Patent Publication Number: US-11653907-B2

Title: Joint gap balancing lever and methods of use thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 16/837,543, filed Apr. 1, 2020, which claims the benefit of and priority to U.S. Provisional Application No. 62/845,577, filed May 9, 2019, the entire disclosure of which is incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     The present disclosure relates generally to surgical tools for use during planning and preparation of a joint replacement procedure, and more particularly to a joint gap balancing lever for use during joint distraction. 
     Over time, as a result of disease, injury, or longevity of use, bones of a joint may degenerate, resulting in pain and diminished functionality. To reduce pain and restore functionality, a joint replacement procedure may be necessary. Examples of such procedures may be total or partial knee arthroplasty, total hip arthroplasty, or knee or hip resurfacing. In these procedures, portions of a patient&#39;s joint are replaced with artificial components. Particularly, a surgeon uses a surgical cutting tool to remove portions of bone to prepare the bone to receive a prosthetic device. Prior to resection of the bone, the surgeon plans bone preparation specific to the patient&#39;s anatomy, size, current state of the target joint, and several other factors in order to determine the portions of the bone that will be removed and replaced by one or more prosthetic components, as well as to determine proper positioning of the one or more prosthetic components. 
     One step of surgical planning for a partial knee resurfacing procedure involves a knee joint distraction, that is, forced separation of the distal femur from the proximal tibia. For partial knee resurfacing, this is intended to correct knee joint deformity and cause proper re-tensioning of the ligaments of the knee to determine a desired, post-procedure joint construction. In one exemplary method, prior to resection and prior to a creating a final implant plan, the knee joint deformity is corrected at multiple flexion positions or flexion angles by distracting the joint. An instantaneous six degree-of-freedom (DOF) position (i.e. the pose) of the femur with respect to the six DOF position of the tibia is captured at each of the multiple flexion positions. Resection, implant positioning, and implant characteristics are then planned based on the gathered poses so as to maintain this preferred soft tissue balance. Once the bone is resected at this desired plan and the trials and/or implants are positioned in the joint, the desired joint balance should be achieved. 
     SUMMARY 
     One implementation of the present disclosure is a joint distraction device. The joint distraction device includes a lever body and a foot extending from a bottom surface of the lever body. The foot is coupled to the lever body via a hinge such that the lever body is rotatable relative to the foot. A first plate and a second plate extend from a distal portion of the lever body, and the first plate and the second plate are separated by a gap. Each of the first plate and the second plate include a stopper extending upwards from a top surface of the first plate and the second plate. A force measurement device is coupled to the bottom surface of the lever body and configured to measure a distraction force applied by the lever body at the foot during a joint distraction procedure in which a torque is applied at a proximal portion of the lever body. 
     Another implementation of the present disclosure is a method for performing joint distraction. The method includes moving a joint comprising a first bone and a second bone into a first flexion position and inserting a joint distraction device into a space between the first bone and the second bone. The joint distraction device includes a lever body and a foot extending from a bottom surface of the lever body. The foot is configured to contact the front surface of the second bone. The joint distraction device also includes a first plate and a second plate extending from a distal portion of the lever body, such that the first plate and the second plate are separated by a gap. Each of the first plate and the second plate include a stopper extending upwards from a top surface of the first plate and the second plate. The force measurement device is configured to measure a distraction force applied at the foot during a distraction procedure for a joint during which a force is applied at a proximal portion of the lever body. The method also includes applying the force to the proximal portion of the lever body to cause a torque on the joint distraction device, receiving feedback from the force measurement device related to the amount of distraction force being applied to the second bone at the foot, receiving feedback from a tracking system related to a position of the first bone and the second bone, and using the combination of the feedback from the force measurement device and the feedback from the tracking system to determine an optimal gap distance between the first and second bone. 
     This summary is illustrative only and is not intended to be in any way limiting. Other aspects, features, and advantages of the devices or processes described herein will become apparent in the detailed description set forth herein, taken in conjunction with the accompanying figures, wherein like reference numerals refer to like elements. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG.  1    is a perspective view of a joint gap balancing lever, according to an exemplary embodiment. 
