Systems, devices, and methods for measuring forces for balancing a knee during total knee arthroplasty

Abstract

A system for balancing a knee of a patient includes a force measurement device configured to measure forces between a femoral bone and a tibia bone as a force is applied to the knee and a computing system configured to determine a separation distance between a point or region associated with the femur and a point or region associated with tibia based on force information from the force measurement device. The force measurement device may include at least one paddle configured for placement between the femur and tibia and including at least one force sensing element for sensing forces associated with the femur or tibia. The computing system may be configured to normalize a measured force and identify the separation distance based on the normalized force, wherein the identified separation distance is substantially the same over a range of forces measured by the force measurement device.

Description

125520-10402-762494011 / 19 / 2025SYSTEMS, DEVICES, AND METHODS FOR MEASURING FORCES FOR BALANCING A KNEE DURING TOTAL KNEE ARTHROPLASTYCROSS-REFERENCE TO RELATED APPLICATION(S)

[0001] This patent application claims the benefit of United States Provisional Patent Application No. 63 / 724,594 entitled SYSTEMS, DEVICES, AND METHODS FOR MEASURING FORCES FOR BALANCING A KNEE DURING TOTAL KNEE ARTHROPLASTY filed November 25, 2024 (Attorney Docket No. 125520.10401), which is hereby incorporated herein by reference in its entirety.

[0002] The subject matter of this patent application may be related to the subject matter of United States Provisional Patent Application No. 63 / 635,087 entitled BALANCING A KNEE DURING TOTAL KNEE ARTHROPLASTY filed April 17, 2024 (Attorney Docket No. 125520.10203), which is a follow-on to United States Provisional Patent Application No. 63 / 633,479 entitled BALANCING A KNEE DURING TOTAL KNEE ARTHROPLASTY filed April 12, 2024 (Attorney Docket No. 125520.10201), each of which is hereby incorporated herein by reference in its entirety.

[0003] The subject matter of this patent application also may be related to the subject matter of commonly-owned PCT Application No. PCT / US2022 / 046146 entitled SURGICAL SYSTEM AND METHOD FOR FORMING LESS THAN ALL BONE CUT SURFACES FOR IMPLANT PLACEMENT filed October 10, 2022 and published as PCT Publication No. WO / 2023 / 059931 on April 13, 2023, which claims priority from United States Provisional Patent Application No. 63 / 253,923 filed October 8, 2021, each of which is hereby incorporated herein by reference in its entirety.

[0004] The subject matter of this patent application also may be related to the subject matter of commonly-owned PCT Application No. PCT / US2024 / 049974 filed October 4, 2024 (Attorney Docket No. 125520.10102), which claims priority from U.S. Provisional Patent Application No. 63 / 657,517 entitled IMPLANT AGNOSTIC COMPUTER- ASSISTED SURGICAL SYSTEM, APPARATUS, AND METHOD filed October 5, 2023 (Attorney Docket No. 125520.10103) and from U.S. Provisional Patent Application No. 63 / 542,624 entitled IMPLANT AGNOSTIC COMPUTER-ASSISTED SURGICAL SYSTEM, APPARATUS, AND METHOD filed October 5, 2023 (Attorney Docket No. 125520.10101), each of which is hereby incorporated herein by reference in its entirety.125520-10402-762494011 / 19 / 2025TECHNICAL FIELD

[0005] The invention relates generally to total knee arthroplasty procedures and, more particularly, to measuring forces for balancing a knee during total knee arthroplasty.BACKGROUND

[0006] Throughout a lifetime, bones and joints become damaged and worn through normal use, disease, and traumatic events. Arthritis is a leading cause of joint damage that over time leads to cartilage degradation, pain, stiffness, and bone loss. Arthritis can also cause the muscles articulating the joints to lose strength and become painful. If the pain associated with the dysfunctional joint is not alleviated by less-invasive therapies, a joint arthroplasty procedure is considered as a treatment. Joint arthroplasty is an orthopedic procedure in which an arthritic or dysfunctional joint surface is replaced with an orthopedic implant.

[0007] One such joint arthroplasty procedure is total knee arthroplasty (TKA), commonly referred to as total knee replacement. During a TKA procedure, the worn or damaged articular cartilage and bone is removed on the distal femur and proximal tibia to provide surfaces (“cut surfaces”) on the remaining bone. Implants, typically formed of metal or plastic, include contact surfaces that contact the cut surfaces to create a new articulating joint. The position and orientation (POSE) of the cut surfaces determine the final placement and POSE of the implants within the joint. Generally, surgeons plan and create the cut surfaces so the final placement of the implants restores the mechanical axis or kinematics of the patient’s leg while preserving the balance of the surrounding knee ligaments. Even small implant alignment errors outside of clinically acceptable ranges correlate with worse outcomes and increased rates of revision surgery.

[0008] Current TKA implants are designed to be installed using specific manual instrumentation (e.g., cutting jigs, cutting blocks, alignment fixtures). The manual instrumentation is used to assist the user in forming the cut surfaces. Femoral implants typically have five femoral contact surfaces and one or more stabilizing features (e.g., pegs, boxes). The five femoral contact surfaces are intended to contact five cut surfaces on the remaining femur. The stabilizing features of a femoral implant may include pegs or a box to stabilize the femoral implant on the femur. The pegs or box are intended to be inserted into stabilizing cut features (e.g., holes) cut into the bone, typically through a cut surface of the femur and are typically formed perpendicular to a cut surface. Tibial implants typically have one tibial contact surface125520-10402-762494011 / 19 / 2025 and a stabilizing feature (e.g., a keel). The one tibial contact surface is intended to contact one cut surface on the remaining tibia. The stabilizing features of a tibial implant may include a keel to stabilize the tibial implant on the tibia. The keel is intended to be inserted into a stabilizing cut feature (e.g., a hole) that is cut into the bone, typically through the cut surface of the tibia, and is typically formed perpendicular to the cut surface. FIGs. 1 A - 1C illustrate a patient’s distal femur 10 and a contour matching femoral implant 12 for a TKA procedure, where five contact surfaces on the implant are intended to contact five cut surfaces on the femur. The anterior cut surface 14 is intended to contact the anterior contact surface 13, the anterior chamfer cut surface 16 is intended to contact the anterior chamfer contact surface 15, the distal cut surface 18 is intended to contact the distal contact surface 17, the posterior chamfer cut surface 20 is intended to contact the posterior chamfer contact surface 19, and the posterior cut surface 22 is intended to contact the posterior contact surface 21. The femoral implant 12 also includes stabilizing features in the form of pegs (23, 24) intended to be inserted into stabilizing cut features (e.g., holes, not shown) formed into the distal cut surface 18 of the femur 10. The femoral implant 12 further includes an outer articulating surface 25 that contacts the articulating surface of the tibial implant. The manual instrumentation is aligned and affixed to the bone to guide the formation of each cut surface. One of the key struggles associated with manual TKA is the proper alignment of the manual instrumentation on the bone. The user has to reference various anatomical landmarks and adjust the cutting jigs based on measurements to ensure the instruments are properly aligned. Aligning the cutting jigs to assist the user in forming these cut surfaces is particularly difficult.

[0009] Another important step during a TKA procedure is the balancing the soft tissues (e.g., collateral ligaments) surrounding the knee. The surrounding soft tissues should be balanced (e.g., not too tight or too lax) when the implants are installed in the knee. An unbalanced knee may cause knee instability and poor clinical outcomes. A common technique for balancing the knee is gap balancing. FIG. 2 depicts a graphical user interface (GUI) 30 for gap balancing the knee in the operating room. Before gap balancing, a first tracking array is affixed to the femur and a second tracking array is affixed to the tibia. The bone data is then registered to the femur and tibia (and more specifically to the coordinate system of the tracking arrays affixed to each bone, respectively) using techniques known in the art. For example, the 3-D bone models of the femur and tibia may be registered to the locations of each bone, respectively, by matching points digitized on the bone with corresponding points / surfaces on the 3-D bone models. A tracking system may then track the location and movement of the femur and tibia by way of125520-10402-762494011 / 19 / 2025 the tracking arrays affixed thereto and the system can determine the corresponding location and motion of the 3-D bone models using the registration data (i.e., the registered location of each 3-D bone model in the coordinate system of each tracking array, respectively). The system can also determine the planned location for forming the cut surfaces on bone relative to the real-time location of each bone, respectively, using the tracked location of the registered 3- D bone models and a pre-defined (or planned) location for forming those cut surfaces as defined with respect to the 3-D bone models. Likewise, the system can determine the planned location of the implant models relative to the real-time location of each bone, respectively, using the tracked location of the registered 3-D bone models and a pre-defined (or planned) location where those implant models were positioned with respect to the 3-D bone models.

[0010] To perform gap balancing, the user applies tension to the surrounding ligaments by either placing a tensioner between the two bones or by applying a lateral or medial force to the knee to force tension on the ligaments. While applying tension on the ligaments, the user flexes and extends the knee throughout the knee’s range of motion (e.g., 0 degrees is fully extended and as much as the knee can flex >0 degrees). It should be noted that gap balancing may occur before any bone cuts are made, or in some case, the user may choose to make the tibia bone cut first and then perform gap balancing. The tracking system records the movement of the bones, via the tracking arrays, and determines the corresponding motion of the registered bone models throughout this motion. In some embodiments, the GUI 30 may display the 3-D bone models (e.g., femoral bone model 32 and tibial bone model 34) and movement of the 3-D bone models corresponding to the real-time movement of the bones.

[0011] A computer operatively coupled to the tracking system determines the medial and lateral gap distances between the bones at two or more flexion-extension locations (one with the knee fully extended and another with the knee fully flexed). The computer may determine the gap distances by measuring the distance between the distal portion of the femoral bone model (e.g., a point on the outer surface of the femoral bone model that is closest to the tibia bone model) and the proximal portion of the tibial bone model (e.g., a point on the outer surface of the tibia bone model) for each angle throughout this flexion-extension motion. It should be appreciated however that while FIG. 2 shows the gap distances being measured between one or more points located on the distal portion of the femoral bone model and one or more points located on the proximal portion of the tibia bone model, embodiments of the present invention may utilize these points or other points or regions for measuring useful distances to perform125520-10402-762494011 / 19 / 2025 soft tissue balancing, where these distances are generally described herein as “separation distances”.

[0012] The graph on the right shows the gaps at six different flexion-extension locations (or angles), where the pattern filled bars are the medial gap measurements 36 and the un-filled bars represent the lateral gap measurements 38. One of the goals of gap balancing is to obtain an equal gap (medial gap = lateral gap) in both flexion and extension. If the gaps aren’t balanced, the user may choose to adjust the planned location for a bone cut. For example, the user may rotate the implant internally or externally to obtain an equal medial-lateral gap in flexion, and varus or valgus to obtain an equal medial-lateral gap in extension. The user may also move the implant distally or proximally to decrease or increase the size of the gap in extension, or posterior or anterior to decrease or increase the size of the gap in flexion, to make sure there is enough room for the implants to fit in the knee and that the ligaments will be properly tensioned when the implants are positioned in the knee. The bone models (32, 34) shown on the left of the GUI 30 shows equal gaps in extension and the bone models (32, 34) shown in the middle of the GUI 30 shows equal gaps in flexion.

[0013] However, one of the primary problems with gap balancing is the variability in the amount of pressure or lateral / medial force that different surgeons apply to the knee while capturing the gap distances. One surgeon might apply more force than another surgeon, which might cause the recorded gap distance to be larger for that surgeon compared to the other surgeon for the same patient. For example, surgeon “A” may apply a medial force of “X” newtons to the knee of patient “C” resulting in a recorded medial gap distance of 18 millimeters, while surgeon B may apply a medial force of “X+Y” newtons to the knee of patient “C” resulting in a recorded medial gap distance of 22 millimeters. Thus, there is variability in the recorded gap distances depending on the amount of lateral or medial force a surgeon applies to the knee, and this will vary from surgeon to surgeon. This may result in different planned placements of the implant between surgeons and thus could hypothetically result in different clinical outcomes for a particular patient. In other words, surgeon “A” may rotate the planned placement of the implant in to open (or increase) the medial gap distance, while surgeon “B” may rotate the planned placement of the implant to close (or decrease) the medial gap distance.SUMMARY

[0014] In accordance with certain embodiments, systems, methods, and devices for balancing a knee of a patient includes a force measurement device configured to measure forces125520-10402-762494011 / 19 / 2025 between a femoral bone and a tibia bone as a force is applied to the knee and a computing system configured to determine a separation distance between a point or region associated with the femur and a point or region associated with tibia based on force information from the force measurement device. The force measurement device may include at least one paddle configured for placement between the femur and tibia and including at least one force sensing element for sensing forces associated with the femur or tibia. The computing system may be configured to normalize a measured force and identify the separation distance based on the normalized force, wherein the identified separation distance is substantially the same over a range of forces measured by the force measurement device.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Those skilled in the art should more fully appreciate advantages of various embodiments of the invention from the following “Description of Illustrative Embodiments,” discussed with reference to the drawings summarized immediately below.

[0016] FIG. 1A is a schematic diagram depicting a femoral bone and a femoral implant, where the femoral bone was cut to form five cut surfaces to accommodate the femoral implant.

[0017] FIG. IB is a schematic diagram showing a side view representation of a femoral implant.

[0018] FIG. 1C is a schematic diagram showing a perspective view representation of a femoral implant.

[0019] FIG. 2 depicts a graphical user interface (GUI) for gap balancing the knee in the operating room.

[0020] FIG. 3 is a schematic diagram showing a representation of a particular embodiment of a force measurement device, where FIG. 3 A is a perspective view thereof, FIG. 3B is a top view thereof, and FIG. 3C is a side view thereof.

[0021] FIG. 4 is a schematic diagram showing a representation of a femoral tracking array affixed to the femur bone, a tibia tracking array affixed to the tibia bone, and the force measurement device inserted between the femur and tibia.

[0022] FIGs. 5A and 5B schematically depict a method for balancing a knee during TKA with the force measurement device, where the user may apply a medial lateral force to the knee as shown in FIG. 5 A to tension the medial collateral ligament and the user may apply a lateral force to the knee as shown in FIG. 5B to tension the lateral collateral ligament.125520-10402-762494011 / 19 / 2025

[0023] FIG. 6 is a schematic diagram showing a representation of a particular embodiment of a force measurement device for applying an initial amount of tension on the ligaments when positioned in the knee.

