Systems and methods for providing guidance for planning bone tunnels

Abstract

Some examples are directed to processor-implemented methods and systems for providing visual guidance for planning a bone tunnel. Some examples are directed to processor-implemented methods and systems for providing guidance about feasibility of a potential bone tunnel.

Description

SYSTEMS AND METHODS FOR PROVIDING GUIDANCE FOR PLANNING BONE TUNNELSCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 755,783 filed on February 7, 2025 and titled “METHODS AND SYSTEMS FOR BONE TUNNEL EXIT PLANNING FOR NAVIGATED SURGERY.” The contents of this provisional patent application are incorporated herein by reference as if reproduced in full herein.BACKGROUND

[0002] The Anterior Cruciate Ligament (ACL) is one of the key ligaments providing stability to the knee joint. Playing sports that involve sudden stops or changes in direction is one of the main causes of ACL injury, an example of which is a complete tear of the ligament. ACL tear is a common medical condition with annually more than 200,000 cases in the United States of America alone, as reported by Samitier et al. (Samitier, G., Marcano, A.I., Alentorn-Geli, E., Cugat, R., Farmer, K.W., Moser, M.W.: Failure of anterior cruciate ligament reconstruction. In: ABJS (2015)).

[0003] A standard treatment for a torn ACL is arthroscopic reconstruction, according to which the torn ligament is replaced by a tissue graft that is pulled into the knee joint through tunnels drilled in both the femur and tibia bones of the knee joint. This technique is explained by Brown et al. (Brown, C.H., Spalding, T., Robb, C.: Medial portal technique for single-bundle anatomical anterior cruciate ligament (ACL) reconstruction. In: Int Orthop (2013)).

[0004] It is reportedly crucial to knee stability and patient satisfaction to drill such femoral or tibial ligament tunnels in an anatomically correct position. According to Samitier et al., failure rates in primary ACL reconstructions are in the range of 10-15%.

[0005] As for the femoral tunnel, the appropriate location of its entry point on the lateral wall of the femoral intercondylar notch has been the subject of many studies and is frequently described using the grid system proposed by Bernard et al. (Bernard M, Hertel P, Hornung H, Cierpinski T: Femoral insertion of the ACL. Radiographic quadrant method. Am J Knee Surg. 1997 Winter; 10(1): 14-21; discussion 21 -2), which is used both for planning and for post-operative assessment, as explained for examplePT-6211-WO-PCTby Brown et al. referred to above, and in Parkar, A. P., Adriaensen, M. E. A. P. M., Giil, L. M., & Solheim, E. (2019). Computed Tomography Assessment of Anatomic Graft Placement After ACL Reconstruction: A Comparative Study of Grid and Angle Measurements. Orthopaedic Journal of Sports Medicine.

[0006] While the location of the femoral tunnel entry is important, surgeons also decide on both the diameter and depth of the socket in which the graft will be fixated within the tunnel, as well as the orientation and exit point of the tunnel. The tunnel orientation itself is an important consideration, as orientation constrains the available tunnel length and available bone support. The tunnel orientation is reported to play a role in the success of the ACL reconstruction surgery, as explained for example in (a) H. Wang, J. E. Fleischli, I. D. Hutchinson, and N. N. Zheng, “Knee Moment and Shear Force Are Correlated With Femoral Tunnel Orientation After Single-Bundle Anterior Cruciate Ligament Reconstruction.,” The American Journal of Sports Medicine, vol.42, no. 10, pp. 2377-2385, Sep. 2014, 2377-2385, Sep. 2014; (b) K. D. Illingworth, D. Hensler, Z. M. Working, J. A. Macalena, S. Tashman, and F. H. Fu, “A Simple Evaluation of Anterior Cruciate Ligament Femoral Tunnel Position.,” The American Journal of Sports Medicine, vol. 39, no. 12, pp. 2611-2618, Dec. 2011; and (c) Hodel, S., Mania, S., Vlachopoulos, L. et al. “Influence of femoral tunnel exit on the 3D graft bending angle in anterior cruciate ligament reconstruction.,” J EXP ORTOP 8, 44 (2021).

[0007] The femoral tunnel length should be sufficiently long to allow a sufficiently long socket for the graft insertion. The length of graft that will be inserted into the femur socket is important as it is related to the processes of graft harvesting and preparation. Furthermore, the femoral tunnel length should also be such that sufficient bone support towards the exit of the tunnel - known as bone bridge - is available. Furthermore, for some techniques, femoral tunnel length should be sufficient to provide a gap in the socket for flipping the fixation device (known as “flipping distance”).

[0008] The femoral tunnel should also be oriented such that the socket for the graft insertion has enough bone around it, especially towards the posterior femoral cortex. That is, the thickness of the bone between the tunnel socket and the posterior wall -known as back wall thickness - should be sufficient large to avoid the occurrence ofPT-6211-WO-PCTposterior wall blowout, as explained for example in Mitchell, J. J., Dean, C. S., Chahla, J., Menge, T. J., Cram, T. R., & LaPrade, R. F. (2016, June 1). Posterior Wall Blowout in Anterior Cruciate Ligament Reconstruction. Orthopaedic Journal of Sports Medicine, 4(6), 232596711665212; and in Rue, J. P., Busam, M., Detterline, A., & Bach, B. (2008). Posterior Wall Blowout in Anterior Cruciate Ligament Reconstruction -Avoidance, Recognition, and Salvage. Journal of Knee Surgery, 21(03), 235-240.

[0009] In addition to tunnel shape and bone support, tunnel orientation may also be constrained by factors of accessibility during execution, as well as the desire to minimize iatrogenic injury. For example, the manipulations for placement of the tunnel guidewire and then drilling the socket itself can be limited by shape of the bone proximal to a candidate entry point from which the tunnel is to extend. For instance, the medial condyle can hinder the accessibility of tunnels with highly posterior exit points, as reported by Hodel et al., and some distance margin should be considered so that the medial condyle is not itself damaged during positioning of surgical instruments used to drill a femoral tunnel. In addition to hindrances rearward of the tunnel entry point such as the medial condyle, iatrogenic damage on the lateral knee structures caused when a guidewire exits the femur from a tunnel exit point should be considered, and preferably minimized, as reported in Sholahuddin Rhatomy, Jaka Fatria Yudhistira, Noha Roshadiansyah Soekarno, Riky Setyawan, Iatrogenic injury of posterolateral structures during femoral tunneling in anterior cruciate ligament reconstruction: A cadaveric study, Annals of Medicine and Surgery, Volume 59, 2020, Pages 14-16, ISSN 2049-0801, https: / / doi.Org / 10.1016 / j.amsu.2020.09.012.

[0010] In view of the various considerations given above, and others, it would be useful to provide systems and methods for facilitating at least surgical planning that can take the various considerations into account.SUMMARY

[0011] One example is a system for providing visual guidance for planning a bone tunnel, the system comprising: a display device; memory storing one or more instructions; and one or more processing devices configured to execute the one or more instructions, wherein executing the one or more instructions causes the system to: receive a 3D digital model of a bone; receive at least one initial tunnel constraint,PT-6211-WO-PCTthe at least one initial tunnel constraint comprising a tunnel entry location; generate the visual guidance using the 3D digital model, the at least one initial tunnel constraint, and at least one additional tunnel constraint, wherein the visual guidance indicates an assessment of feasibility with respect to the at least one additional tunnel constraint of each of a plurality of potential orientations of a bone tunnel that conforms to the at least one initial tunnel constraint; and display the visual guidance on the display device.

[0012] In the example system, executing the one or more instructions may cause the system to: receive a user selection of one or more of the plurality of potential orientations of the bone tunnel; and store the user selection in association with the digital 3D model of the bone.

[0013] In the example system, the at least one initial tunnel constraint may further comprise a minimum bone tunnel length.

[0014] In the example system, the at least one additional tunnel constraint may comprise at least one of: a minimum bone tunnel length, a minimum back wall thickness, and a minimum lateral distance of a longitudinal axis of the bone tunnel from an anatomical feature opposite the tunnel entry location.

[0015] In the example system, the bone may be a femur and the anatomical feature opposite the tunnel entry location may be a medial condyle of the femur.

[0016] In the example system, the at least one additional tunnel constraint may comprise: a minimum distance within the bone of the bone tunnel from a pre-existing bone tunnel.

[0017] In the example system, the at least one additional tunnel constraint may comprise: a minimum distance of a tunnel exit location from an anatomical feature opposite the tunnel exit location.

[0018] In the example system, the at least one additional tunnel constraint may comprise: accessibility of the bone tunnel to a surgical instrument via a skin portal.

[0019] In the example system, the tunnel entry location may be a region encompassing a plurality of potential bone tunnel entry points, wherein the visual guidance indicates the assessment of feasibility in respect of two or more of the potential bone tunnel entry points.PT-6211-WO-PCT

[0020] In the example system, the tunnel entry location may be a single tunnel entry point.

[0021] In the example system, the visual guidance may include a feasibility map.

[0022] In the example system, the feasibility map may comprise one or more regions corresponding to potential bone tunnels that would conform to all of the at least one additional tunnel constraint.

[0023] In the example system, there may be a plurality of additional tunnel constraints, and the feasibility map may comprise one or more regions corresponding to potential bone tunnels that would conform to fewer than all of the additional tunnel constraints.

[0024] In the example system, executing the one or more instructions may cause the system to display the visual guidance on the display device by overlaying the feasibility map on a representation of the digital 3D model of the bone displayed on the display device.

[0025] One example is a processor-implemented method of providing visual guidance for planning a bone tunnel, the method comprising: receiving, by one or more processor, a 3D digital model of a bone; receiving, by the one or more processor, at least one initial tunnel constraint, the at least one initial tunnel constraint comprising a tunnel entry location; generating, by the one or more processor, the visual guidance using the 3D digital model, the at least one initial tunnel constraint, and at least one additional tunnel constraint, wherein the visual guidance indicates an assessment of feasibility with respect to the at least one additional tunnel constraint of each of a plurality of potential orientations of a bone tunnel that conforms to the at least one initial tunnel constraint; and providing, by the one or more processor, the visual guidance for display on a display device.

[0026] The example processor-implemented method may further comprise receiving a user selection of one or more of the plurality of potential orientations of the bone tunnel; and storing the user selection in association with the digital 3D model of the bone.

[0027] In the example processor-implemented method, the at least one initial tunnel constraint may further comprise a minimum bone tunnel length.PT-6211-WO-PCT

[0028] In the example processor-implemented method, the at least one additional tunnel constraint may comprise at least one of: a minimum bone tunnel length, a minimum backwall thickness, and a minimum lateral distance of a longitudinal axis of the bone tunnel from an anatomical feature opposite the tunnel entry location.

[0029] In the example processor-implemented method, the bone may be a femur and the anatomical feature opposite the tunnel entry location may be a medial condyle of the femur.

[0030] In the example processor-implemented method, the at least one additional tunnel constraint may comprise: a minimum distance within the bone of the bone tunnel from a pre-existing bone tunnel.

[0031] In the example processor-implemented method, the at least one additional tunnel constraint may comprise: a minimum distance of a tunnel exit location from an anatomical feature opposite the tunnel exit location.

[0032] In the example processor-implemented method, the at least one additional tunnel constraint may comprise: accessibility of the bone tunnel to a surgical instrument via a skin portal.

[0033] In the example processor-implemented method, the tunnel entry location may be a region encompassing a plurality of potential bone tunnel entry points, wherein the visual guidance may indicate the assessment of feasibility in respect of two or more of the potential bone tunnel entry points.

[0034] In the example processor-implemented method, the tunnel entry location may be a single tunnel entry point.

[0035] In the example processor-implemented method, the visual guidance may include a feasibility map.

[0036] In the example processor-implemented method, the feasibility map may comprise one or more regions corresponding to potential bone tunnels that would conform to all of the at least one additional tunnel constraint.

[0037] In the example processor-implemented method, there may be a plurality of additional tunnel constraints, and the feasibility map may comprise one or more regions corresponding to potential bone tunnels that would conform to fewer than all of the additional tunnel constraints.PT-6211-WO-PCT

[0038] In the example processor-implemented method, providing, by the one or more processor, the visual guidance for display on a display device may comprise providing the feasibility map as an overlay for a representation of the digital 3D model of the bone to be displayed on the display device.

[0039] One example is a non-transitory processor-readable medium embodying processor-readable program code executable by at least one processor to carry out the processor-implemented method.

[0040] One example is a system for providing guidance about feasibility of a potential bone tunnel, the system comprising: a user interface; memory storing one or more instructions; and one or more processing devices configured to execute the one or more instructions, wherein executing the one or more instructions causes the system to: receive a 3D digital model of a bone; receive at least one tunnel constraint; receive potential bone tunnel data defining the potential bone tunnel, the potential bone tunnel data comprising a first point along an axis of the potential bone tunnel and at least one of: (a) a second point along the axis of the potential bone tunnel and (b) an orientation of the axis of the potential bone tunnel; generate the guidance using the 3D digital model, the at least one tunnel constraint, and the potential bone tunnel data, wherein the guidance indicates an assessment of feasibility with respect to the at least one tunnel constraint of the potential bone tunnel; and present the guidance using the user interface.

[0041] In the example system, the user interface may comprise a display device, and the guidance comprises visual guidance displayed on the display device.

[0042] In the example system, the visual guidance may comprise a change in content displayed on the display device responsive to the potential bone tunnel being assessed as infeasible with respect to the at least one tunnel constraint.

