Patent Publication Number: US-11660083-B2

Title: Force measuring joint distraction lever

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is a divisional of U.S. patent application Ser. No. 14/724,381, filed May 28, 2015, which claims the benefit of and priority to U.S. Provisional Patent Application No. 62/004,015, filed May 28, 2014 and titled “Force Measuring Joint Distraction Lever,” the entireties of which are incorporated by reference herein. 
    
    
     BACKGROUND 
     The present invention relates generally to the field of surgical tools for use during planning and preparation of a joint replacement procedure, and more particularly to a force measuring 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. For example, a common flexion position is near full extension where the surgeon applies a valgus torque to the tibia when the leg is at approximately 5-10 degrees of flexion. The valgus torque corrects the limb alignment deformity and returns the ligaments to a proper tension state. Another common flexion position is 90 degrees flexion. With these two poses, the knee joint is in the desired post-resection final position. After collection of poses, bone resection, implant positioning, and implant characteristics are planned so as to maintain this relative alignment by making the femoral and tibial components contact (or be slightly gapped to allow for some laxity). Once the bone is resected at this desired plan and the trials and/or implants are secured to the bone, the leg will then be in the pre-resected posed positions. 
     A first technique currently used to apply a joint distraction force includes manually applying a valgus torque (for a varus knee) to the tibia portion of a patient&#39;s leg to pivot the knee joint about the contralateral compartment (lateral compartment for a varus knee). Another technique includes applying a distraction force using a common surgical osteotome by levering the osteotome off the front of the tibia and lifting the femur vertically. Similarly, joint distraction may be performed by placing shim-like spoons or gap sticks between the femur and tibia, or by using laminar spreaders to create the distance between the femur and the tibia. 
     However, for each of these techniques, the “proper” joint distraction force is subjective, varies from surgeon-to-surgeon, and is difficult for surgeons to learn. In addition, for the first technique described above, applying a valgus torque to the tibia for any pose after 30 degrees flexion is extremely difficult because the femur tends to rotate about the femoral head. 
     Other types of distractors include spring-based, electromechanical, or hydraulic opposing plate spreaders. However, these tend to be large and complex, and due to their size generally require at least some bone to be removed first (provisional resection) to accommodate the device&#39;s opposing plates. Yet another device is a force sensing shim. However, like the shim-like spoons or gap sticks, this device generally requires iteratively inserting the device into the joint with various thicknesses until the desired force is achieved, making it time consuming and cumbersome. 
     SUMMARY 
     According to one aspect, the present disclosure is directed to a joint distraction lever, having a lever body having a handle portion and a working portion. The lever body includes a fulcrum extending from a bottom surface of the working portion of the lever body and a distal tip, wherein the distal tip is raised above a top surface of the working portion of the lever body. The joint distraction lever is configured to measure a distraction force applied at the distal tip during a distraction procedure when a torque is applied by an external force applied on the handle portion of the lever body. The joint distraction lever further includes an indicator configured to provide feedback related to the distraction force applied at the distal tip, as measured by the joint distraction lever. 
     According to another aspect, the present disclosure is directed to a method for performing joint distraction that includes moving a joint including a first bone and a second bone into a first flexion position and inserting a joint distraction lever into the space between the first bone and the second bone. The joint distraction lever includes a lever body having a handle portion and a working portion, a fulcrum extending from a bottom surface of the working portion of the lever body, and a distal tip, wherein the distal tip is raised above a top surface of the working portion of the lever body. The joint distraction lever further includes a force measurement device configured to measure a distraction force applied at the distal tip during a distraction procedure when a torque is applied by an external force applied on the handle portion of the lever body. The joint distraction lever further includes an indicator configured to demonstrate the distraction force applied at the distal tip, as measured by the joint distraction lever. The method further includes applying a force to the handle portion of the lever body of the joint distraction lever to cause a torque on the joint distraction lever and receiving feedback from the indicator related to the amount of distraction force being applied to the first bone at the distal tip. 