[0024] FIG. 7 schematically depicts a method for balancing a knee during TKA with the force measurement device of FIG. 6, where a user toggles the force measurement device to apply additional tension on the ligaments, to further open up or separate the knee, and / or to apply additional forces to the bones.

[0025] FIG. 8 is a schematic diagram showing a representation of a particular embodiment of a force measurement device for measuring force information on a single side of the knee.

[0026] FIG. 9 is a schematic diagram depicting a particular embodiment of a force measurement device including a fourth LED having a different light emitting orientation than the first three LEDs.

[0027] FIG. 10 is a schematic diagram depicting another embodiment of a force measurement device including a force sensing element in the form of a torque sensor.

[0028] FIG. 11 is a schematic diagram depicting another embodiment of a force measurement device including two first force sensing elements, where each force sensing element is in the form of a torque sensor.

[0029] FIG. 12 is a flowchart depicting a method for balancing the knee using the force measurement device, in accordance with certain embodiments.

[0030] FIG. 13 is a schematic diagram showing use of a normalization model that normalizes forces different user applies to the knee to output a consistent separation distance measurement.

[0031] FIG. 14 depicts a ligament tension curve for determining a normalized force to output a consistent separation distance measurement.

[0032] FIG. 15 is a schematic diagram showing a computer-assisted surgical system, in accordance with certain embodiments.

[0033] FIG. 16A is a schematic diagram showing a 2-DOF device of the computer-assisted surgical system in a first working POSE.

[0034] FIG. 16B is a schematic diagram showing a 2-DOF device of the computer-assisted surgical system in a second working POSE.

[0035] It should be noted that the foregoing figures and the elements depicted therein are not necessarily drawn to consistent scale or to any scale. Unless the context otherwise suggests, like elements are indicated by like numerals. The drawings are primarily for illustrative125520-10402-762494011 / 19 / 2025 purposes and are not intended to limit the scope of the inventive subject matter described herein.DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0036] Definitions. As used in this description and the accompanying claims, the following terms shall have the meanings indicated, unless the context otherwise requires. 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.

[0037] All publications, patent applications, patents and other references mentioned herein are incorporated by reference in their entirety.

[0038] 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.

[0039] 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, 2-3, 2-4, 3-4, and 1-4 and possibly other values including in some cases fractions of range values (e.g., 1.1, 1.2, etc.). The citation of a range being “around” or “about” a range such as 1 to 4 could include values slightly outside of the range (e.g., 0.9 to 4.1) as the context may suggest or require.

[0040] Unless indicated otherwise, explicitly or by context, the following terms are used herein as set forth below.

[0041] As used herein, like reference numerals described in or with respect to subsequent drawings have the meaning imparted thereto with respect to the previously detailed drawings.

[0042] 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; the125520-10402-762494011 / 19 / 2025 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 of example, 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 “bone model” may refer to a full representation of a bone (e.g., a whole femur bone) or a partial representation of a bone (e.g., only a distal region of a femur bone). The term “virtual” may also be referred to herein as “digital”, meaning the data is stored, generated, and / or processed by a computer.

[0043] 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, serialchain 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 bone data) used by the CAS device; ii) a CAS device and125520-10402-762494011 / 19 / 2025 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.).

[0044] 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 device operating data (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 device operating data. The device operating data may also be referred to as data used for operating a device. The device operating data may also, or alternatively, be used to provide feedback (e.g., display instructions on a GUI) to a user for navigating one or more non-robotically controlled instruments (e.g., a tracked cutting tool, a tracked drill) relative to a bone.

[0045] 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.125520-10402-762494011 / 19 / 2025

[0046] As used herein, the term “digitizing” refers to the collecting, measuring, designating, and / or recording of physical locations in space using a digitizer. In some embodiments, “digitizing” may refer to the conversion of a designated location, area, or volume in space to a digital format. For example, a tracking system may determine the location of a digitizer probe tip in contact with a point on the bone, where the determined location of that point is saved to computer memory.

[0047] 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 device operating data 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 readily mapped 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: (i) bone data (e.g., a 3-D bone model, planned location for forming one or more cut surfaces; planned location for an implant model relative to a bone model); and / or a surgical plan (e.g., a predefined location for a targeted virtual plane that was defined with respect to bone data, a predefined location of device operating data that was defined with respect to bone data); and (ii) the coordinate system of a tracking array affixed to the bone (if present); or 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 object125520-10402-762494011 / 19 / 2025 required to perform the procedure. In other embodiments, the registration is performed using imageless registration.

[0048] 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.

[0049] As used herein, the term “feedback” may refer to visual feedback provided on a display. This “feedback” may also be provided in other forms, which may be in lieu of or in addition to visual feedback. For example, 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 surgical device may turn green or red depending on the amount of error between the surgical device and a planned cut surface).

[0050] As used herein, the term “separation distance” refers to the distance between at least one of: (i) a point or region located on a surface of a first bone (or first bone model) and a point or region located on a surface of a second bone (or second bone model); (ii) a point or region located on a planned cut surface to be formed on a first bone (or first bone model) and a point or region located on a surface of a second bone (or second bone model); (iii) a point or region located on a planned cut surface to be formed a first bone (or first bone model) and a point or region located on a planned cut surface to be formed on a second bone (or second bone model); (iv) a point or region located on a planned cut surface to be formed on a first bone (or first bone model) and a point or region located on a surface of an implant model, where the implant model is located at a desired location for mounting an implant on a second bone; (v) a point or region located on a surface of a first implant model and a point or region located on a surface of a second implant model, where the first implant model is located at a desired location for mounting a first implant on a first bone and the second implant model is located at a desired location for mounting a second implant on a second bone; (vi) a point or region located on a cut surface formed on a first bone and a point or region located on a surface of a second bone (or second bone model); (vii) a point or region located on a cut surface formed on a first bone125520-10402-762494011 / 19 / 2025 and a point or region located on a cut surface formed on a second bone; (viii) a point or region located on a cut surface formed on a first bone and a point or region located on a planned cut surface to be formed on a second bone; (ix) a point or region on a cut surface formed on a first bone and a point or region on a surface of an implant model, where the implant model is located at a desired location for mounting the implant on a second bone; (x) a first ligament attachment point on a first bone and the opposing ligament attachment point on a second bone (e.g., a medial collateral ligament (MCL) attachment point on the tibia and the MCL attachment point on the femur); and (xi) any combination thereof.

[0051] Certain embodiments provide systems, devices, and methods to reduce the variability in the separation distance measurements caused by the amount of lateral or medial forces different surgeons might apply to the knee while balancing the soft tissues. In certain embodiments, a force measurement device is used to measure the force applied to the knee while balancing the soft tissues. The system may automatically record the separation distance such as when a threshold force is reached. The system may include a tracking system for tracking the location of the femur and the tibia. 3-D bone models of the femur and tibia may be registered to their respective bones in the coordinate system of a femoral tracking array and a tibia tracking array, respectively. The force measurement device may include a communication system for communication with a computing system (e.g., to convey force information to the computing system). The communication system may employ wired or wireless communication technologies (where a wired connection could include an optical fiber or other optical conduit for wired optical light communication). Wireless communication technologies may include radio frequency wireless communication technologies (e.g., Bluetooth, Near-Field Communication, WiFi, or other radio frequency technology), optical light communication technology (e.g., LED or laser-based communication), or other wireless communication technology. For example, in certain specific embodiments, the force measurement device may include one or more LEDs that can be controlled (e.g., modulated) to optically convey (e.g., transmit, send, communicate) signals comprising data to a computing or tracking system (e.g., where the computing or tracking system may include a photosensor for receiving the conveyed signals). The force measurement device also may include one or more photosensors for receiving optically conveyed signals such as from the computing or tracking system. The force measurement device may include three or more LEDs to permit a tracking system to track the real-time location of the force measurement device.125520-10402-762494011 / 19 / 2025

[0052] In certain embodiments, the force measurement device is configured for placement between the femur and tibia and includes one or more force sensing elements for measuring the applied force of the bone on the force sensor. To start the soft tissue balancing step, the force measurement device is placed between the femur and tibia. The force measurement device is typically placed prior to any cuts being made to the tibia or femur, although the force measurement device may be placed prior to or after cuts are made to the tibia or femur. In one embodiment, the user applies a lateral or medial force to the knee to tension either the lateral or medial ligament, respectively, while in another embodiment, the force measurement device itself tensions the one or more ligaments when placed in the knee and the user then toggles (e.g., moves or rotates) the force measurement device relative to the femur and tibia to open up the knee and / or provide additional tension the ligaments. In either embodiment, the force sensing elements sense or measures the applied force of the femur bone (e.g., the medial and / or lateral condyle) and / or tibial bone (e.g., medial and / or lateral side of the tibia plateau) on the force sensing elements. Force information (e.g., static forces, dynamic forces, complex forces) is then determined from the data collected by the force sensing elements and compared to one or more predetermined parameters (e.g., a threshold force). The system then automatically records the separation distance as soon as the determined force information satisfies one or more of the predetermined parameters (e.g., a sensed force reaches a threshold). For example, the system may automatically record the separation distance as soon as a sensed force equals (or approximately equals) a threshold force. In some embodiments, the force information is determined by computing components housed in the force measurement device, where the force information is then conveyed (e.g., transmitted, sent, communicated) to an external computing system that automatically records the separation distance once the conveyed force information satisfies the predetermined parameter. The predetermined parameters (e.g., a threshold force) may be set by the user, or the predetermined parameters may be a default value in the system. The separation distances may be recorded with the knee in full extension, full flexion, and any flexion degree (e.g., 45 degrees of flexion) between 0 degrees and full flexion as the user desires. This ensures that the recorded separation distance measurement is consistent between different surgeons and therefore reduces the variability in the separation distance measurements that was otherwise caused by the differing amounts of forces that different users applied to the knee with traditional gap balancing methods (e.g., FIG. 2).

[0053] Another embodiment of the present invention normalizes the forces that different users apply to the knee to output a consistent separation distance measurement. For example,125520-10402-762494011 / 19 / 2025 surgeon “A” may apply a lateral force of “X” newtons on the knee of patient “M” and Surgeon “B” may apply a lateral force of “X+Y” newtons on the knee of the same patient “M”. These forces are recorded by the force measurement device and transferred as an input into a normalization model. Other inputs into the normalization model may include patient characteristics of patient “M,” for example, biomechanical characteristics or patient specific biomechanical models, morphology of the ligament (e.g., ligament length in extension and flexion, ligament thickness), the morphology of the bones and cartilage, disease severity, imaging data, and / or other patient characteristics (e.g., patient age, weight, gender, height, BMI). The normalization model then normalizes the forces applied by surgeon “A” and surgeon “B’ to output the same separation distance. For example, the normalization model may output a separation distance measurement of 21 millimeters for both surgeon “A” and surgeon “B” even though surgeon “B” applied more lateral force to the knee (the higher lateral force might have otherwise caused the separation distance measurement to be higher for surgeon “B” than surgeon “A”). The normalization model may provide the consistent separation distance by analyzing an inflection point in a recorded ligament tension curve (force vs. ligament elongation, strain, or change in length). The normalization model may further adjust the normalized force and / or the determined separation distance based on the patient characteristic data. Thus, the normalization model may also reduce the variability in the separation distance measurements caused by the differing amounts of forces that different users apply to the knee with traditional gap balancing techniques (e.g., FIG. 2).

[0054] With reference to FIGs. 3A - 3C, a particular embodiment of a force measurement device 40a is shown, where FIG. 3A is a perspective view thereof, FIG. 3B is a top view thereof, and FIG. 3C is a side view thereof. The force measurement device 40a may include a handle 42, a first paddle 44, one or more force sensing elements 46 associated with the first paddle 46, a second paddle 48, and one or more force sensing elements 50 associated with the second paddle 48, where the force measurement device 40a is configured to be placed between the femur and the tibia with one of the paddles used to sense forces associated with the medial femoral condyle (and / or medial tibia) and the other paddle used to sense forces associated with the lateral femoral condyle (and / or lateral tibia). In particular embodiments, one or more force sensing elements are positioned on a femur-facing surface of a paddle and one or more force sensing elements are positioned on a tibia-facing surface of a paddle. A given paddle surface may include a single force sensing element or multiple force sensing elements (e.g., an array of force sensing elements). The force sensing elements are configured to sense and / or measure125520-10402-762494011 / 19 / 2025 the force, pressure, and / or torque that an object (e.g., bone) applies to the force sensing element. Examples of force sensing elements, without limitation, may include a load cell, strain gauge, wheatstone bridge, force sensing resistor, force sensing capacitor, torque sensor, pressure sensor, piezoelectric force sensor, optical force sensor, magnetic force sensor, inductive force sensor, machined accelerometers, etc. In particular embodiments, the force sensing element is an array of transducers manufactured as a thin film structure that is capable of measuring forces in one to six degrees-of-freedom, such as the product, ForceFilm™, manufactured by ForceN (Toronto, Canada). Computing components (e.g., processor, controller, memory storage, circuits, etc.) (not shown) housed in the force measurement device 40a may be operatively coupled to the force sensing elements to process raw data (e.g., electrical signals) from the force sensing elements. Processing of the raw data may include calculating, measuring, and / or determining force information, where the force information may include at least one of: static forces, dynamic forces (e.g., forces that change with time or bone position), complex forces (e.g., force acting in more than one degree-of-freedom, twisting forces, shearing forces), absolute forces, relative forces, force vectors, force profiles (e.g., heat map of forces over a given area or surface), torques, pressures, and any combination thereof. The computing components may further convey (e.g., transmit, send, communicate) the force information to an external computing system for additional processing. In other embodiments, the raw data (e.g., electrical signals) or minimally processed raw data (e.g., static forces, dynamic forces, complex forces, etc.) are conveyed to an external computing system (not housed on the force measurement device 40) for further processing. For example, the force measurement device 40a may include computing components for minimally processing the raw data to determine static, dynamic, and / or complex forces, where the determined static, dynamic, and / or complex forces are then conveyed to an external computing system that then determines a profile of forces over an area or surface of the bone.