[0043] In the example system, the change in content displayed on the display device may be selected from the group consisting of: a change in appearance of an indicia being displayed on the display device, a display of an indicia on the display device, and a removal from display of an indicia on the display device.

[0044] In the example system, the visual guidance may comprise a change in content displayed on the display device responsive to the potential bone tunnel being assessed as feasible with respect to the at least one tunnel constraint.PT-6211-WO-PCT

[0045] In the example system, the change in content displayed on the display device may be selected from the group consisting of: a change in appearance of an indicia being displayed on the display device, a display of an indicia on the display device, and a removal from display of an indicia on the display device.

[0046] In the example system, the guidance may comprise at least one of: visual guidance, audible guidance, and haptic guidance.

[0047] In the example system, the audible guidance may comprise an audible sound presented by the user interface responsive to the potential bone tunnel being assessed as feasible with respect to the at least one tunnel constraint.

[0048] In the example system, the audible guidance may comprise an audible sound presented by the user interface responsive to the potential bone tunnel being assessed as infeasible with respect to the at least one tunnel constraint.

[0049] In the example system, the guidance may indicate that the potential bone tunnel is feasible only responsive to the potential bone tunnel conforming to all of the at least one tunnel constraint.

[0050] In the example system, the guidance may indicate that the potential bone tunnel is infeasible responsive to the potential bone tunnel conforming to fewer than all of the at least one tunnel constraint.

[0051] In the example system, the at least one tunnel constraint may comprise at least two tunnel constraints, and the guidance may comprise: a first guidance that indicates that the potential bone tunnel is feasible with respect to a first of the at least two tunnel constraints; and a second guidance different from the first guidance and that indicates that the potential bone tunnel is feasible with respect to a second of the at least two tunnel constraints.

[0052] In the example system, the guidance may further comprise: a third guidance different from the first guidance and from the second guidance and that indicates that the potential bone tunnel is feasible with respect to all of the at least two tunnel constraints.

[0053] One example is a processor-implemented method of providing guidance about feasibility of a potential bone tunnel, the method comprising: receiving, by one or more processor, a 3D digital model of a bone; receiving, by the one or more processor, at least one tunnel constraint; receiving, by the one or more processor,PT-6211-WO-PCTpotential bone tunnel data defining the potential bone tunnel, the potential bone tunnel data comprising a first point along an axis of the potential bone tunnel and at least one of: (a) a second point along the axis of the potential bone tunnel and (b) an orientation of the axis of the potential bone tunnel; generating, by the one or more processor, the guidance using the 3D digital model, the at least one tunnel constraint, and the potential bone tunnel data, wherein the guidance indicates an assessment of feasibility with respect to the at least one tunnel constraint of the potential bone tunnel; and providing, by the one or more processor, the guidance for presentation by a user interface device.

[0054] In the example processor-implemented method, the user interface may comprise a display device, and the guidance may comprise visual guidance displayed on the display device.

[0055] In the example processor-implemented method, the visual guidance may comprise a change in content displayed on the display device responsive to the potential bone tunnel being assessed as infeasible with respect to the at least one tunnel constraint.

[0056] In the example processor-implemented method, the change in content displayed on the display device may be selected from the group consisting of: a change in appearance of an indicia being displayed on the display device, a display of an indicia on the display device, and a removal from display of an indicia on the display device.

[0057] In the example processor-implemented method, the visual guidance may comprise a change in content displayed on the display device responsive to the potential bone tunnel being assessed as feasible with respect to the at least one tunnel constraint.

[0058] In the example processor-implemented method, the change in content displayed on the display device may be selected from the group consisting of: a change in appearance of an indicia being displayed on the display device, a display of an indicia on the display device, and a removal from display of an indicia on the display device.

[0059] In the example processor-implemented method, the guidance may comprise at least one of: visual guidance, audible guidance, and haptic guidance.PT-6211-WO-PCT

[0060] In the example processor-implemented method, the audible guidance may comprise an audible sound presented by the user interface responsive to the potential bone tunnel being assessed as feasible with respect to the at least one tunnel constraint.

[0061] In the example processor-implemented method, the audible guidance may comprise an audible sound presented by the user interface responsive to the potential bone tunnel being assessed as infeasible with respect to the at least one tunnel constraint.

[0062] In the example processor-implemented method, the guidance may indicate that the potential bone tunnel is feasible only responsive to the potential bone tunnel conforming to all of the at least one tunnel constraint.

[0063] In the example processor-implemented method, the guidance may indicate that the potential bone tunnel is infeasible responsive to the potential bone tunnel conforming to fewer than all of the at least one tunnel constraint.

[0064] In the example processor-implemented method, the at least one tunnel constraint may comprise at least two tunnel constraints, and the guidance may comprise: a first guidance that indicates that the potential bone tunnel is feasible with respect to a first of the at least two tunnel constraints; and a second guidance different from the first guidance and that indicates that the potential bone tunnel is feasible with respect to a second of the at least two tunnel constraints.

[0065] In the example processor-implemented method, the guidance may further comprise: a third guidance different from the first guidance and from the second guidance and that indicates that the potential bone tunnel is feasible with respect to all of the at least two tunnel constraints.

[0066] One example is a non-transitory processor-readable medium embodying processor-readable program code executable by at least one processor to carry out the processor-implemented method.BRIEF DESCRIPTION OF THE DRAWINGS

[0067] For a detailed description of example embodiments, reference will now be made to the accompanying drawings in which:PT-6211-WO-PCT

[0068] FIG. 1 shows a portion of a three-dimensional (3D) representation of a digital 3D bone model of a femur from a first perspective, showing in overlay a potential bone tunnel through the femur and a feasibility measurement for use in a feasibility assessment corresponding to tunnel length.

[0069] FIG. 2 shows another portion of the 3D representation of the digital 3D bone model of a femur from a second perspective, showing in overlay the potential bone tunnel and a feasibility measurement for use in a feasibility assessment corresponding to back wall distance.

[0070] FIG. 3 shows another portion of the 3D representation of the digital 3D bone model of a femur from a third perspective, showing in overlay the potential bone tunnel and a feasibility measurement for use in a feasibility assessment corresponding to clearance.

[0071] FIG. 4 shows a representation of a digital 3D bone model from a first perspective and five (5) potential bone tunnels for which feasibility measurements would be done according to an exhaustive approach.

[0072] FIG. 5 shows a representation of a digital 3D bone model from a second perspective and the five (5) potential bone tunnels for which feasibility measurements would be done according to the exhaustive approach.

[0073] FIG. 6 shows visual guidance indicating an assessment of feasibility, with respect to tunnel constraints, of multiple potential orientations of bone tunnel, in this example in the form of a feasibility map presenting regions of differing feasibilities in a two-dimensional spherical coordinate system.

[0074] FIG. 7 shows a legend corresponding to the feasibility map of FIG. 6, the legend presenting guidance as to which regions in the feasibility map itself correspond to conformity with which feasibility metrics.

[0075] FIG. 8 shows visual guidance indicating an assessment of feasibility, with respect to tunnel constraints, of multiple potential orientations of bone tunnel, in this example in the form of a feasibility map presenting regions of differing feasibilities overlaid atop a representation of the bone itself.

[0076] FIG. 9 shows visual guidance indicating one region of partial feasibility, with respect to tunnel constraints, of multiple potential orientations of bone tunnel, in thisPT-6211-WO-PCTexample in the form of a feasibility map presenting the one region of partial feasibility overlaid atop a representation of the bone itself.

[0077] FIG. 10 shows a representation of a bone model of a distal femur showing, visually, the intersection with the bone of a representation of a sphere centered at a determined tunnel entry point and having a radius corresponding to the minimum tunnel length required of any feasible bone tunnel.

[0078] FIG. 11 shows the representation of the bone model of the distal femur of FIG. 10, with a contour corresponding to the intersection of the 3D periphery of the sphere with the bone model.

[0079] FIG. 12 shows visual guidance indicating an assessment of feasibility, with respect to an initial tunnel constraint of bone tunnel length, of multiple potential orientations of bone tunnel, in this example in the form of a feasibility map presenting a region of infeasibility (that is, potential orientations that would not conform to the bone tunnel length constraint) and a region of feasibility (that is, potential orientations that would conform to the bone tunnel length constraint) in a two-dimensional spherical coordinate system.

[0080] FIG. 13 shows a representation of a bone model of a distal femur showing, visually, the spatial determination of amount of clearance from an anatomical feature - in this example a medial condyle of the femur - rearward of a bone tunnel entry point that may be required in order to gain access for creating the bone tunnel with low risk of iatrogenic injury.

[0081] FIG. 14 shows another representation of the bone model of the distal femur of FIG. 13 showing, visually, the spatial determination of the amount of clearance from the anatomical feature.

[0082] FIG. 15 shows visual guidance indicating an assessment of feasibility, with respect to both an initial tunnel constraint of bone tunnel length and an additional constraint of clearance, of multiple potential orientations of bone tunnel, in this example in the form of a feasibility map presenting regions of different feasibilities with respect to the constraints.

[0083] FIG. 16 shows visual guidance indicating an assessment of feasibility, with respect to an initial tunnel constraint of bone tunnel length and additional constraints of clearance and back wall thickness, of multiple potential orientations of bone tunnel,PT-6211-WO-PCTin this example in the form of a feasibility map presenting regions of different feasibilities with respect to the constraints.

[0084] FIG. 17 shows a representation of a bone model of a distal femur showing, visually, the spatial determination of accessibility through a skin portal for forming potential bone tunnels passing through a tunnel entry point.

[0085] FIGS. 18A and 18B show representations of the bone model of FIG. 17 from respective perspectives and the spatial determination of accessibility from respective ones of the azimuth and elevation angles.

[0086] FIG. 19 shows visual guidance indicating an assessment of feasibility, with respect to both tunnel and skin portal accessibility constraints, of multiple potential orientations of bone tunnel, in this example in the form of a feasibility map presenting regions of differing feasibilities in a two-dimensional spherical coordinate system and a delineated overlapping region presenting those of the regions that are accessible through the skin portal.

[0087] FIG. 20 shows a method of providing visual guidance for planning a bone tunnel, in accordance with at least some examples.

[0088] FIG. 21 shows an example computer system.

[0089] FIGS. 22A, 22B, and 22C show guidance about feasibility of a potential bone tunnel.

[0090] FIGS. 23A, 23B, and 23C show guidance about feasibility of a potential bone tunnel.

[0091] FIG. 24 shows a processor-implemented method of providing guidance about feasibility of a potential bone tunnel.DEFINITIONS

[0092] Various terms are used to refer to particular system components. 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 in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to... .” Also, the term “couple” or “couples” is intended to mean either an indirect or direct connection. Thus, if a first device couples to a second device, thatPT-6211-WO-PCTconnection may be through a direct connection or through an indirect connection via other devices and connections.

[0093] Herein, examples are provided in which medical images of human femur bones of respective knee joints are depicted and described. It will be appreciated that the images of human knee joints are provided only as useful examples, and that the principles described and depicted in the present application would be understood as pertaining more widely to images of other anatomical structures, for which tunnel feasibility planning may be desirable.

[0094] In this description, tunnel entry point refers to the internal (within-joint) endpoint of the femoral ACL tunnel, and tunnel exit point refers to the external endpoint of the femoral ACL tunnel.DETAILED DESCRIPTION

[0095] The following discussion is directed to various examples. Although one or more of these examples may be preferred, the examples disclosed should not be interpreted, or otherwise used, as limiting the scope of the disclosure, including the claims. In addition, one skilled in the art will understand that the following description has broad application, and the discussion of any example is meant only to be exemplary of that example, and not intended to intimate that the scope of the disclosure, including the claims, is limited to that example.

[0096] With respect to femoral tunnels, it may be advantageous to take into account femoral tunnel orientation in coordination with the tunnel entry point and socket shape during tunnel planning. Furthermore, it may be useful to have methods and tools for planning the tunnel, pre-operatively and / or intra-operatively, that can take into account various tunnel metrics and preferences. At present, the orientation of the femoral tunnel tends to be heavily dependent on and constrained by the used reconstruction technique (for example, whether a transtibial technique is used or not), the patient specific bone, and the individual surgeon’s experience and preferences (Wang et al., Illingworth et al., and Hodel et al.) As such, although as explained herein the tunnel orientation is also important, planning at present tends to be focused primarily on tunnel entry position. It is also the case that if navigation systems are not being used, the impetus for planning is diminished. Techniques tend to rely mostly on intra-PT-6211-WO-PCToperative instrumentation to guide and evaluate the femoral tunnel, such that planning is minimal. As a result, studies available today are often dedicated to the analysis of post-operative results.