     According to another aspect, the present disclosure is directed to an instrumented osteotome including a lever body having a handle portion and a working portion. A fulcrum extends from a bottom surface of the working portion of the lever body and a distal tip is raised above a top surface of the working portion of the lever body. The osteotome further includes a strain gauge for measuring a stress on the lever body to determine a distraction force applied at the distal tip, and a power source for providing voltage to the strain gauge. The osteotome also includes a display electrically coupled to the output of the strain gauge and configured to provide feedback related to the distraction force applied at the distal tip, as measured by the strain gauge. The display is further configured to be in a first state when a first distraction force is applied and to be in a second state when a second distraction force is applied. 
     The invention is capable of other embodiments and of being practiced or being carried out in various ways. Alternative exemplary embodiments relate to other features and combinations of features as may be generally recited in the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The invention will become more fully understood from the following detailed description, taken in conjunction with the accompanying drawings, wherein like reference numerals refer to like elements, in which: 
         FIG.  1    is a top side view of a joint distraction lever according to a first exemplary embodiment. 
         FIG.  2 A  is a lateral side view of the joint distraction lever of  FIG.  1   . 
         FIG.  2 B  is a lateral side view of a joint distraction lever according to another exemplary embodiment. 
         FIG.  2 C  is a second lateral side view of the joint distraction lever of  FIG.  2 B . 
         FIG.  3 A  is a bottom side view of the joint distraction lever of  FIG.  1   . 
         FIG.  3 B  is a bottom side view of a joint distraction lever according to another exemplary embodiment. 
         FIG.  3 C  is a bottom side view of the joint distraction lever of  FIG.  2 B . 
         FIG.  4    depicts joint distraction of a patient&#39;s knee joint using the joint distraction lever of  FIG.  1   . 
         FIG.  5    depicts a closer view of joint distraction of a patient&#39;s knee joint using the joint distraction lever of  FIG.  1   . 
         FIG.  6    depicts joint distraction of a patient&#39;s knee joint using a joint distraction lever according to another exemplary embodiment. 
         FIGS.  7 A- 7 C  depict joint distraction of a patient&#39;s knee joint using a joint distraction lever having an indicator according to an exemplary embodiment. 
         FIG.  8    illustrates one embodiment of a method for performing joint distraction using a joint distraction lever according to an exemplary embodiment. 
         FIG.  9    illustrates a surgical system with which a joint distraction lever according to an exemplary embodiment may be used. 
     
    
    
     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 lever is shown. In certain embodiments, the joint distraction lever is an osteotome  10 . Though the present description will refer to the joint distraction lever as the osteotome  10 , it is to be understood that the features disclosed herein may be used with and provided in a variety of lever-type devices, which are considered to be within the scope of the present disclosure. As shown in  FIGS.  1 - 3   , the various embodiments of osteotome  10  include a lever body  12  having a handle portion  14  and a working portion  16 . A fulcrum  18  extends from a bottom face  12   b  of the working portion  16  of the lever body  12 . At a distal end of lever body  12  there is provided a distal tip  20 . Distal tip  20  is raised to extend above the top face  12   a  of the lever body  12 . In the embodiments shown, the distal tip  20  curves upwardly from the working portion  16  at the distal end of the lever body  12 . 
     The osteotome  10  preferably has a thin, narrow lever body  12  sized to be inserted into a pre-resection narrow joint space. The lever body  12  may be between 1-3 mm thick at the working portion  16 , and in a preferred embodiment is no more than 2 mm thick. In some preferred embodiments, the thickness of the working portion  16  tapers towards the distal tip  20  to no more than 1 mm thick at the tip  20 . The width of the working portion  16  may be between 10-22 mm wide to accommodate compartments of various sizes, and in a preferred embodiment is approximately 15 mm wide. 
