created from a three-dimensional bone model. Shown on the rendering 1100 is a recommended region 1102, which is a portion of the bone surface to be painted as part of the registration process. Shown in the lower right corner of the exemplary display is a representation of the bone, which may also be a rendering 1104 of the bone created from a three-dimensional bone model. Shown on the rendering 1104 are a number of positions 1106 of the bone model that are associated with positions on the outer surface of the bone as part of the registration process. Also shown in the lower right corner of the exemplary display is a progress indicator 1108 that indicates progress in providing and receiving positions on the bone. The exemplary progress indicator 1108 is a horizontal bar having a length proportional to the number of positions received. In the exemplary case, the progress indicator 1108 grows or extends in length from a fixed position on the left to the right, although any suitable graphical or numerical display of progress may be used (e.g., 0% to 100%).

[0151] With reference to both the main display and the rendering at the bottom right, as the surgeon touches and / or paints on the outer surface of the bone in the images captured by the arthroscope 408 (FIG. 4) and camera head 410 (FIG. 4), the surgical controller 418 (FIG. 4) receives the locations on the bone and displays each location as a dot or location 1106 in the main display and in the rendering shown in the bottom right corner. More specifically, the example surgical controller 418 overlays a display of the received locations 1106 on the display of the images captured by the arthroscope 408 and camera head 410, and in the example case shown, also on the rendering 1104 of the bone model. Additionally, as the number of received locations 1106 increases, the surgical controller 418 also updates the progress indicator 1108.

[0152] Still referring to FIG. 11, despite the diligence of the surgeon, not all of the positions received by the surgical controller 418 (FIG. 4) based on the surgeon's movement of the touch probe 504 (FIG. 5) are valid positions on the bone surface. In the example of FIG. 11, when the surgeon moved the touch probe 504 from the inner surface of the lateral condyle 1002 to the inner surface of the medial condyle 1004, the surgical controller 418 received multiple positions 1110 that may represent positions in the three-dimensional coordinate space of the arthroscopic view where the distal end of the touch probe 504 was not in contact with the bone. Nevertheless, as shown in the lower right corner, these positions 1110 may be erroneously attributed to positions on the outer surface of the bone. Thus, relating a three-dimensional bone model to a bone visible in the three-dimensional coordinate space of the arthroscopic view is not necessarily a perfect determination procedure. Some received positions may need to be ignored in the correlation, some received positions that should be used may be ignored, and other received positions that should be ignored may be used nonetheless, which may result in inaccurate correlation between the three-dimensional bone model and the bones visible in the image anchored by the bone fiducials 1006. The present specification now turns to a description of human-in-the-loop registration verification.

[0153] 12 illustrates an exemplary video display during a registration procedure, showing a portion of a femur, bone fiducials, and an overlaid representation of a three-dimensional bone model. The display may be shown on a display device 414 (FIG. 4), for example, in association with the device cart 402 (FIG. 4) or in any other suitable location. To address potentially invalid registration between the three-dimensional bone model and the bone visible in the image, in an exemplary method and system, an initial registration between the bone visible in the video image and the three-dimensional bone model is verified using a human-in-the-loop process. More specifically, in an exemplary case, after receiving a plurality of locations of the outer surface of the bone visible in the image and performing an initial registration to the three-dimensional bone model, the surgical controller 418 displays a representation of the three-dimensional bone model superimposed onto the portion of the bone visible in the video image, either on the display device 414 or in another suitable location. That is, the exemplary surgical controller 418 overlays a representation of the three-dimensional bone model (e.g., via a polygon mesh, or mesh model) onto the display of images captured by the arthroscope 408 and camera head 410, where the rotational and translational alignment of the three-dimensional bone model correlates to the bones visible in the video image when anchored by the bone reference points 1006.

[0154] The surgeon then determines whether the registration process is correct by visually inspecting the superimposed representation of the three-dimensional bone model against the underlying bones visible in the video image. More specifically, the surgeon determines whether the three-dimensional bone model sufficiently matches the bones visible in the video image by visually comparing the superimposed representation of the three-dimensional bone model against the bone portions visible in the video image. Like the registration process itself, the human-in-the-loop verification of registration is a non-deterministic operation. Although slight differences between the three-dimensional bone model and the bones visible in the video image may be tolerated, the registration process may nevertheless be considered correct in the sense that the three-dimensional bone model may be reliably used to help guide the placement of a tunnel path (e.g., here, the femoral tunnel path) or in the sense that the three-dimensional bone model may be reliably used to assist the surgeon in intraoperatively modifying the planned tunnel path. In such a case, the surgeon may provide, and the surgical controller 418 may receive, indications indicating that the three-dimensional bone model has been properly registered to the bones visible in the video image.

[0155] On the other hand, if the registration of the three-dimensional bone model indicates a misalignment with respect to the bone visible in the video image, the surgeon may choose to restart the registration process, such as by providing multiple positions for the bone's outer surface to the surgical controller 418 and having the surgical controller 418 receive them again. In that case, the surgical controller 418 may perform the registration procedure anew. In other cases, the surgeon may choose to provide additional positions on the bone's outer surface, in which case the surgical controller 418 may perform the registration procedure using both the original positions received and the additional positions received after the registration process. This process is repeated until the surgeon approves the registration. The present specification now turns to a description of intraoperative tunnel path planning.