[0097] Therefore, this document discloses a method that, given a digital 3D model of a bone having known anatomical directions, such as a distal femur, and at least one initial tunnel constraint corresponding to a surgeon’s preferences or surgical requirements, including a tunnel entry point plan, enables the assessment of potential bone tunnel orientations with respect to at least one additional tunnel constraint corresponding to bone tunnel feasibility. An additional tunnel constraint may correspond to the surgeon’s preferences or surgical requirements. For example, an additional constraint may be a minimum tunnel length, a minimum backwall thickness, or a risk of collision of a surgical instrument for producing a bone tunnel with an anatomical feature. Such an anatomical feature may be, in the case of a femur, the medial condyle of the femur. Multiple such additional constraints may be considered. One of the outputs of such a method is visual guidance indicating an assessment of feasibility with respect to the at least one additional tunnel constraint of multiple orientations of a bone tunnel that conforms to the at least one initial tunnel constraint. The visual guidance may be provided in the form of a feasibility map. A feasibility map may have regions indicating which orientations of bone tunnel satisfy each of the additional constraints. A feasibility map may have regions indicating which orientations of bone tunnel satisfy all of the additional constraints. A feasibility map may be configurable with options enabling a user to variously display regions according to selection criteria, so as to provide the user with simplified, or richer, visual guidance as to feasibility of different potential orientations of bone tunnel. Such a feasibility map may be very useful for a surgeon to decide where to place the tunnel exit point of a bone tunnel, such as a femoral ACL tunnel during the planning of the ACLR surgery. The assessment of feasibility with respect to the at least one additional tunnel constraint may enable the generation of various kinds of visual guidance, useful for example for enabling the surgeon to find optimal tunnel exit points - and thus, along with tunnel entry points, the tunnel orientations - assessed against additional optimization criteria, such as preferred orientations or the objective of reducing orPT-6211-WO-PCTminimizing a probability of failing the feasibility criteria due to execution error when the bone tunnel is actually formed according to the planning.

[0098] In an example of providing visual guidance, a processor-based system such as a computer surgical planning workstation, tablet, or other suitable device is provided with, and therefore receives, a digital three-dimensional (3D) digital model of a bone (a “digital 3D model”). By way of background, a 3D digital model may have been generated on the basis of imaging of the bone conducted using, for example, X-ray imaging, computed tomography (CT), magnetic resonance imaging (MRI), and / or another imaging modality of combination of modalities. In the case of an ACL repair, such imaging may be conducted of the knee of the patient, including the relevant anatomy like the lower portion of the femur, the upper portion of the tibia, and the articular cartilage. The discussion that follows assumes MRI imaging, but again many different types of imaging may be used. The anatomy can be segmented from the image slices such that a digital volumetric model or digital 3D model of the anatomy is created. Any suitable currently available, or after developed, segmentation technology may be used to create the digital 3D model. More specifically to the example of ACL repair and specifically selecting a tunnel path through the femur as described particularly herein, a digital 3D model of the lower portion of the femur, including the femoral condyles, is created from the images slices. The digital 3D model is encoded with anatomical directions so as to have a 3D orientation within a 3D coordinate system, and may be in the form of a 3D surface or mesh. Variations representations for the 3D model are possible, such as triangular meshes, signed distance fields, voxels, and others.

[0099] The processor-based system also receives at least one initial tunnel constraint. In this example, the at least one initial tunnel constraint includes a tunnel entry location. The tunnel entry location may be determined during creation of the digital 3D model as being within the footprint of the original anatomical ACL entry point, or may be provided to the processor-based system by a surgeon after initial creation of the digital 3D model based on the surgeon’s study, preferences and / or other surgical requirements. For example, planning the location of the entry point of the femoral tunnel is often done using the Bernard-Hertel’s grid system. In some examples, the tunnel entry location may actually be a small region encompassing a plurality of potential bone tunnel entry points, such that visual guidance can indicate the assessment of feasibility in respect ofPT-6211-WO-PCTtwo or more of the potential bone tunnel entry points, rather than only one. That is, a surgeon may wish to indicate, with respect to the digital 3D model, a region on the surface of the femur rather than only one specific point, since the surgeon may feel that any tunnel entry point within that region would be, as a tunnel entry point, suitable for the ACL repair, and thus may wish that more than one of the potential bone tunnel entry points be assessed by the methods described herein against additional constraints for feasibility. In other examples, the tunnel entry location is a single tunnel entry point, such that the surgeon has simply selected a single tunnel entry point and does not wish for feasibility to be assessed for orientations of a set of tunnels, for each of multiple tunnel entry point.

[0100] In examples, the tunnel entry location / point may be the only initial tunnel constraint. In other examples, one or more further initial tunnel constraints in addition to the tunnel entry location / point may collectively be the initial tunnel constraints. For example, if there is one initial tunnel constraint, it will be the tunnel entry location / point. If there are two initial tunnel constraints, they will collectively be the tunnel entry location / point plus some other tunnel entry constraint, such as tunnel length. If there are three initial tunnel constraints, they will collectively be the tunnel entry location / point plus some other two tunnel entry constraints, and so forth.

[0101] FIG. 1 shows a portion of a three-dimensional (3D) representation 100 of a digital 3D bone model of a femur from a first perspective, showing in overlay a potential bone tunnel 150 through the femur and a feasibility measurement 200 for use in a feasibility assessment corresponding to tunnel length. In this example, the tunnel length for this potential orientation of tunnel may be computed by extending a straight line along the tunnel axis 705 from a tunnel entry point in the candidate orientation, through the 3D model, and calculating the distance the straight line travels from the tunnel entry point until the periphery of the digital 3D model of the bone, corresponding to the tunnel exit point. However, in other examples, there may be two or more initial tunnel constraints. For example, a first of the initial tunnel constraints may be tunnel entry location, and a second of the initial tunnel constraints may be a minimum tunnel length. Approaches to generating visual guidance corresponding to feasibility may differ based on the number and kind of initial tunnel constraints, as will be explained. It willPT-6211-WO-PCTfurther be appreciated that tunnel diameter - expressed for example as a minimum and / or maximum tunnel diameter - may itself serve as an initial tunnel constraint.

[0102] Other initial tunnel constraints may be received, with the greater number of initial tunnel constraints received generally corresponding to a lower number of potential bone tunnel orientations to be assessed for feasibility with respect to one or more additional tunnel constraints. That is, as will be described, those potential bone tunnel orientations that do not even conform to the one or more initial tunnel constraints will not be assessed for feasibility with respect to any of the additional tunnel constraints, thereby generally reducing the overall amount of processing required to generate visual guidance as compared to situations in which a fewer number of initial tunnel constraints is received. It may, for example, be useful to consider that initial tunnel constraints are the kinds of constraints that a surgeon feels must all be conformed to, whereas additional tunnel constraints, examples of which are described herein, are the kinds of constraints that the surgeon may wish to use to present comparisons so the surgeon can decide which of the additional tunnel constraints are to be conformed to in a particular situation, and which of the additional tunnel constraints may not - in the surgeon’s judgement - need to be strictly conformed to in the particular situation. For example, a surgeon may require a particular tunnel entry point and tunnel length, and therefore may specify these as initial tunnel constraints, but may wish to learn in advance of actually drilling a tunnel which of the potential bone tunnel orientations having that tunnel entry point and tunnel length would have a sufficient back wall thickness and which potential bone tunnel orientations would not. It may be that the surgeon, after considering the visual guidance, would actually choose a tunnel orientation that resulted in a backwall thickness that was not sufficient when compared in isolation with a minimum back wall thickness provided as a distance value to the system, but that in her professional judgement would actually be sufficiently large to prevent backwall blowout, given the patient’s health and any other considerations, such that a bone tunnel oriented in this way would actually be a useful option.

[0103] The processor-based system generates the visual guidance using the 3D digital model, the at least one initial tunnel constraint, and at least one additional tunnel constraint. The visual guidance indicates an assessment of feasibility with respect toPT-6211-WO-PCTthe at least one additional tunnel constraint of each of a plurality of potential orientations of a bone tunnel that conforms to the at least one initial tunnel constraint.

[0104] As described above, FIG. 1 shows a feasibility measurement 200 for use in a feasibility assessment corresponding to tunnel length. It will be appreciated that determining the tunnel length for potential bone tunnel 150, when tunnel length has not been specified as an initial constraint, is useful for helping to determine whether potential bone tunnel 150 is feasible by comparing the determined tunnel length to any additional constraint related to tunnel length.

[0105] FIG. 2 shows another portion of the three-dimensional (3D) representation 100 of the digital 3D bone model of a femur from a second perspective, showing in overlay the potential bone tunnel 150 and a feasibility measurement 210 for use in a feasibility assessment corresponding to back wall distance. It will be appreciated that determining the backwall distance of potential bone tunnel 150 is useful for helping to determine whether potential bone tunnel 150 is feasible by comparing the determined back wall distance to any additional constraint related to back wall distance.

[0106] FIG. 3 shows another portion of the 3D representation 100 of the digital 3D bone model of a femur from a third perspective, showing in overlay the potential bone tunnel and a feasibility measurement 220 for use in a feasibility assessment corresponding to clearance. More particularly, feasibility measurement 220 is a minimum distance (i.e. a closest distance) of the longitudinal axis 705 of potential bone tunnel 150 when extending backwards along from a tunnel entry point of potential bone tunnel 150, from an anatomical feature - in this example the medial condyle of the femur. It will be appreciated that determining the closest distance of the longitudinal axis 705 of potential bone tunnel 150 from an anatomical feature is useful for helping to determine whether potential bone tunnel 150 is feasible by comparing the determined closest distance to any additional constraint related to minimum clearance distance. That is, to determine feasibility in connection with whether a surgical tool is likely to contact the anatomical feature when being positioned to actually form the potential bone tunnel 150.

[0107] Generating of the visual guidance may be done using different approaches, such as by using an exhaustive approach or by using an analytical approach, as will be described. In one example, an exhaustive approach determines all possible potentialPT-6211-WO-PCTbone tunnels through the bone - constrained by only the tunnel entry point as the initial constraint - and then calculates feasibility measurements corresponding to respective additional constraints, for each of the potential bone tunnels. The number of all possible potential bone tunnels through the bone would depend on the density of the digital 3D bone model, in the sense that defining a potential bone tunnel through the bone would be done by receiving a selection of the fixed tunnel entry point and then, one by one, automatically selecting another of the points on the surface of the digital 3D bone model to serve as the potential bone tunnel exit point, and thus establishing the orientations of straight lines corresponding to the longitudinal main axis of the potential bone tunnel passing through the fixed tunnel entry point and the automatically selected exit point. As such, the denser the digital 3D bone model in terms of surface point resolution, the more potential bone tunnels that could be determined, accordingly scaling the number of feasibility measurements that would have to be done. Approaches for reducing the amount of processing required for such an approach even with a dense digital 3D bone model may include establishing only one representative potential bone tunnel exit point each for a number of small patches of the surface of the digital 3D bone model, thus requiring processing for each of the feasibility metrics only once per small patch, rather than for every potential exit point pixel within that small patch. For example, a given patch may be a 2-mm x 2-mm patch, thus if choosing only one representative potential bone tunnel exit point for the 2x2 mm2patch, reducing the number of exit points and accordingly number of potential bone tunnels by % compared to the situation in which all points in the patch are processed as potential exit points. In another example, a given patch may be a 3-mm x 3-mm patch, thus if choosing only one representative potential bone tunnel exit point for the 3x3 mm2patch, reducing the number of exit points and accordingly number of potential bone tunnels being assessed by 8 / 9 compared to the situation in which all points in the patch are processed as potential exit points. Alternatives, including mixes of various approaches, are possible.

[0108] FIG. 4 shows a representation of a digital 3D bone model 100 from a first perspective and five (5) potential bone tunnels for which feasibility measurements would be done according to the exhaustive approach. FIG. 5 shows a representation of a digital 3D bone model 100 from a second perspective and the five (5) potential bone tunnels for which feasibility measurements would be done according to the exhaustivePT-6211-WO-PCTapproach. The five potential bone tunnels shown are only a small subset of the potential bone tunnels that would be determined and used to make feasibility measurements.

[0109] Using the exhaustive approach, computation of feasibility measurements (such as, tunnel length, backwall distance, clearance, and any other feasibility measurements corresponding in kind to additional constraints in relation to which feasibility is to be assessed), and computation of physical relationships between the feasibility measurements and the additional constraints (such as, whether a given feasibility measurement conforms to a corresponding additional constraint, by what margin the given feasibility measurement conforms, whether a given feasibility measurement does not conform to a corresponding additional constraint, by what margin the given feasibility measurement does not conform, etc.), can be conducted. These computations may then be used to generate the visual guidance.

[0110] The processor-based system may provide the visual guidance for display on a display device. A surgeon may thereafter view the visual guidance to aid with assessment of different bone tunnel orientations. FIG. 6 shows visual guidance indicating an assessment of feasibility, with respect to tunnel constraints, of multiple potential orientations of bone tunnel, in this example in the form of a feasibility map 300 presenting regions of differing feasibilities in a two-dimensional spherical coordinate system. Using spherical coordinates for representation of orientations of potential bone tunnels is useful since potential bone tunnels can be represented using two dimensions: azimuth angle ( 9 ) and elevation angle ( <t> ).

[0111] The various visually-distinguishable regions 310, 312, 314, 316, 318, 320, and 322, correspond to orientations of potential bone tunnels and the level of conformity of their feasibility measurements with a set of three (3) additional tunnel constraints. In this example, the additional tunnel constraints are: a minimum tunnel length, a minimum back wall thickness, and a minimum clearance distance to the medial condyle. Therefore, the feasibility assessments are: sufficient tunnel length (i.e., assess: is the tunnel length of the potential bone tunnel greater than or equal to the minimum tunnel length, or is it not?), sufficient backwall thickness (i.e., assess: is the backwall thickness extending from the potential bone tunnel greater than or equal to the minimum backwall thickness, or is it not?), and sufficient clearance to medial condyle (i.e., assess: is the minimum distance of the longitudinal axis of the potential bone tunnel to the medialPT-6211-WO-PCTcondyle greater than or equal to the minimum clearance distance to the medial condyle, or is it not?).