[0055] The force measurement device 40a may further include one or more light emitting diodes (LEDs) (52a, 52b, 52c) and a photosensor 54. The one or more LEDs (52a, 52b) may be actuated (e.g., the light is modulated or the light blinks on-and-off) by computing components to optically convey (e.g., transmit, send, communicate) data to a computing system (e.g., computing system 204 shown in FIG. 15). For example, the one or more LEDs may be actuated to convey force information, or raw sensor data, to a photosensor operatively coupled to an external computing system. The photosensor 52 (e.g., a photodiode, a camera) on the force measurement device 40a may detect light signals from an LED associated with a tracking125520-10402-762494011 / 19 / 2025 system for optically receiving data from an external computing system (e.g., computing system 204 shown in FIG. 15), where the light signals are processed by the computing components housed in the force measurement device 40a. Details of optical communication between various devices in an operating room (OR) is described in U.S. Pat. No. 11,229,487 assigned to the assignee of the present application. In particular embodiments, the force measurement device 40 includes three or more LEDs (52a, 52b, 52c) to permit a tracking system to track the location of the force measurement device 40a. One or more of these three or more LEDs (52a, 52b, 52c) may be dedicated to optically communicating data as well as being used to permit a tracking system to track the location of the force measurement device 40a. In other embodiments, the force measurement device 40a includes three or more LEDs for tracking, and one or more additional LEDs dedicated to optical data communication.

[0056] In particular embodiments, the paddles (44 and 48) are concave in shape as best seen in FIG. 3C to approximately match or follow the concave shape of the distal femur. This allows the paddles (44 and 48) to easily slide and fit between the femur and the tibia to balance the knee before any bone cut surfaces are formed on the femur or tibia.

[0057] A TKA procedure may begin with the creation of a surgical plan using planning software. The planning software may include bone image data of the patient’s femur and tibia and implant data to plan the location for mounting the implants on their respective bones. In specific embodiments, the planning software includes 3-D bone models of the femur and tibia generated from images collected from an imaging modality (e.g., CT scan, MRI scan, ultrasound, etc.). The planning software may further include a library of 3-D implant models (e.g., in the form CAD files). The software, or the user, may then select a desired implant model in the library and position the implant model relative to the 3-D bone model to designate the best fit and / or position for mounting the implants on the bones. The planned location (also referred to as pre-determined location) for mounting the implants on the bones is then saved as a surgical planning file on a computing system. The surgical planning file may include the 3- D bone models, and at least one of: (i) the planned location of the 3-D implant models positioned relative to the 3-D bone models; (ii) the planned location for forming the cut surfaces on the bones such that the implants will mount to the bones in the planned location; or both. While the surgical plan may be created pre-operatively, it should be appreciated that the surgical plan may be created intra-operatively, or pre-operatively and then modified intra- operatively.125520-10402-762494011 / 19 / 2025

[0058] Intra-operatively, the TKA procedure may begin by exposing the distal femur and proximal tibia in a conventional manner. As shown in FIG. 4, a femoral tracking array 60 is then affixed to the femur bone 10 and a tibia tracking array 62 is affixed to the tibia bone 11. The femoral bone model is then registered to the femur 10 in the coordinate system of the femoral tracking array 60 using techniques known in the art. Likewise, the tibial bone model is registered to the tibia 11 in the coordinate system of the tibial tracking array 62. A GUI may display the 3-D bone models and movement of the 3-D bone models corresponding to the realtime movement of their respective bones. The GUI may also display the surgical plan for review by the user, which may include: the 3-D implant models; the planned location for the 3-D implant models positioned relative to the 3-D bone models; the resection amounts (e.g., femoral distal resection amount); varus-valgus rotation; internal-external rotation; relevant axes (e.g., mechanical axis); as well as other data to assist the user in planning the placement for mounting the implants on the bones. The GUI may further include options for the user to update or change the planned location of the 3-D implant models relative to the 3-D bone models. These updates or changes may be prompted by the soft tissue balancing step, which is shown in FIGs. 5 A and 5B.

[0059] FIGs. 5A and 5B depict a method for balancing a knee during TKA with the force measurement device 40a. Before balancing the knee, the paddles (44 and 48) are positioned between the femur 10 and the tibia 11 as shown in FIG. 4. More particularly, the first paddle 44 is positioned between the lateral femoral condyle and the lateral side of the tibial plateau, and the second paddle 48 is positioned between the medial femoral condyle and the medial side of the tibial plateau. The user should position the paddles (44 and 48) to ensure the femoral condyles can make contact with their respective force sensing elements (46 and 50) located on the paddles (44 and 48). The user may then apply a lateral force to the knee as shown in FIG. 5 A, to tension the lateral collateral ligament 64. As the user applies the lateral force to the knee, the force sensing element 50 on the second paddle 48 senses or measures the forces applied by the medial femoral condyle on the force sensing element 50. Computing components housed in the force measurement device 40a may determine force information (e.g., static forces, dynamic forces, complex force) based on the raw data from the force sensing element 50 and then convey the force information to an external computing system (e.g., computing system 204 as shown in FIG. 15). In other embodiments, raw data from the force sensing element 50 is directly conveyed to an external computing system to process the raw data and determine the force information. Once the external computing system receives or determines that the force125520-10402-762494011 / 19 / 2025 information satisfies a predetermined parameter, the external computing system automatically records the lateral separation distance. For example, as soon as the external computing system receives or determines that a sensed or measured force is equal (or approximately equal) to a threshold force, the external computing system automatically records the lateral separation distance. After the lateral separation distance is recorded, the user then applies a medial force to the knee as shown in FIG. 5B, to tension the medial collateral ligament 66. As the user applies the medial force to the knee, the force sensing element 46 on the first paddle 44 senses or measures the force applied by the lateral femoral condyle on the force sensor 46. Computing components housed in the force measurement device 40a may determine force information (e.g., static forces, dynamic forces, complex force) based on the raw data from the force sensing element 46 and then conveys that force information to an external computing system (e.g., computing system 204 as shown in FIG. 15). In other embodiments, raw data from the force sensing element 46 is directly conveyed to the external computing system to process the raw data and determine the force information. Once the external computing system receives or determines that the force information satisfies a predetermined parameter, the external computing system automatically records the medial separation distance. For example, once the external computing system receives or determines that a sensed or measured force is equal (or approximately equal) to a threshold force, the external computing system automatically records the medial separation distance. Of course, the medial and lateral forces can be applied in any order, i.e., medial followed by lateral as described above or lateral followed by medial. In this exemplary embodiment, the one or more LEDs (52a, 52b, 52c) may optically convey the determined force information (or raw data from the force sensing elements (46, 50)) in realtime, such that the external computing system can record the separation distances as soon as the force information satisfies the predetermined parameter.

[0060] The one or more predetermined parameters (e.g., a threshold force) may be set by the user before the procedure. In other embodiments, the one or more predetermined parameters are a set default value programmed in the computing system. A set default value may ensure consistency in the measured separation distance from surgeon to surgeon when balancing a knee (e.g., the same separation distance is captured for patient ‘A’ regardless of the surgeon balancing the knee). In a particular embodiment, the predetermined parameter is set based on the biomechanical properties of the ligaments as determined from experimental data, historical data, or data available in the literature. For example, the threshold force may be set to the average load applied that fully stretches the ligaments, before failure, for the general population125520-10402-762494011 / 19 / 2025 or a sub-set of the general population (e.g., a population of people having characteristics like age, weight, etc. that is consistent with the patient’s characteristics). For example, the predetermined parameter may be set to the average force, among a population, that when applied to the ligament results in a fully elongated ligament before failure as described in Wilson, William T., et al. "Comparative analysis of the structural properties of the collateral ligaments of the human knee." journal of orthopaedic & sports physical therapy 42.4 (2012): 345-351. In another specific embodiment, the system may have a user preferences option that allows individual users to set their predetermined parameters, such that when a given user is performing a TKA procedure, their predetermined parameters are automatically used. Allowing the user to set their own value(s) for the predetermined parameter ensures consistency in balancing knees from patient to patient for that particular user. In other words, surgeon ‘A’ will always capture a separation distance corresponding to that set value (e.g., a set threshold force) for patient ‘A’, patient ‘B’, patient ‘C’, etc. Thus, the user does not have to worry about accidentally applying different amounts of varus / valgus load from one patient case to another.

[0061] The computing system may determine the separation distances using: (i) the tracked location of the bones via their respective tracking arrays; (ii) the registered location of the bone models in the coordinate system of their respective tracking arrays; and (iii) may further use the planned location of the implant models relative to their respective bone models, if needed (e.g., to determine and record a separation distance between a point or region located on a surface of an implant model associated with a first bone model and a point or region located on a planned cut surface as defined with respect to a second bone model).

[0062] The above procedure for recording the separation distances may be completed for the knee in full extension (0° flexion), full flexion (e.g., >90° flexion), and for any degree of knee flexion in between (e.g., 45 degrees of flexion) as the user desires. The separation distances may be recorded for both the medial and lateral sides of the knee for each of these desired flexion angles. The user may flex and extend the knee in real-time while the force sensing elements sense the forces in real-time and the computations / determinations occur in real-time. For example, the user may flex and extend the knee while applying lateral or medial forces. The force sensing elements continuously sense the forces applied by the bones on the force sensing elements during this flexion and extension and the computing components (or external computing system) continuously determine the force information. The external computing system also continuously compares the force information to the predetermined parameters and automatically records the separation distance when the predetermined125520-10402-762494011 / 19 / 2025 parameter is satisfied. This allows for a seamless and quick recordation of the separation distances to reduce the overall operating time and improve the time required to balance the soft tissues. Alternatively, the user may perform the soft tissue balancing in a more step-wise approach until all the desired separation distances are recorded.

[0063] The system may automatically record the separation distances based on different types of force information satisfying different types of predetermined parameters. As described above, the force information may include, for example: static forces, dynamic forces, complex forces, relative forces, absolute forces, force vectors, force profiles, torques, pressures, and any combination thereof. The predetermined parameters may therefore include: a threshold force, a threshold torque, a threshold pressure, a threshold force in one or more specific degrees of freedom, a pattern of complex forces (e.g., when pre-defined twisting or shearing motions are being applied by (or to) the knee), a pattern of dynamic forces (e.g., a pre-defined change of forces over time or bone position, a rate of change of forces), a pre-defined profile of forces, a pre-defined surface geometry of the bone based on the measured forces, a pre-defined heatmap pattern of forces; and any combination thereof. For example, the system may automatically record one or more separation distances when at least one of the following is satisfied: (i) a measured static force meeting a threshold force; (ii) a measured force in a specific degree-of- freedom (e.g., a normal force, a shearing force, a twisting force) meeting a threshold force in that specific degree-of-freedom; (iii) a pattern of measured complex forces resembling or matching (e.g., within a statistical range) a pre-defined pattern of complex forces; a pattern of measured dynamic forces resembling or matching (e.g., within a statistical range) a pre-defined pattern of dynamic forces; (iv) a measured profile of forces resembling or matching (e.g., within a statistical range) a pre-defined profile of forces; (v) measured forces indicating a particular surface geometry of the bone resembling or matching (e.g., within a statistical range) a pre-defined surface geometry of the bone; (vi) a measured heatmap pattern of forces resembling or matching (e.g., within a statistical range) a pre-defined heatmap pattern of forces; and (vii) any combination thereof.

[0064] In particular embodiments, with reference to FIG. 6, another embodiment of a force measurement device 40b is shown. The force measurement device 40b may have the same components (e.g., LEDs (52a, 52b, 52c), force sensing elements (46, 50), photosensor 54, handle 42, computing components) as the aforementioned force measurement device 40a shown in FIG. 3A, except the paddles (44, 48) have a thickness capable of tensioning the ligaments of the knee when placed between the femur and tibia. In other words, the thickness125520-10402-762494011 / 19 / 2025 of the paddles (44, 48) when inserted in the knee increases the distance between the femur and the tibia in the distal-proximal direction to apply an initial amount of tension to the ligaments.

[0065] A TKA procedure with the force measurement device 40b of FIG. 6 may begin in the same manner as previously described with respect to the force measurement device 40a of FIG. 3A. This may include generating a surgical plan, exposing the bones, affixing tracking arrays (60, 62) to the femur 10 and tibia 11, and registering the bones. Then, to balance the soft tissues, the force measurement device 40b is first placed between the femur 10 and tibia 11 as shown in FIG. 7. This tensions the ligaments (64, 66) by an initial amount. The user may then toggle (e.g., move or rotate) the force measurement device 40b (e.g., move or rotate the device 40b, such as in the directions depicted by the arrows in FIG. 7) to apply additional tension to the ligaments and / or further increase the distance between the femur and tibia on the medial and / or lateral side of the knee. This increase in distance may also be referred to as, “opening up the knee”, which will increase the amount of force the bones apply on the force sensing elements. For example, the user may push down on the handle 42 to spread the joint via a leveraging technique to further open up the knee. As the user is applying the additional tension to the ligaments (and / or further opening up the knee), the force sensing elements (46, 50) sense or measure the forces applied by the bones on their respective force sensing element. For example, a first force sensing element positioned on a femur-facing side of the first paddle 44 may sense the forces applied by the lateral femoral condyle, a second force sensing element positioned on tibia-facing side of the first paddle 44 may sense the forces applied by the lateral side of the tibia plateau, a third force sensing element positioned on a femur-facing side of the second paddle 48 may sense the forces applied by the medial femoral condyle, and a fourth sensing element positioned on a tibia-facing side of the second paddle 48 may sense the forces applied by the medial side of the tibial plateau. In instances where the user is pushing down on the handle 42, the forces applied by the femur on the femur-facing force sensing elements will be laterally displaced and in different directions than the forces applied by the tibia on the tibiafacing force sensing elements. As such, it should be appreciated that the force sensing elements on the femur-facing side of the paddles are not positioned directly on top of the force sensing elements on the tibia-facing side paddles. The force sensing elements may therefore be positioned at different or several locations across the area of the femur-facing side and tibiafacing side of the paddles in order to sense or measure the forces of the femur and / or tibia for different user movements of the force measurement device 40b. As the user toggles the force measurement device 40b in the knee, the computing components may process the raw data125520-10402-762494011 / 19 / 2025 from the force sensing elements to determine force information (e.g., static forces, dynamic forces, complex force) and then convey the force information to an external computing system (e.g., computing system 204 as shown in FIG. 15). In other embodiments, raw data from the force sensing elements are directly conveyed to an external computing system to process the raw data and determine the force information. The external computing system then automatically records the separation distance for the medial or lateral side of the knee as soon as the force information for either the medial side or lateral side of the knee satisfies one or more predetermined parameters (e.g., a measured force is equal (or approximately equal) to a threshold force). For example, the external computing system automatically records the medial separation distance when the force information derived from the force sensing element positioned on the medial side of the knee (e.g., paddle 48) satisfies the one or more predetermined parameters, and automatically records the lateral separation distance when the force information derived from the force sensing element positioned on the lateral side of the knee (e.g., paddle 44) satisfies the one or more predetermined parameters.