[0156] -Tunnel route planning

[0157] Using the three-dimensional bone model, a surgical plan is created that includes a planned tunnel path through the bone, including the location of the opening into the bone to define both ends of the tunnel. However, in some cases, the surgeon may choose not to use the planned tunnel path, and thus may choose not to use the planned entry location, the planned exit location, or both. Such a selection may be based on any of a number of reasons. For example, during surgery, the surgeon may not be able to access the entry location for the planned tunnel path, and therefore may need to move the entry location to ensure sufficient access. As another example, during an intraoperative procedure, the surgeon may determine that the planned tunnel entry location is misaligned with respect to the attachment location of the natural ACL to the femur. Still further, during an intraoperative procedure, the surgeon may determine that the tunnel entry location is too close to the posterior wall of the femur, increasing the likelihood of bone chipping, sometimes referred to as a "posterior wall blowout." Regardless of the reason for choosing to change the tunnel path, in an exemplary system, the surgical controller 418 allows the surgeon to intraoperatively select a modified tunnel entrance, a modified tunnel exit (if necessary), and thus a modified tunnel path through the bone.

[0158] FIG. 13 is an exemplary video display showing intraoperative changes to a tunnel path, according to at least some embodiments. The display may be shown on a display device 414 (FIG. 4), such as in association with the device cart 402 (FIG. 4) or in any other suitable location. In particular, FIG. 13 shows a portion of a bone in a video image captured by an arthroscope 408 (FIG. 4) superimposed against a mesh model of a three-dimensional bone model and against a selected planned tunnel path 1300 including a planned tunnel entrance 1302 and a planned tunnel exit 1304. However, for various reasons, the surgeon may choose to change the tunnel entrance location and / or the tunnel exit location, and thus the planned tunnel path. Thus, the surgeon may provide, and the surgical controller 418 (FIG. 4) may receive, the modified tunnel entrance location, or simply the modified tunnel entrance 1306. Providing the modified tunnel entrance 1306 may include the surgeon using a tracking tool, such as a touch probe 504 (FIG. 5) or a sight 426 (FIG. 4), to touch a proposed location on the bone shown in the video image. In some cases, the surgeon may select the modified tunnel entrance 1306 based solely on what the surgeon sees with respect to the bone shown in the video image. As a more specific example, the surgeon may select and provide the modified tunnel entrance 1306 based on a location that the sight 426 can reach. In still other cases, the surgical controller 418 may generate a simulated fluoroscopic image from the three-dimensional bone model and may project a Bernard and Hertel quadrant or grid onto the simulated fluoroscopic image. The surgeon may then select the modified tunnel entrance 1306 using the additional guidance provided by the Bernard and Hertel quadrant.

[0159] FIG. 14 is an exemplary video display showing planned changes to the tunnel path. The display may be shown on a display device 414 (FIG. 4), for example, in association with the device cart 402 (FIG. 4) or in any other suitable location. In particular, FIG. 14 shows, in the left half, a portion of the bone in a video image captured by an arthroscope 408 (FIG. 4), superimposed against a mesh model of the three-dimensional bone model and against a representation of the previously selected planned tunnel path 1300. On the right side, FIG. 14 shows an exemplary virtual perspective image 1400 with a Bernard-Härtel quadrant 1402 superimposed thereon, the virtual perspective image being created by rendering the three-dimensional bone model in a partially transparent form. Alternatively, the virtual perspective image 1400 may be created as a cross-sectional rendering of the three-dimensional bone model viewed laterally from a central position, with the cutting plane for the cross-section passing through the center of the intercondylar recess.

[0160] In the exemplary system and method illustrated in FIG. 14, the selection of the corrected tunnel entrance 1306 may be guided and / or informed by the virtual fluoroscopic image 1400 and by the Bernard and Hertel quadrant 1402. In particular, a proposed location for the corrected tunnel entrance 1306 may be displayed in the left half of the display as an overlay on the bone in the video image and simultaneously displayed on the right half in the Bernard and Hertel quadrant 1402. For example, the surgeon may use the touch probe 504 ( FIG. 5 ) or the sight 426 ( FIG. 4 ) to provide the proposed corrected tunnel entrance 1306. Continuing with the explanation assuming that the touch probe 504 is being used, as the surgeon moves the touch probe 504 within the field of view of the arthroscope 408 ( FIG. 4 ), not only can the location of the corrected tunnel entrance 1306 be seen in relation to the bone in the video image, but the location of the corrected tunnel entrance 1306 is displayed on the Bernard and Hertel quadrant 1402. Thus, the surgeon may select a modified tunnel entrance 1306 based on the tissues and structures visible in the video image, as well as additional information provided by the position relative to the Bernard & Hertel quadrant 1402. The final modified entrance position 1306 may be communicated to the surgical controller 418 in any suitable form, such as dwelling the touch probe 504 with the distal end of the touch probe abutting the desired position for a predetermined period of time, or the final selection may be communicated in other forms (e.g., interaction with a keyboard, handheld tablet device, or voice command).