[0112] FIG. 7 is a legend 305 showing the correspondence between additional constraint conformity and regions in feasibility map 300 of FIG. 6. Therefore, in this example, region 320 corresponds to the orientations of potential bone tunnels that conform to none of the three constraints (shown as all X’s and no checkmarks); region 312 corresponds to the orientations of potential bone tunnels that conform to all of the three constraints (shown as all checkmarks and no X’s); region 318 corresponds to the orientations of potential bone tunnels that conform to just one the three constraints: the one being clearance (shown as two X’s and one checkmark); region 322 corresponds to the orientations of potential bone tunnels that conform to just one of the three constraints: the one being sufficient tunnel length (shown as one checkmark and two X’s); region 314 corresponds to the orientations of potential bone tunnels that conform to two of the three constraints: these being sufficient tunnel length and sufficient back wall thickness (shown as two checkmarks and one X); region 310 corresponds to the orientations of potential bone tunnels that conform to two of the three constraints: these being sufficient tunnel length and sufficient clearance (shown as two checkmarks and one X); and region 316 corresponds to the orientations of potential bone tunnels that conform to just one of the three constraints: the one being sufficient back wall thickness (shown as one checkmark and two X’s). It will be appreciated that only region 312 conforms to all of the additional constraints (all checkmarks), such that only potential bone tunnels with orientations corresponding to region 312 would conform to all constraints. However, this visual guidance including one or more regions corresponding to potential bone tunnels that would conform to fewer than all of the additional tunnel constraints enables a surgeon to apply professional judgement to select for drilling even the orientation of a potential bone tunnel that does not conform to all constraints given by the system but is otherwise, in the professional judgement of the surgeon, a useful and clinically sound orientation for a potential bone tunnel that may satisfy other constraints that are not specifically being brought to bear by the visual guidance system itself.

[0113] FIG. 8 shows visual guidance indicating an assessment of feasibility, with respect to tunnel constraints itemized in FIG. 7, of multiple potential orientations ofPT-6211-WO-PCTbone tunnel, in this example in the form of a feasibility map 400 presenting regions, such as regions 310, 312, 314, of differing feasibilities overlaid atop a representation of the bone 100 itself when displayed on a display device. It will be appreciated that the shape of the display of regions for visual guidance appropriate to a bone overlay such as in FIG. 8 will be different from the shape of the display of regions for visual guidance appropriate to a spherical coordinate system such as in FIG. 6.

[0114] FIG. 9 shows visual guidance 450 indicating a region 312 of full feasibility, with respect to the tunnel constraints itemized in FIG. 7, of multiple potential orientations of bone tunnel, in this example in the form of a feasibility map presenting just the one region 312 of full feasibility overlaid atop a representation of the bone 100 itself. A surgeon may be given the opportunity to select, using a user interface element, to simply show the region of all exit points that are fully feasible (that is, conform to all applied additional constraints). Within the one region 312 is shown a potential bone tunnel exit point 452 that may itself be made manipulable using a user interface element, to a selected position within the region 312. It will be appreciated that the bone of FIG. 9 and the bone of FIG. 8 may themselves be different such that the region 312 in FIG. 8 is not the same as the region 312 in FIG. 9. Rather, these two examples have been shown simply to illustrate that different manipulations of user interface elements may enable a user to adjust the manner in which visual guidance may be provided, such as by providing either complex, multi-faceted guidance (FIGS.6 and 8 being examples of this) or simple guidance (FIG. 9 being an example of this). It will also be appreciated that visual guidance may be provided as a 2D overlay over a 3D representation of a bone, rather than as a 3D overlay over the 3D representation of the bone as shown in FIGS. 8 and 9.

[0115] In examples, for example where only a tunnel entry location / point is provided as the initial tunnel constraint, the at least one additional tunnel constraint may be one or more of: a minimum bone tunnel length, a minimum back wall thickness, and a clearance, determined as a minimum lateral distance of a longitudinal axis of the bone tunnel from an anatomical feature opposite the tunnel entry location (such as the medial condyle), thereby to provide an assessment of feasibility in respect of clearance, as will be described herein.PT-6211-WO-PCT

[0116] Regarding tunnel lengths, currently, to measure tunnel lengths surgeons can use gauge devices that are applied to a guidewire after it has been already drilled through the bone.

[0117] Regarding back wall thicknesses, so-called “offset” aimers are surgical instruments offering the opportunity to execute femoral tunnels with a controlled amount of back wall thickness. Offset aimers have a 10 mm “tongue” that exits the aimer tip side towards the front, running along a fixed “offset” distance from the tunnel axis. Offset aimers with different offset distances are available. By pulling an offset aimer tongue against the femoral back wall, the surgeon can aim tunnels that will have a back wall thickness given by the margin between that aimer specific offset distance and the tunnel socket radius.

[0118] Regarding clearance, currently the accessibility for the tunnel execution is approximated by the clearance (in distance units) between a backward extension of the tunnel and the medial condyle and is measured as the shortest distance between both. This metric is relevant when using a straight aimer to place the guidewire as the geometry of a straight aimer increases the probability of collision with the medial condyle. Also, when drilling in an outside-in manner, this additional constraint is important to avoid and preferably prevent iatrogenic damage to the medial condyle.

[0119] Other clearance criteria may be added as additional constraints, for example, to avoid intersecting with or coming close to pre-existing ACL tunnels when conducting an ACL revision surgery, or to avoid a drill wire extending beyond an exit point interfering with another anatomical feature thereby to avoid iatrogenic injury near to the exit point.

[0120] In the examples of the present disclosure, measuring tunnel length of a given potential bone tunnel may be done by determining the distance between the tunnel entry point and the tunnel exit point. Determining orientation may be done by determining the azimuth and elevation angles of a straight line extending between the tunnel entry point and the tunnel exit point.

[0121] In examples of the present disclosure, to measure the tunnel back wall thickness the processor-implemented method simulates the use of a “dynamic” offset aimer. That is, given a potential bone tunnel, in an example the method computes how much "offset" an aimer would have to have so that such a potential bone tunnelPT-6211-WO-PCTcould be realized. In this example, that offset is computed as the shortest distance between the bone surface and the tunnel axis, measured perpendicular to the tunnel at a "tongue distance" of 10 mm from its entry. The back wall thickness is then measured as the difference between the computed offset and the tunnel’s radius.

[0122] By considering the path that is traversed by the line segment that joins the tunnel entry and the tunnel exit points of the potential ACL femoral tunnel, the described exhaustive approach is able to identify situations in which the tunnel has a portion that is located outside the 3D model and generate a feasibility map or other visual guidance while accounting for this issue. However, it has the disadvantage of being time-consuming and requiring significant processing resources because of the need to compute the metrics for all model points or potential bone tunnel orientations. As explained above, this can increase with the density of the digital 3D model. Instead, an analytical approach may be used.

[0123] A tunnel constraint related to tunnel length is that ACL femoral tunnels must have a length larger than a predefined threshold (the minimum tunnel length). To determine a region in a spherical (elevation 0 - azimuth <t>) map that corresponds to potential bone tunnels that satisfy this minimum tunnel length constraint, a sphere centered in the entry point with radius equal to the minimum tunnel length is considered. The periphery of this sphere is intersected with the model, to yield a 3D contour formed by model points at the periphery’s intersection with the model. Put another way, an example of an analytical approach may be to regard the minimum tunnel length as an initial tunnel constraint along with the tunnel entry point, such that there are two initial tunnel constraints, and feasibility metrics are not required to be assessed for any potential bone tunnels that do not conform to the two initial tunnel constraints.

[0124] FIG. 10 shows a representation of a bone model 100 of a distal femur showing, visually, the intersection with the bone of a representation of a sphere 500 centered at a determined tunnel entry point (not itself shown) and having a radius corresponding to the minimum tunnel length of any feasible bone tunnel. FIG. 11 shows the representation of the bone model 100 of the distal femur of FIG. 10, with a 3D contour 510 corresponding to the intersection of the 3D periphery of the sphere 500 with the bone model 100. Each point along the 3D contour 510 formed as a resultPT-6211-WO-PCTof the intersection may be assessed against any additional constraints as potential exit points for respective potential bone tunnels, and may be represented in visual guidance as spherical coordinates in a 6 - <t> map.

[0125] FIG. 12 shows visual guidance indicating an assessment of feasibility, with respect to initial tunnel constraints of tunnel entry point and bone tunnel length, of multiple potential orientations of bone tunnel, in this example in the form of a feasibility map 600 presenting a region 612 of infeasibility (that is, potential orientations that would not conform to the bone tunnel length constraint) and a region 610 of feasibility (that is, potential orientations that would conform to the bone tunnel length constraint) in a two-dimensional spherical coordinate system. That is, line 605 represents the points along 3D contour 510 represented in the spherical coordinates, and accordingly the dividing line between feasibility and infeasibility with respect to the tunnel length constraint.

[0126] In examples of the present disclosure, the minimum lateral distance of the longitudinal axis of the bone tunnel from an anatomical feature is intended to represent the amount of clearance from the anatomical feature during actual formation of the tunnel. As indicated above, in order to avoid iatrogenic injury, it may be useful to assess feasibility of a particular orientation of bone tunnel on the basis of how likely it would be that surgical tools used to form that particular bone tunnel would come into contact with the anatomical feature. In the particular example of the bone being a femur, such an anatomical feature may be the medial condyle of the femur. It would be useful to assess feasibility of a particular tunnel orientation in connection with how likely it would be that drilling tools used to form the tunnel in the bone would scrape against, or otherwise contact, the medial condyle. If, for example, it would be very difficult, or impossible, to form a particular orientation of potential bone tunnel without contacting the medial condyle with surgical instruments, a surgeon may eliminate that particular orientation from consideration, aided by the visual guidance provided herein. An assessment of this likelihood may be made by considering how close the longitudinal axis of the potential bone tunnel extending backwards from the tunnel entry location / point comes to the medial condyle or other anatomical feature, with too little a distance generally being associated with lower feasibility or infeasibility due to risk of iatrogenic damage during the surgical procedure.PT-6211-WO-PCT

[0127] FIG. 13 shows a representation of a bone model 100 of a distal femur showing, visually, the spatial determination of amount of clearance from an anatomical feature - in this example a medial condyle of the femur - rearward of a bone tunnel entry point that may be required in order to gain access for creating the bone tunnel with low risk of iatrogenic injury. FIG. 14 shows another representation of the bone model 100 of the distal femur of FIG. 13 showing, visually, the spatial determination of the amount of clearance from the anatomical feature.

[0128] More particularly, in the case of the anatomical feature being the medial condyle, the constraint related to the clearance to the medial condyle can be translated into considering as feasible only potential bone tunnels for which the distance between their longitudinal axes and the medial condyle is larger than some threshold c. In an example, to determine the allowed region in the feasibility map shown in FIG. 12, the processor-implemented method begins by determining a search region 700, as shown in FIG. 13. Determining search region 700 may be conducted using an automatic approach such as transference through statistical shape modeling (SSM) or identification of the medial side of the digital 3D bone model from the known anatomical directions of the digital 3D bone model. Then, for each point t in search region 700, a normal vector n_t is computed to identify the contour I depicted in FIG.6A by selecting the points t that satisfy the condition set forth in Equation 1 , below:n^(P - t) = 0, (Equation 1 )where:T represents the transpose operator and P is the tunnel entry point.

[0129] The operation represented by Equation 1 corresponds to finding the model points that, together with the tunnel entry point P, define lines that are tangent to the medial condyle.

[0130] Consider c as the minimum allowed distance between the tunnel axis and medial condyle - a constraint. The process determines directions i depicted in FIG.PT-6211-WO-PCT14 as the vectors that contain the entry point P and the selected points t shifted along their normals by this minimum allowed distance c, as set forth in Equation 2, below:i = p - (t + cn^) (Equation 2)where:normals n_t are assumed to point outwards.

[0131] Put another way, clearance with the medial condyle may be determined by finding contour points I on the region 700 of the medial condyle that originate lines that are tangent to the model. These points are then shifted to account for the minimum clearance distance c, originating directions i T By representing each direction i using spherical coordinates in the 9 - <t> map, the line 615 is obtained to be added to the spherical feasibility map, as shown in FIG. 15. A region 620 of allowed directions according to the criterion related to the clearance to the medial condyle is shown in FIG. 15. Therefore, FIG. 15 shows visual guidance in the form of a spherical feasibility map indicating an assessment of feasibility, with respect to both an initial tunnel constraint of bone tunnel length and an additional constraint of clearance, of multiple potential orientations of bone tunnel. The region at which both of regions 610 and 620 are present represents the orientations that satisfy both of these two constraints.

[0132] The back wall thickness is measured as the shortest orthogonal distance between the surface and the point that is 10mm from the entry point along the direction of the tunnel minus the radius of the tunnel. The criterion for the back wall thickness can then be assessed by considering a sphere centered at the entry point with a 10mm-radius and selecting the points that are located inside the sphere. Then, for each selected sphere point, the plane that is tangent to the sphere at that point is intersected with the model and the distance between each intersection point and the sphere point is computed. Sphere points for which the minimum of all the distances is larger than some threshold w correspond to feasible tunnel directions.