[0066] The above procedure for capturing the separation distances by toggling the force measurement device 40b may be completed for the knee in full extension, full flexion, and for any degree of knee flexion (e.g., 45 degrees of flexion) the user desires. The separation distances may be recorded for both the medial and lateral sides of the knee for each of these desired flexion angles. The user may flex and extend the knee in real-time while the force sensing elements sense the forces in real-time and the computations / determinations occur in real-time. The different types of force information and pre-determined parameters as previously described with respect to force measurement device 40a shown in FIG. 3 A may also be used by the external computing system to trigger the automatic recordation of the separation distances when using the force measurement device 40b shown in FIG. 6.

[0067] In a specific embodiment, the first paddle 44 of the force measurement device 40b may include a first top paddle portion and a first bottom paddle portion, where the distance between the first top paddle portion and the second paddle portion can be adjusted to change the overall thickness of the first paddle 44 and therefore the distance between the femur and the tibia when the force measurement device 40b is positioned in the knee. The second paddle 48 may likewise have a second top paddle portion and a second bottom paddle portion for the same purpose (optionally allowing for the distance to be controlled independently on the medial and lateral sides of the paddle). In this embodiment, the force sensing elements may be positioned on the femur-facing side of the top paddle portions and / or the tibia-facing side of125520-10402-762494011 / 19 / 2025 the bottom paddle portions. It should further be appreciated that the force measurement devices (40a, 40b) may include only a single paddle that traverses both the medial femoral condyle and lateral femoral condyle when the force measurement devices (40a, 40b) are positioned in the knee. If only a single paddle exists, the medial and lateral sides of the single paddle may be concave to approximately match the concave shape of the femoral condyles. A single paddle similarly may have a top paddle portion and a bottom paddle portion with the ability to adjust the distance between the top paddle portion and the bottom paddle portion. The distance between top and bottom paddle portions can be controlled, for example, manually (e.g., including a screw, ratchet, rack-and-pinion, pivoting, or other distance control mechanism), electrically (e.g., using an electric motor), pneumatically, or in any other way. The system can include sensors for sensing the distance between top and bottom paddles can feed distance information to the computing system such as for use in bone / knee modeling or soft tissue balancing. It should be appreciated that the one or more paddles may be of any shape.

[0068] With respect to FIG. 8, another embodiment of a force measurement device 40c is shown. The force measurement device 40c is configured to be placed between the femur and tibia but only on a single side of the knee. This allows the user to record the separation distances for either the lateral side of the knee, the medial side of the knee, or both sides of the knee in succession. The force measurement device 40c may include a handle 42 (shown here in a pistolgrip configuration, which may be applied to any of the force measurement device described herein), a paddle 44, a force sensing element associated with the paddle 44, three or more LEDs, and a photosensor. The above procedures and methods for automatically recording the separation distances as described with respect to the force measurement devices (40a, 40b) as shown in FIGs. 3A - 7 may also be applied to the force measurement device of FIG. 8. However, instead of recording the separation distances for both sides of the knee with a single device, the force measurement device 40c is used to automatically record the separation distances for a single side of the knee, or both sides of the knee in succession. The force measurement device 40c may be particularly useful for unicondylar or partial knee procedures.

[0069] FIG. 9 depicts a particular embodiment of a force measurement device 40d. The force measurement device 40d includes a fourth LED 52d having a different light emitting orientation than the first three LEDs (52a, 52b, 52c). The fourth LED 52d ensures that the force information (or raw data, or minimally processed data) is optically conveyed to the external computing system in the event that the line-of-sight of one or more of the first three LEDs is obstructed due to the flexion angle of the knee during soft tissue balancing. For example, when125520-10402-762494011 / 19 / 2025 the force measurement device 40d is positioned in the knee and the knee is in full flexion, at least one of the first three LEDs (52a, 52b, 52c) may have an unobstructed view to the tracking system (or a photosensor associated with the tracking system dedicated to receiving the optical signals comprising the data). However, when the force measurement device 40d is positioned in the knee and the knee is in full extension, the force measurement device 40d may be oriented perpendicular to the tracking system. In this case, the fourth LED 52d, which may have a perpendicular light emitting orientation relative to the first three LEDs (52a, 52b), can still optically convey the force information to the external computing system. It should be appreciated that any embodiments of the force measurement device described herein may include one or more LEDs having a different light emitting orientation than other LEDs.

[0070] FIGs. 10 depicts another embodiment of a force measurement device 40e. The force measurement device 40e may include a handle 42, at least one LED 52, a photosensor 54, one or more paddles (44, 48), and one or more force sensing elements in the form of torque sensors 70 (e.g., strain gauge, magnetoelastic sensors, optical sensor). The paddles (44, 48) may be coupled to the torque sensor, where the torque sensor 70 is configured to measure the rotational force the bones apply to the paddles (44, 48) and therefore the torque sensor 70 as the user: (i) toggles the force measurement device 40e when the force measurement device 40e is positioned in the knee; and / or (ii) applies lateral or medial forces to the knee when the force measurement device 40e is positioned in the knee. In particular embodiments, the force measurement device 40e may be in the form of a torque wrench osteotome. The paddles of the force measurement device 40e may have a thickness capable of applying an initial amount of tension to the ligaments as described with respect to force measurement device 40b as shown in FIGs. 6-7. As before, the external computing system may automatically record the separation distances when force information derived from the torque sensor 70 satisfies a predetermined parameter. For example, the external computing system may automatically record the separation distance as soon as a measured torque is equal (or approximately equal) to a threshold torque. In some embodiments, the force measurement device 40e includes only a single paddle for recording separation distances on a single side of the knee (or both sides of the knee in succession) like the force measurement device 40c as shown in FIG. 8. In other embodiments, a force measurement device 40f includes a handle 44 (in the form of a pistolgrip), a first paddle 44, a second paddle 48, one or more LEDs 52, a photosensor 54, a first torque sensor 72 associated with the first paddle 44, and a second torque sensor 74 associated with the second paddle 48 as shown in FIG. 11. The force measurement device 40f may allow125520-10402-762494011 / 19 / 2025 for individual force information to be better derived from each side of the knee. For example, the first paddle 44 and corresponding torque sensor 72 may be used to derive force information on the lateral side of the knee, and the second paddle 48 and corresponding torque sensor 74 may be used to derive force information of the medial side of the knee. The above procedures and methods for automatically recording the separation distances as described with respect to the force measurement devices (40a, 40b) as shown in FIGs. 3 A - 7 may also be applied to the force measurement devices (40e, 40f) of FIGs. 10 and 11.

[0071] In particular embodiments, the force measurement devices described herein do not include any LEDs 52 or photosensors, and may be used as a manual instrument without any external computing components. In this embodiment, the force measurement device may house all the computing components required to measure the force information and compare the force information to one or more predetermined parameters. The paddles may be adjustable to change the thickness of the paddles and therefore the separation distance between the bones when the force measurement device is positioned in the knee. As the user adjusts the thickness of the paddles, the force measurement device continuously monitors and compares the force information to one or more predetermined parameters. The force measurement device then automatically records the separation distance (which now corresponds to the thickness of the paddles) as soon as the thickness of the paddles causes the bones to apply a force on the force sensing elements that satisfies one or more predetermined parameters. The force measurement device may include a display for displaying the separation distances to a user in real-time.

[0072] FIG. 12 depicts a method 80 of using the force measurement devices (40a - 40f) for automatically recording separation distances in accordance with embodiments of the invention. A computing system may receive, load, or otherwise read a predetermined parameter at step 82. The predetermined parameter may be read as a user input into the system, or read as a default parameter saved in the system. The user then places the force measurement device between the femur and tibia with the knee in extension. The user may then: (i) apply a medial force on the knee; and / or (ii) toggle the force measurement device relative to the knee (e.g., rotate the force measurement device to further open up the medial side of the knee). The force measurement device conveys force information to the computing system in real-time. The computing system then automatically records the medial separation distance when the force information satisfies one or more predetermined parameters (e.g., a measured force reaches a threshold force) in step 84. The user then: (i) applies a lateral force on the knee; and / or (ii) toggles the force measurement device relative to the knee (e.g., rotate the force measurement125520-10402-762494011 / 19 / 2025 device to further open up the lateral side of the knee). The force measurement device conveys force information to the computing system in real-time. The computing system then automatically records the lateral separation distance when the force information satisfies a predetermined parameter (e.g., a measured force reaches a threshold force) reached in step 86. The user then flexes the knee to a desired flexion angle, such as full flexion. Steps 84 and 86 are repeated with the knee in the desired flexion angle as shown as steps 86 and 88. Then based on the separation distance measurements, the user has the option to update or adjust the planned position of the implant models relative to the bone models to achieve a desired separation goal (e.g., equal medial and lateral separation distances in flexion and extension, a desired separation distance on the medial and / or lateral side) using implant adjustment tools displayed on the GUI in step 92. After the user is satisfied with the planned position for mounting the implants on the bone, a CAS device may be used to assist the user in forming the cut surfaces on the bones such that the implants will mount onto the bones in the planned location.

[0073] In specific embodiments, a CAS system assists the user in positioning the force measurement device (40a-40f) in the knee at a predetermined location. This is to account for the different forces that the force measurement device may measure depending on where the force measurement device is positioned between the femur and the tibia. For example, the user may unknowingly position the paddles more medially in the knee, which may result in the measured forces being higher on the medial side of knee and lower on the lateral side. Ultimately, it is desirous to measure the forces at locations that is consistent with the final placement of the implants in the knee. Therefore, the CAS system may provide the user with feedback on positioning the force measurement device in the knee consistent with the planned placement for mounting the implants on the bones. The CAS system may utilize the planned placement of the implant models relative to the bone models to identify the correct location for positioning the force measurement device in the knee and then output feedback (e.g., instructions or graphics on a GUI, real-time audible feedback, real-time navigation feedback) to guide the user in positioning the force measurement device. For example, from the surgical plan, the CAS system knows the planned internal-external rotation for the tibia implant component on the tibia. The CAS system may then display to the user graphics, or real-time navigation (e.g., the real-time location of the force measurement device relative to the realtime location of the bones), that guides the user in positioning the force measurement device in the knee at that same internal-external rotational location as in the surgical plan. The same125520-10402-762494011 / 19 / 2025 may be done to guide the user to position the force measurement device at the planned medial- lateral location for mounting the implants on the bones.In another particular embodiment, the force measurement device or CAS system may extrapolate the measured / sensed forces, from the location of where it is measured / sensed, to where each ligament is actually physically located. This may be done from multiple sensing locations, such as a sensing surface located on the force measurement device, or from just two distinct sensing contact points located on the force measurement device, one for the medial side of the knee and one for the lateral side of the knee. The system then extrapolate the measured / sensed forces from where the readings are captured over to where the ligament is physically located. For example, say the lateral collateral ligament is located at 0 millimeters (mm) relative to the knee and the medial collateral ligament is located at 80mm. And say the force sensors on the paddles, when positioned in the knee, are located at positions 20mm and 60 mm. The user then toggles the force measurement device to apply more forces on the medial side of the knee. At that time, the force sensor positioned at 20mm may sense / measure a force of 400 newtons (N) on the lateral side of the knee, and the force sensor positioned at 60 mm may sense / measure a force of 600 N. The system may then extrapolate those forces to the location of the ligaments, so the extrapolated force at the location of the lateral collateral ligament (0mm) may be 350 N, and the extrapolated force at the location of the medial collateral ligament (80mm) may be 650 N. The extrapolated forces may be calculated using a fitted equation (e.g., least squares or other statistical technique) from experimental or other data. This provides a more accurate reading of the forces applied on the ligaments at their actual location.Normalizing Forces to Output Consistent Separation Distances

[0074] In particular embodiments, with reference to FIG. 13, the system is configured to normalize the lateral or medial forces (or within a range of lateral or medial forces) and / or normalize the separation distances to account for the different forces users apply to the knee to output a consistent separation distance measurement. The system is configured to receive or determined measured forces from a force measurement device 40 (e.g., force measurement devices 40a - 40f) and determine separation distances as the measured forces are collected to then normalize the measured forces and / or separation distances to output a consistent separation distance (e.g., what the separation distance should be). For example, as shown in FIG. 13, user 1 may apply a maximum lateral force of “X” newtons on the knee of patient “M”, and user 2 may apply a maximum lateral force of “X+Y” newtons on the knee of the same125520-10402-762494011 / 19 / 2025 patient “M”. Alternatively, user 1 may toggle the force measurement device 40 relative to the knee to apply a maximum force of “X” newtons on the knee of patient “M”, and user 2 may toggles the force measurement device 40 relative to the knee to apply a maximum force of “X+Y” newtons. During this step, the force measurement device 40 measures the forces experienced on the force sensing elements up to the maximum force applied (e.g., “X” newtons for user 1, and “X+Y” newtons for user 2), where these measured forces are transferred as an input to a normalization model (e.g., an algorithm that determines the normalized forces and / or normalized separation distances). The separation distances are also recorded during this step and transferred as an input into the normalization model. Other inputs into the normalization model may also include patient characteristics of patient “M”, for example, biomechanical characteristics or a patient specific biomechanical model, morphology of the ligament (e.g., ligament thickness, ligament length, change in ligament length), the morphology of the bones and cartilage, disease severity, imaging data, and / or other patient characteristics (e.g., patient age, weight, gender, height, BMI). The normalization model then outputs a consistent separation distance of “Y” millimeters for both users even though user 2 applied a larger maximum force than user 1. The normalization model may further use the patient characteristic data to adjust the normalized separation distance or normalized force to account for differences between patients and to provide a more accurate representation of the specific patient’s soft tissues (e.g., ligaments). The normalization model thus reduces the variability in the separation distance measurements otherwise caused by the differing amount of forces that different users apply to the knee with traditional gap balancing methods.