         FIG.  2    is a top view of the joint gap balancing lever of  FIG.  1   , according to an exemplary embodiment. 
         FIG.  3    is a lateral side cross-sectional view of the joint gap balancing lever of  FIG.  1   , taken along a lengthwise median line, according to an exemplary embodiment. 
         FIG.  4    is a side view of the joint gap balancing lever in use during a distraction procedure, according to an exemplary embodiment. 
         FIG.  5    is a side view of the joint gap balancing lever in use during a distraction procedure following distraction, according to an exemplary embodiment. 
         FIG.  6    is one embodiment of a method for performing joint distraction using a joint gap balancing lever, according to an exemplary embodiment. 
         FIG.  7    is a surgical system with which a joint gap balancing lever may be used, according to an exemplary embodiment. 
         FIG.  8    is a side view of the joint gap balancing lever in use with the surgical system of  FIG.  7   , according to an exemplary embodiment. 
         FIG.  9    is a graph depicting the convergence point of the gap distance versus the force applied by the joint gap balancing lever, according to an exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Before turning to the figures, which illustrate the exemplary embodiments in detail, it should be understood that the application is not limited to the details or methodology set forth in the description or illustrated in the figures. It should also be understood that the terminology is for the purpose of description only and should not be regarded as limiting. 
     Referring to  FIGS.  1 - 3   , a joint distraction device is shown. In certain embodiments, the joint distraction device is a joint gap balancing lever device  10  (referred to herein as device  10 ). Though the present description will refer to the joint gap balancing lever as the device  10 , it is to be understood that the features disclosed herein may be used with and provided in a variety of distraction lever-type and gap-balancing devices, which are considered to be within the scope of the present disclosure. As shown in  FIGS.  1 - 3   , the various embodiments of device  10  include a lever body  12 , having a top surface  12   a  and a bottom surface  12   b . The lever body includes a proximal portion  14  and a distal portion  16 . A foot  18  extends from the bottom surface  12   b  of the lever body  12  at the distal portion  16 . Also at the distal portion  16 , the lever body  12  splits into two plates  20 , which are separated by a gap  22 . Extending upwards from the top surface  12   a  of each of the plates is a stopper  24 . In some embodiments, the distal portion  16  including the plates  20  of the lever body  12  is slightly curved to accommodate the non-planar surface of the bone. 
     The device  10  has a thin, narrow lever body  12  sized to be inserted into a joint space. In various embodiments, the lever body  12  is between 1.0 mm and 4.0 mm thick at the distal portion  16  at plates  20 . In certain embodiments, the lever body  12  is approximately 2.05 mm thick at the distal portion  16  at plates  20  and, in other embodiments, no more than approximately 3.50 mm thick. The width of the plates  20  is between 70.0 mm and 85.0 mm wide. In certain embodiments, the width of the plates  20  is approximately 81.0 mm wide to accommodate compartments of various sizes, and in a preferred embodiment, are approximately 74.0 mm wide. 
     The proximal portion  14  is configured to be gripped by a user during use of the device  10 . In some embodiments, the proximal portion  14  is shaped like a handle, with a slight curve downward toward the distal end. Although the proximal portion  14  is static in the embodiment shown in  FIGS.  1 - 3   , in some embodiments, the joint gap balancing lever has a rotatable proximal portion  14 . A rotatable proximal portion  14  allows for a reduction in the amount of torque working laterally during joint distraction. For example, when distracting the knee joint, the distraction force should be provided substantially parallel with the mechanical axis of the joint. However, the surgeon may not be able to achieve exact access and grip on the tool such that all forces are being applied in this direction. As a result, some torque may instead be applied sideways on the joint while also being applied in parallel with the mechanical axis. A rotatable proximal portion  14  may counteract some of the sideways torque applied by cooperating with the twisting that may occur on the handle when the force is applied at the proximal portion  14 . 