[0133] FIG. 16 shows visual guidance indicating an assessment of feasibility, with respect to an initial tunnel constraint of bone tunnel length and additional constraintsPT-6211-WO-PCTof both clearance and back wall thickness, of multiple potential orientations of bone tunnel, in this example in the form of a feasibility map 600 presenting regions of different feasibilities with respect to the constraints. In this example, the orientations in the digital 3D model that correspond to potential bone tunnels having the minimum back wall distance amount are represented as line 625, with the region 630 that line 625 encompasses representing orientations having at least the minimum back wall distance amount. Therefore, the region at which all three of regions 610, 620, and 630 are present represents the orientations that satisfy all three of these three constraints.

[0134] An alternative approach to determine the boundary of the feasible region corresponding to the back wall thickness criterion may be conducted as follows. A boundary in the 6 - map may be computed from the tunnel length and clearance to the medial condyle criteria. Then, the following steps may be followed:

[0135] 1. Select a boundary point s in the 0 - <T> map.

[0136] 2. Generate the 3D point G corresponding to s.

[0137] 3. Determine the point E that is 10mm away from the tunnel entry point P along the direction defined by P and G.

[0138] 4. Compute the signed distance d between E and the closest point M in the digital 3D model along the perpendicular direction, d is negative if E is located outside the model and positive otherwise.

[0139] 5. If d > w, where w is the threshold of the constraint, it means the current tunnel is in the feasible region (that is, also has sufficient back wall distance). In this case, record this and then select another boundary point s and return to step 2.

[0140] 6. Determine a unit vector v as follows• v=(E-M) / (||E-M||), if d>0• v=(M-E) / (||E-M||), if d<0• v = N, where N is the normal at M, if d = 0.

[0141] 7. Update the position of E by computing E = E + (w-d)v.

[0142] 8. Retrieve the spherical coordinates of E and update point s in the 6 - 0 map. Return to step 2.

[0143] This sequence of steps 1-8 is to be performed for all boundary points s in the 6 - 0 map. In general, the idea behind this approach is to iteratively update the currentPT-6211-WO-PCTboundary of the feasible region in the 0 - <t> map to result in the boundary of the region of 0 - <D points that satisfy the back wall thickness criterion.

[0144] In examples, an additional tunnel constraint may be a minimum distance within the bone of the bone tunnel from a pre-existing bone tunnel. It will be appreciated that, if a primary ACL reconstruction has already taken place, but the primary ACL reconstruction has failed, a revision ACL reconstruction may require taking into account the existence of bone tunnel that was used for the primary ACL reconstruction. It may be useful to either avoid intersecting a new bone tunnel with the pre-existing bone tunnel that was used for the primary ACL reconstruction altogether, or even substantially aligning the bone tunnel for the revision ACL reconstruction with the pre-existing in some way.

[0145] In examples, an additional tunnel constraint may be a minimum distance of a tunnel exit location from an anatomical feature opposite the tunnel exit location. It will be appreciated that, during ACL repair, a drill wire may first be drilled into the tunnel entry point, and through the bone to exit at the tunnel exit point. After assessment and confirmation of the pilot tunnel formed by the drill wire, a tunnel with the appropriate diameter and length may be drilled only part way - the sufficient tunnel length distance - along the pilot tunnel. However, at the time of drilling the pilot tunnel, a drill wire exiting from the tunnel exit point may then come into contact with another anatomical feature, causing iatrogenic injury. An assessment of this likelihood may be made by considering how close the tunnel exit point of the potential bone tunnel comes to the other anatomical feature, with too little a distance generally being associated with lower feasibility or infeasibility due to risk of iatrogenic damage occurring.

[0146] In examples, an additional tunnel constraint may be accessibility of the bone tunnel to a surgical instrument via a skin portal. It will be appreciated that a minimally-invasive procedure may make use of small skin portals, rather than fully open surgical sites, to provide surgical instruments with access from outside to the surgical site. However, a skin portal of a particular shape constrains the directions of approach by the surgical tools to the surgical site. It may be that a particular orientation of a potential bone tunnel satisfies all of the initial constraints and all of the additional constraints, except for being accessible via a particular planned skin portal. That is, it may be that an otherwise excellent option for a bone tunnel is simply not accessible via a particularPT-6211-WO-PCTskin portal. This may be used to inform where a skin portal ought itself to be formed. However, to the extent that the skin portal is already decided upon or otherwise surgically-required to be in a particular location and have a particular shape, the assessment with respect to the skin portal may operate as an additional tunnel constraint that narrows the set of feasible potential bone tunnels.

[0147] FIG. 17 shows a representation of a bone model 100 of a distal femur showing, visually, the spatial determination of accessibility by a surgical instrument 900 through a skin portal 800 for forming potential bone tunnels passing through a tunnel entry point. FIGS. 18A and 18B show representations of bone model 100 from respective perspectives and the spatial determination of accessibility using a surgical instrument 900 through skin portal 800 from the perspectives of respective ones of the azimuth and elevation angles. In the event that the location of the skin portal through which the aimer or other surgical instrument is to be inserted is known, an additional metric that identifies the possible tunnel orientations should be considered. It can be seen in these figures that, for a particular tunnel entry point, an aimer that is inserted through a portal can only reach a limited range of 9 and <t> values. This range is influenced by factors such as the size and orientation of the incision and the elasticity of the skin.

[0148] Assuming that the boundary of the portal at skin level is known, the range of possible 6, <t> values (representing potential bone tunnels that can be feasibly formed using the skin portal) can be determined by determining the lines that contain the boundary points and the entry point of the tunnel and afterwards computing the 6 and <t> values for each direction. Considering the illustrative portal of FIG. 17 and including this metric in the feasibility map of FIG. 6 would cause the feasible region to diminish, as illustrated by the area within the oval region 850 in the feasibility map 300 of FIG.19. That is, FIG. 19 shows visual guidance indicating an assessment of feasibility, with respect to both tunnel and skin portal accessibility constraints, of multiple potential orientations of bone tunnel, in this example in the form of feasibility map 300 presenting regions of differing feasibilities in a two-dimensional spherical coordinate system and a delineated overlapping region 850 presenting those of the regions that are accessible through the skin portal.PT-6211-WO-PCT

[0149] It will be appreciated that different models may be considered for skin portals: circles, ellipses, discrete or continuous sets of points or a single 3D point, in which case there is a single possible 0, <t> pair. If a skin portal can be represented / modeled by an analytical function, computation of the ranges of possible 0, <t> values can be done in an analytical manner without having to discretize the 3D space.

[0150] In case the true portal location is not known, different criteria may be used to infer its position:• Statistical information of the location of portals retrieved from the literature or from surgeon-based history (it can be assumed that each surgeon has his or her preferred portals and opens them in similar positions across patients (with respect to anatomical landmarks));• Probabilistic approach to define plausible portal locations;• Statistical shape models to transfer pre-defined portal locations to the current patient’s anatomy;• Other heuristics or more complex probabilistic modelling.

[0151] It will also be appreciated that, if the navigation procedure is to be outside-in (i.e., the ACL femoral tunnel is drilled from outside the anatomy) any point in the feasibility map 300 is itself accessible, since there are no surgical tool orientation or entry restrictions from any skin portals.

[0152] With respect to planning an ACL femoral tunnel, in examples, the processorbased system may receive a user selection of one or more of the plurality of potential orientations of the bone tunnel, and may store the selection in association with the digital 3D model of the bone. In this way, the selection of bone tunnel orientation may be made available for downstream planning and / or surgical guidance during a surgical procedure.

[0153] By having the methods and systems described herein to generate visual guidance such as feasibility maps, a surgeon is provided with visual guidance for planning a femoral tunnel location prior to an ACL reconstruction surgery that considers tunnel location, shape and desired variables like minimum back wall thickness and tunnel length. A digital plan generated on the basis of the digital 3D model, the planned tunnel entry location, and any other initial constraints as well as any additional constraints, can be used in conjunction with an intra-operative navigation system thatPT-6211-WO-PCTenables the execution according to the plan (Raposo C, Barreto JP, Sousa C, Ribeiro L, Melo R, Oliveira JP, Marques P, Fonseca F, Barrett D. Video-based computer navigation in knee arthroscopy for patient-specific ACL reconstruction. Int J Comput Assist Radiol Surg. 2019 Sep; 14(9): 1529-1539. doi: 10.1007 / s11548-019-02021-0.).

[0154] With a navigation system, the methods and systems described herein can also be applied on-the-fly, as an aimer is manipulated inside a femur, to assess potential bone tunnels defined by the aimer axis, or after the guidewire is placed, to assess the tunnel it defines. That is, a given potential bone tunnel defined by the aimer axis, whose orientation is determined based on processing of images captured by an image capture device such as an arthroscopic camera, can be processed for feasibility metrics such that visual guidance may be presented in real-time or near-real-time, as the aimer axis is moved within the surgical site and / or as the surgeon requests, from the system, an assessment.

[0155] As the systems and methods described herein provide a way to assess criteria over potentially all of the potential bone tunnel orientation and exit points, it may be possible to be visually guided to find optimal tunnel exit points that not only satisfy the criteria but also optimize additional metrics. For example, the systems and methods may be used to optimize the tunnel orientation so that the margins to the constraint thresholds are maximized, hence reducing the risk of the then executed (i.e. actually drilled, for example) tunnel failing the criteria due to the natural deviations that may arise from limitations on the navigation system accuracy or on the surgeon execution capability. For that objective, the optimization can also take into account the sensibility of the metrics to the tunnel orientation (lyyampillai G, Raman ET, Rajan DV, Krishnamoorthy A, Sahanand S. Determinants of Femoral Tunnel Length in Anterior Cruciate Ligament Reconstruction: CT Analysis of the Influence of Tunnel Orientation on the Length. Knee Surg Relat Res. 2013 Dec; 25(4):207-14. doi: 10.5792 / ksrr.2013.25.4.207.) In other words, it may be taken into account that tunnel length may have more variability in regions where angles between the ACL femoral tunnel and the normal of the bone surface at the tunnel exit point are larger.

[0156] Additional metrics may also be used to guide the solution to more clinically sound orientations. For example, while keeping the feasibility criteria fulfilled, further guidance may be provided to refine the tunnel exit point position towards the proximalPT-6211-WO-PCTand posterior directions, in order to reduce the graft bending angle and excursion according to Hodel et al.

[0157] While embodiments have been described, alternatives are possible.

[0158] For example, in other examples, feasibility metrics may be computed using alternative definitions. For example, a back wall thickness may alternatively be defined not as the smallest perpendicular distance from the tunnel to the bone surface at 10 mm depth alone, but, for example, as a function of the closest bone surface points along the entire tunnel length or by restricting the surface points e.g. by considering only posterior points.

[0159] It will be appreciated that feasibility assessments with respect to clearance from other anatomical structures may be conducted and incorporated into the systems and methods described herein. For example, similar processes as have been described herein may be used to provide guidance that seeks to avoid tunnel interference with the lateral collateral ligament (LCL) attachment, the popliteus tendon, the peroneal nerve, etc. Such additional clearance constraints may require that these anatomical structures be identified with respect to the digital 3D bone model. As for the actual approach, for avoiding the LCL attachment, the ridge of the lateral epicondyle may be determined in the digital 3D model using some manual or automatic approach, and the obtained region used as an exclusion region in a feasibility map. Automatic methods to detect the ridge of the epicondyle may be implemented using deep or machine learning schemes or may consider 3D morphological cues such as the local 3D curvature.

[0160] While approaches to exhaustive feasibility map creation have been described, in other examples the different tunnel feasibility metric computations may be accelerated by relying on accelerated data structures that allow quicker line-surface intersection tests and nearest neighbor search.

[0161] Feasibility metric computations may be implemented in various ways. For example, a given computation may rely mostly on a brute force search, for example, by measuring distances to every model point to find the nearest one. Alternatively or in some combination, it can rely on a multitude of acceleration data structures. Such data structures might be, among others, k-dimensional trees, R-trees, bounding volume hierarchy structures, etc.PT-6211-WO-PCT

[0162] It will be appreciated, the systems and methods described herein may be applied to different situations related to ACL reconstruction surgery, and they may be applied during planning, execution, and post-operative evaluation of a surgical procedure or set of procedures.

[0163] Potential bone tunnel evaluation maps may be computed by evaluating the space of possible potential bone tunnel orientations and then finding each respective tunnel exit point, or can be directly evaluated over the space of possible exit points on the bone surface. The spaces of evaluation may be broad or limited to smaller and more relevant subsets. Also, such maps may be computed by computing the boundaries of the feasibility regions, instead of by explicitly sampling tunnel orientations or exit points.

[0164] The presentation of a given feasibility map or other visual guidance can take various forms, and be in 2D or in 3D as illustrated herein. Additionally, a given feasibility map may present metrics and the criteria fulfillment differently than has been specifically depicted herein. For example, different levels of color or brightness might be used to convey magnitudes of metrics. Multiple combinations of map elements may be used to highlight some metrics and criteria while hiding others. User interface elements may be offered to enable a user to choose different modes of display, so as to enable the user to hone in on details or review possibilities at a higher level of abstraction or lower level of detail.

[0165] Along with the usages presented above, the systems and methods enable many combinations of objective functions and constraints. The ways by which optimizations may be carried out are not, in the present description, meant to be tied to any specific algorithm and could be done using many suitable mathematical optimization techniques available.