     Referring to  FIG.  4   , it is shown that the fulcrum  18  is configured to rest on a first bone of a joint. The embodiments of the joint distraction device are depicted and described herein as being used in a knee joint, though it should be understood that the joint distraction device may be used in any joint that is suitable for a joint distraction procedure. Thus, in the figure, the fulcrum is shown resting on a tibial plateau  31  of a patient&#39;s tibia  30 . This provides the support for the osteotome  10  and the point around which the torque is applied and the distraction force will be provided to the distal end of the patient&#39;s femur  40  through distal tip  20 . As depicted in  FIG.  4   , as an external force is exerted on the handle portion  14  of the lever body  12 , a torque is applied to the lever body  12  about the fulcrum  18 . A resulting force is then applied at the distal tip  20  which causes the distraction of the joint, that is, for example, the separation of the first bone (tibia  30 ) from the second bone (femur  40 ). 
     The joint distraction device according to various embodiments is dependent on the force being applied at two known locations: the fulcrum  18  and the distal tip  20 . To ensure that forces are being applied only at these two locations, the fulcrum  18  and the tip  20  project from the bottom face  12   b  and the top face  12   a , respectively, of lever body  12  such that the lever body  12  does not inadvertently contact either bone of the joint. 
     As such, the fulcrum  18  is designed to project from the bottom face  12   b  to a distance sufficient to prevent contact of the bottom face  12   b  with the tibia  30  during use. In a preferred embodiment, the fulcrum  18  extends proud of the body  12  by at least 2 mm, but may be anywhere between 1-3 mm proud of the body  12 , or more. In certain embodiments, the widest portion of the fulcrum  18  is between 4-8 mm, and the thickest portion is between 1-2 mm. The fulcrum may be instrumented such that the fulcrum itself is configured to measure the load being applied at the fulcrum. In such an embodiment, an instrumented fulcrum can be attached to a standard osteotome to achieve certain features of the disclosed embodiments without further modification to force measuring aspects of the osteotome. As shown in the embodiment of  FIGS.  2 A and  3 A , the fulcrum  18   a  shape may be somewhat tapered or sharp into a pointed tip to allow slight penetration into bone and/or cartilage to provide stability of the osteotome  10  during distraction and while the joint poses are being captured. 
     In the embodiment shown in  FIGS.  2 B,  2 C, and  3 C , the fulcrum is a triangular pad  18   c . The triangular pad  18   c  may be connected to the lever body at a rotatable pivot joint. The triangular pad  18   c  provides greater surface in contact with the bone to minimize penetration into the bone when such penetration would be detrimental or undesirable. Though the pad shown in  FIGS.  2 B,  2 C, and  3 C  is triangular, other configurations having a narrow top portion to form a portion of a pivot joint, and a wider bottom portion to contact the bone can be used to provide a pivot pad for pivoting of the lever body about the fulcrum. In other embodiments, such as that shown in  FIG.  3 B , the fulcrum is a linear fulcrum  18   b  extending laterally across the lever body  12 . This embodiment also provides a greater surface area in contact with the bone and may also reduce the penetration of the fulcrum into the bone during use. 
     The distraction force, and thus the measurement of the distraction force applied through the distal tip  20  (to be discussed in detail below), is sensitive to fulcrum  18  to lift point (tip  20 ) distance. When the distance from the fulcrum  18  to the raised tip  20  is known or selected, which it will be when the joint distraction lever is used, the applied distraction force can be calculated. The fulcrum  18  to tip  20  distance may be fixed or may be variable and/or adjustable. In a fixed fulcrum to tip embodiment, the spacing may be between 10-25 mm. An adjustable distance embodiment may allow for a greater range of the fulcrum to tip distance.  FIG.  3 C  depicts an embodiment wherein the fulcrum  18  to tip  20  distance can be adjusted by moving the pivot joint along slot  19  and securing it at a desired distance from tip  20 . In certain preferred embodiments, the distance between the fulcrum  18  and the tip  20  is fixed at 20 mm. This distance is particularly useful for distraction of the knee joint, as it allows the fulcrum  18  to rest on the anterior plateau  31  of the tibia  30  and the tip  20  to be directly below the femoral condyle  41 . 