     The distal portion  16  is configured to transmit a force provided by the user at the proximal portion  14  to a bone of a joint. Referring now to  FIGS.  4 - 5   , the device  10  is shown in use, according to an exemplary embodiment. As shown in  FIGS.  4 - 5   , the foot  18  of the device  10  is configured to rest on a first bone (e.g., a longitudinal surface of a patient&#39;s tibia  26 ) and apply a force to a second bone (e.g., a femoral condyle  32  of a patient&#39;s femur  30 ). However, it should be understood that while the embodiments of the joint gap balancing lever are depicted and described herein and being used in a knee joint, the joint gap balancing lever may be used in any joint that is suitable for a joint distraction procedure. Resting the foot  18  on the longitudinal surface (such as a front facing surface) of the tibia  26  provides support for the device  10  as a torque is applied at the proximal portion  14 . The torque is then provided to the femur  30  through the plates  20  at the distal portion  16 , which are inserted between the tibia  26  and femur  30 . The provided torque causes distraction of the joint (e.g., separation of the first and second bones of the joint), which is shown in  FIG.  5    as a separation of the tibia  26  and the femur  30 . 
     Accordingly, the joint gap balancing lever according to various embodiments is dependent on the force applied to the bone at two known locations: the foot  18  and the plates  20 . To ensure that forces are being applied only at these two locations, the foot  18  projects from the bottom surface  12   b  of the device, while the plates  20  and corresponding stoppers  24  project from the top surface of the device  10 , such that the lever body  12  does not slide during the distraction procedure and contact is maintained between the bone and the plates  20 . 
     Referring first to the foot  18 , the foot  18  is designed to project from the bottom surface  12   b  of the lever body  12  to a distance sufficient to provide proper torque during use. As an example, the foot  18  is configured to press up against the longitudinal surface of the tibia  26  via a frontal face  34  of the foot  18 . In the embodiment shown in  FIG.  1   , the foot  18  comprises two prongs, such that there are two frontal faces  34  of the foot  18 . In other embodiments, the foot  18  comprises a single prong. The frontal face  34  of the foot  18  is configured to provide a greater surface in contact with the bone to minimization penetration into the bone, when such penetration would be detrimental or undesirable. As such, the frontal face  34  of the foot  18  is configured to abut a surface of the first bone, such that the frontal face  34  rests upon the surface of the first bone, rather than to penetrate into the first bone. The frontal face  34  of the foot  18  may include a plurality of grooves in order to prevent slipping and any other movement of the foot  18  relative to the first bone during a distraction procedure. In some embodiments, the foot  18  is coupled to the bottom surface  12   b  of lever body  12  via a hinge  36 . The hinge  36  allows the lever body  12  to pivot or rotate during a distraction procedure, and may be used to measure the torque applied to the proximal portion  14 . The lever body  12  is allowed to pivot via the hinge  36  relative to the foot  18  during a distraction procedure. Accordingly, the frontal face  34  of the foot  18  presses into the first bone, such as the longitudinal surface of a tibia  26 , when the torque is applied to the proximal portion  14  of the lever body  12 . 
     The joint gap balancing lever, such as device  10 , is configured to measure and provide output related to the distraction force applied to the bone of the joint during a distraction procedure. The distraction force is measured by a force measurement device  40 . In some embodiments, the force measurement device  40  is positioned between a back face  38  of the foot  18  and the bottom surface  12   b  of lever body  12 , such that the force measurement device  40  measures the force provided between the lever body  12  pressing into the back face  38  of the foot  18  when a force is applied to the lever body  12  to distract the joint. In some embodiments, the distraction force measured by the force measurement device is evaluated to perform joint gap balancing. For example, the distance between the first and second bones can be measured throughout the distraction procedure as a function of the distraction force measured by the force measurement device. In some embodiments, an optimal gap distance between the first and second bone, as further discussed below, can be determined based on the feedback from the force measurement device. As an example, the optimal gap distance can be determined by the juncture at which the force continues to rise while the measured gap remains static. 