[0161] Returning to FIG. 13 , in many cases, creating a modified tunnel path involves selecting a modified tunnel entrance 1306, with other features of the tunnel remaining unchanged, such as the tunnel exit location. In some cases, however, as shown in FIG. 13 , the surgeon may change both the tunnel entrance location and the tunnel exit location. Thus, in a still further example, the surgeon may provide the modified tunnel exit location, or simply the modified tunnel exit 1308, to the surgical controller 418 ( FIG. 4 ), which may then receive it. Providing the modified tunnel exit 1308 may include the surgeon using a tracking tool, such as a touch probe 504 ( FIG. 5 ), to touch a proposed location on the bone shown in the video image. In various examples, using the modified tunnel entrance 1306, and optionally using the modified tunnel exit 1308, the surgical controller calculates a modified tunnel path 1310 through the patient's bone, and displays the modified tunnel path 1310 on a display device, as shown in FIG. 13 .

[0162] Additionally, in an exemplary case, the surgery controller 418 (FIG. 4) provides the surgeon with information regarding the relationship between the planned tunnel path 1300 and the modified tunnel path 1310. In particular, the exemplary video display of FIG. 13 further includes various parameters in the lower right corner that aid the surgeon in assessing the feasibility of the newly created modified tunnel path 130. For example, the surgery controller 418 may calculate and provide a value indicative of the overlap between the planned tunnel path 1300 and the modified tunnel path 1310, and the surgery controller 418 may display a visual representation of the value indicative of the overlap. In the example of FIG. 13, the visual representation of the value indicative of the overlap is a numerical value expressed as a percentage (e.g., here, 3%). The overlap as a percentage may conceptually range from 0% to slightly less than 100%, since a 100% overlap would result in the modified tunnel path being the same as the planned tunnel path. In some cases, the surgery controller 418 calculates the value indicative of the overlap as a percentage, taking into account the expected tunnel diameter. If any portion of the planned tunnel path 1300 intersects with any portion of the modified tunnel path 1310, the intersection is considered an overlap. In other cases, the overlap may be calculated with respect to the planned pilot tunnel and the modified pilot tunnel. Although the example planned tunnel path 1300 and modified tunnel path 1310 in Figure 13 are selected to be sufficiently separated to be visible and distinguishable in the diagram of Figure 13, in reality, the position change between the planned tunnel path 1300 and the modified tunnel path 1310 may be small and therefore may have a significant overlap, taking into account the expected diameter of the tunnel paths.

[0163] Still considering the information provided to the surgeon regarding the planned tunnel path 1300 and the corrected tunnel path 1310, in a still further example, the surgery controller 418 (FIG. 4) may calculate and provide an entrance position offset between the planned tunnel entrance 1302 and the corrected tunnel entrance 1306, and the surgery controller 418 may display a visual representation of the offset. In the example of FIG. 13, the visual representation of the offset is a numerical value shown in units of measurement (e.g., millimeters). The surgery controller 418 may also calculate and provide an exit position offset between the planned tunnel exit 1304 and the corrected tunnel exit 1308, and the surgery controller 418 may display a visual representation of the offset in units of measurement. In the example of FIG. 13, the entrance offset is shown as 9 mm and the exit offset is shown as 17 mm. Again, although the example planned tunnel path 1300 and corrected tunnel path 1310 in Figure 13 are selected to be sufficiently separated to be visible and distinguishable in the diagram of Figure 13, in reality they may have a smaller offset since the position change between the planned tunnel path 1300 and the corrected tunnel path 1310 may be slight. In many cases the corrected tunnel exit will be the same as the planned tunnel exit, in which case the exit offset will be zero.

[0164] Still considering the information provided to the surgeon regarding the planned tunnel path 1300 and the corrected tunnel path 1310, in a still further example, the surgical controller 418 (FIG. 4) may calculate and provide a value indicative of a posterior wall breach. The value indicative of a posterior wall breach in FIG. 13 has two exemplary aspects: a quantized breach probability (e.g., low, medium, and high) and a numerical value indicative of the posterior wall breach probability. In an exemplary case, the numerical value indicative of the posterior wall breach probability may be the distance between the expected outer diameter of the corrected tunnel path 1310 as calculated by the surgical controller 418 and the outer surface of the bone in the three-dimensional bone model. More particularly, in an exemplary case, the numerical value indicative of the posterior wall breach is the calculated shortest distance between the expected inner diameter of the corrected tunnel path and the outer surface of the three-dimensional bone model. In some cases, the quantized burst likelihood is associated with a numerical value indicative of a posterior wall burst likelihood, for example, a "low" burst likelihood may be indicated when the shortest distance between the expected inner diameter of the corrected tunnel path and the outer surface of the three-dimensional bone model is 8 mm or greater, a "medium" burst likelihood may be indicated when the shortest distance between the expected inner diameter of the corrected tunnel path and the outer surface of the three-dimensional bone model is between 4 mm and 8 mm, and a "high" burst likelihood may be indicated when the shortest distance between the expected inner diameter of the corrected tunnel path and the outer surface of the three-dimensional bone model is 4 mm or less. Often, tunnel paths through bone will have a counterbored hole associated with the intercondylar recess side of the tunnel, although the counterbored aspect is not shown in FIG. 13. The counterbored portion of the tunnel may have a larger inner diameter compared to the tunnel near the exit location, and in an exemplary case, the surgical controller 418 takes into account the expected inner diameter of the counterbored hole when calculating the value indicative of a posterior wall burst likelihood.

