System and method for assessing accuracy of a cut plane formed, or to be formed, on a bone

Abstract

A method and system are disclosed to assist in proper alignment of a cutting guide relative to a bone in preparation for a joint implant. Separately, or in combination with the cutting guide alignment, the planarity of a cut surface is measured, in order to modify the cut surface prior to mounting an implant on the bone. Location feedback of a digitizer tip relative to a bone coupled cutting guide is used to determine the position and orientation (POSE) of a cut plane to be formed on the bone using a cutting device in conjunction with the guide slot(s) of the cutting guide. The POSE of the digitizer is determined using a tracking system. The POSE of the determined cut plane overlaid on a bone model and compared to the POSE of a planned cut plane better positions the cutting guide prior to actual bone cuts using the cutting guide.

Description

SYSTEM AND METHOD FOR ASSESSING ACCURACY OF A CUT PEANE FORMED, OR TO BE FORMED, ON A BONERELATED APPLICATIONS

[0001] This application claims priority benefit of U.S. Provisional Application Serial No. 63 / 535,142 filed on August 29, 2023, the contents of which are hereby incorporated by reference.FIELD OF THE INVENTION

[0002] The present invention generally relates to computer assisted surgery, and more specifically to systems and methods that provide feedback to assess the locational accuracy of a cut plane formed, or to be formed, on a bone with respect to a pre-determined location for a planned cut plane. The systems and methods may further provide feedback to assess the planarity of a cut plane surface formed on the bone either independently or with respect to a predetermined location for a planned cut plane.BACKGROUND OF THE INVENTION

[0003] Total joint arthroplasty (TJA) is an orthopedic surgical procedure in which the worn or otherwise compromised articular surfaces of the joint are replaced with prosthetic components, or implants. A TJA procedure involving the knee joint is commonly referred to as total knee arthroplasty (TKA). TKA requires the removal of worn or damaged articular cartilage and bone in the area of the knee joint surfaces in need of being replaced. The removed cartilage and bone are then replaced with synthetic implants, typically formed of metal or plastic, to create new joint surfaces.

[0004] One of the most difficult aspects of TKA is the accurate removal of bone, referred to as bone cuts, to form cut surfaces on the remaining bone for mounting the implant thereon in a desired position and orientation (POSE). Generally, surgeons plan and make the bone cuts so the final placement of the implants when mounted onto the cut surfaces restores the mechanical axis or kinematics of the patient's leg while preserving the balance of the surrounding knee ligaments. In TKA, at least five planar bone cuts are made on the distal femur to form at least five cut planes, where the planar contact surfaces of a femoral implant are mounted to the cut surfaces of the cut planes. The proximal tibia requires one planar bone cut to form a proximal cut plane, where the planar contact surface of a tibial implant is mounted to the cut surface of the proximal cut plane. Any malalignment in any one of the cut planes may have drastic consequences on the final result of the procedure and the wear pattern of the implant. The results of such misalignment might include discomfort, limited range of motion, revision, and reduced implant longevity.

[0005] A traditional TKA procedure involves the use of manual devices including the use of several cutting guides, also referred to herein as cutting blocks or jigs, to form the cut surfaces. These cutting guides typically include at least one guide slot, and various alignment and installation mechanisms to align the guide slot in a desired POSE with respect to the bone. These cutting guides require reference to various anatomical landmarks and often include the use of an intramedullary rod in order to align the guide slot in a desired POSE. Once the guide slot is aligned, a user may advance a surgical saw through the guide slot to form a cut plane. Overall, these manual tools are cumbersome, require considerable surgical experience, time intensive to deploy, and the accuracy of the placement of the cutting guides cannot be assured once mounted to the target bone; and instead, the surgeon has to trust that it is in the proper POSE. Attempts toaddress these placement concerns as to a cutting guide have included resort to a tracked paddle placed either in the cut slot or on an already formed cut surface. Using a tracked paddle placed in the cut slot has been met with limited success owing to the requirement of a dedicated device that is able to fit inside the guide slot, which is typically only a few millimeters wide, to measure the cut plane. Using a tracked paddle placed on an already formed cut surface does not help the user before the cut is made, which leaves the user with limited options to adjust the already formed cut plane, especially if it was overcut.

[0006] Despite the aforementioned limitations, these cutting guides do provide a few advantages. For one, the one or more guide slots, once aligned relative to the bone, constrains the surgical saw to the desired POSE and helps stabilize the bone removal device during cutting to reduce deflection from the desired plane. Second, a single cutting guide may include multiple guide slots (referred to herein as an N-in-1 cutting block) which can define more than one cutting plane to be accurately resected, such as a 4-in-l block, 5-in-l block . . . N-in-1 block. Thus, the surgeon can resect two or more planes once the cutting guide is accurately oriented on the bone. Still another advantage is that the guide slots and the working end of the oscillating saw are typically planar in shape and relatively thin, which make them ideal for creating planar- cut surfaces.

[0007] However, even with the aforementioned advantages of using a cut guide, it is still a common occurrence for the saw blade to deflect, or skive, while forming a cut plane especially in bone locations farther away from the location of the cutting guide. This can be attributed in part to the difference in bone density across anatomy as the cutting device engages cortical bone relative to softer cancellous bone tissue. It may also be attributed to the user’s technique and experience while advancing the thin saw blade across the bone. As a result, the actual bone cutsurfaces can have both undulations and parametric planar deviations from a desired cut plane. In other words, the deflection and skiving of the saw blade may produce a cut plane the deviates from ideal planarity even when the guide slot is accurately positioned in a desired POSE. This in turn affects the accuracy of the final placement of the implant on the bone. It further affects how the contact surfaces of the implant might mate with the cut surfaces. The contact surfaces of the implant are typically flat and planar in shape. Therefore having a flat and planar cut surface is important for maximizing the contact area between the implant contact surfaces and the cut surfaces.

[0008] To overcome the tedious task of manually aligning cutting guides on the bone, several robotic surgical systems have been developed to accurately form the cut surfaces including the TSolution One® Surgical System (THINK Surgical, Inc., Fremont, CA) and the RIO® Robotic Arm (Stryker-Mako, Kalamazoo, MI). The TSolution One® Surgical System aids in the planning and execution of total hip arthroplasty (TH A) and total knee arthroplasty (TKA). Other robotic systems may assist in robotically aligning a cutting guide in a desired POSE such as the ROSA® Robotic System (Zimmer Biomet, Warsaw, IN) and the hand-held robotic surgical system described in U.S. Pat. No. 11,457,980 and incorporated herein by reference in its entirety. The hand-held robotic system includes a hand-held robotic device that robotically aligns a pin with a virtual plane having a pre-determined location relative to the bone. The pins are inserted in the bone coincident with the virtual plane. A cut guide having a guide slot is then clamped onto the pins. The location of the virtual plane, and therefore the pins inserted in the bone coincident with the virtual plane, is defined such that when the cut guide is clamped onto the pins, the guide slot is aligned with the desired POSE to form a cut plane. The hand-held robotic system uses this method to assist in forming all five cut planes on the distal femur and the cutplane on the tibia. While the hand-held robotic device assists in accurately aligning the guide slot in a desired POSE, there is currently no method for verifying that the guide slot is properly positioned before the cut plane is formed. Further, the same aforementioned cut plane planarity issues may exist since a standard oscillating saw is still used with the cut guide when forming the cut plane.[00091 Thus, there exists a need to assess the positional accuracy of a cutting guide relative to the bone prior to forming a cut plane on the bone. There also exists a need for identifying topographical deviations of a formed cut surface on the bone relative to a planned cut plane, which may afford an opportunity to modify the cut surface prior to mounting an implant on the bone.SUMMARY OF THE INVENTION

[0010] A method is provided for assessing a locational accuracy or planarity of a cut plane formed, or to be formed, on a bone The method includes determining a projected location for a cut plane to be formed on the bone using a plurality of points collected at locations on a cutting guide when the cutting guide is coupled to the bone; and providing feedback comparing the projected location for the cut plane relative to a pre-determined location for a planned cut plane.

[0011] A system is provided for assessing a locational accuracy or planarity of a cut plane formed, or to be formed, on a subject’s bone. The system includes a computer having a processor configured to determine a projected location for a cut plane to be formed on the subject’s bone using a plurality of points collected at locations on a cutting guide when the cutting guide is coupled to the subject’s bone, and to provide feedback comparing the projected location for the cut plane relative to a pre-determined location for a planned cut plane.

[0012] A method is provided for assessing a locational accuracy or planarity of a cut plane surface formed on a bone. The method includes determining a location and shape of at least a portion of a cut plane surface formed on a bone using a plurality of points collected at locations on the cut plane surface, and providing feedback comparing the location or shape of the at least portion of the cut plane surface to a pre-determined location for a planned cut plane surface.

[0013] A system is provided for assessing a locational accuracy or planarity of a cut plane surface formed on a bone. The system includes a computer having a processor configured to determine a location and shape of at least a portion of a cut plane surface formed on a bone using a plurality of points collected at locations on the cut plane surface, and provide feedback comparing the location or shape of the at least portion of the cut plane surface to a predetermined location for a planned cut plane surface.

[0014] A method is provided for assessing planarity of a cut plane surface formed on a bone. The method includes fitting a plane to a plurality of points collected at locations on the cut plane surface, and providing feedback statistically comparing the fitted plane to the plurality of points to assess the planarity of the cut plane surface.

[0015] A system is provided for assessing planarity of a cut plane surface formed on a bone. The system includes a computer having a processor configured to fit a plane to a plurality of points collected at locations on the cut plane surface, and provide feedback statistically comparing the fitted plane to the plurality of points to assess the planarity of the cut plane surface.

[0016] A method is provided for assessing a locational accuracy or planarity of a cut plane surface formed on a bone. The method includes displaying an uncut view of a virtual bone model, wherein a portion of the virtual bone model includes a virtual volume of bone to beremoved, and wherein the virtual bone model is registered to the bone, determining a location of a digitizer tip relative to a location of the virtual bone model registered to the bone, and switching from displaying the uncut view of the virtual bone model to a resected view of the virtual bone model when the location of the digitizer tip crosses inside the virtual volume of bone to be removed.[00171 A system is provided for assessing a locational accuracy or planarity of a cut plane surface formed on a bone. The system includes a display for displaying an uncut view of a virtual bone model, wherein a portion of the virtual bone model includes a virtual volume of bone to be removed, and wherein the virtual bone model is registered to a location of the bone, a tracking system for tracking locations of a digitizer and the bone; and a computing system operatively coupled to the tracking system and the display. The computing system includes one or more processors configured to determine a location of a digitizer tip relative to a location of the virtual bone model registered to the bone, and control the display to switch from displaying the uncut view of the virtual bone model to a resected view of the virtual bone model when the location of the digitizer tip crosses inside the virtual volume of bone to be removed.BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The present invention is further detailed with respect to the following drawings that are intended to show certain aspects of the present of invention, but should not be construed as limit on the practice of the invention, wherein:

[0019] FIG. 1 depicts in perspective view a cutting guide in accordance with embodiments of the invention coupled to a target bone with pins;

[0020] FIG. 2 is a top view of the cutting guide depicted in FIG. 1

[0021] FIG. 3 depicts a digitizer in contact with a surface of the cutting guide as coupled onto the pins of FIG. 1 for collecting a plurality of points on the cutting guide in accordance with embodiments of the invention;

[0022] FIG. 4 depicts a projected cut plane calculated from a plurality of points collected on the cutting guide in accordance with embodiments of the invention;

[0023] FIG. 5 depicts a reference plane calculated from a plurality of points collected on the cutting guide, where the reference plane is used to calculated a projected cut plane in accordance with embodiments of the invention;

[0024] FIG. 6 depicts a visual display displaying the projected cut plane of FIG. 6 overlaid on a virtual bone model and relative to a planned cut plane, denoted as the frame therein, in accordance with embodiments of the invention;

[0025] FIG. 7 depicts use of a planar and non -penetrating tipped digitizer in contact with a cut surface for collecting a plurality of points on the cut surface in accordance with embodiments of the invention;

[0026] FIG. 8 depicts a plate configured to couple with a digitizer tip, where the digitizer tip when coupled to the plate is used to contact a cut surface for collecting a plurality of points on the cut surface in accordance with embodiments of the invention;

[0027] FIG. 9A depicts a visual display displaying a measured cut surface calculated from a plurality of points collected on a cut surface overlaid on a virtual bone model and relative to a planned cut plane, denoted as the frame therein, in accordance with embodiments of the invention;

[0028] FIG. 9B depicts a visual display displaying a 3D model of error between a planned cut plane and a measured cut plane relative to a virtual bone model, denoted as the frame therein, in accordance with embodiments of the invention.