[0075] In a particular embodiment, the normalization model may generate a ligament tension curve for a particular patient as shown in FIG. 14 to output a consistent separation distance. A TKA procedure may being in the same manner as previously described with respect to the force measurement device 40a of FIG. 3 A. This may include generating a surgical plan, exposing the bones, affixing tracking arrays (60, 62) to the femur 10 and tibia 11, and registering the bones. A force measurement device 40 (e.g., force measurement device 40a - 40f) is placed in the knee between the femur and tibia. The user may then: (i) apply a medial or lateral force to the knee as shown in FIG.s 4A and 4B; and / or (ii) toggle the force measurement device 40 relative to the knee to apply forces to the bones, tension the ligaments, and / or further open up the knee on the medial side, lateral side, or both sides of the knee as shown in FIG 6. The measured forces derived from the force sensing elements while the forces are applied (or while the device 40 is toggled) is transferred as an input to normalization model.125520-10402-762494011 / 19 / 2025The recorded separation distances are also transferred as an input to the normalization model, measured forces and recorded separation distances are then plotted to generate a ligament tension curve as shown in FIG. 14. In some embodiments, the normalization model uses the recorded separation distance between a first ligament attachment point on a first bone (e.g., a MCL and / or LCL attachment point on the tibia) and an opposing ligament attachment point on a second bone (the MCL and / or LCL attachment on the femur) to generate the ligament tension curve. The location of the attachment points may be determined using a volume rendering of the knee derived from imaging data (e.g., CT scan data) and / or the locations of the attachment points may be digitized by a user wielded digitizer when the knee is exposed. The location of those attachment points are stored in the computing system and used to determine the separation distances while balancing the soft tissues. However, it should be appreciated that other separation distances may be used to generate the ligament tension curve. A typical ligament tension curve generated by the normalization model is shown in FIG. 14 Initially, in region “A” the measured forces are low and correlate to a large increase in the separation distance (or ligament elongation) as the ligaments go from a lax state to a more tensioned state. The ligament tension curve then enter s a linear region “B”, where the amount of measured force correlates linearly to the recorded separation distance (or ligament elongation). Then, there is a third region “C”, where the ligament is fully stretched and any additional increase in force have minimal effect on the change in the separation distance (or ligament elongation). The normalization model may determine an inflection point in the graph, where this inflection point is represented by the transition from region “B” to “C”, labeled by the dashed line “normalized.” The normalization model may then output a separation distance corresponding to the separation distance at the inflection point, even though the user may apply more force to the knee and “overstretch” the ligament. For example, the user may apply a force past the inflection point in region “C,” which would typically give the user the separation distance in region “C” at that applied force. However, the normalization model in these embodiments identifies the inflection points and outputs the separation distance at the inflection point to provide a consistent separation distance measurement to the user. Thus, no matter how much force a user applies to the knee, the normalization model always outputs a consistent separation distance that corresponds to the inflection point of the ligament tension curve. It should be appreciated, however, that other points on the graph (i.e., other than the inflection point) may be used as the normalized force and normalized separation distance. The normalization model125520-10402-762494011 / 19 / 2025 may output the separation distance on a GUI, and may include separation distances for the medial and lateral sides of the knee at various knee flexion angles.

[0076] In another embodiment, the normalization model may be generated based on biomechanical models, historical data, artificial intelligence (e.g., machine learning), and / or experimental data. For example, experimental data may be collected on patient “M” to build the normalization model. The experiment may include multiple users (e.g., 10 users, 100 users) performing soft tissue balancing on patient ‘M.’ For each user, the medial and lateral forces are measured by the force measurement device 40 and the separation distances are recorded. This provides a range of forces and corresponding range of separation distances. The range of forces and separation distances are then normalized to determine a normalized force and corresponding normalized separation distance for that patient, patient population, or set of patient characteristics. Characteristics of patient ‘M’ may also be collected and built into the normalization model. The patient characteristics may include biomechanical characteristics or a patient specific biomechanical model (e.g., patient’s gait, the motion of the ligaments throughout the knees range-of-motion (ROM), motion of the femur and tibia throughout the knees ROM), morphology of the ligament (e.g., ligament thickness, change in ligament lengths in extension and flexion), the morphology of the bones and cartilage, angles of the bones relative to different axes (e.g., varus-valgus of the bones / knee relative to the mechanical axis of the bones / knee), disease severity (e.g., amount of cartilage loss, patients with severe valgus deformity, patients with severe varus deformity, etc.), imaging data, and / or other patient characteristics (e.g., patient age, weight, gender, height, BMI). Now, the normalization model includes a set of patient characteristics (e.g., patient characteristics of patient “M") that can be mapped to a range of applied forces having a normalized force and a corresponding normalized separation distance to output a single, or consistent, separation distance. For example, let’s say an applied force can go from 1 to 10, and from the experimental data it is determined that surgeons typically apply a force of 8 (which is the determined normalized force from the experimental data) which results in a normalized separation distance of “x” millimeters (mm). The experimental data also revealed that an applied force of 9 stretches the ligaments by 1 mm compared to an applied force of 8 (e.g., x+1 mm), an applied force of 10 stretches the ligaments by 1.5 mm compared to an applied force of 8 (e.g., x+1.5 mm), and a force of 7 keeps the ligaments 2 mm shorter than a force of 8 (e.g., x-2 mm). In this scenario, if a surgeon applies a force from 7 through 10, then the normalization model outputs a separation distance as if a force of 8 was applied (e.g., “x” mm), even though more or less force may be applied. So the125520-10402-762494011 / 19 / 2025 separation distance shown on the GUI would be the same (i.e., “x” mm) no matter how much force between 7 and 10 is applied.

[0077] Essentially, the same separation distance measurements are output no matter how much force you put on the knee to spread it apart (e.g., open up the knee), as long as the applied force is beyond a minimum amount of force and / or within a range of forces. In this way, different surgeons, who put different amounts of force on the knee during their soft tissue analysis, would get the same separation distance measurement when balancing the soft tissues on the same patient. And if the surgeon puts more or less force on the knee, the separation distance measurement stays essentially the same instead of varying based on how much force the surgeon applies.

[0078] The normalization model may further account for patient characteristics, such as the ligament thickness, to modify the normalized force and / or normalized separation distance as a function of those patient characteristics. In a particular embodiment, the patient characteristics include measurements of the patient’s ligaments, which are factored into the normalization model. A volume rendering derived from imaging data (e.g., CT scan) may be used to determine the size and thickness of the ligaments based on density variations of the bone at the ligament attachment points, which may be used to determine the ligament attachment diameter. Th ligament attachment diameter may correlate with the ligament thickness, which may correlate to the elasticity (e.g., stretchiness) of the ligaments. Then depending on the measured thickness of the ligaments, the normalized force and / or normalized separation distance may be adjusted up or down to account for the differences in ligament elasticity from patient to patient. Physical measurements of the ligaments may also be performed intraoperatively. The system may display a measurement (e.g., separation distance) of how tight or loose the knee will be for their current surgical plan (e.g., the current planned placement for mounting the implant on the bone), which changes as the user updates the planned position for the implant position, and this type of information about the patient’s specific ligaments may be helpful for the user to provide accuracy and consistency across a population of patients. For example, a thicker ligament may be less “stretchy” than a thinner ligament, where the normalized force or normalized separation distance are automatically adjusted by the normalization model to output a consistent separation distance that correlates with patient’s having thicker ligaments.

[0079] Thus, when new users encounter patients with similar patient characteristics as patient “M”, the normalization model will output a consistent separation distance for force applied on the knee, or for any applied forces within a range of forces (e.g., the range of forces125520-10402-762494011 / 19 / 2025 that were recorded in the above experiment). The separation distance may be displayed on the GUI to assist the user in adjusting the planned location of the implant model (or implant) relative to the bone model (or bone) to achieve a desired soft tissue balancing goal.

[0080] The above experiments on patient ‘M’ may be expanded to multiple patients, patient populations, and / or types of patients to build a normalization model for all types of patients. Historical data may be used to build the normalization model, where data from previous patient cases are used, including: (i) measured medial and lateral forces on the knee; (ii) the resulting recorded separation distances; and (iii) and the patient’s characteristics. Artificial intelligence (e.g., machine learning) may be trained on this experimental and / or historical data to build the normalization model. The normalization model may be regularly updated to further refine the model overtime.

[0081] The normalization model may be stored and executed on a computer system (e.g., computing system 204 shown in FIG. 15). During soft tissue balancing, the forces measured by the force sensors on the force measurement device 40 may be optically transferred to the computing system in real-time. Patient characteristics of the patient may be pre-loaded into the normalization model prior to the procedure. The normalization model then calculates and / or determines the consistent separation distance based on the inputted patient characteristics and the measured forces. The GUI then displays the determined separation distance. The user, or the system, may then adjust the planned location for the implant model (or implant) relative to the bone model (or bone) to achieve a desired gap goal. After the user is satisfied with the plan, the cut surfaces on the bone may be formed with the aid of a CAS device. The implants are mounted on the bone cut surfaces to complete the TKA procedure.

[0082] The aforementioned use of the normalization model is advantageous because it reduces the variability in the separation distance measurements caused by the differing amounts of forces different users apply to the knee.Computer- Assisted Surgical System

[0083] Referring now to FIGs. 15, 16A, and 16B, embodiments of the present inventive system and method generally includes a computer-assisted surgical system. In some inventive embodiments, a 2-DoF device 100 is provided for maintaining alignment of an end-effector 206 (e.g., bone pin) coincident with a virtual plane. FIG. 15 is a schematic view showing the computer-assisted surgical system 200 including a 2-DoF device 100, a computing system 204,125520-10402-762494011 / 19 / 2025 and a tracking system 206. In other inventive embodiments, the system includes an end effector 306 extending from a robotic arm.

[0084] The computing system 204 generally includes hardware and software for executing a surgical procedure. By way of example but not limitation, in one preferred form of the present invention, the computing system 204 is configured to control the actuation of the working portion 104 relative to the hand-held portion 102 of the 2-DoF 100 device to maintain alignment of the end-effector axis 307 (FIG. 16A) coincident with a virtual plane defined in a surgical plan. The end-effector 206 coupled to the working portion 104 in operation modifies (e.g., inserts pins, cuts, mills, etc.) subject bone. The computing system 204 may generate control signals to accurately maintain the end-effector axis 207 coincident with a virtual plane defined in the surgical plan based on: a) the location of the virtual plane as registered to the location of the bone (or more specifically to the coordinate system of a tracking array affixed to the bone); and b) the tracked POSE of the 2-DoF device 100.

[0085] The computing system 204 of the computer-assisted surgical system 200 may include: one or more device computers (208, 209) including a planning computer 210; a tracking computer 211, and peripheral devices. Each computer may include one or more processors. Processors operate in the computing system 204 to perform computations and execute software associated with the inventive system and method. The device computer(s) (208, 209), the planning computer 210, and the tracking computer 211 may be separate entities as shown in FIG. 15, 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 200. For example, the tracking computer 211 may have operational data to control the 2-DoF device 100 without the need for a device computer (208, 209). Furthermore, if desired, any combination of the device computers (208, 209), planning computer 210, and / or tracking computer 211 may be connected together via a wired or wireless connection. 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 in the present invention. In addition, the data gathered by, and / or the operations performed by, the tracking computer 211 and device computer(s) (208, 209) may work together to control the 2-DoF device 100 and, as such, the data gathered by, and / or the operations performed by, the tracking computer 211 and device computer(s) (208, 209) to control the 2-DoF device 100 may be referred to herein as a “control system.”

[0086] The peripheral devices allow a user to interface with the computing system 204 and may include, but are not limited to, one or more of the following: one or more user-interfaces,125520-10402-762494011 / 19 / 2025 such as a display or monitor (212a, 212b) to display a graphical user interface (GUI); and userinput mechanisms, such as a keyboard 214, mouse 222, pendent 224, joystick 226, and foot pedal 228. If desired, the monitor(s) (212a, 212b) may have touchscreen capabilities, and / or the 2-DoF device 100 may include one or more input mechanisms (e.g., buttons, switches, etc.). Another peripheral device may include a tracked digitizer probe 205 to assist in the registration process, or to digitize portions of an implant or cut guide / block. A tracking array 61 is assembled to the digitizer probe 205 to permit the tracking system 206 to track the POSE of the digitizer probe 205 in space. The digitizer probe 205 may further include one or more user input mechanisms to provide input to the computing system 204. For example, a button on the digitizer probe 205 may allow the user to signal to the computing system 204 to digitize a point in space to assist in registering a bone to a surgical plan.

[0087] The device computer(s) (208, 209) 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 2-DoF device 100. By way of example but not limitation, one or more of the device computers (208, 209) may include software to control the 2-DoF device 202, e.g., generate control signals for the actuators to move the working portion 104 relative to the hand-held portion 102 to a targeted POSE, receive and process tracking data, control the rotational or oscillating speed of the end-effector 306 by controlling motor 305, execute registration algorithms, execute calibration routines, provide workflow instructions to the user throughout a medical procedure, as well as any other suitable software, data or utilities required to successfully perform the procedure in accordance with embodiments of the invention.