[0165] Regardless of the exact information provided to the surgeon regarding the relationship between the planned tunnel path 1300 and the modified tunnel path 1310, the modified tunnel path 1310 may be discarded and the selection of a modified tunnel entrance may begin anew if the surgeon so chooses based on the information provided. Although the description herein continues assuming that the surgeon selects and uses the modified tunnel path 1310, it is not necessary that the modified tunnel path 1310 be selected in all cases, and thus the continued description based on the modified tunnel path 1310 should not be construed as a limitation. The description herein now turns to a description of the formation of tunnels through various examples.

[0166] -Tunnel formation

[0167] Once the modified tunnel path 1310 is selected, the next step in the exemplary method is to actually form the tunnel. In most cases, forming the tunnel is a multi-step process that involves drilling an initial or pilot tunnel using a drill wire (e.g., drill wire 424 (FIG. 4)) and then using the drill wire as a guide wire for one or more reamers to increase the diameter of the pilot tunnel to form the full diameter actual tunnel through the bone. In some cases, the actual tunnel will have a counterbored hole associated with the intercondylar recess to accommodate the width of the autograft, in which case an additional reamer may be used to form the counterbored hole.

[0168] FIG. 15 is an exemplary video display showing computer guidance for pilot tunnel placement. The display may be shown on a display device 414 (FIG. 4), such as in association with the device cart 402 (FIG. 4) or in any other suitable location. In particular, FIG. 15 shows in the main portion of the display a portion of a bone in a video image captured by an arthroscope 408 (FIG. 4) superimposed against a mesh model of the three-dimensional bone model, against a representation of the modified tunnel path 1310, and against a representation of the distal end of an exemplary sight 426. In the lower right corner, FIG. 15 shows an exemplary graphic 1500 showing the relative position of the central longitudinal axis of the sight 426 (which corresponds to the drill axis for the drill wire 424 (FIG. 4)) and the central longitudinal axis of the modified tunnel path 1310.

[0169] Referring first to the sight 426, the portion of the sight 426 visible in the view captured by the arthroscope 408 (FIG. 4) includes a tube with a bore therethrough, the tube and bore defining a central longitudinal axis. In an exemplary embodiment, the surgeon uses the sight 426 to hold and guide the drill wire 424 (FIG. 4). Because the drill wire 424 may have an outer diameter on the order of about 2.4 mm, the sight 426 is selected to have an inner diameter that forms a snug fit over the drill wire such that the central longitudinal axis of the sight 426 is coaxial with the central longitudinal axis of the drill wire 424. Additionally, the portion of the sight 426 visible in the video image captured by the arthroscope includes a sight reference point 1502. Based on the video image, the surgical controller 418 can "see" the sight reference point 1502 and can therefore calculate both the position of the distal end of the sight 426 and the orientation of the central longitudinal axis of the sight 426 and drill wire 424, such that the position and orientation are known within the three-dimensional coordinate space of the field of view captured by the arthroscope 408.

[0170] During initial placement of the sight 426, the surgeon may rely on viewing the relative position of the sight 426 and the modified tunnel path 1310 in the video image. However, to finely align the sight 426 with respect to the modified tunnel entrance 1306, and to align the central longitudinal axis of the sight 426 with respect to the central longitudinal axis of the modified tunnel path 1310, in an exemplary embodiment, the surgeon may rely on a graphic 1500 generated and displayed by the surgical controller 418 (FIG. 4). In particular, according to the exemplary system, the surgical controller 418 receives video images captured by the arthroscope 408 (FIG. 4) and the camera head 410 (FIG. 4) to track the position of the distal end of the sight 426 with respect to the modified tunnel entrance 1306, and displays on a display device a graphic 1500 indicating the relative position of the distal end of the sight 426 to the modified tunnel entrance 1306.

[0171] In particular, the bottom right corner of the exemplary display displays a graphic 1500 including a tunnel path target 1504 representative of the modified tunnel entrance 1306, illustratively shown as an extended length of crosshairs. Also displayed within the exemplary graphic 1500 is a distal end target 1506 representing the location of the distal end of the sight 426, illustratively shown as a crosshair embedded within a smaller circle. In the exemplary system and method, the surgical controller 418 displays the tunnel path target 1504 at a fixed location on the display device and the distal end target 1506 at a variable location to illustrate the relative location of the distal end of the sight 426 and the modified tunnel entrance 1306. Although the exemplary video display of FIG. 15 may be displayed on a display device having a size (e.g., measured diagonally) of 120 centimeters or more, the relative spacing between the distal end of the sight 426 and the corrected tunnel entrance 1306 may be only a few centimeters. Thus, the relative positions shown by the tunnel path target 1504 and the distal end target 1506 may include magnification to provide magnified visual feedback to the surgeon. The surgeon's goal is to align and position the distal end target 1506 relative to the tunnel path target 1504 before beginning drilling of the pilot tunnel with the drill wire 424 (FIG. 4). The drill wire 424 may be placed inside the sight 426 during the alignment process, or the surgeon may align the sight 426 before fitting the drill wire 424 into the sight 426.