[0166] The location of the skin portal through which the surgical instruments are to be inserted may be inputted to the system by the surgeon that selects a location in a 2D or 3D representation of the anatomy. Alternatively, the portal location may be estimated automatically using the methods described in Applicant’s co-pending PCT (International) Patent Application No <TBD> entitled “Portal Estimation in Minimally Invasive Surgery (073888-24401),” the contents of which are incorporated herein by reference.PT-6211-WO-PCT

[0167] It will also be appreciated that some surgeons perform knee flexion when drilling a femoral tunnel. Knee flexion may cause a skin portal location to change with respect to the femur. In order to account for this, it may be possible to estimate the skin portal for the flexion used during drilling, before navigating the tunnel. Another option may be to use a motion model of the knee when it is rotating, in order to predict the new location of the portals or even use some motion model of the portals’ location. Such an estimation or a model may be used to modify the skin portal constraint itself before it is combined with the other constraints for determining feasible ones of the potential orientations of bone tunnel.

[0168] An alternative approach to providing guidance, or an approach that may be made available in combination with the approaches described herein, may be to provide guidance about feasibility of a potential bone tunnel that has been selected in particular, such that the assessment of feasibility is made only in respect of that selected potential bone tunnel. For example, a surgeon during planning may propose a particular bone tunnel by defining the particular bone tunnel in terms of at least a first point along the axis of the potential bone tunnel (such as an entry point) and a second point along the axis of the potential bone tunnel (such as an exit point). The surgeon may define the particular bone tunnel in terms of the first point and an orientation of the axis of the potential bone tunnel. This may be done by the surgeon selecting a point on a displayed representation of the 3D digital bone model to itself be displayed and serve as the entry point for a potential bone tunnel, and then manipulating a user interface element to move a displayed axis of the potential bone tunnel about the entry point to a particular elevation and azimuth in association with the displayed representation of the 3D digital bone model. This may alternatively be done by the surgeon selecting a first point on the 3D digital bone model to be displayed and serve as the entry point for a potential bone tunnel, and then selecting a second point on the 3D digital bone model to be displayed and serve as the exit point for the potential bone tunnel, with the axis of the potential bone tunnel extending at least from the entry point to the exit point. Whichever approach may be used to define the potential bone tunnel with respect to the 3D digital bone model, the surgeon may then view the potential bone tunnel during this planning, and in accordance with the present description, the system may thereafter automatically generate, or be caused throughPT-6211-WO-PCTa user interface request to generate, the guidance. The guidance may be generated using the 3D digital bone model, at least one tunnel constraint, and the potential bone tunnel data (i.e. , the first point along the potential bone tunnel axis and at least one: of a second point along the potential bone tunnel axis and an orientation of the potential bone tunnel axis). In this way, the surgeon can approach the task of selecting a bone tunnel by defining a potential bone tunnel using the system and having the system provide guidance indicating an assessment of feasibility for that potential bone tunnel, rather than providing guidance indicating an assessment of feasibility for a plurality of potential bone tunnels, as in other examples described herein.

[0169] FIGS. 22A, 22B, and 22C show guidance about feasibility of a potential bone tunnel, in particular visual guidance about feasibility of the potential bone tunnel, presented on a video display device 2014, according to examples. In particular, FIG.22A shows contents of a display device with a first visual guidance area 3100 for showing indicia representing feasibility of the potential bone tunnel with respect to individual tunnel constraints, in this example three (3) tunnel constraints, and a second visual guidance area 3200 for showing indicia representing overall feasibility of the potential bone tunnel. In FIG. 22A, an assessment of feasibility has not yet been generated in respect of any of the individual tunnel constraints, nor has there yet been generated an overall assessment of feasibility of the potential bone tunnel.

[0170] In this example, a user, such as a surgeon, who has defined a potential bone tunnel as explained herein or has received a definition of the potential bone tunnel for the purpose of feasibility assessment, may select user interface element 3002 in order to cause the system to generate guidance indicating an assessment of feasibility with respect to the three (3) tunnel constraints of: sufficient length, sufficient back wall thickness, and sufficient clearance.

[0171] In FIG. 22B, first visual guidance area 3100 has changed in content by indicating, in respect of each of the three tunnel constraints, whether or not (indicated as Y for YES or N for NO) the potential bone tunnel conforms to the constraint. As can be seen, the assessment has determined that the potential bone tunnel conforms only to the first and second of the three tunnel constraints, and not to the third. In accordance with the assessment, due to the potential bone tunnel having been assessed as infeasible with respect to at least one tunnel constraint, second visualPT-6211-WO-PCTguidance area 3200 has changed in content by indicating that the potential bone tunnel is infeasible. The user may wish to be guided only by the information in second visual guidance area 3200, or may wish to determine which of the multiple tunnel constraints to which the potential bone tunnel would fail to conform.

[0172] The user may choose a different potential bone tunnel to conduct another assessment. For example, in FIG. 22C, first visual guidance area 3100 has changed in content by indicating, in respect of each of the three tunnel constraints, whether or not (indicated as Y for YES or N for NO) the different potential bone tunnel conforms to the constraint. As can be seen, the assessment has determined that the potential bone tunnel conforms to all three of the tunnel constraints (all Y’s). In accordance with the assessment, due to the potential bone tunnel having been assessed as feasible with respect to all of the tunnel constraints, second visual guidance area 3200 has changed in content by indicating that the potential bone tunnel is feasible.

[0173] Various approaches to presenting a visual assessment of feasibility of the potential bone tunnel may be conducted. For example, in FIGS. 23A, 23B, and 23C, only a second visual guidance area 3200, providing an indication of feasible or infeasible, is displayed. In this example, the assessment of feasibility with respect to the one or more tunnel constraints would be conducted upon selection by the user of the “Check Current Potential Tunnel”, but only the overall outcome of Feasible or Infeasible for whichever potential bone tunnel is being assessed is presented to the user. A user may be provided with the option to select this simplified display or a more detailed display such as that shown in FIGS. 22A-22C.

[0174] Therefore, numerous approaches for providing visual guidance with respect to a particular potential bone tunnel may be enabled. For example, generally, visual guidance may include a change in content displayed on a display device responsive to the potential bone tunnel being assessed as infeasible with respect to the at least one tunnel constraint. Such a change in content may be one or more of: a change in appearance of an indicia being displayed on the display device, a display of an indicia on the display device, and a removal from display of an indicia on the display device. Alternatively or in some combination, visual guidance may include a change in content displayed on a display device responsive to the potential bone tunnel being assessed as feasible with respect to the at least one tunnel constraint. Such a change in contentPT-6211-WO-PCTmay be one or more of: a change in appearance of an indicia being displayed on the display device, a display of an indicia on the display device, and a removal from display of an indicia on the display device.

[0175] Other approaches for presenting guidance may be provided. For example, guidance could be visual as in examples provided. Alternatively, or in some combination, guidance presented by a user interface device could be audible guidance or haptic guidance or another form of perceivable guidance. For example, audible guidance may include an audible sound such as a particular tone presented by the user interface responsive to the potential bone tunnel being assessed as feasible with respect to the at least one tunnel constraint. Alternatively or in some combination, audible guidance may include an audible sound such as a particular tone presented by the user interface responsive to the potential bone tunnel being assessed as infeasible with respect to the at least one tunnel constraint.

[0176] Various ways of providing guidance, whether it be visual, audible, haptic, or some combination of these, may be provided. For example, as in the examples of FIGS. 22A-22C and 23A-23C, the guidance indicates that the potential bone tunnel is feasible only responsive to the potential bone tunnel conforming to all of the at least one tunnel constraint, and the guidance indicates that the potential bone tunnel is infeasible responsive to the potential bone tunnel conforming to fewer than all of the at least one tunnel constraint.

[0177] In other examples, where there are at least two tunnel constraints, the guidance may include a first guidance that indicates that the potential bone tunnel is feasible with respect to a first of the at least two tunnel constraints; and a second guidance different from the first guidance and that indicates that the potential bone tunnel is feasible with respect to a second of the at least two tunnel constraints. For example, while assessing just one potential bone tunnel, a visual, audible and / or haptic guidance may be different for each tunnel constraint. As one example, upon assessment of feasibility that find that the potential bone tunnel conforms to a first tunnel constraint but not a second tunnel constraint, the user interface may present a first predetermined sequence of tones that is indicative of a positive result (such as a short happy song) and then second, different, short sequence of tones that is indicative of a negative result (such as a short sad song). In this way, the user would be madePT-6211-WO-PCTaware that only the first of the tunnel constraints would be conformed to by the potential bone tunnel. A third guidance different from such first guidance and second guidance may be presented when all tunnel constraints are conformed to, such as a third short sequence of tones that is indicative of a triumphant result (such as a short triumphant song). Variations are possible.SOFTWARE AND HARDWARE

[0178] FIG. 20 shows a processor-implemented method of providing visual guidance for planning a bone tunnel, in accordance with at least some examples. In particular, the method starts (block 1800) and comprises: receiving, by one or more processor, a 3D digital model of a bone (block 1802); receiving, by the one or more processor, at least one initial tunnel constraint, the at least one initial tunnel constraint comprising a tunnel entry location (block 1804); generating, by the one or more processor, the visual guidance using the 3D digital model, the at least one initial tunnel constraint, and at least one additional tunnel constraint, wherein the visual guidance indicates an assessment of feasibility with respect to the at least one additional tunnel constraint of each of a plurality of potential orientations of a bone tunnel that conforms to the at least one initial tunnel constraint (lock 1806); and providing, by the one or more processor, the visual guidance for display on a display device (block 1808). Thereafter the method ends (block 1810). The example method may be executed repeatedly with different numbers and / or kinds of initial and / or additional tunnel constraints, in order to provide visual guidance of feasibility in respect of the different numbers and / or kinds of initial and / or additional tunnel constraints. The example method may be executed along with additional steps. The example method may be implemented by computer instructions stored in memory and executed by the processor and / or multiple processors of a computer system, for output of the visual guidance on a display device. A non-transitory processor-readable medium may embody processor-readable program code executable by at least one processor to carry out the processor-implemented method.

[0179] FIG. 21 shows an example computer system 2000. In one example, computer system 2000 may correspond to a surgical planning system, a surgical controller, a tablet device within a surgical room, or any other system that implementsPT-6211-WO-PCTany or all the various methods discussed in this specification as part of a surgical planning and / or guidance system. The computer system 2000 may be connected (e.g., networked) to other computer systems in 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 in use in a surgical procedure). The 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 taken by that device. Further, while only a single computer system is illustrated, the term “computer” shall also be taken to include any collection of computers that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methods discussed herein.

[0180] 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.

[0181] Processing device 2002 represents one or more general-purpose processing devices such as a microprocessor, central processing unit, or the like. More particularly, the processing device 2002 may be a complex instruction set computing (CISC) microprocessor, reduced instruction set computing (RISC) microprocessor, very long instruction word (VLIW) microprocessor, or a processor implementing other instruction sets or processors implementing a combination of instruction sets. The processing device 2002 may also be one or more special-purpose processing devices such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), network processor, or the like. The processing device 2002 is configured to execute instructions for performing any of the operations and steps discussed herein. Once programmed with specific instructions, the processing device 2002, and thus the entire computer system 2000, becomes a special-purpose device, such as the surgical controller 418.

[0182] 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 also may include a video display 2014 (e.g., display devicePT-6211-WO-PCT414), one or more input devices 2016 (e.g., a microphone, a keyboard, and / or a 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 i.e. liquid crystal display touch screen).

[0183] The data storage device 2008 may include a computer-readable storage medium 2020, or “memory,” on which the instructions 2022 (e.g., implementing any methods and any functions performed by any device and / or component depicted described herein) embodying any one or more of the methodologies or functions described herein is stored. 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. As such, the main memory 2004 and the processing device 2002 also constitute computer-readable media or memory. In certain cases, the instructions 2022 may further be transmitted or received over a network via the network interface device 2012.

[0184] While the computer-readable storage medium 2020 is shown in the illustrative examples to be a single medium, the term “computer-readable storage medium” or “memory” should be taken to include a single medium or multiple media (e.g., a centralized or distributed database, and / or associated caches and servers) that store the one or more sets of instructions. The term “computer-readable storage medium” shall also be taken to include any medium that is capable of storing, encoding or carrying a set of instructions for execution by the machine and that cause the machine to perform any one or more of the methodologies of the present disclosure. The term “computer-readable storage medium” shall accordingly be taken to include, but not be limited to, solid-state memories, optical media, and magnetic media. The computer-readable storage medium may be non-transitory.

[0185] FIG. 24 shows a processor-implemented method of providing guidance about feasibility of a potential bone tunnel, in accordance with at least some examples. In particular, the method starts (block 3500) and comprises: receiving, by one or more processor, a 3D digital model of a bone (block 3502); receiving, by the one or more processor, at least one tunnel constraint (block 3504); receiving, by the one or more processor, potential bone tunnel data defining a potential bone tunnel, the potential bone tunnel data comprising a first point along an axis of the potential bone tunnel and atPT-6211-WO-PCTleast one of: (a) a second point along the axis of the potential bone tunnel and (b) an orientation of the axis of the potential bone tunnel (block 3506); generating, by the one or more processor, the guidance using the 3D digital model, the at least one initial tunnel constraint, and the potential bone data, wherein the guidance indicates an assessment of feasibility with respect to the at least one tunnel constraint of the potential bone tunnel (block 3508); and providing, by the one or more processor, the guidance for presentation by a user interface device (block 3510). Thereafter the method ends (block 3512). The example method may be executed repeatedly with different numbers and / or kinds of tunnel constraints, in order to provide guidance of feasibility in respect of the different numbers and / or kinds of tunnel constraints. The example method may be executed along with additional steps. The example method may be implemented by computer instructions stored in memory and executed by the processor and / or multiple processors of a computer system, for output of the visual guidance on a display device. A non-transitory processor-readable medium may embody processor-readable program code executable by at least one processor to carry out the processor-implemented method.