     In some embodiments, the force measurement device is a force gauge. One or more force gauges may be coupled at the foot  18  of the lever body  12  and configured to receive an input voltage provided by a power source. In certain embodiments, the power source is a battery. The battery may be disposable, rechargeable, or take the form of a chargeable capacitor. As the electrical conductor of the force gauge measures the rise in force, the distraction lever elevates the joint. When torque is applied to distract the bones of the joint, the electrical resistance of the electrical conductor of the force gauge changes. Thus, from the measured electrical resistance of the force gauge(s), computed using the known or measured input voltage and measured output voltage, the amount of applied stress to distract the joint can be measured and the distraction force computed. A plurality of force gauges may be arranged and included in the foot  18  to form a load cell. The output of the load cell transducer can then be used to convert the force or stress determined by the force gauges into an electrical signal. 
     Other mechanisms or tools for measuring the distraction force applied by the joint gap balancing lever at the foot  18  include piezoelectric pressure sensors wherein a charge is generated when a piezoelectric crystal, or other suitable material, of the pressure sensor is stressed. The charge output, or the charge output converted to a voltage signal, for example, may be used to compute and indicate the distraction force being applied by the distraction lever. Similarly, stress to the lever body  12  to compute the distraction force applied at the foot  18  can be determined using optical sensors in a cantilever beam configuration. The optical sensors may include an array of optical fibers capable of providing computation of stress and strain by way of wavelength variations between the light source and a detector caused by modifications in the optical fiber body. Finally, a magnetic contact switch may be used to indicate the presence of a load being applied, or can be configured to indicate how much load is being applied. 
     Referring back to  FIGS.  1 - 3   , the plates  20  extend from the distal portion  16  of the lever body  12 . In the embodiments shown, there are two plates  20 . In other embodiments, a single plate  20  extends from the distal portion  16  of the lever body  12 . There is a gap  22  between the two plates  20 . In the embodiment shown, the plates  20  form a relatively flat surface, and have a slightly rounded shape towards the most distal portion. In some embodiments, the plates  20  are slightly curved to fit with the outer surface of the bone. In some embodiments, the plates  20  are specifically configured for a particular bone or the anatomy of a particular patient. The configuration of the plates  20  provides greater contact surface area for torque transmission efficiency as well as to reduce penetration of the bone being distracted. In some embodiments, the surface of the plates  20  have a plurality of grooves or other indents that are configured to minimize movement of the bone relative to the plates  20 . Other configurations of the plates  20  and the distal portion  16  are also used in accordance with additional embodiments of the present disclosure. 
     The plates  20  each comprise a stopper  24  extending vertically upwards from the top surface  12   a  of the plates  20  on the distal portion  16  of the lever body  12 . In the embodiment shown, the stoppers  24  each have a frontal face  28 . In some embodiments, the frontal face  28  is slightly concave. The frontal face  28  of the stoppers  24  is configured to abut a surface of the second bone, such as the femoral condoyle  32  of the femur  30 . In some embodiments, the stoppers  24  do not transmit a significant force to the second bone. Rather, the frontal face  28  of the stoppers  24  is configured to provide a resting spot for the second bone, and to prevent forward movement of the second bone during a distraction procedure or slippage of the device  10 . In some embodiments, the frontal face  28  of the stoppers  24  have a plurality of grooves or other indents that are further configured to prevent movement of the second bone relative to the stoppers  24 . The stoppers  24  of the plates  20  may further be configured to provide support and stability to the lever body  12  throughout the distraction procedure. 
     Referring to  FIG.  6   , a method  600  for performing gap balancing using a joint gap balancing lever is depicted, according to an exemplary embodiment. In step  602 , a joint, such as the knee joint including the tibia  26  and the femur  30 , is first moved into a first flexion position. For example, the first flexion position is full flexion, though any range of flexion may be used. 