[0088] In some embodiments, the system 200 may include a first device computer 208 located separate from the 2-DoF device 100 and a second device computer 209 housed in the 2-DoF device 100 to provide on-board control. The first device computer 208 may be dedicated to several processes, such as: the control of the surgical workflow via a GUI; the registration process and the associated calculations; the display of 3-D models and 3-D model manipulation or animation; recording locations of a digitizer tip; receiving or reading a desired predetermined parameter (e.g., a threshold force) for soft tissue balancing; receiving force information from a force measurement device 40; determining force information for raw data conveyed from a force measurement device 40; determining force information for minimally processed raw data conveyed from a force measurement device 40; comparing force information to one or more predetermined parameters to determine if the force information satisfies one or more of the125520-10402-762494011 / 19 / 2025 predetermined parameters; determining separation distances; recording separation distances; executing a normalization model; receiving patient characteristics for input into the normalization model; determining a normalized force value; determining a normalized separation distance; outputting (e.g., displaying on a GUI) at least one of a normalized separation distance (e.g., a consistent separation distance) and / or a normalized force; as well as other processes for executing the embodiments described herein. The second device computer 209, also referred to herein as an on-board device computer, may be dedicated to the control of the 2-DoF device 100. For example, the on-board device computer 209 may compute and generate the control signals for the actuator motors (210a, 210b) based on: i) received signals / data corresponding to the real-time POSE of the 2-DoF device 100 from the tracking system; and ii) received signals / data corresponding to the real-time POSE of the virtual plane computed by first device computer 208. The on-board device computer 209 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 2-DoF device 100 and a tracking system 206 are further described below.

[0089] The planning computer 210 in some inventive embodiments is dedicated to planning the procedure. By way of example but not limitation, the planning computer 210 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 bone models; generating a volume rending of a bone or joint from imaging data (e.g., CT scan); automatically determine (or provide software tools for a user to determine) locations of ligament attachment points within imaging data or a volume rendering derived from imaging data; storing and providing computer-aided design (CAD) files such as implant CAD files; planning the POSE for cut surfaces, virtual planes, screws, pins, implants, grafts, and fixation hardware relative to preoperative bone data; generating the surgical planning data for use with the system 200, and providing other various functions to aid a user in planning the surgical procedure. The planning software is particularly programmed for planning TKA procedures for an implant agnostic system as described above. The final surgical plan data may include one or more images of a bone or virtual models of the bone, registration data, subject identification information, the POSE for inserting or mounting one or more pins, screws, implants, grafts, fixation hardware125520-10402-762494011 / 19 / 2025 relative to the bone, and / or the POSE of one or more virtual planes defined relative to the bone models. The device computer(s) (208, 209) and the planning computer 210 may be directly connected in the operating room, or the planning computer 210 may exist as separate entities outside the operating room. The final surgical plan is readily transferred to a device computer (208, 209) and / or tracking computer 211 through a wired (e.g., electrical connection) or a wireless connection (e.g., optical communication) 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)) if the planning computer 210 is located outside the operating room (or if otherwise desired). As described above, the computing system 204 may comprise one or more computers, with multiple processors capable of performing the functions of the device computer 208, the tracking computer 211, the planning computer 210, or any combination thereof.

[0090] The tracking system 206 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 particular embodiments of the present invention, the tracking system 206 is an optical tracking system such as the optical tracking system described in U.S. Pat. No. 6,061,644 (which patent is hereby incorporated herein by reference), having two or more optical detectors 207 (e.g., cameras) 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 an 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 (60, 61, 62), where each tracking array has a unique geometry / arrangement of fiducial markers, or a unique transmitting wavelength / frequency (if the markers are active LEDS), such that the tracking system 206 can distinguish between each of the tracked objects.

[0091] If desired, the tracking system 206 may be incorporated into an operating room light 218, located on a boom, a stand, or built into the walls or ceilings of the operating room. The tracking system computer 211 includes tracking hardware, software, data, and / or utilities to determine the POSE of objects (e.g., tissue structures, the 2-DoF device 100) in a local or global coordinate frame. The output from the tracking system 206 (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) (208, 209) through a wired or wireless connection. In125520-10402-762494011 / 19 / 2025 a particular embodiment, the tracking computer 206 processes the tracking data and provides control signals directly to the 2-DoF device 100 and / or device computer 208 based on the processed tracking data to control the position of the working portion 104 of the 2-DoF device 100 relative to the hand-held portion 102. In another embodiment, the tracking computer 206 sends tracking data to a receiver located on the 2-DoF device 100, where an on-board device computer 209 generates control signals based on the received tracking data.

[0092] 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. These operations / processes may be executed directly on the tracking system computer 211 or executed on a separate computer (e.g., first device computer 208) in communication with the tracking system 206.

[0093] Bi-directional optical communication (e.g., light fidelity or Li-Fi) may occur between the 2-DoF device 100 and the tracking system 206 by way of a modulated light source (e.g., light emitting diode (LED)) and a photosensor (e.g., photodiode, camera). The 2-DoF device 100 may include an LED and a photosensor (i.e., a receiver) disposed on the working portion 104 or hand-held portion 102, where the LED and photosensor are in communication with a processor such as modem or an on-board device computer. Data generated internally by the 2- DoF device 100 may be sent to the tracking system 206 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., cameras) or a dedicated photosensor and processed by the tracking system computer 211. The tracking system 206 may likewise send data to the 2-DoF device 100 with a modulated LED associated with the tracking system 206. Data generated by the tracking system 206 may be sent to the 2-DoF device 202 by modulating the LED on the tracking system 206, where the light signals are detected by the photosensor on the 2-DoF device 100 and processed by a processor in the 2-DoF device 100. Examples of data sent from the tracking system 206 to the 2-DoF device 100 includes operational data, surgical planning data, informational data, control data, positional or tracking data, pre-operative bone data, or instructional data. Examples of data sent from the 2-DoF device 100 to the tracking system 206 may include motor position data, battery life, operating status, logged data, operating parameters, warnings, or faults. In some embodiments, data generated by the first125520-10402-762494011 / 19 / 2025 device computer 208 is sent to the tracking system 206, where that generated data is transferred to the 2-DoF device 100 via the LED on the tracking system 206.

[0094] It should be appreciated that in some embodiments of the present invention, other tracking systems are incorporated with the surgical system 200. By way of example but not limitation, the surgical system 200 may comprise an electromagnetic field tracking system, ultrasound tracking systems, accelerometers and gyroscopes, and / or a mechanical tracking system. 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.

[0095] FIGs. 16A and 16B are schematic views showing the 2-DoF device 100 in greater detail. More particularly, FIG. 16A shows the 2-DOF device 100 in a first working POSE, and FIG. 16B illustrates the 2-DOF device 100 in a second working POSE. The 2-DoF device 100 comprises a hand-held portion 102 (or handle) and a working portion 104. The hand-held portion 102 comprises an outer casing 303 of ergonomic design which can be held and wielded by a user (e.g., a surgeon). In particular embodiments, the 2-DoF device 100 is intended to be fully supported by the hands of the user in that there are no additional supporting links connected to the 2-DoF device 100 and the user supports the full weight of the 2-DoF device 100. The working portion 104 comprises an end-effector 306 having an end-effector axis 307. The end-effector 306 may be removably coupled to the working portion 104 (via a coupler (e.g., chuck)) and driven by a motor 305. The hand-held portion 102 and working portion 104 are connected to one another, for example, by a first linear actuator 307a and a second linear actuator 307b in order to control the pitch and translation of the working portion 104 relative to the hand-held portion 102, as will hereinafter be discussed in further detail. In a particular embodiment, the working portion 104 is removably coupled to the hand-held portion 102 to permit different types of working portions to be assembled to the hand-held portion 102. For example, a first working portion 104 may illustratively be a laser system having components to operate a laser for treating tissue, a second working portion 104 may illustratively be a drill for rotating a bone pin, and a third working portion 104 may illustratively be an oscillating saw.125520-10402-762494011 / 19 / 2025

[0096] A tracking array 312, having three or more fiducial markers of the sort well known in the art, is preferably rigidly attached to the working portion 104 in order to permit the tracking system 206 (FIG. 15) to track the POSE of the working portion 104. The three or more fiducial markers may, alternatively, be integrated directly with the working portion 104. The fiducial markers may be active markers such as light emitting diodes (LEDs), or passive markers such as retroreflective spheres. The 2-DoF device 100 may further include one or more user input mechanisms such as triggers (e.g., trigger 314) or button(s). The user input mechanisms may permit the user to perform various functions illustratively including: activating or deactivating the motor 305; activating or deactivating the actuation of the working portion 104 relative to the hand-held portion 102; notifying the computing system 204 to change from targeting one virtual plane to a subsequent virtual plane; and pausing the surgical procedure.

[0097] Within the outer casing of the hand-held portion 102 is a linear actuator 307a and a second linear actuator 307b. Each linear actuator (307a, 307b) may include a motor (310a, 310b) to power a screw (316a, 316b) (e.g., a lead screw, a ball screw), a nut (318a, 318b), and a linear member (308a, 308b). In some inventive embodiments, the motors (first motor 310a, second motor 310b) are electric servo-motors that bi-directionally rotate the screws (316a, 316b). Motors (310a, 310b) may also be referred to herein as linear actuator motors. The nuts (318a, 318b) (e.g., ball nuts, elongated nuts) are operatively coupled to the screws (316a, 316b) to translate along the screws (316a, 316b) as each screw is rotated by its respective motor (310a, 310b). A first end of each linear member (308a, 308b) is coupled to a corresponding nut (316a, 316b) and the opposing end of each linear member (308a, 308b) is coupled to the working portion 104 via hinges / links (320a, 320b), such that the hinges / links (320a, 320b) allow the working portion 104 to pivot relative to the linear rails (308a, 308b). The motors (310a, 310b) power the screws (316a, 316b) which in turn cause the nuts (318a, 318b) to translate along the axis of the screws (316a, 316b). Translation of nuts 318a, 318b along ball screws 316a, 316b, respectively, causes translation of front linear member 308a and back linear member 308b, respectively, whereby to permit (a) selective linear movement of working portion 104 relative to hand-held portion 102, and (b) selective pivoting of working portion 304 relative to handheld portion 302 of 2-DoF device 100. Accordingly, the translation “d” and pitch “a” (FIG. 16B) of the working portion 104 may be adjusted depending on the position of each nut (318a, 318b) on their corresponding screw (316a, 316b). A linear guide 322 (FIG. 16A) may further constrain and guide the motion of the linear member (308a, 308b) in the translational direction “d ” In a particular embodiment, the nuts (316a, 316b) are elongated and couple directly to the125520-10402-762494011 / 19 / 2025 working portion 104 via the hinges / links (320a, 320b), in which case the linear members (308a, 308b) are no longer a component of the linear actuators (307a, 307b). It should be appreciated that other linear actuation mechanisms / components may be used to adjust the POSE of the working portion 104 relative to the hand-held portion 102 such as linear motors, pneumatic motors, worm drives and gears, rack and pinion gears, and other arrangements of motors and transmissions.

[0098] The 2-DoF device 100 may receive power via an input / output port (e.g., from an external power source) and / or from on-board batteries (not shown).

[0099] The motors (305, 310a, 310b) of the 2-DoF device 100 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 2-DoF device 100 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 2-DoF device 100 includes a receiver for receiving control signals from the computing system 204 (FIG. 15). 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 204 directly to the motors (305, 310a, 310b) of the 2-DoF device 100, or the receiver may be in communication with a computer (e.g., an on-board device computer 209 as further described below) that processes signals received by the receiver and then generates the control signals for the motors (305, 310a, 310b) based on the received signals.

[0100] It also should be noted that force measurement devices of the types described herein can be used in other ways and in other types of procedures, such as, for example, knee balancing procedures of the types described in United States Provisional Patent Application No. 63 / 635,087 entitled BALANCING A KNEE DURING TOTAL KNEE ARTHROPLASTY filed April 17, 2024 (Attorney Docket No. 125520.10203) and United States Provisional Patent Application No. 63 / 633,479 entitled BALANCING A KNEE DURING TOTAL KNEE ARTHROPLASTY filed April 12, 2024 (Attorney Docket No. 125520.10201), which were incorporated by reference above. These patent applications describe a system and method for determining adjustments to a planned position or orientation125520-10402-762494011 / 19 / 2025 of implant data (e.g., an implant model) relative to bone data (e.g., a bone model) that will stabilize the knee in mid-flexion. Mid-flexion instability is a common complaint from patients post-operatively and surgeons currently have a difficult time planning the placement of the implant that avoids such mid-flexion instability.

[0101] It should be noted that the figures and all text and concepts contained in the figures are considered to be included in this detailed description as part of the specification and disclosure of this patent application.

[0102] It should be noted that some or all features of certain embodiments may be aspirational (e.g., contemplated or intended for future or optional implementation) notwithstanding any description using past tense or present tense wording (e.g., a feature was or is or does or provides something, which does not necessarily mean that the feature has already been implemented or ever will be implemented). Similarly, some or all performance information (e.g., that a particular embodiment will produce or provide a particular performance level or outcome) may be aspirational or anticipated as opposed to being already tested or proven.

[0103] Various embodiments of the invention may be implemented at least in part in any conventional computer programming language. For example, some embodiments may be implemented in a procedural programming language (e.g., “C”), or in an object-oriented programming language (e.g., “C++”). Other embodiments of the invention may be implemented as a pre-configured, stand-alone hardware element and / or as preprogrammed hardware elements (e.g., application specific integrated circuits, FPGAs, and digital signal processors), or other related components.

[0104] In alternative embodiments, the disclosed apparatus and methods (e.g., as in any flow charts or logic flows described above) may be implemented as a computer program product for use with a computer system. Such implementation may include a series of computer instructions fixed on a tangible, non-transitory medium, such as a computer readable medium (e.g., a diskette, CD-ROM, ROM, or fixed disk). The series of computer instructions can embody all or part of the functionality previously described herein with respect to the system.

[0105] Those skilled in the art should appreciate that such computer instructions can be written in a number of programming languages for use with many computer architectures or operating systems. Furthermore, such instructions may be stored in any memory device, such as a tangible, non-transitory semiconductor, magnetic, optical or other memory device,125520-10402-762494011 / 19 / 2025 and may be transmitted using any communications technology, such as optical, infrared, RF / microwave, or other transmission technologies over any appropriate medium, e.g., wired (e.g., wire, coaxial cable, fiber optic cable, etc.) or wireless (e.g., through air or space).

[0106] Among other ways, such a computer program product may be distributed as a removable medium with accompanying printed or electronic documentation (e.g., shrink wrapped software), preloaded with a computer system (e.g., on system ROM or fixed disk), or distributed from a server or electronic bulletin board over the network (e.g., the Internet or World Wide Web). In fact, some embodiments may be implemented in a software-as-a-service model (“SAAS”) or cloud computing model. Of course, some embodiments of the invention may be implemented as a combination of both software (e.g., a computer program product) and hardware. Still other embodiments of the invention are implemented as entirely hardware, or entirely software.