[0029] FIG. 10 depicts a visual display displaying a fitted plane with respect to a plurality of points collected on a cut surface and statistically comparing the plurality of points to the fitted plane to determine the planarity of the cut plane in accordance with embodiments of the invention;

[0030] FIG. 11 depicts a composite verification screen display such that when the digitizer tip is positioned relative to the bone at a location corresponding to the inside of the registered bone model, the view of the virtual bone model changes to a resected view to verify the distance of the digitizer tip to the planned cut plane of the bone to assess areas of topographical deviation of the actual cut plane, the view of the original virtual bone model then reappears when the digitizer tip is positioned relative to the bone at a location corresponding to the outside of the registered bone model;

[0031] FIG. 12 depicts a vision-based system for assessing the accuracy of a cut plane to be formed on a bone in accordance with embodiments of the invention;

[0032] FIG. 13 depicts a surgical system to perform embodiments described herein in accordance with embodiments of the invention;

[0033] FIGS. 14A and 14B are a detailed view of a hand-held robotic device in accordance with embodiments of the invention;

[0034] FIG. 15 depicts the hand-held robotic device aligning a pin for inserting a set of pins coincident with a virtual plane having a pre-determined location relative to a femoral bone in accordance with embodiments of the invention;DETAILED DESCRIPTION OF THE INVENTION

[0035] The present invention has utility as a method and system for providing feedback to assist in the proper alignment of a cutting guide relative to a bone for preparing a bone for a joint implant. Separately, or in combination with the alignment of the cutting guide, the planarity of a cut surface is also measured, which may provide utility for modifying the cut surface prior to mounting an implant on the bone.

[0036] Some embodiments of the present invention utilize feedback as to the location of a digitizer tip relative to a bone coupled cutting guide to determine the POSE of a cut plane to be formed on the bone using a cutting device in conjunction with the guide slot(s) of the cutting guide. The POSE of the digitizer is determined using a tracking system as detailed herein. The POSE of the determined cut plane can be overlaid on a bone model and compared to the POSE of a planned cut plane to afford a user (e.g., surgeon) an opportunity to better position the cutting guide prior to making an actual bone cut using the cutting guide. As a result, the POSE of the actual cut plane may be formed more accurately to the POSE for the planned cut plane. The positional feedback may be provided in real time. “Real time” is the context of feedback is intended to mean that a human user perceives the updates as happening with little or no lag time relative to a command or physical movement. It is appreciated that while a femur and an associated cutting guide, in the context of a total knee arthroplasty (TKA) are used to illustrate the inventive system and method, other surgical procedures for joint replacements involving the knee, hip, shoulder, elbow, jaw, as well as for other structures in the body including the vertebra of the spine may benefit from the concepts presented herein.

[0037] The present invention will now be described with reference to the following embodiments. As is apparent by these descriptions, this invention can be embodied in differentforms and should not be construed as limited to the embodiments set forth herein. For example, features illustrated with respect to one embodiment can be incorporated into other embodiments, and features illustrated with respect to a particular embodiment can be deleted from that embodiment. In addition, numerous variations and additions to the embodiments suggested herein will be apparent to those skilled in the art in light of the instant disclosure, which do not depart from the instant invention. Hence, the following specification is intended to illustrate some particular embodiments of the invention, and not to exhaustively specify all permutations, combinations, and variations thereof.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0039] All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety.

[0040] The following description provides examples related to knee replacement; however, it should be appreciated that the embodiments described herein are readily adapted for use in a myriad of applications where it is desirous to position implants for joint replacement procedures in other portions of the body.

[0041] It is to be understood that in instances where a range of values are provided that the range is intended to encompass not only the end point values of the range but also intermediate values of the range as explicitly being included within the range and varying by the last significant figure of the range. By way of example, a recited range from 1 to 4 is intended to include 1-2, 1-3, 2-4, 3-4, and 1-4.Definitions

[0042] Unless indicated otherwise, explicitly or by context, the following terms are used herein as set forth below.

[0043] As used in the description of the invention and the appended claims, the singular forms “a,” “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0044] Also, as used herein, “and / or” refers to and encompasses any and all possible combinations of one or more of the associated listed items, as well as the lack of combinations when interpreted in the alternative (“or”).

[0045] As used herein, like reference numerals described in with respect to subsequent drawings have the meaning imparted thereto with respect to the previously detailed drawings.

[0046] As used herein, the term “bone data” refers to data related to one or more bones. The bone data may be determined: (i) prior to making modifications (e.g., bone cuts, insertion of a pin or screw, etc.) to one or more bones, referred to as pre-operative bone data; and / or (ii) determined after one or more modifications have been made to a bone, referred to as postmodification bone data. The bone data may include: the shapes of the one or more bones; the sizes of the one or more bones; angles and axes associated with the one or more bones (e.g., epicondylar axis of the femoral epicondyles, longitudinal axis of the femur, the mechanical axis of the femur); angles and axes associated with two or more bones relative to one another (e.g., the mechanical axis of the knee); anatomical landmarks associated with the one or more bones (e.g., femoral head center, knee center, ankle center, tibial tuberosity, epicondyles, most distal portion of the femoral condyles, most proximal portion of the femoral condyles); bone density data; bone microarchitecture data; and stress / loading conditions of the bone(s). By way ofexample, the bone data may include one or more of the following: an image data set of one or more bones (e.g., an image data set acquired via fluoroscopy, computed tomography (CT), magnetic resonance imaging (MRI), ultrasound, other x-ray modalities, laser scan, etc.); three- dimensional (3-D) bone models, which may include a virtual generic 3-D model of the bone, a physical 3-D model of the bone, a virtual patient- specific 3-D model of the bone generated from an image data set of the bone; and a set of data collected directly on the bone intra-operatively commonly used with imageless CAS devices (e.g., laser scanning the bone, painting the bone with a digitizer). The term “virtual” may also be referred to herein as “digital”, meaning the data is stored, generated, and / or processed by a computer.

[0047] As used herein, the terms “computer-assisted surgical device” and “CAS device” refer to devices used in surgical procedures that are at least in part assisted by one or more computers. Examples of CAS devices illustratively include tracked / navigated instruments and surgical robots. Examples of a surgical robot illustratively include robotic hand-held devices, serial-chain robots, bone mounted robots, parallel robots, or master-slave robots, as described in U.S. Patent Nos. 5,086,401; 6,757,582; 7,206,626; 8,876,830; 8,961,536; 9,707,043; and 11,457,980; which patents and patent application are incorporated herein by reference. The surgical robot may be active (e.g., automatic / autonomous control), semi-active (e.g., a combination of automatic and manual control), haptic (e.g., tactile, force, and / or auditory feedback), and / or provide power control (e.g., turning a robot or a part thereof on and off). It should be appreciated that the terms “robot” and “robotic” are used interchangeably herein. The terms “computer-assisted surgical system” and “CAS system” refer to a system comprising at least one CAS device and may further include additional computers, software, devices, or instruments. An example of a CAS system may include: i) a CAS device and software (e.g., cutting instructions, pre-operative bonedata) used by the CAS device); ii) a CAS device and software (e.g., surgical planning software) used with a CAS device; iii) one or more CAS devices (e.g., a surgical robot); iv) a combination of i), ii), and iii); and iv) any of the aforementioned with additional devices or software (e.g., a tracking system, tracked / navigated instruments, tracking arrays, bone pins, rongeur, an oscillating saw, a rotary drill, manual cutting guides, manual cutting blocks, manual cutting jigs, etc.).

[0048] Also referenced herein is a “surgical plan.” A surgical plan is generated using planning software. The surgical plan may be generated pre-operatively, intra-operatively, or pre- operatively and then modified intra-operatively. The planning software may be used to plan the location for an implant with respect to a bone and / or plan a location to make one or more modifications (e.g., bone cuts, location for inserting bone pins) to the bone. The planning software may include various software tools and widgets for planning the surgical procedure. This may include, for example, planning: (i) a location for implant data (e.g., a 3-D implant model) with respect to bone data (e.g., a 3-D bone model) to define a location for the implant with respect to the bone; (ii) a location for one or more bone cuts to be made relative to bone data to define the locations for one or more cuts to be made on the bone, and / or (iii) one or more locations for inserting hardware (e.g., bone pins, screws) relative to bone data. All of which may be used to define locations for robot operating instructions (e.g., a cut-file, a virtual plane, virtual boundary, a virtual axis) with respect to the bone data, where a CAS device is directed to control movement of an end-effector (e.g., the hardware, a burr, end-mill, drill bit) with respect to the bone according to the robot operating instructions.

[0049] As used herein, the term “digitizer” refers to a device capable of measuring, collecting, recording, and / or designating the position of physical locations (e.g., points, lines, planes,boundaries, etc.) in three-dimensional space. By way of example but not limitation, a “digitizer” may be: a “mechanical digitizer” having passive links and joints, such as the high-resolution electro-mechanical sensor arm described in U.S. Patent No. 6,033,415 (which U.S. patent is hereby incorporated herein by reference); a non-mechanically tracked digitizer probe (e.g., optically tracked, electromagnetically tracked, acoustically tracked, and equivalents thereof) as described for example in U.S. Patent 7,043,961 (which U.S. patent is hereby incorporated herein by reference); an end-effector of a robotic device; or a laser scanner.

[0050] As used herein, the term “digitizing” refers to the collecting, measuring, designating, and / or recording of physical locations in space using a digitizer.

[0051] As used herein, the term “registration” refers to: the determination of the spatial relationship between two or more objects; the determining of a coordinate transformation between two or more coordinate systems associated with those objects; the mapping of an object onto another object; and a combination thereof. Examples of objects routinely registered in an operating room (OR) illustratively include: CAS systems / devices; anatomy (e.g., bone); bone data (e.g., 3-D virtual bone models); a surgical plan (e.g., location of virtual planes defined relative to bone data, cutting instructions defined relative to bone data, or other robot operating instructions defined relative to bone data); and any external landmarks (e.g., a tracking array affixed to a bone, an anatomical landmark, a designated point / feature on a bone, etc.) associated with the bone (if such landmarks exist). Methods of registration known in the art are described in U.S. Pat. No. 6,033,415; 8,010, 177; 8,036,441 ; and 8,287,522; and 10,537,388. In particular embodiments with orthopedic procedures, the registration procedure relies on the manual collection of several points (i.e., point-to-point, point-to-surface) on the bone using a tracked digitizer where the surgeon is prompted to collect several points on the bone that are readilymapped to corresponding points or surfaces on a 3-D bone model. The points collected from the surface of a bone with the digitizer may be matched using iterative closest point (ICP) algorithms to generate a transformation matrix. This transformation matrix and various other transformation matrices provides the mathematical locational relationship between two or more of: (i) a surgical plan (e.g., a pre-defined location for a targeted virtual plane that was defined with respect to bone data, a pre-defined location of cutting instructions that was defined with respect to bone data); (ii) the coordinate system of a tracking array affixed to the bone (if present); (iii) a CAS device (e.g., the base coordinate system of the CAS device, or a coordinate system of a tracking array affixed to the CAS device and, if needed, calibration data and / or kinematic data that define the location of an end-effector relative to the tracking array); and any other coordinate system or object required to perform the procedure. In other embodiments, the registration is performed using image or imageless registration.