     Referring to  FIGS.  2  and  4 - 7   , it is shown that the distal tip  20  projects above the top face  12   a  of the lever body  12 . In the embodiments shown, the distal tip  20  of the working portion  16  curves upward to form distal tip  20 . Again, in order that forces are applied to the bones of the joint only at the fulcrum  18  and distal tip  20 , the distal tip  20  is configured such that the top face  12   a  of the lever body  12  does not contact the femur  40  during distraction of the joint. The raised tip  20  may stand 1-5 mm proud of the top face  12   a  of the lever body  12 , and in a preferred embodiment is curved to be 4 mm proud of the body  12 . As shown in the embodiment of  FIGS.  2 ,  4 ,  5 , and  7   , the lever body  12  may taper towards the distal tip  20 , such that distal tip  20  is pointed. The pointed tip, in a preferred embodiment, has a width of about 1 mm. 
     The profile of the lever body  12 , particularly the distal tip  20 , may take on various profiles, not limited to the pointed distal tip shown in the previous embodiments. In one exemplary configuration, such as that shown in  FIG.  6   , the distal tip  20  takes on the shape of a plate  20   a . The shape may be slightly curved to fit with the outer surface of the bone. In some embodiments, the plate  20   a  at the distal tip is specifically configured for a particular bone or the anatomy of a particular patient. This configuration provides greater contact surface area for torque transmission efficiency as well as to reduce penetration of the bone being distracted. Other configurations of the distal tip may also be used in accordance with additional embodiments of the present invention. 
     The joint distraction lever may have a rotatable handle portion  14 . The rotatable handle  14  may allow for a reduction in the amount of torque working laterally during joint distraction. For example, when distracting the knee joint, it is intended to provide the distraction force 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. Some torque, instead, may be applied sideways on the joint while also being applied in parallel with the mechanical axis. The rotatable handle  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 handle  14 . 
     The joint distraction lever, such as osteotome  10 , is configured to measure and provide output related to the distraction force applied to the bone of the joint, such as the distal femur  40 , by the distal tip  20  during a distraction procedure. The distraction force is measured by a force measurement device. The embodiment of  FIG.  1    shows a mechanical force measurement osteotome. In this embodiment, the lever body  12  includes a cut out portion forming a cantilever beam  8 . Upon application of an applied force, the cantilever bean  8  tilts upward (as depicted in  FIGS.  2 C and  4   ). The cantilever beam  8  may be used to determine the applied force based on its relationship with a reference feature. For example, as shown in  FIGS.  2 C and  4   , the cantilever beam  8  may move towards alignment with tab  9  extending from the handle  14 . The joint distraction lever can be configured such that alignment of the cantilever beam is with the tab  9  indicates a predetermined force value. 
     Another non-electronic configuration for determining the distraction force applied at the distal tip  20  is an analog torque wrench that is configured to apply a set specific torque to the wrench body or, particularly, lever body  12 . Analog graduations of torque settings may be available, and once determined and set, the lever body  12  will be configured to apply a torque and thus cause a distraction force at the distal tip  20  until a predetermined, desired force is applied. When the preset torque has been met, the wrench, or lever, is configured to indicate that the preset torque has been reached, or otherwise prevent further torque from being applied through the lever body. 
     In another exemplary embodiment, the force measurement device is a strain gauge. One or more strain gauges may be coupled with 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 strain gauge deforms, as the joint distraction lever deforms as the torque is applied to distract the bones of the joint, the electrical resistance of the electrical conductor of the strain gauge changes. Thus, from the measured electrical resistance of the strain gauge(s), computed using the known or measured input voltage and measured output voltage, the amount of applied stress to the joint distraction lever can be measured and the distraction force computed. A plurality of strain gauges may be arranged and included in the joint distraction lever 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 strain gauges into an electrical signal. 