     At step  604 , a joint gap balancing lever, such as device  10  according to the exemplary embodiments disclosed herein, is inserted into the space between the first and second bones of the joint. An external force is then applied to the proximal portion  14  of the lever body  12  to cause a torque on the joint gap balancing lever (step  606 ). As a result, in step  608  the user receives feedback related to the amount of distraction force being applied to the first or the second bone of the joint at the foot  18  of the joint gap balancing lever, as measured by a force measurement device  40 . Additionally, at step  608 , the user receives feedback related to the corresponding gap distance between the first bone and the second bone of the joint, such as the tibia  26  and the femur  30 . To measure the gap distance, the joint gap balancing lever may be used in conjunction with anatomy navigation systems and methods associated with a surgical system, such as those depicted in  FIG.  7    and described below. At step  610 , the user modifies, if necessary, the amount of distraction force applied to the proximal portion  14  of the lever body  12  in order to obtain an optimal gap distance between the first bone and the second bone of the joint for proper balancing of the soft tissue. In some embodiments, the optimal gap distance is correlated to amount of force applied to the proximal portion  14  of the lever body  12 . For example, as seen in  FIG.  9   , there is a point of convergence between the gap distance and the force applied. In some embodiments, this point of convergence corresponds to the optimal gap distance. 
     At step  612 , a pose of the first and second bones of the joint is captured at the optimal gap distance and using the corresponding force needed to achieve the optimal gap distance. Capturing the pose of the first bone and the second bones of the distracted and properly balanced joint assists with surgical planning to ultimately attain the desired, properly aligned joint post-resection and post-prosthetic implantation. 
     At step  614 , the joint is optionally moved to a second flexion position and may further be moved to any number of additional flexion positions as needed. In moving the joint to a subsequent flexion position, the user again receives feedback related to the amount of distraction force being applied at the foot  18  of the joint distraction lever and the gap distance between the first and second bone until the optimal gap distance is achieved, and the pose of the bones captured. 
     In various arrangements, these poses of the flexion position(s), with the distraction force to achieve optimal gap distance applied, represent the desired post-resection final position of the joint (e.g., the knee joint). Accordingly, bone resection, implant positioning, and implant characteristics are planned (e.g., using the computing system  720  described below) using the poses captured during the gap balancing process  600 . Once the bone is resected at this desired plan and the trials and/or implants are secured to the bone, the leg will ideally experience the proper balance through the range of motion. 
     The surgical system  700  depicted in  FIG.  7   , used in conjunction with the joint gap balancing lever  10 , is used, for example, to capture the poses of the bones of the joint, as well as others aspects of surgical planning.  FIG.  7    illustrates a surgical system  700  that includes a computing system  720 , a surgical tool such as haptic device  730 , and a tracking system  740 . In operation, the surgical system  700  enables comprehensive surgical planning, which may include performing distraction of a joint using the device  10  described herein. 
     Determining the gap distance between the first and second bones in step  608  and determining the pose of the first and second bones in step  612  may make use of the tracking system  740 . The tracking (or localizing) system  740  of the surgical system  700  is configured to determine a pose (i.e., position and orientation) of one or more objects during a surgical procedure to detect movement and capture poses of the object(s). For example, the tracking system  740  includes a detection device  741  that obtains a pose of an object with respect to a coordinate frame of reference of the detection device. As the object moves in the coordinate frame of reference, the detection device  741  tracks the pose of the object to detect (or enable the surgical system  700  to determine) movement of the object. Tracked objects include, for example, tools/instruments, patient anatomy, implants/prosthetic devices, and components of the surgical system  700 . Using pose data from the tracking system  740 , the surgical system  700  is also able to register, map, or associate coordinates in one space to those in another to achieve spatial alignment or correspondence (e.g., using a coordinate transformation process as is well known). Objects in physical space are registered to any suitable coordinate system, such as a coordinate system being used by a process running on the computer  721 . 