[0052] As used herein, the term “display” is intended to encompass a variety of the digital devices that during operation provide an image (including multiple images in succession to form a video feed) recognizable to human viewing. Digital devices operative herein as displays illustratively include a graphical user interface (GUI), a computer or television (TV) monitor, a holographic display, a mobile display, a smartphone display, a video wall, a head-mounted display, a heads-up display, a virtual reality headset, a broadcast reference monitor, any of the aforementioned with a touchscreen capability, and a combination thereof. One or more computers comprising a processor may be operatively coupled to the display for controlling the output of the display.

[0053] As used herein, the term “feedback” may refer to visual feedback provided on a display. This “feedback” may also be provided in lieu of or addition to visual feedback. Forexample, the “feedback” may include audio feedback, haptic / tactile feedback (e.g., a buzz or vibration when a digitizer tip is located at in an area of max deviation), or other visual feedback (e.g., a light on the digitizer may turn green or red depending on the amount of error between the digitizer tip and a planned cut surface). Furthermore, disclosed herein is the displaying of virtual bone models on a display. This may include: (i) the display of an entire virtual bone model (e.g., an entire femoral bone model that includes the femoral head to the distal condyles); or (ii) the display of only the relevant portions of the virtual bone model such as the distal portion of the femur and / or proximal portion of the tibia for TKA procedures.

[0054] Referring now to FIGS. 1 and 2, a cutting guide is shown generally at 100. The cutting guide 100 is depicted as coupled to a bone, B in FIG. 1; here shown in exemplary form as being the distal portion of a human femur. The cutting guide 100 includes a body 101, a guide slot 102, and an attachment portion 104. The guide slot 102 may be located on a portion of the body 101 and extends through the width of the body 101. The guide slot 102 defines a planar projection therethrough and is adapted to having a cutting tool, such as a surgical saw blade per FIGS. 3A and 3B, advanced through the guide slot 102 to form a cut plane on the bone. The guide slot 102 may be rectangular’ in shape (with angled or rounded corners) having a bottom surface, a top surface, and straight or rounded sides, where the height between the bottom surface and the top surface is anywhere between 0.5 millimeters and 3 millimeters to accommodate and stabilize the thickness of a standard surgical saw blade within the guide slot 102. The bottom surface and the top surface of the guide slot 102 are both planar in shape to match the planar shape of the surgical saw blade. The attachment portion 104 is configured to couple the cutting guide 100 to one or more bone pins (106a, 106b) inserted in the bone B. The bone pins (106a,106b) may have been inserted in the bone using a hand-held robotic device as described below.In some inventive embodiments, the cutting guide 100 includes a clamping mechanism 108 (e.g., a screw, a cam) to control clamping of the attachment portion 104 to the bone pins (106a, 106b). In still other inventive embodiments, the cutting guide includes a gimbal to allow for secure coupling in additional degrees of freedom in general and with respect to rotation in particular’. Other mechanisms for coupling the cutting guide 100 to the bone pins (106a, 106b) include a press-fit and the use of fastening elements. It is appreciated that while two bone pins are depicted in FIG. 1, the present invention is operative with a single bone pin or more than the two bone pins so depicted.

[0055] With reference to FIG. 2, a top view of the cutting guide 100 is shown. The body 101 further includes an outer surface 112 and an inner surface 114. The inner surface 114 resides closest to the bone B when the cutting guide 100 is coupled to the bone pins (106a, 106b). The outer surface 112 in some inventive embodiments is curved or faceted. The cutting guide 100 further includes at least one digitizing surface (115a, 115b) and / or digitizing feature 116 to provide contact locations for a digitizer tip 202 of a digitizer 200 (as shown in FIG. 3). A plurality of points (e.g., at least three non-collinear points) may be collected on a digitizing surface (115a, 115b) or digitizing feature 116 (e.g., dimples, pits, holes, divots, indentations, channels) and used to determine the projected location for forming a cut plane on the bone (e.g., determine the POSE of the guide slot 102 as coupled to the bone) as further described below. The digitizing surface(s) (115a, 115b) and / or digitizing features may be located at one or more locations on the cutting guide 100 and have a known geometry with respect to the POSE of the guide slot 102. While the digitizing surface(s) (115a, 115b) are shown in FIGs. 1 and 2 as a continuous feature, it is appreciated that the plurality of points may be collected on any portion of the cutting guide 100 as long as the digitizing surface or digitizing feature (where the pointsare collected) has a known geometry with respect to the POSE of the guide slot 102. In the embodiment of the digitizing surface(s) (115a, 115b) shown in FIGS 1 and 2, a first digitizing surface 115a is depicted as a ledge contiguous with the bottom surface of the guide slot 102, and a second digitizing surface 115b is depicted as a top surface of the cutting guide body 101. The first digitizing surface 115a is depicted as a ledge. The ledge may be formed on the cutting guide 100 by designing the bottom portion of the body 101 (i.e., below the bottom surface of the guide slot 102) to have a larger depth (z-axis shown in FIG. 2) than a top portion of the body 101 (i.e., above the bottom surface of the guide slot 102). The ledge may also be formed by extending an outer edge of the bottom surface of the guide slot 102 beyond the outer edge of the top surface of the guide slot 102. It is appreciated that any predefined geometrical relationship between a digitizing surface (115a, 115b) (and / or any other digitizing feature (e.g., screw holes, dimples, channels) on the cutting guide 100) having a known geometry with respect to the guide slot 102 is operative herein. While parallel and coplanar digitizing surface(s) (115a, 115b) and the guide slot 102 are depicted herein, it is appreciated that other angular and displacement geometrical relationships therebetween are also operative herein. By way of example, an orthogonal digitizing surface (e.g., the outer surface 112 of the cutting guide 100) relative to the guide slot is also operative herein. It is also appreciated that a plurality of digitizing surfaces or digitizing features may be provided for: (i) additional computation verifications; (ii) to improve the measurement accuracy in one or more degrees of freedom (e.g., to obtain a desired tilt or slope measurement accuracy); and / or (iii) to pre-validate additional cut planes associated with other guide slots in the same cutting guide (e.g., a 4-in-l cutting block). It should further be appreciated that a particular digitizing surface or digitizing features may provide a better measurement accuracy for computing a reference plane (as described below) compared to otherdigitizing surfaces or digitizing features, where a user may choose which digitizing surface(s) or digitizing feature(s) to use in the operating room (OR).

[0056] In operation, and as best shown with respect to FIG. 3, the cutting guide 100 allows a user to check the position of the guide slot 102 prior to making a bone cut. The user wielding a digitizer 200 having a digitizer tip 202 may move the digitizer 200 to contact the digitizer tip 202 with a plurality of locations on a digitizing surface (115a, 115b). In some embodiments, the plurality of locations is at least three non-collinear points on a digitizing surface (115a, 115b), at least three non-collinear digitizing features, or a combination of non-collinear points collected on a digitizing surface (115a, 115b) or digitizing feature. As best shown in FIG. 2, the ledge which forms the first digitizing surface 115a is curved or faceted, which ensures the user can contact the digitizer tip 202 with at least three non-collinear points on the first digitizing surface 115a. In other words, the two opposing outer regions of the first digitizing surface 115a are non-collinear with the middle region to ensure the digitizer tip 202 can contact at least three non-collinear points on the first digitizing surface 115a. A digitizing surface (115a, 115b) may further include digitizing features 116 to assist and guide the user in contacting the digitizer tip 202 with at least three non-collinear points on the digitizing surface (115a, 115b). In a particular embodiment, the digitizer tip 202 may be moved back and forth (e.g., in a sliding motion) along / across a digitizing surface (115a, 115b) to designate the position of a multitude of points on the digitizing surface (115a, 115b). In other embodiments, the cutting guide 100 includes digitizing features 116 that may not necessarily form a digitizing surface, where the user may contact the digitizer tip 202 with these digitizing features 116 in lieu of or in addition to contacting the digitizer tip 202 with a digitizing surface (115a, 115b). Points collected at the location of the digitizing features may provide enough information to calculate a reference plane as further described below. A trackingsystem 706 as described below with respect FIG. 12 tracks the movement of the digitizer 200 and records the location of the digitizer tip 202 when the digitizer tip 202 is in contact with a digitizing surface (115a, 115b) or a digitizing feature. The recording of a point’s location may also be referred to herein as collecting or digitizing a point. An input mechanism (e.g., a trigger, button, switch, hand gesture, audible que from the user) may be used to provide a signal to the tracking system to record the location of the digitizer tip 202 to ensure that only points on a digitizing surface (115a, 115b) or digitizing feature are collected as intended by the user.

[0057] In other embodiments, the plurality of points may be collected on portions of the cutting guide 100 using other point collection devices such as a laser scanner, depth camera, or a conventional visual light camera. These other point collection devices may be coupled to a tracking array to permit a tracking system to track the location of the point collection device and determine the location of the points collected on the cutting guide 100.

[0058] With respect to FIG. 4, the plurality of points collected by the tracking system are used to determine / calculate the location of a digitizing surface (115a, 115b) or digitizing feature 116 of the cutting guide 100. A computer operatively coupled to the tracking system may calculate the location of the digitizing surface (115a, 115b) by fitting a reference plane, RP, to the plurality of points collected on said surface. Then, using the location of the determined reference plane, RP, (corresponding to the location of the digitizing surface (115a, 115b) of the cutting guide 100) and the known geometry of the digitizing surface (115a, 115b) or digitizing feature with respect to the guide slot 102, the computer may determine a projected cut plane, PP. The projected cut plane, PP, or the projected location for the cut plane, is the cut plane that would be formed on the bone if a user were to advance a saw blade through the guide slot 102 as currently positioned on the bone. FIG. 4 depicts one example for calculating a projected cut plane, PP.First, a plurality of points are collected on the first digitizing surface 115a, which is an extension of the bottom surface of the guide slot 102. The computer then calculates a reference plane, RP, which here, corresponds to the location of the bottom surface of the guide slot 102. And since the bottom surface of the guide slot 102 is substantially coplanar with the cut plane that will be formed on the bone when the bone cuts are made, the reference plane, RP, also represents the projected cut plane, PP. Therefore, there are advantages of having a digitizing surface that is an extension of the bottom surface of the guide slot 102. In another example, with reference to FIG. 5, the second digitizing surface 115b may be used to collect the plurality of points. In this example, a reference plane, RP2, is calculated which corresponds to the top surface of the cutting guide 100. Then the projected cut plane, PP, is calculated as a plane offset from the reference plane, RP2, by the known geometry of the top surface of the cutting guide 100 to the bottom surface of the guide slot 102 (i.e., the perpendicular distance between the top surface of the cutting guide 100 and the bottom surface of the guide slot 102). It should be appreciated that any digitizing surface or digitizing feature may be used in this manner to calculate the projected cut plane, PP, using the known geometry of the cutting guide 100.