[0172] There are at least two alignments that the surgeon must consider when positioning the sight 426 for drilling the pilot tunnel: 1) proximity or alignment of the actual tunnel entrance location to the corrected tunnel entrance 1306; and 2) proximity or coaxiality of the pilot tunnel central longitudinal axis to the corrected tunnel path 1310. Closely aligning the distal end target 1506 to the tunnel path target 1504 only addresses the first alignment consideration. Although the distal end target 1506 may be closely aligned to the tunnel path target 1504, when the pilot tunnel is drilled, the tunnel orientation may differ significantly from the corrected tunnel path 1310. To enable better axis alignment according to further examples, the surgical controller 418 still receives video images captured by the arthroscope 408 (FIG. 4) and camera head 410 (FIG. 4) to track the position of the central longitudinal axis of the sight 426 relative to the central longitudinal axis of the corrected tunnel path 1310 and displays a graphic on the display device indicating the relative orientation of the central axes.

[0173] Referring again to the graphic 1500 in the lower right corner, in the exemplary system and method, the surgical controller 418 (FIG. 4) further generates and displays a proximal end target 1508 representing a proximal portion of the sight 426, illustratively shown as a partial cross embedded within a larger circle. In the exemplary system and method, the surgical controller 418 displays the proximal end target 1508 at a variable position relative to the distal end target 1506 to indicate the orientation of the central longitudinal axis of the sight 426 relative to the central longitudinal axis of the modified tunnel path 1310. That is, in the graphic 1500, the central longitudinal axis of the modified tunnel path 1310 may be considered to be perpendicular to the front surface of the display device 414 (FIG. 4) and located at the intersection or center of the tunnel path target 1504. The central longitudinal axis of the sight 426 may be considered to be a line extending between the centers of the proximal and distal targets 1508, 1506. The surgeon's goal is to align the proximal target 1508 with respect to the distal target 1506, and further to align the aligned crosshairs 1508 / 1506 with respect to the tunnel entrance target 1504. When all of the crosshairs are aligned, the central longitudinal axis of the sight 426, the drill wire 424 (FIG. 4) within the sight 426, and the corrected tunnel path 1310 will be coaxial.

[0174] The discussion of FIG. 15 and FIG. 1500 assumes the use of the sight 426 to identify the location of the drill wire 424 (FIG. 4) prior to drilling the pilot hole. Regardless of whether the drill wire is placed in the sight 426 during the alignment process, the central longitudinal axis of the sight 426 still represents the expected drill axis after drilling of the pilot tunnel has begun. In other cases, the sight 426 may be omitted and the drill wire 424 itself may be tracked. That is, the drill wire 424 may include a wire reference point having one or more machine-readable patterns based on which the surgical controller 418 may determine the location of the distal end of the drill wire 424 and the orientation of the central longitudinal axis of the drill wire (at least proximate to the bone in the surgical site). Thus, the discussion thus far assuming the use of the sight 426 as a mechanism for enabling placement and orientation of the drill wire prior to drilling should not be construed as limiting the scope of the claims.

[0175] After the aimer 426 is aligned with the corrected tunnel trajectory 1310, drilling of the pilot tunnel begins. If the drill wire 424 (FIG. 4) is not already threaded into the aimer 426, the surgeon threads the drill wire 424 into the aimer 426. Drilling may involve the surgeon holding the aimer 426 in the desired orientation as shown in graphic 1500 and applying rotational energy to the drill wire 424, such as by an external drill assembly. After the drill wire enters the bone, it drills straight through the bone and eventually exits the bone on the opposite side. In the case of an inside-out procedure, the drill wire also exits the skin onto the outer portion of the leg. After the drill wire 424 has completed the pilot tunnel, with the sight 426 still fitted over the drill wire 424, the placement of the pilot tunnel relative to the revised tunnel path 1310 may be analyzed.

[0176] -Tunnel layout analysis

[0177] According to an exemplary method and system, prior to using a reamer(s) to form a full diameter tunnel through the bone, the surgical controller 418 (FIG. 4) may provide the surgeon with information regarding the relationship between the pilot tunnel and the modified tunnel path 1310 to enable the surgeon to determine whether to use the pilot tunnel as a guide in forming the actual tunnel through the bone.