[0107] Computer program logic implementing all or part of the functionality previously described herein may be executed at different times on a single processor (e.g., concurrently) or may be executed at the same or different times on multiple processors and may run under a single operating system process / thread or under different operating system processes / threads. Thus, the term “computer process” refers generally to the execution of a set of computer program instructions regardless of whether different computer processes are executed on the same or different processors and regardless of whether different computer processes run under the same operating system process / thread or different operating system processes / threads. Software systems may be implemented using various architectures such as a monolithic architecture or a microservices architecture.

[0108] It should be noted that terms such as “computer” or “computing system” or “communication system” may be used herein to describe devices or systems that may be used in certain embodiments of the present invention and should not be construed to limit the present invention to any particular device or system type unless the context otherwise requires. Such devices or systems typically include one or more network interfaces for communicating over a communication network and at least one processor (e.g., a microprocessor with memory and other peripherals and / or application-specific hardware) configured accordingly to perform device or system functions. Communication networks generally may include public and / or private networks; may include local-area, wide-area, metropolitan-area, storage, and / or other types of networks; and may employ communication technologies including, but in no way limited to, analog technologies, digital technologies, optical technologies, wireless125520-10402-762494011 / 19 / 2025 technologies (e.g., Bluetooth, WiFi, cellular, etc.), networking technologies, and internetworking technologies.

[0109] It should also be noted that devices and systems may use communication protocols and messages (e.g., messages created, transmitted, received, stored, and / or processed by the device or system), and such messages may be conveyed by a communication network or medium. Unless the context otherwise requires, the present invention should not be construed as being limited to any particular communication message type, communication message format, or communication protocol. Thus, a communication message generally may include, without limitation, a frame, packet, datagram, user datagram, cell, or other type of communication message. Unless the context requires otherwise, references to specific communication protocols are exemplary, and it should be understood that alternative embodiments may, as appropriate, employ variations of such communication protocols (e.g., modifications or extensions of the protocol that may be made from time-to-time) or other protocols either known or developed in the future.

[0110] It should also be noted that logic flows may be described herein to demonstrate various aspects of the invention, and should not be construed to limit the present invention to any particular logic flow or logic implementation. The described logic may be partitioned into different logic blocks (e.g., programs, modules, functions, or subroutines) without changing the overall results or otherwise departing from the true scope of the invention. Often times, logic elements may be added, modified, omitted, performed in a different order, or implemented using different logic constructs (e.g., logic gates, looping primitives, conditional logic, and other logic constructs) without changing the overall results or otherwise departing from the true scope of the invention.

[0111] The present invention may be embodied in many different forms, including, but in no way limited to, computer program logic for use with a processor (e.g., a microprocessor, microcontroller, digital signal processor, or general purpose computer), programmable logic for use with a programmable logic device (e.g., a Field Programmable Gate Array (FPGA) or other PLD), discrete components, integrated circuitry (e.g., an Application Specific Integrated Circuit (ASIC)), or any other means including any combination thereof. Computer program logic implementing some or all of the described functionality is typically implemented as a set of computer program instructions that is converted into a computer executable form, stored as such in a computer readable medium, and executed by one or more processors optionally under the control of an operating system. Hardware-based logic implementing some or all of the125520-10402-762494011 / 19 / 2025 described functionality may be implemented using one or more appropriately configured FPGAs or other programmable logic devices.

[0112] Computer program logic implementing all or part of the functionality previously described herein may be embodied in various forms, including, but in no way limited to, a source code form, a computer executable form, and various intermediate forms (e.g., forms generated by an assembler, compiler, linker, or locator). Source code may include a series of computer program instructions implemented in any of various programming languages (e.g., an object code, an assembly language, or a high-level language such as Fortran, C, C++, JAVA, Python, or HTML) for use with various operating systems or operating environments. The source code may define and use various data structures and communication messages. The source code may be in a computer executable form (e.g., via an interpreter), or the source code may be converted (e.g., via a translator, assembler, or compiler) into a computer executable form.

[0113] Computer program logic implementing all or part of the functionality previously described herein may be executed at different times on a single processor (e.g., concurrently) or may be executed at the same or different times on multiple processors and may run under a single operating system process / thread or under different operating system processes / threads. Thus, the term “computer process” refers generally to the execution of a set of computer program instructions regardless of whether different computer processes are executed on the same or different processors and regardless of whether different computer processes run under the same operating system process / thread or different operating system processes / threads.

[0114] The computer program may be fixed in any form (e.g., source code form, computer executable form, or an intermediate form) either permanently or transitorily in a tangible storage medium, such as a semiconductor memory device (e.g., a RAM, ROM, PROM, EEPROM, or Flash-Programmable RAM), a magnetic memory device (e.g., a diskette or fixed disk), an optical memory device (e.g., a CD-ROM), a PC card (e.g., PCMCIA card), or other memory device. The computer program may be fixed in any form in a signal that is transmittable to a computer using any of various communication technologies, including, but in no way limited to, analog technologies, digital technologies, optical technologies, wireless technologies (e.g., Bluetooth), networking technologies, and internetworking technologies. The computer program may be distributed in any form as a removable storage medium with accompanying printed or electronic documentation (e.g., shrink wrapped software), preloaded with a computer system (e.g., on system ROM or fixed disk), or distributed from a server or125520-10402-762494011 / 19 / 2025 electronic bulletin board over the communication system (e.g., the Internet or World Wide Web).

[0115]

[0063] Hardware logic (including programmable logic for use with a programmable logic device) implementing all or part of the functionality previously described herein may be designed using traditional manual methods, or may be designed, captured, simulated, or documented electronically using various tools, such as Computer Aided Design (CAD), a hardware description language (e.g., VHDL or AHDL), or a PLD programming language (e g., PALASM, ABEL, or CUPL).

[0116] Programmable logic may be fixed either permanently or transitorily in a tangible storage medium, such as a semiconductor memory device (e.g., a RAM, ROM, PROM, EEPROM, or Flash-Programmable RAM), a magnetic memory device (e.g., a diskette or fixed disk), an optical memory device (e.g., a CD-ROM), or other memory device. The programmable logic may be fixed in a signal that is transmittable to a computer using any of various communication technologies, including, but in no way limited to, analog technologies, digital technologies, optical technologies, wireless technologies (e.g., Bluetooth), networking technologies, and internetworking technologies. The programmable logic may be distributed as a removable storage medium with accompanying printed or electronic documentation (e.g., shrink wrapped software), preloaded with a computer system (e.g., on system ROM or fixed disk), or distributed from a server or electronic bulletin board over the communication system (e.g., the Internet or World Wide Web). Of course, some embodiments of the invention may be implemented as a combination of both software (e.g., a computer program product) and hardware. Still other embodiments of the invention are implemented as entirely hardware, or entirely software.

[0117] While the invention has been particularly shown and described with reference to specific embodiments, it will be understood by persons of ordinary skill in the art that various changes in form and detail may be made without departing from the spirit and scope of the invention as defined by the appended clauses. While some of these embodiments have been described in the claims by process steps, an apparatus comprising a computer capable of executing the process steps is also included in the present invention. Likewise, a computer program product comprising a tangible, non-transitory computer readable medium having embodied therein computer executable instructions for executing the process steps is included in the present invention. Data signals embodying computer program instructions and / or messages received or transmitted over a communication system are also included in the present125520-10402-762494011 / 19 / 2025 invention. Unless the context requires otherwise, the various functions and features described herein can be used in combination even if disclosed or claimed individually. Thus, for example, it is contemplated that dependent claims included below could be rewritten into multiple dependent form to depend from the base claim and an intervening claim(s).

[0118] Importantly, it should be noted that embodiments of the present invention may employ conventional components such as conventional computers (e.g., off-the-shelf PCs, mainframes, microprocessors), conventional programmable logic devices (e.g., off-the shelf FPGAs or PLDs), or conventional hardware components (e.g., off-the-shelf ASICs or discrete hardware components) which, when programmed or configured to perform the non- conventional methods described herein, produce non-conventional devices or systems. Thus, there is nothing conventional about the inventions described herein because even when embodiments are implemented using conventional components, the resulting devices and systems are necessarily non-conventional because, absent special programming or configuration, the conventional components do not inherently perform the described non- conventional functions.

[0119] The activities described and claimed herein provide technological solutions to problems that arise squarely in the realm of technology. These solutions as a whole are not well-understood, routine, or conventional and in any case provide practical applications that transform and improve computers and computer routing systems.

[0120] While various inventive embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and / or structures for performing the function and / or obtaining the results and / or one or more of the advantages described herein, and each of such variations and / or modifications is deemed to be within the scope of the inventive embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and / or configurations will depend upon the specific application or applications for which the inventive teachings is / are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific inventive embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, inventive embodiments may be practiced otherwise than as specifically described and claimed. Inventive embodiments of the present disclosure are125520-10402-762494011 / 19 / 2025 directed to each individual feature, system, article, material, kit, and / or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and / or methods, if such features, systems, articles, materials, kits, and / or methods are not mutually inconsistent, is included within the inventive scope of the present disclosure.

[0121] Various inventive concepts may be embodied as one or more methods, of which examples have been provided. The acts performed as part of the method may be ordered in any suitable way. Accordingly, embodiments may be constructed in which acts are performed in an order different than illustrated, which may include performing some acts simultaneously, even though shown as sequential acts in illustrative embodiments.

[0122] All definitions, as defined and used herein, should be understood to control over dictionary definitions, definitions in documents incorporated by reference, and / or ordinary meanings of the defined terms.

[0123] The indefinite articles “a” and “an,” as used herein in the specification and in the claims, unless clearly indicated to the contrary, should be understood to mean “at least one.”

[0124] The phrase “and / or,” as used herein in the specification and in the claims, should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Multiple elements listed with “and / or” should be construed in the same fashion, i.e., “one or more” of the elements so conjoined. Other elements may optionally be present other than the elements specifically identified by the “and / or” clause, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, a reference to “A and / or B”, when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A only (optionally including elements other than B); in another embodiment, to B only (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

[0125] As used herein in the specification and in the claims, “or” should be understood to have the same meaning as “and / or” as defined above. For example, when separating items in a list, “or” or “and / or” shall be interpreted as being inclusive, i.e., the inclusion of at least one, but also including more than one, of a number or list of elements, and, optionally, additional unlisted items. Only terms clearly indicated to the contrary, such as “only one of’ or “exactly one of,” or, when used in the claims, “consisting of,” will refer to the inclusion of exactly one element of a number or list of elements. In general, the term “or” as used herein shall only be interpreted as indicating exclusive alternatives (i.e., “one or the other but not125520-10402-762494011 / 19 / 2025 both”) when preceded by terms of exclusivity, such as “either,” “one of,” “only one of,” or “exactly one of.” “Consisting essentially of,” when used in the claims, shall have its ordinary meaning as used in the field of patent law.

[0126] As used herein in the specification and in the claims, the phrase “at least one,” in reference to a list of one or more elements, should be understood to mean at least one element selected from any one or more of the elements in the list of elements, but not necessarily including at least one of each and every element specifically listed within the list of elements and not excluding any combinations of elements in the list of elements. This definition also allows that elements may optionally be present other than the elements specifically identified within the list of elements to which the phrase “at least one” refers, whether related or unrelated to those elements specifically identified. Thus, as a non-limiting example, “at least one of A and B” (or, equivalently, “at least one of A or B,” or, equivalently “at least one of A and / or B”) can refer, in one embodiment, to at least one, optionally including more than one, A, with no B present (and optionally including elements other than B); in another embodiment, to at least one, optionally including more than one, B, with no A present (and optionally including elements other than A); in yet another embodiment, to at least one, optionally including more than one, A, and at least one, optionally including more than one, B (and optionally including other elements); etc.

[0127] As used herein in the specification and in the claims, all transitional phrases such as “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” “holding,” “composed of,” and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases “consisting of’ and “consisting essentially of’ shall be closed or semi-closed transitional phrases, respectively, as set forth in the United States Patent Office Manual of Patent Examining Procedures, Section 2111.03.

[0128] Although the above discussion discloses various exemplary embodiments of the invention, it should be apparent that those skilled in the art can make various modifications that will achieve some of the advantages of the invention without departing from the true scope of the invention. Any references to the “invention” are intended to refer to exemplary embodiments of the invention and should not be construed to refer to all embodiments of the invention unless the context otherwise requires. The described embodiments are to be considered in all respects only as illustrative and not restrictive.

Claims

125520-10402-762494011 / 19 / 2025CLAIMSWhat is claimed is:

1. A system, comprising: a force measurement device, comprising: at least one paddle configured for placement between the femur and tibia and including at least one force sensing element for sensing forces associated with the femur or tibia; and a communication system configured to convey force information derived from the force sensing element; and a computing system configured to receive the force information and automatically record a separation distance between a point or region associated with the femur and a point or region associated with the tibia when the force information satisfies a predetermined parameter.

2. The system of claim 1, wherein the at least one paddle comprises: a single paddle configured to traverse both the medial femoral condyle and the lateral femoral condyle when the force measurement device is positioned in the knee, wherein at least one medial force sensing element is positioned on a medial side of the paddle and at least one lateral force sensing element is positioned on a lateral side of the paddle.

3. The system of claim 2, where: the at least one medial force sensing element comprises at least a first medial force sensing element positioned on a femur-facing side of the paddle and at least a second medial force sensing element positioned on a tibia-facing side of the paddle; and the at least one lateral force sensing element comprises at least a first lateral force sensing element positioned on a femur-facing side of the paddle and at least a second lateral force sensor positioned on a tibia-facing side of the paddle.

4. The system of claim 2, wherein each of the medial and lateral sides of the paddle are concave to approximately match the concave shape of the femoral condyles.

5. The system of claim 1, wherein the at least one paddle comprises: a medial paddle including the at least one medial force sensing element; and125520-10402-762494011 / 19 / 2025 a lateral paddle including the at least one lateral force sensing element.