[0059] With reference to FIG. 6, the location of the projected cut plane, PP, as calculated above is then compared to the planned location for a cut plane, PP’ , where the planned location for the cut plane, PP’, may have been determined as part of a surgical plan using planning software. The comparison may be displayed on a display 300 and visualized by displaying the location of the projected cut plane, PP, and the planned location for the cut plane, PP’, with respect to a bone model, M, of the bone, B. As a result, a comparison may be made between: (i) the alignment of the guide slot 102 (which if a user advanced a surgical saw blade through the guide slot 102, the saw blade would form a cut plane on the bone at the location of the calculatedprojected cut plane, PP); and (ii) a planned location for forming the cut plane, PP’. The alignment of the guide slot 102 may then be corrected, if needed, to within a desired threshold of coplanarity. As shown in FIG. 6, the outer frame of the display 300 denotes the boundaries of the display 300. As shown in FIG. 6, the outer frame of the display 300 denotes the boundaries of the display 300.[00601 In those instances, in which the location of the projected cut plane, PP, is misaligned with the location for the planned cut plane, PP’, beyond that acceptable to a user or by a preselected threshold programmed into the computer providing the display 300, the position of the cutting guide 400, or the guide slot 102, may be adjusted to better align the guide slot 102 to the planned location for the cut plane, PP’. The cutting guide 100 may be moved by repositioning the cutting guide 100 relative to the bone pins in a variety of ways conventional to the art (e.g., a gimbal that allows the guide slot 102 to move relative to the bone pins, or other adjustment mechanisms (e.g., screws, rack and pinion, worm gears) operative to translate and / or rotate the guide slot 102 relative to the bone pins). In other embodiments, new bone pins may be inserted in the bone at a new location to adjust the location of the cutting guide 100, and therefore, the guide slot 102 to better align with the planned location for the cut plane, PP’. The method may be iteratively repeated to determine a second projected cutting plane and so compared until satisfactory to a user, such as a surgeon. A cutting device (e.g., an oscillating saw blade) is then advanced through the guide slot 102 to form the actual cut plane on the bone.

[0061] During the formation of the actual cut plane on the bone with the saw blade, there is the potential for the saw blade to skive or dive relative to the bone. The resulting cut plane on the remaining bone may have topographical deviations relative to at least one of: (i) the planned location for the cut plane, PP’; and (ii) a true planar surface (e.g., a perfectly flat or planarsurface). These topographical deviations may affect: (i) the final location for the implant on the bone, which may now deviate from the planned location for the implant on the bone; and (ii) how the planar contact surfaces of an implant mate with the cut plane surface (e.g., gaps may form between an uneven or undulating cut plane surface and the planar contact surfaces of the implant). Algorithms for determining the relationship between two planes or two surfaces are conventional to the art such as point-to-plane distance algorithms, point-to- surface distance algorithms, and statistical analyses to determine the error between two planes or two surfaces.

[0062] According to certain aspects of the present invention, a cut plane, CP, having a cut plane surface, S, on the now modified bone, B’, is digitized as shown in FIG. 7. In the specific embodiment shown in FIG. 7, the digitizer 200 may include a blunted tip 202’, which may be formed by coupling a blunted adapter on the end of the digitizer tip 202 shown in FIG. 3, or the digitizer tip 202 (or probe having the digitizer tip 202) is replaced with a devoted blunted digitizer tip. The blunted tip 202’ precludes penetration into cancellous bone that may distort the topographical data so collected on the cut plane surface, S. A blunted tip 202’ having a bone contacting facial area of between 1 and 10 square centimeters is well suitable to preclude penetration into the surface, S. In a particular embodiment, with reference to FIG. 8, the digitizer tip 202 (e.g., a pointed digitizer tip) may be adapted to couple with a plate 204 by way of a coupling mechanism 206 (e.g., a receptacle for receiving the digitizer tip 202 and secured with a clip, clamp, or press-fit interaction; or the digitizer tip 202 may be outfitted with a male adapter for connecting to a female adapter on the plate 204). The coupling mechanism 206 may further keep the longitudinal axis 208 of the digitizer 200 angled (non-perpendicular) relative to the face of the plate 204. The angle may be anywhere between 10 and 70 degrees, and preferably between 35 and 55 degrees. The digitizer 200 may further be permitted to rotate about its longitudinalaxis 208 when coupled to the plate 204 to allow the user to maintain the line-of-sight between the digitizer tracking array 210 and a tracking system 706 (FIG. 12). In another embodiment, the digitizer 200 may be permitted to freely rotated about the digitizer tip 202 when the digitizer tip 202 is coupled to the plate 204 (e.g., by way of a swivel mechanism). The use of the plate 204 also precludes the penetration of the digitizer tip 202 into the cut plane surface, S. Furthermore, the plate 204 provides a contact surface area that can conform to the shape of the cut plane surface, S, at areas on the cut plane surface, S, where specific points may be difficult to collect with a pointed digitizer tip 202 (e.g., areas that are obstructed by a cutting guide overhanging the cut plane surface, S; or areas where an opposing bone is obstructing access to specific areas on the target bone). By angling the digitizer 200 relative to the plate 204, the user can wedge a portion of the plate 204 in contact with those difficult areas for collecting a point that better represents that area of the cut plane surface, S.

[0063] To digitize the cut plane surface, S, a user wielding the digitizer 200 contacts the blunted tip 202’ or plate 204 to a plurality of locations on the cut plane surface, S. In one embodiment, the user may contact the blunted tip 202’ or plate 204 at locations around the perimeter of the cut plane surface, S. This is akin to tracing an outline of the perimeter of the cut plane surface, S, which provides enough digitized points for calculating the location and overall shape of the actual cut plane surface, S, formed on the bone. In other embodiments, the user may contact the blunted tip 202’ or plate 204 at a plurality of locations on the cut plane surface, S, by sweeping and / or painting the cut plane surface, S, with the blunted tip 202’ or plate 204.

[0064] A tracking system 706 as described below with respect to FIG. 12 tracks the movement of the digitizer 200 and records the location of the blunted tip 202’ when the blunted tip 202’ is in contact with the cut plane surface, S, to collect (or digitize) a plurality of points onthe cut plane surface, S. An input mechanism (e.g., a trigger, hutton, switch, hand gesture, audible que from the user) may be used to provide a signal to the tracking system to record the location of the blunted tip 202 to ensure that only points on the cut plane surface, S, are collected as intended by the user. In other embodiments, the plurality of points may be collected on the cut plane surface, S, using other point collection devices such as a laser scanner, depth camera, or a conventional visual light camera. A computer operatively coupled to the tracking system then determines or calculates a measured cut plane surface, MP, from the plurality of points collected on the cut plane surface, S, using techniques known in the art. It should be appreciated that the measured cut plane surface, MP, may be calculated as: (i) a plane using at least three or more non-collinear points collected on the cut plane surface, S; (ii) a plane fitted to the plurality of collected points using statistical analysis (e.g., a plane best-fit to the collected points using least squares or multiple regression); (iii) a surface having planar and / or non-planar areas that better represents the true cut plane surface, S, using computer processing techniques known in the art (e.g., using interpolation and / or parameterization to calculate a surface from the plurality of collected points); or (iv) a polygon fit to a plurality of points collected around the perimeter of the cut plane surface, S. In other embodiments, the computer simply represents the measured cut plane, MP, as a point cloud, where the points in the point cloud are the plurality of points collected on the cut plane surface, S.

[0065] Referring now to FIG. 9A, the measured cut plane surface, MP, and the location of the measured cut plane surface, MP, as calculated above may then be compared to the planned location for a cut plane, PP’ . The comparison may be displayed on a display 300 and visualized by displaying the measured cut plane surface, MP, at its determined location, and the planned location for the cut plane, PP’, all with respect to a modified bone model, M’, of the bone, B.The modified bone model, M’, may be a resected view of the bone model showing a representation of the cut plane surface that was formed on the bone (e.g., the portion of the bone model distal to the distal cut plane is removed from the bone model to reveal a modified bone model M’ with the cut plane surface). The location of the cut plane surface on the modified bone model may correspond to the planned location for the cut plane, PP’, or to the location of the actual cut plane formed on the bone. In some embodiments, the measured cut plane surface, MP, is used to create the view of the modified bone model, M’, by removing portions of the bone model beyond the location of the measured cut plane surface, MP (e.g., removing portions of the bone model distal to the measured cut plane, MP, for the distal cut plane). The measured cut plane surface, MP, may be displayed as at least one of a: (i) a plane calculated from at least three non-collinear points collected on the cut plane surface, S; (ii) a plane fitted to the plurality of collected points using statistical analysis (e.g., a plane best-fit to the collected points using least squares or multiple regression); (iii) a surface having planar and / or non-planar areas as calculated using computer processing techniques known in the art (e.g., parameterization of point cloud data); (iv) a polygon fit to a plurality of points collected around the perimeter of the cut plane surface, S; or (v) the location of the plurality of points collected directly on the cut plane surface, S (i.e., a point cloud).

[0066] In a specific embodiment, the display 300 is further configured to provide visual feedback to show areas where the measured cut plane surface, MP, deviates above or below the planned location for the cut plane, PP’. Areas where the measured cut plane surface, MP, deviates above the planned location for the cut plane, PP’, represent undercuts 402 caused by the saw blade skiving while forming the actual cut plane. Areas where the measured cut plane surface, MP, deviates below the planned location for the cut plane, PP’, represent overcuts 404caused by the saw blade diving while forming the actual cut plane. The visual feedback may be provided using a color scheme, a gradient scheme, the use of different shapes, or other visual feedback tools. For example, the areas of undercuts 402 may be shown in red, the areas of overcuts 404 may be shown in blue, and areas of coplanarity may be shown in green. The intensity of the color, different colors, or a blinking frequency of a color, may denote areas that have the greatest deviation or are above a pre-defined threshold deviation. FIG. 9A shows the deviations using a gradient scheme where the undercuts 402 are shown using a first gradient pattern and the overcuts 404 are shown using a different gradient pattern. With the resulting information shown on the display 300, a user has the ability to revise the cut plane surface, S, to reduce the topographical deviation between the measured cut plane surface, MP, and the planned location for the cut plane, PP’, including the option of adding a biocompatible material to fill the overcuts 404. In a particular embodiment, a user may revise the bone by wielding a surgical saw or other cutting device to re-cut, or shave down, the areas of undercuts 402 according to the visual feedback (e.g., cutting down areas shown in red) shown on the display 300. The user therefore has the option, and feedback, for re-cutting the cut plane surface, S, to achieve a desired level of accuracy for the cut plane surface, S, to match with the planned location for the cut plane, PP’, as well as the option to achieve a desired level of planarity and topographical deviation within a user’s discretion or consistent with a preselected threshold present in the computer associated with the display 300. The above may be repeated until a desired accuracy is achieved.

[0067] With reference now to FIG. 9B, another embodiment of displaying the error between a measured cut plane, MP, and planned cut plane, PP, is shown. After the cut plane is formed on the bone, a user may wield a digitizer to collect a plurality of points on the formed cut plane. Acomputer operatively coupled to the tracking system then determines or calculates a measured cut plane surface, MP, from the plurality of points collected on the cut plane surface, S, using techniques known in the art. Any of the aforementioned techniques may be used to determine the measured cut plane surface, MP (e.g., fitting a plane, etc.). The computer may then determine the location of the measured cut plane surface relative to the registered POSE of the virtual bone model. For example, the computer may determine where the measured cut plane, MP, (e.g., a plane fitted to the plurality of collected points) intersects with the virtual bone model as registered to the bone. The computer may then generate a modified view of the bone model, M’, showing a 3D model of error 406 (denoted by the diagonal hatching) between the measured cut plane, MP, and the planned cut plane PP’. The computer may generate this modified view by removing any portion of the bone model distal to the measured cut plane, MP, from the bone model. The computer may display the 3D model of error 406 (which corresponds to the volume of bone between the measured cut plane, MP, and the planned cut plane, PP’) in a visually different manner than the remainder of the bone model, M’. For example, the computer may display the 3D model of error 406 as: (i) shaded; (ii) cross-hatched (or other hatching such as the diagonal hatching shown in FIG. 9B); (iii) in a different color; (iv) as a gradient with areas of larger error in one color (e.g., red) and areas of smaller error in another color (e.g., yellow); (v) change in opacity; and / or (vi) any other manner that differentiates the 3D model of error 406 from the remainder of the bone model, M’. This allows the user to quickly visualize any errors in three-dimensions.