     For example, utilizing pose data from the tracking system  740 , the surgical system  700  is able to associate the physical anatomy with a representation of the anatomy (e.g., an image displayed on a display device  745 ). Based on tracked object and registration data, the surgical system  700  determines, for example, a spatial relationship between the image of the anatomy and the relevant anatomy. Additionally, by tracking the relevant anatomy, the surgical system  700  can compensate for and ascertain movement of the relevant anatomy during the surgical procedure, as needed for capturing the pose of the distracted joint at the flexion position. 
     Registration may include any known registration technique, such as, for example, image-to-image registration (e.g., monomodal registration where images of the same type or modality, such as fluoroscopic images or MR images, are registered and/or multimodal registration where images of different types or modalities, such as MM and CT, are registered); image-to-physical space registration (e.g., image-to-patient registration where a digital data set of a patient&#39;s anatomy obtained by conventional imaging techniques is registered with the patient&#39;s actual anatomy); and/or combined image-to-image and image-to-physical-space registration (e.g., registration of preoperative CT and Mill images to an intraoperative scene). 
     The tracking system  740  may also be used to track the anatomy and the device  10 , while applying the distraction force. By tracking the pose (i.e., position and orientation) and the movement of the device  10  and the bones of the joint, such as tibia  26  and femur  30 , the computing system  720  is able to determine the directional components of the force being produced. In addition to the forces acting along the mechanical axis of the bone being moved, the distraction force may also act in a lateral direction or other direction off-axis from the mechanical axis. Tracking of the objects used during a distraction procedure and determination of the directional components may allow for a determination of the amount of force that is off of the intended axis. This may help the surgeon adjust the application of force for more efficient load transmission and/or to reduce any injury or damage that may occur while applying distraction forces in directions that are off of the intended axis. 
     The tracking system  740  is any tracking system that enables the surgical system  700  to continually determine (or track) a pose of the relevant anatomy of the patient and a pose of the tool  735  (and/or the haptic device  730 ). For example, the tracking system  740  comprises a non-mechanical tracking system, a mechanical tracking system, or any combination of non-mechanical and mechanical tracking systems suitable for use in a surgical environment. 
     A mechanical tracking system relies on a physical connection between the detection device  741  and the tracked object. For example, a mechanical tracking system includes one or more mechanical arms that are coupled to the tracked object and to the detection device  741 . The detection device  741  detects the position and orientation of the object based on the movement of the tracked object that is sensed by the mechanical arm(s). 
     A non-mechanical tracking system includes, for example, an optical (or visual), magnetic, radio, or acoustic tracking system. Such systems include a detection device adapted to locate in a predefined coordinate space specially recognizable trackable elements (“trackers”) that are detectable by the detection device and that are either configured to be attached to the object to be tracked or are an inherent part of the object to be tracked. For example, a trackable element includes an array of markers having a unique geometric arrangement and, when attached to the tracked object (e.g., the femur  30  and tibia  26  of a patient), a known geometric relationship to the tracked object. These markers include any known marker, such as extrinsic markers (or fiducials) and/or intrinsic features of the tracked object. Extrinsic markers are artificial objects that are attached to the patient (e.g., markers affixed to skin, markers implanted in bone, stereotactic frames, etc.) and are designed to be visible to and accurately detectable by the detection device  741 . Intrinsic features are salient and accurately locatable portions of the tracked object that are sufficiently defined and identifiable to function as recognizable markers for the detection device  741  on their own (e.g., landmarks, outlines of anatomical structure, shapes, colors, or any other sufficiently recognizable visual indicator). 
     The markers may be located using any suitable detection method, such as, for example, optical, electromagnetic, radio, or acoustic methods as are well known. For example, an optical tracking system having a detection device  741  implemented as stationary stereo camera pair sensitive to infrared radiation may be used to track markers that emit infrared radiation either actively (e.g., as LEDs) or passively (e.g., spherical markers with surfaces that reflect infrared radiation). Similarly, a magnetic tracking system may include a stationary field generator that emits a spatially-varying magnetic field sensed by small coils integrated into the tracked object. 