[0178] FIG. 16 is an exemplary video display showing intraoperative analysis of a pilot tunnel path relative to a modified tunnel path. The display may be shown on a display device 414 (FIG. 4), such as in association with the device cart 402 (FIG. 4) or in any other suitable location. In particular, FIG. 16 shows a portion of a bone in a video image captured by an arthroscope 408 (FIG. 4), superimposed against a mesh model of a three-dimensional bone model, against a modified tunnel path 1310 including a modified tunnel entrance 1306 and a modified tunnel exit 1308, and against an overlay showing a captured and calculated central longitudinal axis 1600 of the pilot tunnel. The entrance of the pilot tunnel may actually be visible, but is not shown in FIG. 16 so as not to further complicate the drawing. The exemplary video display of FIG. 16 further includes various parameters in the lower right corner that aid the surgeon in assessing the viability of the pilot tunnel relative to the modified tunnel path 1310. For example, the surgical controller 418 may calculate and provide a value indicative of the overlap of the tunnel along the path of the pilot tunnel relative to the modified tunnel path 1310, and the surgical controller 418 may display a visual representation of the value indicative of the overlap. In the example of FIG. 16, the visual representation of the value indicative of the overlap is a numerical value (e.g., here, 97%) in percent. The overlap as a percentage may conceptually range from 0% to 100%, where 0% is a complete failure and 100% means that the central longitudinal axis 1600 of the pilot tunnel is coaxial with the central longitudinal axis of the modified tunnel path 1310. As above, the surgical controller 418 calculates the value indicative of the overlap as a percentage taking into account the expected tunnel diameter, and if any portion of the expected tunnel diameter intersects with any portion of the modified tunnel path 1310, the intersection is considered an overlap.Alternatively, the surgical controller 418 may calculate a value indicative of overlap based on the pilot tunnel and the pilot tunnel that will determine the modified tunnel path 1310.

[0179] Still considering the information provided to the surgeon regarding the relationship of the pilot tunnel and the expected tunnels along the corrected tunnel path 1310, in a still further example, the surgical controller 418 (FIG. 4) may calculate and provide an entrance position offset between the pilot tunnel and the corrected tunnel entrance 1306, and the surgical controller 418 may display a visual representation of the offset. In the example of FIG. 16, the visual representation of the offset is a numerical value shown in units of measurement. The surgical controller 418 may also calculate and provide an exit position offset between the pilot tunnel and the corrected tunnel exit 1308, and the surgical controller 418 may display a visual representation of the offset in units of measurement. In the example of FIG. 16, the entrance offset is shown as 2 mm and the exit offset is shown as 3 mm. The example offsets of 2 mm and 3 mm may indicate that the surgeon failed to hold the aimer 426 (FIG. 4) accurately in the desired position at the start of drilling and / or that the surgeon failed to keep the central longitudinal axis of the aimer 426 coaxial with the central longitudinal axis of the corrected tunnel trajectory 1310. Nevertheless, an offset of 2 mm or 3 mm may be sufficient given related art tunnel placement errors on the order of 8.3 mm to 13.9 mm.

[0180] Still considering the information provided to the surgeon regarding the pilot tunnel for the modified tunnel path 1310, in yet a further example, the surgical controller 418 (FIG. 4) may calculate and provide a value indicative of a posterior wall breakthrough. As with the intraoperative modifications to create the modified tunnel path 1310, the value indicative of a posterior wall breakthrough of FIG. 16 has two exemplary aspects: a quantized breakthrough probability (e.g., low, medium, and high) and a numerical value indicative of a posterior wall breakthrough probability. The numerical value indicative of a posterior wall breakthrough probability may again be a distance calculated by the surgical controller 418 as the distance between the expected outer diameter of the tunnel formed along the pilot tunnel and the outer surface of the bone in the three-dimensional bone model. More particularly, in the exemplary case, the numerical value indicative of a posterior wall breakthrough probability is calculated as the shortest distance between the expected inner diameter of the tunnel formed along the pilot tunnel and the outer surface of the three-dimensional bone model. Again, the quantized burst probability may be related to a numerical value indicative of the burst probability of the rear wall, for example a "low" burst probability may be indicated when the shortest distance between the predicted inner diameter of the tunnel formed along the pilot tunnel and the outer surface of the three-dimensional bone model is 8 mm or more, a "medium" burst probability may be indicated when the shortest distance is between 4 mm and 8 mm, and a "high" burst probability may be indicated when the shortest distance is 4 mm or less.

[0181] Regardless of the exact information provided to the surgeon regarding the relationship between the expected inner diameter of the tunnel formed along the pilot tunnel and the revised tunnel path 1310, the pilot tunnel may be abandoned and a new pilot tunnel may be drilled using the procedures described above if the surgeon so chooses based on the information provided. If the second or subsequent pilot tunnel meets the surgeon's approval, the exemplary method proceeds to use a reamer(s) to form a full diameter tunnel through the bone along the tunnel path, including the counterbored hole on the intercondylar side of the femur.

[0182] Software and Hardware

[0183] 17 illustrates a method for calibrating an endoscopic optical system, such as an arthroscope and an attached camera head, according to at least some embodiments. In particular, the method begins (block 1700) by placing an endoscope in a calibration assembly that holds the endoscope in a fixed relationship to a calibration target on an inner surface of the calibration assembly (block 1702), capturing a plurality of images of the calibration target, where each image is captured with a unique rotational relationship between the camera head and the endoscope, the unique rotational relationship being relative to a central longitudinal axis of the endoscope (block 1704), and creating a characterization function that characterizes the optical distortion between the calibration target and the capture array of the camera head (block 1706). The exemplary method then ends (block 1708). Portions of the exemplary method may be implemented by computer instructions executed by a processor of a computer system, such as the surgical controller 418 (FIG. 4).