     Other mechanisms or tools for measuring the distraction force applied by the joint distraction lever at the distal tip  20  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 distal tip  20  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 to  FIGS.  7 A- 7 C , osteotome  10  includes an indicator  22 . The indicator  22  provides feedback to a user related to the distraction force being applied to a first bone of the joint, such as the distal femur, at the distal tip  20 . The feedback may indicate the current value of the force being applied, or it may be representative of a particular range of force values, i.e. provide feedback when a predetermined force value has been reached or exceeded. The feedback provided via indicator  22  allows for consistent, repeatable, trainable force application. Distinct from prior methods and systems for joint distraction where force is subjective, changes between surgeons, and is difficult to learn, the joint distraction lever according to the disclosed embodiments provides feedback to the user such that consistent force can be quantified and applied uniformly among different surgeons, between one distraction procedure and the next, and can be applied at any flexion angle. In certain embodiments, the osteotome  10  is configured to apply a force of 85N+/−15N. Accordingly, the indicator  22  is configured to provide feedback to the user when the distraction force achieves some predetermined relationship with the desired force value. 
       FIGS.  7 A- 7 C  depict osteotome  10  having an indicator  22  according to a preferred embodiment, wherein the indicator  22  is a light-emitting diode (LED)  24 . As shown in  FIG.  7 A , the LED  24  is in a first illumination state as a first range of distraction force is being applied. For example, as the osteotome  10  is first inserted in the joint space and no force is being applied, or only a low amount of force is being applied, the LED  24  may emit light of a certain color, or remain off.  FIG.  7 B  depicts the LED  24  in a second state once the distraction force has achieved or passed a certain predetermined value. For example, the second illumination state may cause the LED to emit light of a second color. In an exemplary embodiment, the second state may occur when the distraction force reaches 70N+/−5N. Finally,  FIG.  7 C  depicts the LED  24  in a third illumination state, indicating to the user the a predetermined, desired distraction force, or a maximum distraction force, has been achieved. For example, the LED may emit light of a third color once the predetermined force has been reached. In an exemplary embodiment, the third state may occur when the distraction force reaches 100N+/−5N. Alternatively, the LED may provide other illumination states such as a slow or rapid flashing state to provide an indication that a predetermined force has been reached. 
     Some embodiments may use a plurality of LEDs. For example, when any force is applied, a first LED may illuminate. Additional LEDs may illuminate successively as the force increases, each illuminating once the force meets a predetermined value. The desired distraction force may be indicated when all of the LEDs on the lever are illuminated. 
     Similarly, instead of an LED  24 , the indicator  22  may provide feedback in the form of a sound emitted from the osteotome, such as a beep or click, or arrangement thereof indicating, for example, a first, second, and third state. Alternatively, the osteotome  10  may provide a single beep, click, or other sound only when the desired, predetermined force value has been reached. Likewise, the indicator  22  may provide feedback in the form of haptic vibration of the joint distraction lever. As with the LED  24  and the sound indicator, the haptic vibration may indicate to a user various of ranges of distraction force being achieved, or provide feedback only at the desired, predetermined distraction force value. 
     In the mechanical embodiment of  FIG.  1   , the indicator is the movement of the cantilever beam  8  above the top face  12   a  of the working portion  16 , relative to the height of the reference tab  9  extending from the handle portion  14 . In an embodiment wherein the force computation occurs by an analog torque wrench, the indicator  22  is the analog graduations provided. In electronic embodiments, the output of the various strain sensors may be converted into a signal to display a digital representation of the force value on a display window on the lever body  12  itself or on a display or indicator device coupled thereto. The device may further be configured to communicate the computed force wirelessly with an external system which may display the force value on a display device or provide the sound feedback or other indicator to the user of the forces being applied by the joint distraction lever. 