6. The system of claim 5, wherein: the at least one medial force sensing element comprises at least a first medial force sensing element positioned on a femur-facing side of the medial paddle and at least a second medial force sensing element positioned on a tibia-facing side of the medial paddle; and the at least one lateral force sensor comprises at least a first lateral force sensing element positioned on the femur-facing side of the lateral paddle and at least a second lateral force sensor positioned on a tibia-facing side of the lateral paddle.

7. The system of claim 5, wherein each of the medial and lateral paddles are concave to approximately match the concave shape of the femoral condyles.

8. The system of claim 5, wherein the medial paddle includes a top paddle portion and a bottom paddle portion, wherein the distance between the top and bottom paddle portions is adjustable to change the overall thickness of the medial paddle.

9. The system of claim 8, wherein the at least one medial force sensing element comprises at least a first medial force sensing element positioned on a femur-facing side of the top paddle portion and at least a second medial force sensing element positioned on a tibia-facing side of the bottom paddle portion.

10. The system of claim 5, wherein the lateral paddle includes a top paddle portion and a bottom paddle portion, wherein the distance between the top and bottom paddle portions is adjustable to change the overall thickness of the lateral paddle.

11. The system of claim 10, wherein the at least one lateral force sensor comprises at least a first lateral force sensing element positioned on a femur-facing side of the top paddle portion and at least a second lateral force sensor positioned on a tibia-facing side of the bottom paddle portion.

12. The system of any one of claims 1-11, wherein the force sensor is a torque sensor.125520-10402-762494011 / 19 / 202513. The system of claim 12, wherein the communication system is a wired communication system.

14. The system of claim 12, wherein the communication system is a wireless communication system.

15. The system of claim 12, wherein the communication system is an optical light communication system including at least one light source that is controlled to produce lightbased communication signals.

16. The system of claim 15, wherein the at least one light source comprises at least one LED.

17. The system of claim 1, wherein the predetermined parameter is a measured force reaching a threshold force.

18. The system of claim 1, wherein the predetermined parameter is input to the system by a user.

19. The system of claim 1, wherein the point or region associated with the femur is at least one of: (i) a point or region located on a surface of a femoral implant model, wherein the femoral implant model is positioned relative to a femoral bone model at a planned location; (ii) a point or region located on a surface of the femoral bone model; (iii) a point or region located at a planned location for forming a cut surface on the femur; or (iv) a point or region located on a cut surface formed on the femur.

20. The system of claim 1, wherein the point or region associated with the tibia is at least one of: (i) a point or region located on a surface of a tibia implant model, wherein the tibia implant model is positioned relative to a tibia bone model at a planned location; (ii) a point or region located on a surface of the tibia bone model; (iii) a point or region located at a planned location for forming a cut surface on the tibia; or (iv) a point ore region located on a cut surface formed on the tibia.125520-10402-762494011 / 19 / 202521. The system of claim 1, further comprising a tracking system for tracking movement of a femoral tracking array affixed to the femur and a tibial tracking array affixed to the tibia.

22. The system of claim 21, wherein the computing system is configured to map a location of a femoral bone model relative to a location of the femur based on: (i) registration data between the femoral bone model and the femur; and (ii) a tracked location of the femoral tracking array.

23. The system of claim 22, wherein the computing system is further configured to map a location of a tibia bone model relative to a location of the tibia based on: (i) registration data between the tibia bone model and the tibia; and (ii) a tracked location of the tibia tracking array.

24. The system of claims 23, wherein the computing system is further configured to calculate separation distances between the point or region associated with the femur and the point or region associated with the tibia using the mapped locations of the femoral bone model and the mapped locations of the tibia bone model.

25. The system of claim 1, wherein the force information comprises at least one of: static forces, dynamic forces, complex forces, absolute forces, relative forces, force vectors, force profiles, torques, pressures, and any combination thereof.

26. The system of claim 25, wherein the predetermined parameter comprises at least one of: a threshold force, a threshold torque, a threshold pressure, a threshold force in one or more specific degrees of freedom, a pattern of complex forces, a pattern of dynamic forces, a predefined profile of forces, a pre-defined surface geometry of the bone based on the measured forces, a pre-defined heatmap pattern of forces, and any combination thereof.

27. The system of claim 1, wherein the force information comprises a measured force and the predetermined parameter comprises a threshold force, wherein the computing system automatically records the separation distance when the measured force reaches a threshold force.

28. A system for balancing a knee of a patient, comprising:125520-10402-762494011 / 19 / 2025 a force measurement device configured to measure forces between a femoral bone and a tibia bone as a force is applied to the knee; and a computing system configured to: receive a measured force from the force measurement device; normalize the measured force; identify a separation distance corresponding to the normalized force, wherein the separation distance is a distance between a point or region associated with the femur and a point or region associated with tibia, and wherein the identified separation distance is substantially the same over a range of forces measured by the force measurement device; and output the identified separation distance.

29. The system of claim 28, wherein the computing system is further configured to receive or compute patient characteristic data, wherein at least one of the normalized measured force or identified separation distance is adjusted based on the patient characteristic data.

30. The system of claim 29, wherein the patient characteristic data comprises a thickness of a ligament.

31. The system of claim 30, wherein the thickness of the ligament is determined based on a diameter of a ligament attachment point.

32. The system of claim 31, wherein the diameter of the ligament attachment point is determined using a volume rendering of the femur or tibia.

33. The system of claim 32, wherein the volume rendering is derived from imaging data.

34. The system of claim 29, wherein the patient characteristic data comprises at least one of a patient’s weight, height, gender, age, or disease severity.

35. The system of claim 28, wherein the normalization model is at least partially built using experimental data.125520-10402-762494011 / 19 / 202536. The system of claim 28, wherein the normalization model is at least partially built using machine learning.

37. The system of claim 28, wherein the point or region associated with the femur is at least one of: (i) a point or region located on a surface of a femoral implant model, wherein the femoral implant model is positioned relative to a femoral bone model at a planned location; (ii) a point or region located on a surface of the femoral bone model; (iii) a point or region located at a planned location for forming a cut surface on the femur; or (iv) a point or region located on a cut surface formed on the femur.

38. The system of claim 28, wherein the point or region associated with the tibia is at least one of: (i) a point or region located on a surface of a tibia implant model, wherein the tibia implant model is positioned relative to a tibia bone model at a planned location; (ii) a point or region located on a surface of the tibia bone model; (iii) a point or region located at a planned location for forming a cut surface on the tibia; or (iv) a point ore region located on a cut surface formed on the tibia.

39. The system of claim 28, further comprising a tracking system for tracking movement of a femoral tracking array affixed to the femur and a tibial tracking array affixed to the tibia.

40. The system of claim 39, wherein the computing system is configured to map a location of a femoral bone model relative to a location of the femur based on: (i) registration data between the femoral bone model and the femur; and (ii) a tracked location of the femoral tracking array.

41. The system of claim 40, wherein the computing system is further configured to map a location of a tibia bone model relative to a location of the tibia based on: (i) registration data between the tibia bone model and the tibia; and (ii) a tracked location of the tibia tracking array.

42. The system of claims 41, wherein the computing system is further configured to calculate separation distances between the point or region associated with the femur and the point or region associated with the tibia using the mapped locations of the femoral bone model and the mapped locations of the tibia bone model.125520-10402-762494011 / 19 / 202543. The system of claim 28, wherein the force measurement device comprises: at least one paddle configured for placement between the femur and tibia and including at least one force sensing element for sensing forces associated with the femur or tibia; and a communication system configured to convey force information derived from the force sensing element.

44. The system of claim 43, wherein the at least one paddle comprises: a single paddle configured to traverse both the medial femoral condyle and the lateral femoral condyle when the force measurement device is positioned in the knee, wherein at least one medial force sensing element is positioned on a medial side of the paddle and at least one lateral force sensing element is positioned on a lateral side of the paddle.

45. The system of claim 44, where: the at least one medial force sensing element comprises at least a first medial force sensing element positioned on a femur-facing side of the paddle and at least a second medial force sensing element positioned on a tibia-facing side of the paddle; and the at least one lateral force sensing element comprises at least a first lateral force sensing element positioned on a femur-facing side of the paddle and at least a second lateral force sensor positioned on a tibia-facing side of the paddle.

46. The system of claim 44, wherein each of the medial and lateral sides of the paddle are concave to approximately match the concave shape of the femoral condyles.

47. The system of claim 43, wherein the at least one paddle comprises: a medial paddle including the at least one medial force sensing element; and a lateral paddle including the at least one lateral force sensing element.

48. The system of claim 47, wherein: the at least one medial force sensing element comprises at least a first medial force sensing element positioned on a femur-facing side of the medial paddle and at least a second medial force sensing element positioned on a tibia-facing side of the medial paddle; and125520-10402-762494011 / 19 / 2025 the at least one lateral force sensor comprises at least a first lateral force sensing element positioned on the femur-facing side of the lateral paddle and at least a second lateral force sensor positioned on a tibia-facing side of the lateral paddle.

49. The system of claim 47, wherein each of the medial and lateral paddles are concave to approximately match the concave shape of the femoral condyles.

50. The system of claim 47, wherein the medial paddle includes a top paddle portion and a bottom paddle portion, wherein the distance between the top and bottom paddle portions is adjustable to change the overall thickness of the medial paddle.

51. The system of claim 50, wherein the at least one medial force sensing element comprises at least a first medial force sensing element positioned on a femur-facing side of the top paddle portion and at least a second medial force sensing element positioned on a tibiafacing side of the bottom paddle portion.

52. The system of claim 47, wherein the lateral paddle includes a top paddle portion and a bottom paddle portion, wherein the distance between the top and bottom paddle portions is adjustable to change the overall thickness of the lateral paddle.

53. The system of claim 52, wherein the at least one lateral force sensor comprises at least a first lateral force sensing element positioned on a femur-facing side of the top paddle portion and at least a second lateral force sensor positioned on a tibia-facing side of the bottom paddle portion.

54. The system of any one of claims 43-53, wherein the force sensor is a torque sensor.

55. The system of claim 54, wherein the communication system is a wired communication system.

56. The system of claim 54, wherein the communication system is a wireless communication system.125520-10402-762494011 / 19 / 202557. The system of claim 54, wherein the communication system is an optical light communication system including at least one light source that is controlled to produce lightbased communication signals.

58. The system of claim 57, wherein the at least one light source comprises at least one LED.

59. A method for balancing a knee of a patient, comprising: providing a force measurement device, comprising: at least one paddle configured for placement between the femur and tibia and including at least one force sensing element for sensing forces associated with the femur or tibia; and a communication system configured to convey force information derived from the force sensing element; receiving, by a computing system, the force information from the force measurement device; and automatically recording, by the computing system, a separation distance between a point or region associated with the femur and a point or region associated with the tibia when the force information satisfies a predetermined parameter.

60. A method for balancing a knee of a patient, comprising: providing a force measurement device configured to measure forces between a femoral bone and a tibia bone as a force is applied to the knee; receiving, by a computing system, a measured force from the force measurement device; normalizing the measured force by the computing system; identifying, by the computing system, a separation distance corresponding to the normalized force, wherein the separation distance is a distance between a point or region associated with the femur and a point or region associated with tibia, and wherein the identified separation distance is substantially the same over a range of forces measured by the force measurement device; and output the identified separation distance by the computing system.125520-10402-762494011 / 19 / 202561. A force measurement device for balancing a knee of a patient, comprising: at least one paddle configured for placement between the femur and tibia and including at least one force sensing element for sensing forces associated with the femur or tibia; and a communication system configured to convey force information derived from the force sensing element.

62. The device of claim 61, wherein the at least one paddle comprises: a single paddle configured to traverse both the medial femoral condyle and the lateral femoral condyle when the force measurement device is positioned in the knee, wherein at least one medial force sensing element is positioned on a medial side of the paddle and at least one lateral force sensing element is positioned on a lateral side of the paddle.

63. The device of claim 62, where: the at least one medial force sensing element comprises at least a first medial force sensing element positioned on a femur-facing side of the paddle and at least a second medial force sensing element positioned on a tibia-facing side of the paddle; and the at least one lateral force sensing element comprises at least a first lateral force sensing element positioned on a femur-facing side of the paddle and at least a second lateral force sensor positioned on a tibia-facing side of the paddle.

64. The device of claim 62, wherein each of the medial and lateral sides of the paddle are concave to approximately match the concave shape of the femoral condyles.

65. The device of claim 61, wherein the at least one paddle comprises: a medial paddle including the at least one medial force sensing element; and a lateral paddle including the at least one lateral force sensing element.

66. The device of claim 65, wherein: the at least one medial force sensing element comprises at least a first medial force sensing element positioned on a femur-facing side of the medial paddle and at least a second medial force sensing element positioned on a tibia-facing side of the medial paddle; and125520-10402-762494011 / 19 / 2025 the at least one lateral force sensor comprises at least a first lateral force sensing element positioned on the femur-facing side of the lateral paddle and at least a second lateral force sensor positioned on a tibia-facing side of the lateral paddle.

67. The device of claim 65, wherein each of the medial and lateral paddles are concave to approximately match the concave shape of the femoral condyles.

68. The device of claim 65, wherein the medial paddle includes a top paddle portion and a bottom paddle portion, wherein the distance between the top and bottom paddle portions is adjustable to change the overall thickness of the medial paddle.

69. The device of claim 68, wherein the at least one medial force sensing element comprises at least a first medial force sensing element positioned on a femur-facing side of the top paddle portion and at least a second medial force sensing element positioned on a tibia-facing side of the bottom paddle portion.

70. The device of claim 65, wherein the lateral paddle includes a top paddle portion and a bottom paddle portion, wherein the distance between the top and bottom paddle portions is adjustable to change the overall thickness of the lateral paddle.

71. The device of claim 70, wherein the at least one lateral force sensor comprises at least a first lateral force sensing element positioned on a femur-facing side of the top paddle portion and at least a second lateral force sensor positioned on a tibia-facing side of the bottom paddle portion.

72. The device of any one of claims 61-71, wherein the force sensor is a torque sensor.

73. The device of claim 72, wherein the communication system is a wired communication system.

74. The device of claim 72, wherein the communication system is a wireless communication system.125520-10402-762494011 / 19 / 202575. The device of claim 72, wherein the communication system is an optical light communication system including at least one light source that is controlled to produce lightbased communication signals.

76. The device of claim 75, wherein the at least one light source comprises at least one LED.

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