[0186] Clauses

[0187] Clause 1. A system for providing visual guidance for planning a bone tunnel, the system comprising:

[0188] a display device;

[0189] memory storing one or more instructions; and

[0190] one or more processing devices configured to execute the one or more instructions, wherein executing the one or more instructions causes the system to:

[0191] receive a 3D digital model of a bone;

[0192] receive at least one initial tunnel constraint, the at least one initial tunnel constraint comprising a tunnel entry location;

[0193] generate the visual guidance using the 3D digital model, the at least one initial tunnel constraint, and at least one additional tunnel constraint, wherein the visual guidance indicates an assessment of feasibility with respect to the at least one additional tunnel constraint of each of a plurality of potential orientations of a bone tunnel that conforms to the at least one initial tunnel constraint; and

[0194] display the visual guidance on the display device.PT-6211-WO-PCT

[0195] Clause 2. The system of clause 1, wherein executing the one or more instructions causes the system to:

[0196] receive a user selection of one or more of the plurality of potential orientations of the bone tunnel; and

[0197] store the user selection in association with the digital 3D model of the bone.

[0198] Clause s. The system of clause 1, wherein the at least one initial tunnel constraint further comprises a minimum bone tunnel length.

[0199] Clause 4. The system of clause 1 , wherein the at least one additional tunnel constraint comprises at least one of: a minimum bone tunnel length, a minimum back wall thickness, and a minimum lateral distance of a longitudinal axis of the bone tunnel from an anatomical feature opposite the tunnel entry location.

[0200] Clause 5. The system of clause 4, wherein the bone is a femur and the anatomical feature opposite the tunnel entry location is a medial condyle of the femur.

[0201] Clause 6. The system of clause 1 , wherein the at least one additional tunnel constraint comprises: a minimum distance within the bone of the bone tunnel from a pre-existing bone tunnel.

[0202] Clause 7. The system of clause 1 , wherein the at least one additional tunnel constraint comprises: a minimum distance of a tunnel exit location from an anatomical feature opposite the tunnel exit location.

[0203] Clause 8. The system of clause 1 , wherein the at least one additional tunnel constraint comprises: accessibility of the bone tunnel to a surgical instrument via a skin portal.

[0204] Clause 9. The system of clause 1 , wherein the tunnel entry location is a region encompassing a plurality of potential bone tunnel entry points, wherein the visual guidance indicates the assessment of feasibility in respect of two or more of the potential bone tunnel entry points.

[0205] Clause 10. The system of clause 1, wherein the tunnel entry location is a single tunnel entry point.

[0206] Clause 11. The system of clause 1 , wherein the visual guidance includes a feasibility map.PT-6211-WO-PCT

[0207] Clause 12. The system of clause 11, wherein the feasibility map comprises one or more regions corresponding to potential bone tunnels that would conform to all of the at least one additional tunnel constraint.

[0208] Clause 13. The system of clause 12, wherein there is a plurality of additional tunnel constraints, and the feasibility map comprises one or more regions corresponding to potential bone tunnels that would conform to fewer than all of the additional tunnel constraints.

[0209] Clause 14. The system of clause 11, wherein executing the one or more instructions causes the system to display the visual guidance on the display device by overlaying the feasibility map on a representation of the digital 3D model of the bone displayed on the display device.

[0210] Clause 15. A processor-implemented method of providing visual guidance for planning a bone tunnel, the method comprising:

[0211] receiving, by one or more processor, a 3D digital model of a bone;

[0212] receiving, by the one or more processor, at least one initial tunnel constraint, the at least one initial tunnel constraint comprising a tunnel entry location;

[0213] generating, by the one or more processor, the visual guidance using the 3D digital model, the at least one initial tunnel constraint, and at least one additional tunnel constraint, wherein the visual guidance indicates an assessment of feasibility with respect to the at least one additional tunnel constraint of each of a plurality of potential orientations of a bone tunnel that conforms to the at least one initial tunnel constraint; and

[0214] providing, by the one or more processor, the visual guidance for display on a display device.

[0215] Clause 16. The processor-implemented method of clause 15, further comprising:

[0216] receiving a user selection of one or more of the plurality of potential orientations of the bone tunnel; and

[0217] storing the user selection in association with the digital 3D model of the bone.

[0218] Clause 17. The processor-implemented method of clause 15, wherein the at least one initial tunnel constraint further comprises a minimum bone tunnel length.PT-6211-WO-PCT

[0219] Clause 18. The processor-implemented method of clause 15, wherein the at least one additional tunnel constraint comprises at least one of: a minimum bone tunnel length, a minimum back wall thickness, and a minimum lateral distance of a longitudinal axis of the bone tunnel from an anatomical feature opposite the tunnel entry location.

[0220] Clause 19. The processor-implemented method of clause 18, wherein the bone is a femur and the anatomical feature opposite the tunnel entry location is a medial condyle of the femur.

[0221] Clause 20. The processor-implemented method of clause 15, wherein the at least one additional tunnel constraint comprises: a minimum distance within the bone of the bone tunnel from a pre-existing bone tunnel.

[0222] Clause 21. The processor-implemented method of clause 15, wherein the at least one additional tunnel constraint comprises: a minimum distance of a tunnel exit location from an anatomical feature opposite the tunnel exit location.

[0223] Clause 22. The processor-implemented method of clause 15, wherein the at least one additional tunnel constraint comprises: accessibility of the bone tunnel to a surgical instrument via a skin portal.

[0224] Clause 23. The processor-implemented method of clause 15, wherein the tunnel entry location is a region encompassing a plurality of potential bone tunnel entry points, wherein the visual guidance indicates the assessment of feasibility in respect of two or more of the potential bone tunnel entry points.

[0225] Clause 24. The processor-implemented method of clause 15, wherein the tunnel entry location is a single tunnel entry point.

[0226] Clause 25. The processor-implemented method of clause 15, wherein the visual guidance includes a feasibility map.

[0227] Clause 26. The processor-implemented method of clause 25, wherein the feasibility map comprises one or more regions corresponding to potential bone tunnels that would conform to all of the at least one additional tunnel constraint.

[0228] Clause 27. The processor-implemented method of clause 26, wherein there is a plurality of additional tunnel constraints, and the feasibility map comprises one or more regions corresponding to potential bone tunnels that would conform to fewer than all of the additional tunnel constraints.PT-6211-WO-PCT

[0229] Clause 28. The processor-implemented method of clause 25, wherein providing, by the one or more processor, the visual guidance for display on a display device comprises providing the feasibility map as an overlay for a representation of the digital 3D model of the bone to be displayed on the display device.

[0230] Clause 29. A non-transitory processor-readable medium embodying processor-readable program code executable by at least one processor to carry out the processor-implemented method of clause 15.

[0231] Clause 30. A system for providing guidance about feasibility of a potential bone tunnel, the system comprising:

[0232] a user interface;

[0233] memory storing one or more instructions; and

[0234] one or more processing devices configured to execute the one or more instructions, wherein executing the one or more instructions causes the system to:

[0235] receive a 3D digital model of a bone;

[0236] receive at least one tunnel constraint;

[0237] receive potential bone tunnel data defining the potential bone tunnel, the potential bone tunnel data comprising a first point along an axis of the potential bone tunnel and at least one of: (a) a second point along the axis of the potential bone tunnel and (b) an orientation of the axis of the potential bone tunnel;

[0238] generate the guidance using the 3D digital model, the at least one tunnel constraint, and the potential bone tunnel data, wherein the guidance indicates an assessment of feasibility with respect to the at least one tunnel constraint of the potential bone tunnel; and

[0239] present the guidance using the user interface.

[0240] Clause 31. The system of clause 30, wherein the user interface comprises a display device, and the guidance comprises visual guidance displayed on the display device.

[0241] Clause 32. The system of clause 31 , wherein the visual guidance comprises a change in content displayed on the display device responsive to the potential bone tunnel being assessed as infeasible with respect to the at least one tunnel constraint.

[0242] Clause 33. The system of clause 32, wherein the change in content displayed on the display device is selected from the group consisting of: a change in appearancePT-6211-WO-PCTof an indicia being displayed on the display device, a display of an indicia on the display device, and a removal from display of an indicia on the display device.

[0243] Clause 34. The system of clause 31 , wherein the visual guidance comprises a change in content displayed on the display device responsive to the potential bone tunnel being assessed as feasible with respect to the at least one tunnel constraint.

[0244] Clause 35. The system of clause 34, wherein the change in content displayed on the display device is selected from the group consisting of: a change in appearance of an indicia being displayed on the display device, a display of an indicia on the display device, and a removal from display of an indicia on the display device.

[0245] Clause 36. The system of clause 30, wherein the guidance comprises at least one of: visual guidance, audible guidance, and haptic guidance.

[0246] Clause 37. The system of clause 36, wherein the audible guidance comprises an audible sound presented by the user interface responsive to the potential bone tunnel being assessed as feasible with respect to the at least one tunnel constraint.

[0247] Clause 38. The system of clause 36, wherein the audible guidance comprises an audible sound presented by the user interface responsive to the potential bone tunnel being assessed as infeasible with respect to the at least one tunnel constraint.

[0248] Clause 39. The system of clause 30, wherein the guidance indicates that the potential bone tunnel is feasible only responsive to the potential bone tunnel conforming to all of the at least one tunnel constraint.

[0249] Clause 40. The system of clause 30, wherein the guidance indicates that the potential bone tunnel is infeasible responsive to the potential bone tunnel conforming to fewer than all of the at least one tunnel constraint.

[0250] Clause 41. The system of clause 30, wherein the at least one tunnel constraint comprises at least two tunnel constraints, and the guidance comprises:

[0251] a first guidance that indicates that the potential bone tunnel is feasible with respect to a first of the at least two tunnel constraints; and

[0252] a second guidance different from the first guidance and that indicates that the potential bone tunnel is feasible with respect to a second of the at least two tunnel constraints.PT-6211-WO-PCT

[0253] Clause 42. The system of clause 41 , wherein the guidance further comprises:

[0254] a third guidance different from the first guidance and from the second guidance and that indicates that the potential bone tunnel is feasible with respect to all of the at least two tunnel constraints.

[0255] Clause 43. A processor-implemented method of providing guidance about feasibility of a potential bone tunnel, the method comprising:

[0256] receiving, by one or more processor, a 3D digital model of a bone;

[0257] receiving, by the one or more processor, at least one tunnel constraint;

[0258] receiving, by the one or more processor, potential bone tunnel data defining the potential bone tunnel, the potential bone tunnel data comprising a first point along an axis of the potential bone tunnel and at least one of: (a) a second point along the axis of the potential bone tunnel and (b) an orientation of the axis of the potential bone tunnel;

[0259] generating, by the one or more processor, the guidance using the 3D digital model, the at least one tunnel constraint, and the potential bone tunnel data, wherein the guidance indicates an assessment of feasibility with respect to the at least one tunnel constraint of the potential bone tunnel; and

[0260] providing, by the one or more processor, the guidance for presentation by a user interface device.

[0261] Clause 44. The processor-implemented method of clause 43, wherein the user interface comprises a display device, and the guidance comprises visual guidance displayed on the display device.

[0262] Clause 45. The processor-implemented method of clause 44, wherein the visual guidance comprises a change in content displayed on the display device responsive to the potential bone tunnel being assessed as infeasible with respect to the at least one tunnel constraint.

[0263] Clause 46. The processor-implemented method of clause 45, wherein the change in content displayed on the display device is selected from the group consisting of: a change in appearance of an indicia being displayed on the display device, a display of an indicia on the display device, and a removal from display of an indicia on the display device.PT-6211-WO-PCT

[0264] Clause 47. The processor-implemented method of clause 44, wherein the visual guidance comprises a change in content displayed on the display device responsive to the potential bone tunnel being assessed as feasible with respect to the at least one tunnel constraint.

[0265] Clause 48. The processor-implemented method of clause 47, wherein the change in content displayed on the display device is selected from the group consisting of: a change in appearance of an indicia being displayed on the display device, a display of an indicia on the display device, and a removal from display of an indicia on the display device.

[0266] Clause 49. The processor-implemented method of clause 43, wherein the guidance comprises at least one of: visual guidance, audible guidance, and haptic guidance.

[0267] Clause 50. The processor-implemented method of clause 49, wherein the audible guidance comprises an audible sound presented by the user interface responsive to the potential bone tunnel being assessed as feasible with respect to the at least one tunnel constraint.

[0268] Clause 51. The processor-implemented method of clause 49, wherein the audible guidance comprises an audible sound presented by the user interface responsive to the potential bone tunnel being assessed as infeasible with respect to the at least one tunnel constraint.

[0269] Clause 52. The processor-implemented method of clause 43, wherein the guidance indicates that the potential bone tunnel is feasible only responsive to the potential bone tunnel conforming to all of the at least one tunnel constraint.