     In some embodiments, the joint distraction lever may have a preset target distraction force value, and/or preset force values representing the various force stages. In such embodiments, the various indicators indicate when the preset value is reached. In other embodiments, the joint distraction lever may be adjustable. In this way, the surgeon may set the output, i.e., the feedback provided by the indicator, for a selected amount of force. In one example, the surgeon may use the joint distraction lever to first distract the joint. When the surgeon is applying the necessary and desired amount of force to cause distraction of the joint, he or she can set that as the force value that generates a certain output, for example, the force that causes the LED to illuminate. In this way, the same load can be applied consistently and repeatedly by applying a force until that output is again observed. In one exemplary embodiment, shown in  FIG.  4   , a dial with value hashtags can be adjusted to set the force value and output according to the surgeon&#39;s desired load. In other embodiments, an adjustment of the desired or predetermined values can be adjusted via software implemented in the joint distraction lever and/or with the surgical system  900  (described below). Also, referring to  FIG.  3 C  described above, the distance between the fulcrum and tip can be adjusted such that the doctor can adjust the distraction force without adjusting his or her applied force. 
     Referring to  FIG.  8   , a method  800  for performing joint distraction using a joint distraction lever according to the preferred embodiments is depicted. In step  801 , a joint, such as the knee joint including the tibia and the femur, is moved into a first flexion position. In a preferred method, the first flexion position is full flexion though any range of flexion may be used. In step  802 , a joint distraction lever according to the exemplary embodiments disclosed herein is inserted into the space between the first and second bones of the joint. An external force may then be applied to the handle portion  14  of the lever body  12  to cause a torque on the joint distraction lever (step  803 ). In step  804 , 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 distal tip  20  of the joint distraction lever, as measured by the joint distraction lever. In step  805 , the user, having achieved and having a desired awareness of the distraction force being applied maintains the force to the handle portion  14  to complete the joint distraction procedure. 
     Optionally, after step  805 , a pose of the first and second bones of the joint is captured when the predetermined distraction force is applied and maintained at the distal tip (step  806 ). Capturing the pose of the first and second bones in the distracted joint assists with surgical planning to ultimately attain the desired, properly aligned joint post-resection and post-prosthetic implantation. To provide for capturing the pose of the joint, it is contemplated that the exemplary joint distraction lever may be used in conjunction with anatomy navigation systems and methods, which may further be used with a surgical system, such as that depicted in  FIG.  9   . The figure shows an embodiment of a surgical system  900  that includes a computing system  920 , a surgical tool, such haptic device  930 , and a tracking system  940 . In operation, the surgical system  900  enables comprehensive surgical planning which may include performing distraction of a joint using the osteotome  10  described herein. 
     Determining the pose of the first and second bones in step  806  may make use of tracking system  940 . The tracking (or localizing) system  940  of the surgical system  900  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  940  may include a detection device  941  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 tracks the pose of the object to detect (or enable the surgical system  900  to determine) movement of the object. Tracked objects may include, for example, tools/instruments, patient anatomy, implants/prosthetic devices, and components of the surgical system  900 . Using pose data from the tracking system  940 , the surgical system  900  is also able to register (or 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 may be registered to any suitable coordinate system, such as a coordinate system being used by a process running on the computer  921 . For example, utilizing pose data from the tracking system  940 , the surgical system  900  is able to associate the physical anatomy with a representation of the anatomy (such as an image displayed on the display device  945 ). Based on tracked object and registration data, the surgical system  900  may determine, for example, (a) a spatial relationship between the image of the anatomy and the relevant anatomy. Additionally, by tracking the relevant anatomy, the surgical system  900  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 MRI images to an intraoperative scene). 
     The tracking system  940  may also be used to track the anatomy and the joint distraction lever, or osteotome  10 , while applying the distraction force. By tracking the pose (position and orientation) and the movement of the osteotome  10  and the anatomy, the computing system  920  can determine the directional components of the force being produced. As described above, in addition to the forces acting along the mechanical axis, the distraction force may also act in a lateral direction or other direction off-axis from the mechanical axis. Tracking of the objects and determination of the directional components can allow for a determination of the amount of force that is off of the intended axis. This can help the surgeon, or the system automatically, to adjust the application of force for more efficient load transmission, and/or to reduce any injury or damage that may occur may applying distraction forces in directions that are off of the intended axis. 