[0068] In a specific embodiment, with reference to FIG. 10, a statistical plane, SP, may calculated from a plurality of points collected on the cut plane surface, S, to assess the planarity of the cut plane surface, S. The plurality of points may be collected in the same manner asdescribed with reference to FIG. 10 (i.e., a user wielding a digitizer 200 places the digitizer tip 202 / 202’ in contact with a plurality of locations on the cut plane surface, S, while a tracking system tracks movement of the digitizer and records the location of the digitizer tip 202 / 202’ when the digitizer tip 202 / 202’ is in contact with the cut plane surface, S). In other embodiments, the plurality of points may be collected on the cut plane surface, S, using other point collection devices such as a laser scanner, depth camera, or a conventional visual light camera. FIG. 10 depicts a plurality of the collected points 500. A computer operatively coupled to the tracking system then calculates a statistical plane, SP, from the plurality of collected points 500 using conventional statistical analysis (e.g., best fitting a plane to the plurality of collected points using least squares, multiple regression, etc.). A display 300 may display the plurality of collected points 500, the statistical plane, SP, and may further display error values 502, a bone model, M, (as shown in FIG. 6), and / or a modified bone model, M’ (as shown in FIG. 9A). The error values 502 may displayed as error bars between one or more collected points 500 and the statistical plane, SP. In other embodiments, the error values 502 may be displayed as one or more of: a root mean square error value; an average error; a max error; a minimum error; locations of the max errors; locations of the minimum errors; locations where a pre-defined threshold error is exceeded; as well as other statistical parameters. The error values thus afford topography information for one or more collected points 500 relative to the cut plane surface, S. In a particular embodiment, locations of undercuts or overcuts are highlighted on the statistical plane, SP, in a similar manner as the measured plane, MP, described with respect to FIGs. 9A or 9B. As a result, a user may assess the planarity of the cut plane surface, S, and may revise the cut plane surface, S, to achieve a desired level of planarity and topographical deviation within a user’s discretion or consistent with a preselected threshold present in the computer associated with thedisplay 300. The above may be repeated until a desired accuracy is achieved. Tt should be appreciated that embodiments described with respect to FIG. 10 may standalone (e.g., a user may choose to only assess the planarity of a cut plane surface, S, using a displayed statistical plane, SP, and error values 502), or one or more of those embodiments may be combined with embodiments described with respect to FIGs. 8 and 9 (e.g., a user may choose to assess the planarity and location of the cut plane surface, S, with respect to the planned location of a cut plane, PP’, using any combination of a measured cut plane surface, MP, a statistical plane, SP, and error values).

[0069] Any of the aforementioned techniques that provide visual feedback to assess the location and planarity of a cut plane surface, S, may assist a user to re-cut the bone at the locations of the undercuts to level out the cut plane surface, S, to a desired degree of accuracy. For example, the computer generating the display 1000 may provide statistical evaluations and recommendations that illustratively include: a root mean square error for a plurality of collected points 500, or a subset thereof; details about one or more collected points 500 being above or a below: a statistical plane, SP, a measured cut plane surface, MP, or the planned location for the cut plane, PP’; contour or elevation lines; recommendations as to how to revise the cut surface, S; modifications to a surgical plan; or any number of the aforementioned. One example of a recommendation may include instructions to recut the posterior medial condyle by ‘x’ millimeters, with or without a visual display of the recommended re-cut. The process of collecting points on the cut plane surface, S, and determining a measured cut plane surface, MP, and / or a statistical plane, SP, so detailed herein may be readily repeated after a given revision cut to confirm that a desired degree of accuracy has been achieved.

[0070] With respect to FIG. 1 1 , a specific embodiment for assessing the topographical deviation of a cut plane surface, S, relative to a planned location for a cut plane, PP’, is shown. The system and method may include a display 300, a computer operatively coupled to the display 300, a tracking system, a digitizer 200, a virtual model of the uncut bone, M, and a virtual model of a resected bone, M’. The display 300 may be configured to initially display an uncut bone model, M, (as shown in FIG. 6) and may further display instructions or graphics to guide the user to form a cut plane on the bone at a planned location. The display 300 may further display embodiments associated with FIGs. 1 - 6 to align a guide slot 102 of a cutting guide 100 with a planned location for a cut plane, PP’ . The virtual model of the uncut bone, M, is registered to the location of the bone, B. A portion of the virtual model of the uncut bone, M, includes a bone volume, V, that corresponds to a portion of the bone that will be removed as a result of forming a cut plane, PP’, at the planned location on the bone (e.g., the bone volume, V, may correspond to a portion of the distal femur that will be removed as a result of forming the distal cut plane, PP’, at the planned location on the bone for TKA procedures). The bone volume, V, associated with the virtual model of the uncut bone, M, that is registered to the remaining bone, B’, is outlined in FIG. 10 by the dotted lines distal to the distal cut plane surface, S.

[0071] After the cut plane surface, S, is formed on the bone using any techniques known in the art, the accuracy and planarity of the cut plane surface, S, with respect to the planned location for the cut plane, PP’, may be assessed with the use of the digitizer 200. A user wielding the digitizer 200 may bring the digitizer tip, 202 / 202’, in contact with one or more locations on the cut plane surface, S. A tracking system tracks movement of the digitizer tip, 202 / 202’, and the location of the virtual model of the uncut bone, M, registered to the remaining bone, B’. Once the digitizer tip, 202 / 202’, crosses into the location of the bone volume, V, the display 1100 mayautomatically switch views from the virtual model of the uncut bone, M, to a virtual model of a resected bone, M’, showing the planned cut plane surface, PS, which would have been ideally formed at the planned location for the cut plane, PP’. The location of the bone volume, V, is known in physical space based on: (i) the tracked location of a tracking array affixed to the remaining bone, B’; and (ii) the location of the virtual model of the uncut bone, M, (and more specifically the location of the bone volume, V, associated with the virtual model of the uncut bone, M) registered to the remaining bone, B’, in the coordinate frame of the tracking array. The location of the digitizer tip, 202 / 202’, is known in physical space based on: (i) the tracked location of three or more fiducial markers coupled to the digitizer 200; and (ii) a calibrated and / or known geometry of the digitizer tip, 202 / 202’, relative to the three or more fiducial markers. Therefore, the tracking system, or a computer operatively coupled to the tracking system, can determine when the digitizer tip, 202 / 202’, crosses into the bone volume, V, and then signals or controls the display 300 to change to the view of the virtual model of the resected bone, M’. It should be appreciated that the virtual model of the resected bone model, M’, may be a modified version of the virtual model of the uncut bone, M, where the bone volume, V, is removed, grayed out (e.g., change in opacity), or shown in a different color on the virtual model of the uncut bone, M, to reveal the planned cut plane surface, PS, when the location of the digitizer tip 202 / 202’ crosses into the bone volume, V.

[0072] A representation 600 (e.g., a circle, dot, crosshairs, a virtual model of the digitizer tip, a virtual model of a portion of the digitizer) of the tracked location of the digitizer tip, 202 / 202’ is also shown on the display 300 with respect to the tracked location of the planned cut plane surface, PS. The tracked location of the planned cut plane surface, PS, is known in physical space based on: (i) the tracked location of a tracking array affixed to the remaining bone, B’; and(ii) the location of the virtual model of the uncut bone, M, (and more specifically the planned location for the cut plane, PP’, (or planned cut plane surface, PS) associated with the virtual model of the uncut bone, M) registered to the remaining bone, B’, in the coordinate frame of the tracking array. The tracked location of the digitizer tip, 202 / 202’, in physical space with respect to the planned location for the cut plane, PP’, in physical space, may therefore be displayed on the display 300. To assess the accuracy and / or planarity of the cut plane surface, S, a user may first wield the digitizer 200 to probe, or contact, the digitizer tip, 202 / 202’, on the cut plane surface, S, at a plurality of locations. When the digitizer tip, 202 / 202’, is in contact with a given location on the the cut plane surface, S, the user may visually assess the deviation between: (i) the location of the digitizer tip representation 600 (which represents the location of the cut plane surface, S, at that given location since the digitizer tip, 202 / 202’, is in contact with the cut plane surface, S); and (ii) the location of the planned cut plane surface, PS, on the display 300. Anywhere the location of the digitizer tip representation 600 deviates from the location of the planned cut plane surface, S, signifies an error between the actual cut plane surface, S, formed on the remaining bone, B ’ , and the planned location for the cut plane, PP’ . These may be planarity errors caused by the saw blade skiving or diving while forming the cut plane, or errors in the alignment of the guide slot 102 with the planned location for the cut plane, PP’. hi some inventive embodiments, a deviation measurement 602 (e.g., a deviation bar or deviation value) may be displayed to show the magnitude of the deviation. Multiple deviation measurements may be made across the cut plane surface, S, to provide an overall measurement of the planarity and accuracy of the cut plane surface, S, relative to the planned location for the cut plane, PP’. Other statistical parameters (e.g., average deviation, max deviation, minimum deviation, the locations of the maximum deviations) may be displayed on the display 300 based on multiple deviationmeasurements. The measured deviation(s) and their locations on the cut plane surface, S, may assist a user in revising the cut plane to a desired degree of planarity or accuracy. If the digitizer tip, 202 / 202’, is removed out of the bone volume, V, at any point during this process, the display 300 may be controlled to automatically change the view back to the virtual model of the uncut bone, M.Assessing Cut Plane Accuracy with Vision Based Systems

[0073] In a particular embodiment, the location accuracy of the cut plane is assessed using a vision-based system. With reference the FIG. 12, the vision-based system may include a tracking system 706 having two or more optical detectors 707 (e.g., tracking cameras for detecting infrared light), an imaging camera 650 (e.g., a visible light camera), a display 300, and one or more computers (e.g., 708, 710, 711) of a computing system 704 (as shown in FIG. 13). The imaging camera 652 is configured to capture images of the surgical site during the procedure. For example, the imaging camera 652 may capture a real-time video of the operative bone(s), B, during a TKA procedure. The images and / or video may be displayed on the display 300 to show the captured bone image, BI, and images of other hardware or devices (e.g., a cutting guide image 100’) captured in the field-of-view of the imaging camera 652. The coordinate frame of the imaging camera 652 may be calibrated relative to the coordinate frame of the tracking system 704 such that the location of an object in the images from the imaging camera 652 may be determined relative to the location of an object in the coordinate frame of the tracking system, and vice-versa. These calibration techniques are known in the art, such as those described in U.S.Pat. App. No. 18 / 221,913 assigned to the assignee of the present application.