[0270] Clause 53. The processor-implemented method of clause 43, wherein the guidance indicates that the potential bone tunnel is infeasible responsive to the potential bone tunnel conforming to fewer than all of the at least one tunnel constraint.

[0271] Clause 54. The processor-implemented method of clause 43, wherein the at least one tunnel constraint comprises at least two tunnel constraints, and the guidance comprises:

[0272] a first guidance that indicates that the potential bone tunnel is feasible with respect to a first of the at least two tunnel constraints; andPT-6211-WO-PCT

[0273] a second guidance different from the first guidance and that indicates that the potential bone tunnel is feasible with respect to a second of the at least two tunnel constraints.

[0274] Clause 55. The processor-implemented method of clause 54, wherein the guidance further comprises:

[0275] a third guidance different from the first guidance and from the second guidance and that indicates that the potential bone tunnel is feasible with respect to all of the at least two tunnel constraints.

[0276] Clause 56. A non-transitory processor-readable medium embodying processor-readable program code executable by at least one processor to carry out the processor-implemented method of clause 43.

Claims

PT-6211-WO-PCTCLAIMSWhat is claimed is:

1. A system for providing visual guidance for planning a bone tunnel, the system comprising:a display device;memory storing one or more instructions; andone or more processing devices configured to execute the one or more instructions, wherein executing the one or more instructions causes the system to:receive a 3D digital model of a bone;receive at least one initial tunnel constraint, the at least one initial tunnel constraint comprising a tunnel entry location;generate the visual guidance using the 3D digital model, the at least one initial tunnel constraint, and at least one additional tunnel constraint, wherein the visual guidance indicates an assessment of feasibility with respect to the at least one additional tunnel constraint of each of a plurality of potential orientations of a bone tunnel that conforms to the at least one initial tunnel constraint; and display the visual guidance on the display device.

2. The system of claim 1 , wherein executing the one or more instructions causes the system to:receive a user selection of one or more of the plurality of potential orientations of the bone tunnel; andstore the user selection in association with the digital 3D model of the bone.

3. The system of claim 1 , wherein the at least one initial tunnel constraint further comprises a minimum bone tunnel length.

4. The system of claim 1, wherein the at least one additional tunnel constraint comprises at least one of: a minimum bone tunnel length, a minimum back wall thickness, and a minimum lateral distance of a longitudinal axis of the bone tunnel from an anatomical feature opposite the tunnel entry location.PT-6211-WO-PCT5. The system of claim 4, wherein the bone is a femur and the anatomical feature opposite the tunnel entry location is a medial condyle of the femur.

6. The system of claim 1, wherein the at least one additional tunnel constraint comprises: a minimum distance within the bone of the bone tunnel from a pre-existing bone tunnel.

7. The system of claim 1, wherein the at least one additional tunnel constraint comprises: a minimum distance of a tunnel exit location from an anatomical feature opposite the tunnel exit location.

8. The system of claim 1, wherein the at least one additional tunnel constraint comprises: accessibility of the bone tunnel to a surgical instrument via a skin portal.

9. The system of claim 1, wherein the tunnel entry location is a region encompassing a plurality of potential bone tunnel entry points, wherein the visual guidance indicates the assessment of feasibility in respect of two or more of the potential bone tunnel entry points.

10. The system of claim 1 , wherein the tunnel entry location is a single tunnel entry point.

11. The system of claim 1 , wherein the visual guidance includes a feasibility map.

12. The system of claim 11, wherein the feasibility map comprises one or more regions corresponding to potential bone tunnels that would conform to all of the at least one additional tunnel constraint.

13. The system of claim 12, wherein there is a plurality of additional tunnel constraints, and the feasibility map comprises one or more regions corresponding toPT-6211-WO-PCTpotential bone tunnels that would conform to fewer than all of the additional tunnel constraints.

14. The system of claim 11 , wherein executing the one or more instructions causes the system to display the visual guidance on the display device by overlaying the feasibility map on a representation of the digital 3D model of the bone displayed on the display device.

15. A processor-implemented method of providing visual guidance for planning a bone tunnel, the method comprising:receiving, by one or more processor, a 3D digital model of a bone; receiving, by the one or more processor, at least one initial tunnel constraint, the at least one initial tunnel constraint comprising a tunnel entry location;generating, by the one or more processor, the visual guidance using the 3D digital model, the at least one initial tunnel constraint, and at least one additional tunnel constraint, wherein the visual guidance indicates an assessment of feasibility with respect to the at least one additional tunnel constraint of each of a plurality of potential orientations of a bone tunnel that conforms to the at least one initial tunnel constraint; andproviding, by the one or more processor, the visual guidance for display on a display device.

16. The processor-implemented method of claim 15, further comprising:receiving a user selection of one or more of the plurality of potential orientations of the bone tunnel; andstoring the user selection in association with the digital 3D model of the bone.

17. The processor-implemented method of claim 15, wherein the at least one initial tunnel constraint further comprises a minimum bone tunnel length.

18. The processor-implemented method of claim 15, wherein the at least one additional tunnel constraint comprises at least one of: a minimum bone tunnel length, aPT-6211-WO-PCTminimum back wall thickness, and a minimum lateral distance of a longitudinal axis of the bone tunnel from an anatomical feature opposite the tunnel entry location.

19. The processor-implemented method of claim 18, wherein the bone is a femur and the anatomical feature opposite the tunnel entry location is a medial condyle of the femur.

20. The processor-implemented method of claim 15, wherein the at least one additional tunnel constraint comprises: a minimum distance within the bone of the bone tunnel from a pre-existing bone tunnel.

21. The processor-implemented method of claim 15, wherein the at least one additional tunnel constraint comprises: a minimum distance of a tunnel exit location from an anatomical feature opposite the tunnel exit location.

22. The processor-implemented method of claim 15, wherein the at least one additional tunnel constraint comprises: accessibility of the bone tunnel to a surgical instrument via a skin portal.

23. The processor-implemented method of claim 15, wherein the tunnel entry location is a region encompassing a plurality of potential bone tunnel entry points, wherein the visual guidance indicates the assessment of feasibility in respect of two or more of the potential bone tunnel entry points.

24. The processor-implemented method of claim 15, wherein the tunnel entry location is a single tunnel entry point.

25. The processor-implemented method of claim 15, wherein the visual guidance includes a feasibility map.PT-6211-WO-PCT26. The processor-implemented method of claim 25, wherein the feasibility map comprises one or more regions corresponding to potential bone tunnels that would conform to all of the at least one additional tunnel constraint.

27. The processor-implemented method of claim 26, wherein there is a plurality of additional tunnel constraints, and the feasibility map comprises one or more regions corresponding to potential bone tunnels that would conform to fewer than all of the additional tunnel constraints.

28. The processor-implemented method of claim 25, wherein providing, by the one or more processor, the visual guidance for display on a display device comprises providing the feasibility map as an overlay for a representation of the digital 3D model of the bone to be displayed on the display device.

29. A non-transitory processor-readable medium embodying processor-readable program code executable by at least one processor to carry out the processor-implemented method of claim 15.

30. A system for providing guidance about feasibility of a potential bone tunnel, the system comprising:a user interface;memory storing one or more instructions; andone or more processing devices configured to execute the one or more instructions, wherein executing the one or more instructions causes the system to: receive a 3D digital model of a bone;receive at least one tunnel constraint;receive potential bone tunnel data defining the potential bone tunnel, the potential bone tunnel data comprising a first point along an axis of the potential bone tunnel and at least one of: (a) a second point along the axis of the potential bone tunnel and (b) an orientation of the axis of the potential bone tunnel;generate the guidance using the 3D digital model, the at least one tunnel constraint, and the potential bone tunnel data, wherein the guidance indicates anPT-6211-WO-PCTassessment of feasibility with respect to the at least one tunnel constraint of the potential bone tunnel; andpresent the guidance using the user interface.

31. The system of claim 30, wherein the user interface comprises a display device, and the guidance comprises visual guidance displayed on the display device.

32. The system of claim 31, wherein the visual guidance comprises a change in content displayed on the display device responsive to the potential bone tunnel being assessed as infeasible with respect to the at least one tunnel constraint.

33. The system of claim 32, wherein the change in content displayed on the display device is selected from the group consisting of: a change in appearance of an indicia being displayed on the display device, a display of an indicia on the display device, and a removal from display of an indicia on the display device.

34. The system of claim 31, wherein the visual guidance comprises a change in content displayed on the display device responsive to the potential bone tunnel being assessed as feasible with respect to the at least one tunnel constraint.

35. The system of claim 34, wherein the change in content displayed on the display device is selected from the group consisting of: a change in appearance of an indicia being displayed on the display device, a display of an indicia on the display device, and a removal from display of an indicia on the display device.

36. The system of claim 30, wherein the guidance comprises at least one of: visual guidance, audible guidance, and haptic guidance.

37. The system of claim 36, wherein the audible guidance comprises an audible sound presented by the user interface responsive to the potential bone tunnel being assessed as feasible with respect to the at least one tunnel constraint.PT-6211-WO-PCT38. The system of claim 36, wherein the audible guidance comprises an audible sound presented by the user interface responsive to the potential bone tunnel being assessed as infeasible with respect to the at least one tunnel constraint.

39. The system of claim 30, wherein the guidance indicates that the potential bone tunnel is feasible only responsive to the potential bone tunnel conforming to all of the at least one tunnel constraint.

40. The system of claim 30, wherein the guidance indicates that the potential bone tunnel is infeasible responsive to the potential bone tunnel conforming to fewer than all of the at least one tunnel constraint.

41. The system of claim 30, wherein the at least one tunnel constraint comprises at least two tunnel constraints, and the guidance comprises:a first guidance that indicates that the potential bone tunnel is feasible with respect to a first of the at least two tunnel constraints; anda second guidance different from the first guidance and that indicates that the potential bone tunnel is feasible with respect to a second of the at least two tunnel constraints.

42. The system of claim 41 , wherein the guidance further comprises:a third guidance different from the first guidance and from the second guidance and that indicates that the potential bone tunnel is feasible with respect to all of the at least two tunnel constraints.

43. A processor-implemented method of providing guidance about feasibility of a potential bone tunnel, the method comprising:receiving, by one or more processor, a 3D digital model of a bone; receiving, by the one or more processor, at least one tunnel constraint; receiving, by the one or more processor, potential bone tunnel data defining the potential bone tunnel, the potential bone tunnel data comprising a first point along anPT-6211-WO-PCTaxis of the potential bone tunnel and at least one of: (a) a second point along the axis of the potential bone tunnel and (b) an orientation of the axis of the potential bone tunnel;generating, by the one or more processor, the guidance using the 3D digital model, the at least one tunnel constraint, and the potential bone tunnel data, wherein the guidance indicates an assessment of feasibility with respect to the at least one tunnel constraint of the potential bone tunnel; andproviding, by the one or more processor, the guidance for presentation by a user interface device.

44. The processor-implemented method of claim 43, wherein the user interface comprises a display device, and the guidance comprises visual guidance displayed on the display device.

45. The processor-implemented method of claim 44, wherein the visual guidance comprises a change in content displayed on the display device responsive to the potential bone tunnel being assessed as infeasible with respect to the at least one tunnel constraint.

46. The processor-implemented method of claim 45, wherein the change in content displayed on the display device is selected from the group consisting of: a change in appearance of an indicia being displayed on the display device, a display of an indicia on the display device, and a removal from display of an indicia on the display device.

47. The processor-implemented method of claim 44, wherein the visual guidance comprises a change in content displayed on the display device responsive to the potential bone tunnel being assessed as feasible with respect to the at least one tunnel constraint.

48. The processor-implemented method of claim 47, wherein the change in content displayed on the display device is selected from the group consisting of: a change in appearance of an indicia being displayed on the display device, a display of an indicia on the display device, and a removal from display of an indicia on the display device.PT-6211-WO-PCT49. The processor-implemented method of claim 43, wherein the guidance comprises at least one of: visual guidance, audible guidance, and haptic guidance.

50. The processor-implemented method of claim 49, wherein the audible guidance comprises an audible sound presented by the user interface responsive to the potential bone tunnel being assessed as feasible with respect to the at least one tunnel constraint.

51. The processor-implemented method of claim 49, wherein the audible guidance comprises an audible sound presented by the user interface responsive to the potential bone tunnel being assessed as infeasible with respect to the at least one tunnel constraint.

52. The processor-implemented method of claim 43, wherein the guidance indicates that the potential bone tunnel is feasible only responsive to the potential bone tunnel conforming to all of the at least one tunnel constraint.

53. The processor-implemented method of claim 43, wherein the guidance indicates that the potential bone tunnel is infeasible responsive to the potential bone tunnel conforming to fewer than all of the at least one tunnel constraint.

54. The processor-implemented method of claim 43, wherein the at least one tunnel constraint comprises at least two tunnel constraints, and the guidance comprises: a first guidance that indicates that the potential bone tunnel is feasible with respect to a first of the at least two tunnel constraints; anda second guidance different from the first guidance and that indicates that the potential bone tunnel is feasible with respect to a second of the at least two tunnel constraints.

55. The processor-implemented method of claim 54, wherein the guidance further comprises:PT-6211-WO-PCTa third guidance different from the first guidance and from the second guidance and that indicates that the potential bone tunnel is feasible with respect to all of the at least two tunnel constraints.

56. A non-transitory processor-readable medium embodying processor-readable program code executable by at least one processor to carry out the processor-implemented method of claim 43.

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