     The tracking system  940  may be any tracking system that enables the surgical system  900  to continually determine (or track) a pose of the relevant anatomy of the patient and a pose of the tool  935  (and/or the haptic device  830 ). For example, the tracking system  940  may comprise 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. The non-mechanical tracking system may include an optical (or visual), magnetic, radio, or acoustic tracking system. Such systems typically include a detection device adapted to locate in predefined coordinate space specially recognizable trackable elements (or 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 may include an array of markers having a unique geometric arrangement and a known geometric relationship to the tracked object when the trackable element is attached to the tracked object, such as the femur  40  and tibia  30  of a patient. The markers may include any known marker, such as, for example, 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. Intrinsic features are salient and accurately locatable portions of the tracked object that are sufficiently defined and identifiable to function as recognizable markers (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 stationary stereo camera pair sensitive to infrared radiation may be used to track markers that emit infrared radiation either actively (such as a light emitting diode or LED) or passively (such as a spherical marker with a surface that reflects 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 one embodiment, as shown in  FIG.  9   , the tracking system  940  includes a non-mechanical tracking system. In this embodiment, the non-mechanical tracking system is an optical tracking system that includes a detection device  941  and at least one trackable element (or tracker), such as anatomy tracker  943 , configured to be disposed on (or incorporated into) a tracked object and detected by the detection device  941 . The tracker is configured to be affixed to the tracked object in a secure and stable manner and includes an array of markers having a known geometric relationship to the tracked object. The markers may be active (e.g., light emitting diodes or LEDs) or passive (e.g., reflective spheres, a checkerboard pattern, etc.) and preferably 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  941  detects positions of the markers, and the unique geometry (or firing pattern) and known geometric relationship to the tracked object enable the surgical system  900  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  945 . The display device  945  may also display the distraction force measurement obtained by the force measurement lever. The osteotome  10  may communicate wirelessly or via a coupled connection with the surgical system  900 , or other computing or display system, to provide the distraction force measurement for display on an external device, such as the display device  945 . 
     Computing system  920  may be configured to acquire and use the data obtained during a joint distraction procedure to complete a surgical planning procedure. Thus, computing system  920  may capture and store the pose of the first and second bones of the joint via information provided by tracking system  940 . The captured pose of the joint may be used to plan bone resection and prosthetic implant placement for proper joint balance and alignment. The computing system  920  of surgical system  900  may be further configured to define a surgical plan based on the captured pose(s) of the distracted joint. The computing system  920  then allows surgical system  900  to implement the surgical plan using the tracking system  940  to, for example, track the pose of a surgical tool relative to the patient&#39;s anatomy, and may also provide haptic feedback through haptic device  930  having surgical tool  935  based on a haptic boundary created during surgical planning. Haptic device  930  provides surgical guidance to a surgeon in order to keep the surgical tool  935  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 distraction lever may be used during a joint distraction procedure and for bone resection and implant planning. 
     Referring back to the method depicted in  FIG.  8   , optionally, after step  806 , the joint is moved to a second flexion position (step  807 ) and to any number of additional flexion positions, and the poses are captured with the predetermined resection force applied to the joint. In these poses, with the distraction force applied, the knee joint is in the desired post-resection final position. After collection of poses, bone resection, implant positioning, and implant characteristics are planned so as to maintain this relative alignment by making the femoral and tibial components contact (or be slightly gapped to allow for some laxity). Once the bone is resected at this desired plan and the trials and/or implants are secured to the bone, the leg will then be in the desired pre-resected posed positions. 
     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 embodiments without departing from the scope or spirit of the present inventions. All such modifications are intended to be within the scope of claims associated with this disclosure. 
     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.