[0184] FIG. 18 illustrates a method for intraoperatively verifying registration of a three-dimensional bone model, according to at least some embodiments. In particular, the method begins (block 1800) and includes receiving a three-dimensional bone model of a bone (block 1802), receiving an image of the bone viewed by an endoscope and an attached camera head during a surgical procedure, the image of the bone including an image of a fiducial coupled to the bone (block 1804), receiving a plurality of positions for an outer surface of the bone shown in the image of the bone (block 1806), registering the three-dimensional bone model to the bone using the plurality of positions (block 1808), displaying on a display device a representation of the three-dimensional bone model superimposed onto the image of the bone (block 1810), and receiving an indication that the three-dimensional bone model has been properly registered to the bone in the image of the bone (block 1812). The method then ends (block 1812). The exemplary method may be implemented by computer instructions executed by a processor of a computer system, such as the surgical controller 418 (FIG. 4).

[0185] 19 illustrates a method for implementing tunnel path modification intraoperatively, according to at least some embodiments. In particular, the method begins (block 1900) by displaying a planned tunnel path for a ligament repair on a display device, the planned tunnel path being shown relative to at least a portion of a leg bone, the planned tunnel path being selected preoperatively (block 1902), receiving a modified tunnel entry location during the surgical procedure (block 1904), calculating a modified tunnel path through the patient's leg bone during the surgical procedure and displaying the modified tunnel path on the display device (block 1906), tracking axial alignment of a drill axis of a drill wire relative to a central longitudinal axis of the modified tunnel path prior to drilling (block 1908), and displaying a graphic on the display device indicating the relative position of the drill axis and the central longitudinal axis of the modified tunnel path (block 1910). The method then ends (block 1912). The exemplary methods may be implemented by computer instructions that are executed by a processor of a computer system, such as surgical controller 418 (FIG. 4).

[0186] FIG. 20 illustrates an exemplary computer system 2000. In one example, computer system 2000 may correspond to a surgical controller 418, a tablet device in an operating room, or any other system implementing any or all of the various methods described herein. Computer system 2000 may be connected (e.g., networked) to other computer systems within a local area network (LAN), an intranet, and / or an extranet (e.g., device cart 402 network), or at certain times, the Internet (e.g., when not being used in a surgical procedure). Computer system 2000 may be a server, a personal computer (PC), a tablet computer, or any device capable of executing a set of instructions (sequential or otherwise) that specify actions to be performed by the device. Additionally, although only a single computer system is illustrated, the term "computer" shall also be construed to include any collection of computers that individually or jointly execute a set (or sets) of instructions to perform any one or more methods described herein.

[0187] The computer system 2000 includes a processing device 2002, a main memory 2004 (e.g., read only memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM)), a static memory 2006 (e.g., flash memory, static random access memory (SRAM)), and a data storage device 2008, which communicate with each other via a bus 2010.

[0188] The processing device 2002 represents one or more general-purpose processing devices, such as a microprocessor, a central processing unit, or the like. More specifically, the processing device 2002 may be a complex instruction set computing (CISC) microprocessor, a reduced instruction set computing (RISC) microprocessor, a very long instruction word (VLIW) microprocessor, or a processor implementing other instruction sets or a combination of instruction sets. The processing device 2002 may also be one or more application-specific processing devices, such as an application-specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), a network processor, or the like. The processing device 2002 is configured to execute instructions to perform any of the operations and steps described herein. After being programmed with specific instructions, the processing device 2002, and thus the entire computer system 2000, becomes an application-specific device, such as the surgical controller 418.

[0189] The computer system 2000 may further include a network interface device 2012 for communicating with any suitable network (e.g., the device cart 402 network). The computer system 2000 may also include a video display 2014 (e.g., the display device 414), one or more input devices 2016 (e.g., a microphone, keyboard, and / or mouse), and one or more speakers 2018. In one illustrative example, the video display 2014 and the input device(s) 2016 may be combined into a single component or device (e.g., an LCD touch screen).

[0190] The data storage device 2008 may include a computer-readable storage medium 2020 having stored thereon instructions 2022 embodying any one or more of the methodologies or functions described herein (e.g., instructions 2022 implementing any method and any function performed by any device and / or component illustrated and described herein). The instructions 2022 may also reside, completely or at least partially, within the main memory 2004 and / or within the processing device 2002 during execution thereof by the computer system 2000. Thus, the main memory 2004 and the processing device 2002 also constitute computer-readable media. In certain cases, the instructions 2022 may also be transmitted or received over a network via the network interface device 2012.

[0191] Although the computer readable storage medium 2020 is shown in the illustrated example as being a single medium, the term "computer readable storage medium" shall be interpreted to include a single or multiple media (e.g., a centralized or distributed database and / or associated caches or servers) having one or more sets of instructions stored thereon. The term "computer readable storage medium" shall also be interpreted to include any medium that may store, encode, or carry a set of instructions for execution by a machine, and that cause a machine to perform any one or more methodologies in this disclosure. Thus, the term "computer readable storage medium" shall be interpreted to include, but is not limited to, solid state memory, optical media, and magnetic media.

[0192] The above discussion is meant to be illustrative of the principles and various embodiments of the present invention. Numerous variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to include all such variations and modifications.