[0074] The system may be configured to perform a method for assessing the accuracy of a cut plane to be formed on the bone, which may include the following steps. After the bone pins (106a, 106b) are inserted in the bone and the cutting guide 100 is assembled to the bone pins, the imaging camera 652 captures images of the surgical site include the bone, B, and the cutting guide 100 assembled to the bone pins. The imaging camera 652 may be capturing images continuously throughout the entire procedure, and / or the imaging camera 652 may be prompted (via a user input) to start capturing images at a specific point during the procedure (e.g., after the cutting guide 100 is assembled to the bone pins). The captured images of the cutting guide 100, as assembled to the bone pins, are then analyzed by one or more computers of the computing system to determine the location of the guide slot 102 in physical space in the coordinate frame of the imaging camera 652. In a particular' embodiment, the location of the guide slot 102 is determined by segmenting the location of the cutting guide 100 in the captured images. The segmentation may be performed using image segmentation techniques and / or artificial intelligence techniques known in the art. In a specific embodiment, the segmentation is performed utilizing the known and unique geometry of the cutting guide 100. For example, the computer may match one or more features of the cutting guide 100 captured in the image with one or more corresponding features on a model of the cutting guide 100. Then based on the segmented location of the cutting guide 100 in the image, the location of the guide slot 102 in physical space can be determined in the coordinate frame of the imaging camera 652 using the known geometry of the cutting guide 100, and more specifically where the guide slot 102 is located on the cutting guide 100. In specific embodiments, the imaging camera 652 is a depth camera, or the vision-based system 650 uses two or more imaging cameras 652 (or two or more images captured by a single imaging camera 652 from two different perspectives a knowndistance apart), in order to determine the three-dimensional coordinates (e.g., x, y, and z coordinates) of the guide slot 102 in the coordinate frame of the imaging camera(s) 652. In other embodiments, the depth (e.g., z-coordinate) of the guide slot 102 in the coordinate frame of a single imaging camera 652 may be determined using artificial intelligence techniques, such as a neural network, as described by Zhu, Jack, and Ralph Ma. "Real-time depth estimation from 2D images." (2016). The use of artificial intelligence for segmentation is particularly applicable for this scenario because the cutting guide 100 has a known and unique geometry.

[0075] The one or more computers may then determine a projected cut plane by fitting a plane to the determined location of the guide slot 102, and may more particularly fit a plane to the bottom surface of the guide slot 102. Note, this projected cut plane, PP, is similar’ to the aforementioned projected cut plane, PP, as described with reference to FIG. 4, and represents the location of the cut plane that would be formed on the bone if a user were to advance a saw blade through the guide slot 102 as currently positioned on the bone. The projected cut plane, PP, is then used for comparison with the planned location for forming the cut plane to assess the accuracy of the cut plane to be formed on the bone. In particular embodiments, a calibration transformation is applied to at least one of: (i) the planned location for forming the cut plane in the coordinate frame of a tracking array 720a affixed to the bone; or (ii) the projected cut plane as determined in the coordinate frame of the imaging camera 652. The calibration transformation defines the relationship between the coordinate frame of the imaging camera 652 and the coordinate frame of the tracking system 704. The tracking system 704 can determine the location of the tracking array coordinate frame in the tracking system coordinate frame. Then using the calibration transformation, the location of the tracking array coordinate frame (and thus the location of the planned cut plane as registered thereto) can be determined in the imaging cameracoordinate system. The opposite may also be done, where the location of the projected cut plane in the imaging camera coordinate system is transformed into the coordinate system of the tracking system. Either way, the locations of the planned cut plane and the determined location of the projected cutting plane can be compared in the same coordinate system to assess the accuracy of forming the cut plane on the bone. The accuracy may be assessed by comparing the two planes relative to one another and, in some embodiments, calculating translational and / or rotational errors between the two planes. The accuracy is perfect if the two planes coincide with one another. If errors are identified, the system may display an alert, notification, or a comparison of the two planes to the user as previously described with reference to FIG. 6. It should be appreciated that the capturing of images, segmentation, and plane comparison may all be performed automatically by the computer without any user actions or inputs.

[0076] The advantages of a vision-based system 650 includes: (i) more information to analyze because the assessment is based on captured images; (ii) the collected data is noise free, which leads to more robust and accurate plane fitting; and (iii) the imaging, segmentation, and plane comparison can all be performed automatically and, in some embodiments, does not require any action or inputs from the user (e.g., surgeon).Computer- Assisted Surgical System

[0077] Referring now to FIGs. 13, 14a, and 14b an embodiment of an inventive computer- assisted surgical system is shown generally at 700 for implementing embodiments of the present invention. The computer-assisted surgical system 700 generally includes a hand-held robotic device 702 (referred to hereinafter as “robotic device”), a computing system 704, and a tracking system 706. The robotic device 702, as shown in greater detail in FIGs. 14A and 14B, isconfigured to maintain alignment of an end-effector 806 coincident with a virtual plane having a pre-determined location with respect to a bone for performing a procedure on the bone. In other inventive embodiments, an end effector extends from a robotic arm (e.g., a serial-chain robotic arm). The computing system 04 generally includes hardware and software for executing a surgical procedure. By way of example but not limitation, the computing system 704 is configured to generate control signals to control the actuation (or movement) of the robotic device 702 to maintain alignment of the end-effector axis 807 (FIG. 14a) coincident with a virtual plane based on: a) the tracked location of a tracking array affixed to the bone, B; b) the pre-determined location of the virtual plane registered to the bone in the coordinate frame of the tracking array; and c) the tracked location of the robotic device 702. The computing system 704 in some inventive embodiments includes a non-transitory memory in which data, software, or a combination thereof are stored.

[0078] FIGS. 14A and 14B are schematic views showing the robotic device 702 that is exemplary of those that can be used for pin placement or for forming a bone cut. More particularly, FIG. 14A shows the robotic device 702 in a first working POSE, and FIG. 13B illustrates the robotic device 702 in a second working POSE. The robotic device 702 includes a hand-held portion 802 (or handle) and a working portion 804. The handheld portion 802 includes an outer casing 803 of ergonomic design which can be held and wielded by a user (e.g., a surgeon). In particular inventive embodiments, the robotic device 702 is intended to be fully supported by the hands of the user in that there are no additional supporting links connected to the robotic device 702 and the user supports the full weight of the robotic device 702. The working portion 804 comprises an end-effector 806 having an end-effector axis 807. The endeffector 806 may be removably coupled to the working portion 804 (via a coupler (e.g., chuck))and driven by a motor 805. The hand-held portion 802 and working portion 804 are connected to one another; for example, by a first linear actuator 807a and a second linear actuator 807b in order to control the pitch and translation of the working portion 804 relative to the hand-held portion 802, as will hereinafter be discussed in further detail. In a particular inventive embodiment, the working portion 804 is removably coupled to the hand-held portion 802 to permit different types of working portions to be assembled to the hand-held portion 802. For example, a first working portion 804 may illustratively be a laser system having components to operate a laser for treating tissue, a second working portion 804 may illustratively be a drill for rotating a bone pin, and a third working portion 804 may illustratively be an oscillating saw.

[0079] A tracking array 812, having three or more fiducial markers, is preferably rigidly attached to the working portion 804 in order to permit the tracking system 706 (FIG. 13) to track the POSE of the working portion 804. The three or more fiducial markers may, alternatively, be integrated directly with the working portion 804. The robotic device 702 may further include one or more user input mechanisms such as triggers (e.g., trigger 814) or button(s). The user input mechanisms may permit the user to perform various functions illustratively including: activating or deactivating the motor 805, activating or deactivating the actuation of the working portion 804 relative to the hand-held portion 802, notifying the computing system 704 to change from targeting one virtual plane to a subsequent virtual plane, and pausing the medical procedure.

[0080] Within the outer casing of the hand-held portion 802 is the first linear actuator 807a and the second linear actuator 807b. Each linear actuator (807a, 807b) may include a motor (810a, 810b) to power a screw (816a, 816b) (e.g., a lead screw, a ball screw), a nut (818a, 818b), and a linear rail (808a, 808b). In some inventive embodiments, the motors (first motor 810a, second motor 810b) are electric servomotors that bi-directionally rotate the screws (816a, 816b).Motors (810a, 810b) may also be referred to herein as linear actuator motors. The nuts (818a, 818b) (e.g„ ball nuts, elongated nuts) are operatively coupled to the screws (816a, 816b) to translate along the screws (816a, 816b) as each screw is rotated by its respective motor (810a, 810b). A first end of each linear rail (808a, 808b) is coupled to a corresponding nut (816a, 816b) and the opposing end of each linear rail (808a, 808b) is coupled to the working portion 804 via hinges (820a, 820b) such that the hinges (820a, 820b) allow the working portion 804 to pivot relative to the linear rails (808a, 808b). The motors (810a, 810b) power the screws (816a, 816b) which in turn cause the nuts (818a, 818b) to translate along the axis of the screws (816a, 816b). Translation of nuts (818a, 818b) along ball screws (816a, 816b), respectively, causes translation of front linear rail 808a and back linear’ rail 808b, respectively, whereby to permit (a) selective linear movement of working portion 804 relative to hand-held portion 802, and (b) selective pivoting of working portion 804 relative to hand-held portion 802 of robotic device 702. Accordingly, the translation “d” and pitch “a” (FIG. 14B) of the working portion 804 may be adjusted depending on the position of each nut (818a, 818b) on their corresponding screw (816a, 816b). A linear guide 822 (FIG. 14A) may further constrain and guide the motion of the linear rails (808a, 808b) in the translational direction “d”. In a particular embodiment, the nuts (816a, 816b) are elongated and coupled directly to the working portion 804 via the hinges (820a, 820b), in which case the linear rails (808a, 808b) are no longer a component of the linear actuators (807a, 807b). It should be appreciated that other linear actuation mechanisms / components may be used to adjust the POSE of the working portion 804 relative to the hand-held portion 802 such as linear motors, pneumatic motors, worm drives and gears, rack and pinion gears, and other arrangements of motors and transmissions.

[0081] The robotic device 702 may receive power via an input / output port (e.g., from an external power source) and / or from on-board batteries (not shown).

[0082] The motors (805, 810a, 810b) of the robotic device 702 may be controlled using a variety of methods. By way of example but not limitation, according to one method of the present invention, control signals may be provided via an electrical connection to an input / output port. By way of further example but not limitation, according to another method of the present invention, control signals are communicated to the robotic device 802 via a wireless connection, thereby eliminating the need for electrical wiring. The wireless connection may be made via optical communication. In certain inventive embodiments, the robotic device 702 includes a receiver for receiving control signals from the computing system 704 (FIG. 13). The receiver may be, for example, an input port for a wired connection (e.g., Ethernet port, serial port), a transmitter, a modem, a wireless receiver (e.g., Wi-Fi receiver, Bluetooth® receiver, a radiofrequency receiver, an optical receiver (e.g., photosensor, photodiode, camera)), or a combination thereof. The receiver may send control signals from the computing system 704 directly to the motors (805, 810a, 810b) of the robotic device 702, or the receiver may be in communication with a computer (e.g., an on-board device computer 709 as further described below) that processes signals (e.g., tracking data) received by the receiver and then generates the control signals for the motors (805, 810a, 810b) based on the received signals.

[0083] Referring back to FIG. 13, the computing system 704 of the computer-assisted surgical system 700 may include: one or more device computers (708, 709); a planning computer 710; a tracking computer 711; and peripheral devices. Each computer may include one or more processors and / or one or more units of non-transitory computer-readable media. As used herein, non-transitory and non-volatile in the context of computer media are considered to be synonyms.In some inventive embodiments, a device computer 709 is mounted on or housed in the robotic device 702. Processors operate in the computing system 704 to perform computations and execute software associated with embodiments of the inventive system and method. The device computer(s) (708, 709), the planning computer 710, and the tracking computer 711 may be separate entities as shown in FIG. 13, or it is also contemplated that operations may be executed on one (or more) computers depending on the configuration of the computer-assisted surgical system 700. For example, the tracking computer 711 may have operational data to control the robotic device 702 without the need for a separate device computer (708, 709). Furthermore, if desired, any combination of the device computers (708, 709), planning computer 710, and / or tracking computer 711 may be connected together via a wired or wireless connection. In addition, the data gathered by, and / or the operations performed by, the tracking computer 711 and device computer(s) (708, 709) may work together to control the robotic device 702 and, as such, the data gathered by, and / or the operations performed by, the tracking computer 711 and device computer(s) (708, 709) to control the robotic device 702 may be referred to herein as a “control system.” It is further appreciated that one or more of the computers may be readily located remote from the surgical site. Cloud-based computation is also contemplated for embodiments of the present invention.