     In the embodiment shown in  FIG.  7   , the tracking system  740  includes a non-mechanical tracking system. In this embodiment, the non-mechanical tracking system is an optical tracking system that includes an optical detection device  741  and at least one tracker, such as anatomy trackers  743 , configured to be disposed on, or incorporated into, a tracked object and detected by the detection device  741 . The trackers  743  are configured to be affixed to the tracked object in a secure and stable manner (e.g., to the tibia  26  and the femur  30 , as shown in  FIG.  7   ), and each tracker  743  includes an array of markers having a known geometric relationship to the tracked object. In some embodiments, such as shown in  FIG.  8   , the tracking system  740  comprises both a tibia tracker  802  and a femur tracker  804 . In some embodiments, the tibia tracker  802  and the femur tracker  804  are configured to track a gap distance  806  between the tibia  26  and femur  30  during a distraction procedure, as described further below.  FIG.  8    is a side view of the joint gap balancing lever in use with the surgical system  700 . 
     As described above, the markers may be active (e.g., LEDs) or passive (e.g., reflective spheres, a checkerboard pattern, etc.). In some arrangements, the markers have a unique geometry (e.g., a unique geometric arrangement of the markers) or, in the case of active, wired markers, a unique firing pattern. In operation, the detection device  741  detects the positions and orientations of the markers (e.g., including the unique geometry or firing pattern) and use a known geometric relationship to the tracked object enable the surgical system  700  to calculate a pose of the tracked object based on the positions of the markers. 
     As stated above, a virtual representation of the anatomy, such as the knee joint, can be displayed on display device  745 . In some embodiments, the display device  745  also displays the distraction force measurement obtained by a force measurement device of the joint gap balancing lever. For example, as described above, the device  10  communicates wirelessly (e.g., Bluetooth, RFID, etc.) or via a coupled connection with the surgical system  700  to provide the distraction force measurement for display on an external device, such as the display device  745 . Furthermore, as also described above, the device  10  may include a button in response to which the system  700  captures the pose of the joint using the tracking system  740  (e.g., because pressing the button causes the device  10  to transmit a command to the system  700  to capture the pose of the joint). The system  700  may further display pose information on the display device  745  and/or use the pose information to complete a surgical planning procedure. 
     Accordingly, in various embodiments, the computing system  720  is configured to acquire and use the data obtained during a joint distraction procedure, including pose information (e.g., captured in response to the user pressing a button on the device  10 ), to complete a surgical planning procedure. Thus, computing system  720  may capture and store the pose of the first and second bones of the joint based on information captured and provided by tracking system  740 . For example, the captured pose of the joint may be used to plan bone resection and prosthetic implant placement for proper joint balance and alignment. In some embodiments, the computing system  720  of surgical system  700  is further configured to define a surgical plan based on the captured pose(s) of the distracted joint. In some such embodiments, the surgical system  700  then implements the surgical plan, for example, by using the tracking system  740  to track the pose of a surgical tool relative to the patient&#39;s anatomy and providing haptic feedback through the haptic device  730  (e.g., based on a position and orientation of a surgical tool  735  relative a haptic boundary created during surgical planning). The haptic feedback provided by the haptic device  730  provides surgical guidance to a surgeon in order to keep the surgical tool  735  from deviating from the surgical plan created based on the joint distraction procedure and other aspects of surgical planning. 
     U.S. Pat. No. 8,010,180, titled “Haptic Guidance System and Method,” granted Aug. 30, 2011, which is hereby incorporated by reference herein in its entirety, describes an exemplary surgical system with which the presently described joint gap balancing lever may be used during a joint distraction procedure and for bone resection and implant planning. 