Claims

1. A method for calibrating an endoscopic optical system, comprising: placing the endoscope within a calibration assembly, the calibration assembly holding the endoscope in a fixed relationship to a calibration target on an inner surface of the calibration assembly; capturing, by a surgical controller, a plurality of images of the calibration target, each image being captured in a unique rotational relationship between a camera head and the endoscope, the unique rotational relationship being with respect to a longitudinal central axis of the endoscope; creating, by the surgical controller, a characterization function that characterizes an optical distortion between the calibration target and a capture array of the camera head; A method comprising the above steps.

2. The step of placing the endoscope within the calibration assembly further comprises: (i) the viewing direction of the distal end of the endoscope being perpendicular to the calibration target; (ii) the viewing direction of the distal end of the endoscope being non-perpendicular to the calibration target; or (iii) the longitudinal central axis of the endoscope intersecting the center of the calibration target and the viewing angle of the distal end of the endoscope being perpendicular to the calibration target. The method according to claim 1.

3. The method according to claim 1, further comprising the step of placing water inside the internal volume of the calibration assembly such that the internal volume between the calibration target and the distal end of the endoscope is filled with water or saline.

4. The step of capturing a plurality of the images comprises: (i) capturing a first image of the calibration target in a first rotational orientation between the endoscope and the camera head; subsequently, capturing a second image of the calibration target in a second rotational orientation between the endoscope and the camera head; subsequently, capturing a third image of the calibration target in a third rotational orientation between the endoscope and the camera head; further comprising the above steps, or (ii) further comprising the step of capturing a plurality of the images of the calibration target in a fixed relationship between the endoscope and the calibration assembly. The method according to claim 1.

5. A calibration assembly for calibrating an endoscopic optical system, comprising: A container that defines an internal volume, said internal volume including a container that defines a calibration front face, a calibration target disposed on said calibration front face, a wall of said container that defines an opening into said container, said opening defining a central axis that intersects said calibration target, an axial holding surface defined by said wall associated with said opening, said axial holding surface being located at a predetermined distance measured along said central axis of said opening from said calibration target, and a rotational holding surface associated with said wall, the calibration assembly comprising: **Claim 6** wherein said rotational holding surface (i) is a ridge disposed within a countersunk hole defined by said wall, said rotational holding surface being defined by a wall located on the opposite side of said ridge, or (ii) is a clip configured to hold an optical post of an endoscope, the calibration assembly according to claim 5, further comprising: **Claim 7** wherein said wall further includes a notch that defines a channel, said channel having a closed bottom that forms said axial holding surface, two sides that form said rotational holding surface, and an open top, and optionally, said channel of said notch is perpendicular to said central axis of said opening, the calibration assembly according to claim 5. **Claim 8** wherein said calibration front face (i) is planar, and / or (ii) said calibration front face defines a first portion that defines a first plane and a second portion that defines a second plane, said first plane and said second plane being non-planar, the calibration assembly according to claim 5. **Claim 9** wherein said wall of said container associated with said opening further includes a tube that defines an internal passage, said tube protruding from said container, said internal passage defining said opening that penetrates said wall of said container, the calibration assembly according to claim 5. **Claim 10** wherein said central axis of said opening (i) intersects the center of said calibration target, or (ii) forms an acute angle with a vector perpendicular to said calibration front face, said acute angle being non-zero, the calibration assembly according to claim 5. **Claim 11** A system for calibrating an endoscope optical system, An endoscope system including an endoscope and a camera head coupled to the endoscope, wherein the endoscope defines a longitudinal central axis and an optical post. A calibration assembly, a container defining an inner volume, a calibration surface defined on an inner surface of the container, a calibration target disposed on the calibration surface, an opening penetrating a wall of the container, and a calibration assembly including the same, wherein the endoscope is fitted through the opening such that the longitudinal central axis intersects the calibration target, the calibration assembly is configured to hold a distal end of the endoscope at a predetermined distance from the calibration target, and the calibration assembly is configured to hold the endoscope with a fixed rotational orientation relative to the calibration target. **Claim 12** The calibration assembly further includes (i) a set of rotational retention surfaces defined by ridges disposed inside a countersunk hole defined by the wall, the set of rotational retention surfaces being defined by a wall located on an opposite side of the ridge, the set of rotational retention surfaces holding the endoscope with a fixed rotational orientation relative to the calibration target, and / or (ii) a notch defining a channel having a closed bottom and an open top, the optical post being disposed inside the notch, the notch holding the distal end of the endoscope at the predetermined distance from the calibration target, the notch holding the endoscope with the fixed rotational orientation relative to the calibration target, and / or (iii) a clip coupled to the optical post, the clip holding the endoscope with the fixed rotational orientation relative to the calibration target. The system according to claim 11. **Claim 13** The calibration surface is (i) planar, or (ii) defines a first portion defining a first plane and a second portion defining a second plane, the first plane and the second plane being non-planar. The system according to claim 11. **Claim 14** The calibration assembly further includes a tube that defines an internal passageway, the tube protruding from the container, and the endoscope is fitted through the internal passageway such that the distal end of the endoscope is positioned inside the internal volume of the container. The system according to claim 11.

15. The longitudinal central axis of the endoscope intersects the center of the calibration target. The system according to claim 11.

Images