[0084] The peripheral devices allow a user to interface with the computing system 704 and may include, but are not limited to, one or more of the following: one or more user-interfaces, such as a display (300, 712) to display a graphical user interface (GUI); and user-input mechanisms, such as a keyboard 714, a mouse 722, a pendent 724, a joystick 726, or a foot pedal 728. If desired, the display (300, 712) may have touchscreen capabilities, and / or the robotic device 702 may include one or more input mechanisms (e.g., buttons, switches, etc.). The system700 also includes a tracked digitizer 200 to assist in the registration process and the other inventive embodiments described herein. A tracking array 720c is coupled to the digitizer 200 to permit the tracking system 706 to track the location of the digitizer 200 in space. The digitizer 200 may further include one or more user input mechanisms to provide input to the computing system 704. For example, a button on the digitizer 200 may allow the user to signal to the computing system 704 to collect or digitize a point in space.

[0085] The device computer(s) (708, 709) may include one or more processors, controllers, software, data, utilities, and / or storage medium(s) such as RAM, ROM or other non-volatile or volatile memory to perform functions related to the operation of the robotic device 702. By way of example but not limitation, one or more of the device computers (708, 709) may include software to: control the robotic device 702, (e.g., generate control signals to move the working portion 804 relative to the hand-held portion 802 to a targeted POSE); receive and process tracking data; control the rotational or oscillating speed of the end-effector 806 by controlling motor 805; execute registration algorithms; execute calibration routines; provide workflow instructions to the user throughout a surgical procedure; as well as any other suitable software, data or utilities required to successfully perform the procedure in accordance with embodiments of the invention. In still other inventive embodiments, the device computer (708, 709) is equipped with an alignment alert in lieu of, or in conceit with the aforementioned controls. By way of example, an alignment alert includes an auditory tone, laser projection, vibration in robotic device 702, or a combination thereof that notifies a surgeon as to a correct POSE for a tool to perform a given function. A laser light projection is well-suited to indicate a needed POSE in those instances when a conventional tool decoupled from the control system holds an end effector.

[0086] In some inventive embodiments, the computing system 704 may include a first device computer 708 located separate from the robotic device 702 and a second device computer 709 housed in the robotic device 702 to provide on-board control. The first device computer 708 may be dedicated to the control of the surgical workflow via a GUI, the registration process and the associated calculations, the display of 3-D virtual models and 3-D model manipulation or animation, control the output of the display (300, 712), as well as other processes. In specific embodiments, the first device computer 708 is configured to perform one or more of the following: determine a reference plane, RP; determine a projected plane, PP; control the display 300 to display one or more planes (e.g., a projected plane, PP, and planned location for a cut plane, PP’) with respect to a bone model, M; control the display 300 to display prompts or instructions for a user to digitize points on a cut surface, S, or other portion of the bone; determine a measured cut plane surface, MP; control the display 300 to display a comparison of a measured cut plane surface, MP, to a planned location for a cut plane, PP’ ; determine locations of undercuts 402, overcuts 404, undulations, or unevenness of a measured cut plane surface, MP, relative to a planned location for a cut plane, PP’; determine the planarity of a cut plane surface, S; control the display 300 to display locations of undercuts 402, overcuts 404, undulations, or unevenness of a measured cut plane surface, MP, relative to a planned location for a cut plane, PP’; determine a statistical plane, SP; determine statistical parameters; display error values 502 with respect to a statistical plane, SP; determine when a digitizer tip 202 / 202’ crosses into a bone volume, V; control the display 300 to change views of a virtual bone model; receive and analyze captured images from an imaging camera 652; as well as any other functions or computations required to perform the embodiments described herein. The second device computer 709, also referred to herein as an on-board device computer, may be dedicated to the control of the roboticdevice 702. For example, the on-board device computer 709 may compute and generate the control signals for the actuator motors (810a, 810b) based on: i) received signals / data from the tracking system corresponding to the real-time POSE of the robotic device; and ii) received signals / data corresponding to the real-time POSE of the virtual plane computed by the first device computer 708. The on-board device computer 709 may also send internal data (e.g., operational data, actuator / screw position data, battery life, etc.) via a wired or wireless connection. In some inventive embodiments, wireless optical communication is used to send and receive the signals / data described herein. Details about bi-directional optical communication between a robotic device 702 and a tracking system 706 are further described below.

[0087] The planning computer 710 in some inventive embodiments is dedicated to planning the procedure. By way of example but not limitation, the planning computer 710 may contain hardware (e.g., processors, controllers, memory, etc.), planning software, data, and / or utilities capable of: receiving, reading, and / or manipulating medical imaging data; segmenting imaging data; constructing and manipulating three-dimensional (3D) virtual models; storing and providing computer-aided design (CAD) files such as 3-D implant models or other hardware CAD files; planning the POSE of implant models relative to bone data; defining the location of robot operating instructions (e.g., cut-files, virtual planes, virtual boundaries, virtual axes, virtual targets) relative to bone data; generating the surgical planning data for use with the system 700; and providing other various functions to aid a user in planning the surgical procedure. The final surgical plan data may include: one or more images of the bone or virtual models of the bone; bone registration data; subject identification information; the POSE of one or more pins, screws, implants, grafts, fixation hardware defined relative to the bone data; and / or the POSE of robot operating instructions defined relative to the bone data. The device computer(s) (708, 709) andthe planning computer 710 may be directly connected in the operating room, or the planning computer 710 may exist as separate entities outside the operating room. The final surgical plan is readily transferred to a device computer (708, 709) and / or tracking computer 711 through a wired (e.g., electrical connection) or a wireless connection (e.g., optical communication, Wi-Fi, Bluetooth) in the operating room; or transferred via a non-transient data storage medium (e.g., a compact disc (CD), or a portable universal serial bus (USB drive)). As described above, the computing system 1204 may comprise one or more computers, with multiple processors capable of performing the functions of the device computer(s) (708, 709), the tracking computer 711, the planning computer 710, or any combination thereof.

[0088] The tracking system 706 of the present invention generally includes a detection device to determine the POSE of an object relative to the position of the detection device. In some inventive embodiments, the tracking system 706 is an optical tracking system such as the optical tracking system described in U.S. Pat. No. 6,061,644 (which is hereby incorporated herein by reference), having two or more optical detectors 707 (e.g., tracking cameras for detecting infrared light) for detecting the position of fiducial markers arranged on rigid bodies or integrated directly on the tracked object. By way of example but not limitation, the fiducial markers may include an active transmitter, such as a light emitting diode (LED) or electromagnetic radiation emitter; a passive reflector, such as a plastic sphere with a retro- reflective film; or a distinct pattern or sequence of shapes, lines or other characters. A set of fiducial markers arranged on a rigid body, or integrated on a device, is sometimes referred to herein as a tracking array (720a, 720b, 812), where each tracking array has a unique geometry / arrangement of fiducial markers, or a unique transmitting wavelength / frequency (if themarkers are active LEDS), such that the tracking system 706 can distinguish between each of the tracked objects.

[0089] In specific embodiments, the tracking system 706 may be incorporated into an operating room light 718 as shown in FIG. 13, located on a boom, a stand, or built into the walls or ceilings of the operating room. The tracking system computer 711 includes tracking hardware, software, data, and / or utilities to determine the POSE of objects (e.g., bone structures, the robotic device 702) in a local or global coordinate frame. The output from the tracking system 706 (i.e., the POSE of the objects in 3-D space) is referred to herein as tracking data, where this tracking data may be readily communicated to the device computer(s) (708, 709) through a wired or wireless connection. In a particular embodiment, the tracking computer 711 processes the tracking data and provides control signals directly to the robotic device 702 and / or a device computer(s) (708, 709) based on the processed tracking data controls the position of the working portion 804 of the robotic device 702 relative to the hand-held portion 802. In another embodiment, the tracking computer 711 sends tracking data to a receiver located on the robotic device 702, where an on-board device computer 709 generates control signals based on the received tracking data.

[0090] The tracking data is determined in some inventive embodiments using the position of the fiducial markers detected from the optical detectors and operations / processes such as image processing, image filtering, triangulation algorithms, geometric relationship processing, registration algorithms, calibration algorithms, and coordinate transformation processing.

[0091] Bi-directional optical communication may be implemented between the robotic device 702 and the tracking system 706 by way of a modulated light source (e.g., light emitting diode(LED)) and a photosensor (e.g., photodiode, camera) regardless of the wavelengths employed.The robotic device 702 may include an LED and a photosensor (i.e., a receiver) disposed on the working portion 804 or hand-held portion 802, where the LED and photosensor are in communication with a processor such as modem or an on-board device computer 709. Data generated internally by the robotic device 702 may be sent to the tracking system 706 by modulating the LED, where the light signals (e.g., infrared, visible light) created by the modulation of the LED are detected by the tracking system optical detectors (e.g., tracking cameras for detecting infrared light) or a dedicated photosensor and processed by the tracking system computer 711 or another computer (e.g., first device computer 708) operatively coupled to the tracking system 706. The tracking system 706 may likewise send data to the robotic device 702 with a modulated LED associated with the tracking system 706. Data generated by the tracking system 706 (or another computer (e.g., first device computer 708) operatively coupled to the tracking system 706) may be sent to the robotic device 702 by modulating the LED on the tracking system 706, where the light signals are detected by the photosensor on the robotic device 702 and processed by a processor in the robotic device 702. Examples of data sent from the tracking system 706 to the robotic device 102 includes operational data, surgical planning data, informational data, control data, tracking data, pre-procedure data, or instructional data. Examples of data sent from the robotic device 702 to the tracking system 706 may include motor position data, battery life, operating status, logged data, operating parameters, warnings, or faults.

[0092] It should be appreciated that in some embodiments of the present invention, other tracking systems are incorporated with the surgical system 700. By way of example but not limitation, the surgical system 700 may include an electromagnetic field tracking system, ultrasound tracking systems, accelerometers and gyroscopes, and / or a mechanical trackingsystem. The replacement of a non-mechanical tracking system with other tracking systems will be apparent to one skilled in the art in view of the present disclosure. In one form of the present invention, the use of a mechanical tracking system may be advantageous depending on the type of surgical system used such as the computer-assisted surgical system described in U.S. Pat. No. 6,322,567; assigned to the assignee of the present application and incorporated herein by reference in its entirety.

[0093] FIG. 15 depicts the robotic device 702 maintaining alignment of a pin (900a, 900b) coincident with a virtual plane “VP” having a pre-defined location relative to the bone, B, for inserting one or more pins (900a, 900b) in the bone, B. The location of the virtual plane “VP” may be defined based on the planned location for forming a cut plane on the bone. In some inventive embodiments, the location of the virtual plane “VP” is defined by translating the planned location for the cut plane by a numerical amount corresponding to the geometry of the cutting guide 400 such that the guide slot 402 aligns with the planned location for the cut plane when the cutting guide 400 is coupled to the pins (900a, 900b). The robotic device 702 maintains alignment of a pin coincident with the virtual plane, VP, independent of the user’s gross positioning of the robotic device 702 and to account for the user’s hand tremors. The working portion 804 is actuated (or moved) relative to the hand-held portion 802 in response to control signals generated by the computing system 704 to maintain the alignment of the pin (900a, 900b) coincident with the virtual plane, VP, as described above. FIG. 14 shows two pins 900a, 900b inserted in the bone, B coincident with the virtual plane, VP. A cutting guide 100 may then be coupled to the pins (900a, 900b) as shown in FIG. 1.Other Embodiments

[0094] While at least one exemplary embodiment has been presented in the foregoing detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the described embodiments in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient roadmap for implementing the exemplary embodiment or exemplary embodiments. It should be understood that various changes may be made in the function and arrangement of elements without departing from the scope as set forth in the appended claims and the legal equivalents thereof.