     In some embodiments, surgical system  700  is configured to determine an optimal gap distance between the first and second bones of the joint, such as the tibia  26  and the femur  30 . In some embodiments, the optimal gap distance corresponds to the maximum gap distance that can safely be achieved between the first and second bones. In some embodiments, the gap distance is determined by tibia tracker  802  and femur tracker  804 , which are configured to determine the gap distance between the tibia  26  and the femur  30 . In other embodiments, the optimal gap distance corresponds to the greatest gap distance that is obtained without exceeding a certain force limit. The force limit may be predetermined, or may be determined by a user based on the feedback from the force measurement devices used at the foot  18  of device  10 . As described above, tracking system  740  is configured to provide the location of the bones of the joint during the distraction procedure, which can be captured and stored via the computing system  720 . The display device  745  may be configured to display, in real time, the gap distance between the first and second bones throughout the distraction procedure along with the distraction force applied in order to achieve that gap distance. In some embodiments, the display device  745  provides an alert as to when the maximum gap distance has occurred. 
     Referring now to  FIG.  9   , an exemplary embodiment of a graph  900 , which may be displayed by display device  745 , is shown, where line  902  illustrates the gap distance as a function of the force applied. In the embodiment shown, the gap distance is measured in millimeters, and corresponds to the distance between the tibia  26  and the femur  30 . In some embodiments, the gap distance is measured by tracking system  740 . The force is measured in Newtons, and corresponds to the force measured by the force measurement device  40  at the foot  18  of device  10 . As illustrated in the graph  900 , the gap distance increases substantially or entirely linearly until the convergence point  904  is reached. In other words, the gap distance increases substantially uniformly with the force for a period of time, until the convergence point  904  is reached, after which the force continues to rise while the gap distance remains substantially stable. The convergence point  904  is dependent on a calibrated starting point for both the measured gap distance and the corresponding force. In some embodiments, the convergence point  904  is the point at which the maximum gap distance is achieved. In some embodiments, the maximum gap distance obtained at the convergence point  904  corresponds to the optimal gap distance as described above. Throughout the distraction procedure, the force at the convergence point  904  can be applied to the foot  18  of the device  10  in order to maintain the maximum gap distance without using excessive force. In some embodiments, the surgical system  700  alerts the user as to when the maximum gap distance has been achieved, which helps to prevent the user from applying unnecessary excessive force during distraction. In some embodiments, the force at the convergence point  904  is then be stored by the surgical system  700  for use in future surgical planning. In some embodiments, surgical system  700  is configured to provide an indication to a user, such as by display device  745 , as to when the force needed to achieve the maximum gap distance has been reached. 
     Various exemplary embodiments of the invention are described herein. Reference is made to these examples in a non-limiting sense. They are provided to illustrate more broadly applicable aspects of the invention. Various changes may be made to the invention described and equivalents may be substituted without departing from the true spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation, material, composition of matter, process, process act(s) or step(s) to the objective(s), spirit or scope of the present invention. Further, as will be appreciated by those with skill in the art that each of the individual variations described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several 
     The invention includes methods that may be performed using the subject devices. The methods may include the act of providing such a suitable device. Such provision may be performed by the end user. In other words, the “providing” act merely requires the end user obtain, access, approach, position, set-up, activate, power-up or otherwise act to provide the requisite device in the subject method. Methods recited herein may be carried out in any order of the recited events which is logically possible, as well as in the recited order of events. 
     Exemplary aspects of the invention, together with details regarding material selection and manufacture have been set forth above. As for other details of the present invention, these may be appreciated in connection with the above-referenced patents and publications as well as generally known or appreciated by those with skill in the art. The same may hold true with respect to method-based aspects of the invention in terms of additional acts as commonly or logically employed. 
     In addition, though the invention has been described in reference to several examples optionally incorporating various features, the invention is not to be limited to that which is described or indicated as contemplated with respect to each variation of the invention. Various changes may be made to the invention described and equivalents (whether recited herein or not included for the sake of some brevity) may be substituted without departing from the true spirit and scope of the invention. In addition, where a range of values is provided, it is understood that every intervening value, between the upper and lower limit of that range and any other stated or intervening value in that stated range, is encompassed within the invention.