Claims

CLAIMS1. A method for assessing a locational accuracy or planarity of a cut plane formed, or to be formed, on a bone, comprising: determining a projected location for a cut plane to be formed on the bone using a plurality of points collected at locations on a cutting guide when the cutting guide is coupled to a bone; and providing feedback comparing the projected location for the cut plane relative to a predetermined location for a planned cut plane.

2. The method of claim 1 wherein the plurality of points are collected using a digitizer comprising a digitizer tip.

3. The method of claim 1 wherein the plurality of points are collected at locations on one or more surfaces or one or more features of the cutting guide.

4. The method of claim 1 wherein the cutting guide comprises an opening adapted to receive a cutting device therethrough, wherein the opening is bounded by at least a top surface and a bottom surface, and wherein at least a portion of the plurality of points are collected at locations on the bottom surface.

5. The method of claim 4 wherein the cutting guide further comprises a ledge contiguous with at least a portion of the bottom surface, wherein at least a portion of the plurality of points are collected at locations on the ledge.

6. The method of claim 1 wherein providing feedback comprises displaying on a display a representation of the cut plane at the projected location with respect to a representation of the planned cut plane at the pre-determined location.

7. The method of claim 6 further comprising displaying on the display a virtual bone model, wherein the representation of the cut plane is shown with respect to the virtual bone model at the projected location and the representation of the planned cut plane is shown with respect to the virtual bone model at the pre-determined location.

8. The method of claim 6 wherein providing feedback comprises providing instructions to adjust a position and / or orientation (POSE) of an opening of the cutting guide to move the opening towards overlap with the pre-determined location for the planned cut plane, wherein the opening is adapted to receive a cutting device therethrough.

9. The method of claim 8 wherein the instructions comprises information to adjust the POSE of the opening of the cutting guide by at least one of: (i) adjusting the position of the cutting guide relative to the bone; and (ii) adjusting the opening relative to the cutting guide.

10. The method of claim 1 wherein determining the projected location for the cut plane comprises a calculation using the plurality of points and geometry data of the cutting guide.

11. The method of claim 10 wherein the calculation further comprises calculating a location of a surface or feature of the cutting guide using the plurality of points, wherein the projected location for the cut plane is determined using the geometry of the calculated location of the surface or feature with respect to an opening of the cutting guide, wherein the opening is adapted to receive a cutting device therethrough.

12. A system for assessing a locational accuracy or planarity of a cut plane formed, or to be formed, on a bone, comprising: a computer comprising a processor configured to: determine a projected location for a cut plane to be formed on the bone using a plurality of points collected at locations on a cutting guide when the cutting guide is coupled to a bone; and provide feedback comparing the projected location for the cut plane relative to a pre-determined location for a planned cut plane.

13. The system of claim 12 further comprising a digitizer comprising a digitizer tip for contacting one or more surfaces or features located on the cutting guide.

14. The system of claim 13 further comprising a tracking system for tracking movement of the digitizer.

15. The system of claim 14 wherein the computer is operatively coupled to the tracking system, wherein the computer is further configured to:record the location of each of the plurality of points when the digitizer tip is in contact with a surface or feature located on the cutting guide; and determine the projected location for the cut plane using the plurality of points and geometry data of the cutting guide.

16. The system of claim 12 further comprising a display wherein the feedback is provided by displaying on the display a representation of the cut plane at the projected location with respect to a representation of the planned cut plane at the pre-determined location.

17. A method for assessing a locational accuracy or planarity of a cut plane surface formed on a bone, comprising: determining a location and shape of at least a portion of a cut plane surface formed on a bone using a plurality of points collected at locations on the cut plane surface; and providing feedback comparing the location or shape of the at least portion of the cut plane surface to a pre-determined location for a planned cut plane surface.

18. The method of claim 17 wherein the plurality of points are collected using a digitizer comprising a digitizer tip.

19. The method of claim 18 wherein the digitizer tip comprises a facial area of between 1 and 10 square centimeters.

20. The method of claim 18 wherein the digitizer tip is coupled to a plate.

21. The method of claim 17 wherein the providing feedback comprises displaying on a display: (i) a resected view of a virtual bone model having a resected surface at the predetermined location for the planned cut plane; and at least one of: (a) areas of topographical deviation between the location or shape of the at least portion of the cut plane surface and the resected surface.

22. The method of claim 17 wherein the providing feedback comprises displaying on a display: (i) a representation of the planned cut plane at a pre-determined location; and (ii) areas of topographical deviation between the location or shape of the at least portion of the cut plane surface and the representation of the planned cut plane.

23. The method of claims 21 or 22 wherein the providing feedback further comprises highlighting areas on the display where the topographical deviation is at least one of: a maximum deviation or above a pre-determined threshold deviation.

24. The method of any one of claims 21 or 22 further comprising revising the at least portion of the cut plane surface to reduce the topographical deviation.

25. The method of any one of claims 17 to 22 wherein the shape is determined as at least one of: (i) a plane; (ii) a surface having planar and / or non-planar areas; (iii) a polygon; or(iv) a point cloud.

26. The method of any one of claims 17 to 22 wherein the providing feedback comprises displaying on a display: (i) a resected view of a virtual bone model having a resected surface at the determined location of the cut plane surface formed on a bone; and a three- dimensional model of error situated between the resected surface and the planned location for forming the cut plane.

27. A system for assessing a locational accuracy or planarity of a cut plane surface formed on a bone, comprising: a computer comprising a processor configured to: determine a location and shape of at least a portion of a cut plane surface formed on a bone using a plurality of points collected at locations on the cut plane surface; and provide feedback comparing the location or shape of the at least portion of the cut plane surface to a pre-determined location for a planned cut plane surface.

28. The system of claim 27 further comprising a digitizer comprising a digitizer tip for contacting the cut plane surface at a plurality of locations.

29. The system of claim 28 wherein the digitizer tip is a blunt tip.

30. The system of claim 28 further comprising a digitizer comprising a digitizer tip, wherein the digitizer tip is configured to couple with a plate for contacting locations on the cut plane surface.

31. The system of any one of claims 27 to 30 further comprising a tracking system for tracking movement of the digitizer, wherein the computer is operatively coupled to the tracking system for recording locations of the digitizer tip when the digitizer tip or plate is in contact with the cut plane surface to collect the plurality of points.

32. The system of any one of claims 27 to 30 wherein the shape is determined as at least one of: (i) a plane; (ii) a surface having planar and / or non-planar areas; (iii) a polygon; or (iv) a point cloud.

33. The system of claim 27 further comprising a display for providing the feedback wherein the feedback comprises displaying on the display: (i) a resected view of a virtual bone model having a resected surface at the planned location for the planned cut plane; and (ii) areas of topographical deviation between the location or shape of the at least portion of the cut plane surface and the resected surface.

34. The system of claim 27 further comprising a display for providing the feedback wherein the feedback comprises displaying on the display: (i) a representation of the planned cut plane at the pre-determined location; and (ii) areas of topographical deviation between the location or shape of the at least portion of the cut plane surface and the representation of the planned cut plane.

35. The system of claims 33 or 34 further comprising highlighting areas on the display where the topographical deviation is at least one of: a maximum value or above a predetermined threshold deviation.

36. The system of any one of claims 27 to 30 further comprising a cutting device for revising the bone to reduce the topographical deviation.

37. A method for assessing planarity of a cut plane surface formed on a bone, comprising: fitting a plane to a plurality of points collected at locations on the cut plane surface; and providing feedback statistically comparing the fitted plane to the plurality of points to assess the planarity of the cut plane surface.

38. The method of claim 37 wherein the providing feedback comprises displaying on a display at least one of: (i) a root mean square error value of the plurality of points to the fitted plane; (ii) an average error value of the plurality of points to the fitted plane; (iii) error values and / or locations of one or more points from the plurality of points that exceed a pre-determined threshold error to the fitted plane; or (iv) a combination thereof.

39. The method of claim 38 wherein the error values are displayed as least one of: numerical values; error bars; or a color scheme.

40. The method of any one of claims 37 to 39 wherein the plurality of points are collected using at least one of: a digitizer comprising a digitizer tip; a laser scanner; a depth camera; or a conventional visible light camera.

41. A system for assessing planarity of a cut plane surface formed on a bone, comprising: a computer comprising a processor configured to: fit a plane to a plurality of points collected at locations on the cut plane surface; and provide feedback statistically comparing the fitted plane to the plurality of points to assess the planarity of the cut plane surface.

42. The system of claim 41 further comprising a digitizer comprising a digitizer tip for contacting the cut plane surface at a plurality of locations.

43. The system of claims 42 further comprising a tracking system for tracking movement of the digitizer, wherein the computer is operatively coupled to the tracking system for recording locations of the digitizer tip when the digitizer tip is in contact with the cut plane surface to collect the plurality of points.

44. The system of any one of claims 41 to 43 further comprising a display for providing the feedback wherein the feedback comprises displaying on the display: (i) a root mean square error value of the plurality of points to the fitted plane; (ii) an average error value ofthe plurality of points to the fitted plane; (iii) error values and / or locations of one or more points from the plurality of points that exceed a pre-determined threshold error to the fitted plane; or (iv) a combination thereof.

45. A method for assessing a locational accuracy or planarity of a cut plane surface formed on a bone, comprising: displaying an uncut view of a virtual bone model, wherein a portion of the virtual bone model comprises a virtual volume of bone to be removed, and wherein the virtual bone model is registered to the bone; determining a location of a digitizer tip relative to a location of the virtual bone model registered to the bone; and switching from displaying the uncut view of the virtual bone model to a resected view of the virtual bone model when the location of the digitizer tip crosses inside the virtual volume of bone to be removed.

46. The method of claim 45 further comprising switching from displaying the resected view to the intact view when the location of the digitizer tip is removed from the virtual volume of bone to be removed.

47. The method of claim 45 wherein the resected view of the virtual bone model comprises a virtual bone model having a resected surface at a pre-determined location with respect to the virtual bone model.

48. The method of claim 47 further comprising displaying on the display a representation of the location of the digitizer tip relative to the resected surface.

49. The method of claims 47 or 48 further comprising displaying on the display a distance between the location of the digitizer tip and the resected surface.

50. A system for assessing a locational accuracy or planarity of a cut plane surface formed on a bone, comprising: a display for displaying an uncut view of a virtual bone model, wherein a portion of the virtual bone model comprises a virtual volume of bone to be removed, and wherein the virtual bone model is registered to a location of the bone; a tracking system for tracking locations of a digitizer and the bone; and a computing system operatively coupled to the tracking system and the display, the computing system comprising one or more processors configured to: determine a location of a digitizer tip relative to a location of the virtual bone model registered to the bone; and control the display to switch from displaying the uncut view of the virtual bone model to a resected view of the virtual bone model when the location of the digitizer tip crosses inside the virtual volume of bone to be removed.

51. The system of claim 51 wherein the computing system is further configured to control the display to switch from displaying the resected view of the virtual bone model to theuncut view of the virtual bone model when the location of the digitizer tip is removed from the virtual volume of bone to be removed.

52. The system of claim 50 wherein the resected view of the virtual bone model comprises a virtual bone model having a resected surface at a pre-determined location with respect to the virtual bone model.

53. The system of claim 52 wherein the display is further configured to display a representation of the location of the digitizer tip relative to the resected surface.

54. The system of claims 52 or 53 wherein the display is further configured to display a distance between the location of the digitizer tip and the resected surface.

55. A system for assessing a locational accuracy or planarity of a cut plane formed, or to be formed, on a bone, comprising: a computer comprising a processor configured to: determine a projected location for a cut plane to be formed on the bone using captured images of a cutting guide when the cutting guide is coupled to a bone; and provide feedback comparing the projected location for the cut plane relative to a pre-determined location for a planned cut plane.

56. The system of claim 55 further comprising an imaging camera for capturing the images.

Images