Patent Publication Number: US-2019167447-A1

Title: Devices and methods to prevent joint instability following arthroplasty

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This is an international (PCT) application relating to and claiming the benefit of commonly-owned, copending U.S. Provisional Patent Application No. 62/372,487, filed Aug. 9, 2016, entitled “DEVICES AND METHODS TO TREAT JOINT INSTABILITY FOLLOWING ARTHROPLASTY,” the contents of which are incorporated by reference herein in their entirety. 
    
    
     TECHNICAL FIELD 
     Various embodiments of the present invention relate to methods and systems to optimize the position and orientation of components in order to decrease the occurrence of joint instability after total joint arthroplasty. In particular, various embodiments of the present invention relate to methods and systems to optimize the position and orientation of components in order to decrease the occurrence of joint instability after total knee arthroplasty. 
     BACKGROUND 
     Using the knee as a non-limiting example, joint instability occurs when the soft-tissue structures around the knee are unable to provide the stability necessary for adequate function during standing or walking. Following arthroplasty, instability may be the result of increased soft-tissue laxity (looseness) due to improper positioning and/or alignment of the prosthesis. Pain and/or a sensation of the knee “giving way” may alter knee function and require revision surgery. 
     Joint instability is one of the major causes of revision after total knee arthroplasty (TKA). Aseptic loosening is one of the predominant mechanisms contributing to failure of TKA. 
     Classification of the tibiofemoral instability is based upon the direction of instability. The three basic types include coronal plane instability (collateral ligament instability, extension space instability), sagittal plane instability (anteroposterior instability, flexion space instability), and global instability. 
     Currently, techniques to increase joint stability are imprecise. For example, in TKA, “soft-tissue balancing”; which may involve releasing the medial or collateral ligaments to correct for a varus or valgus deformity and/or re-cutting aspect of the bone is an imprecise art. The amount of soft-tissue to be released to obtain a balanced knee is often uncertain. Similarly, the amount of bone to be re-cut in order to correct the balance of the knee is difficult to assess. In addition, the balance of the knee should be considered in combination with the overall alignment of the leg. 
     SUMMARY OF THE INVENTION 
     In one embodiment, the present invention provides a kit, comprising: (1) an alignment guide for preparing bone elements at a joint for receiving an implant; (2) a distractor comprising a member configured to engage with a first bone member, a member configured to engage with a second bone member, and a sensor, wherein the distractor is configured to move the first bone member away from the second bone member, wherein the sensor is configured to record (at the planning stage) at least one of (i) the force required to separate the first bone member from the second bone member; (ii) the orientation of the force required to separate the first bone member from the second bone member (iii) the pressure mapping resulting from the contact of one of the bone member against the sensor surface; (iv) the distance between the first and second bone members; and (v) the location of the contact of one of bone member against the sensor surface; (3) a plurality of trial members configured to receive at least one sensor; (4) at least one sensor configured to be integrated into an individual trial within the plurality and measure and report (at the verification stage) at least one of (i) the loading of the joint; (ii) the orientation of the load of the joint; (iii) the pressure mapping of the joint; and (iv) the location of the contact between one of the bone member on the sensor; and (5) an implant, optionally configured to receive the trial member assembled with at least one sensor and/or to articulate against the trial member assembled with at least one sensor. 
     In one embodiment, the present invention provides a kit, comprising: (1) an alignment guide for preparing the distal aspect of the femur and the proximal aspect of the tibia for receiving a femoral implant and a tibial implant; respectively; (2) a distractor comprising a tibial member engageable with the tibia and a femoral member engageable with the femur, and a sensor, wherein the distractor is configured to move the femur away from the tibia, wherein the sensor is configured to record (at the planning stage) at least one of (i) the force required to separate the femur from the tibia; (ii) the orientation of the force required to separate the femur from the tibia; (iii) the pressure mapping resulting from the contact of the femur against the sensor surface; (iv) the distance between the femur and tibia; and (v) the location of the contact of the femur against the sensor surface; (3) a plurality of tibial insert trials configured to be selected by a surgeon to assess the proper thickness of the final tibial insert component, wherein the tibial insert trials are further configured to receive at least one sensor; (4) at least one sensor configured to be integrated into an individual tibial insert trial within the plurality and measure and report (at the verification stage) at least one of (i) the loading of the tibiofemoral joint; (ii) the direction of the load; (iii) the pressure mapping of the tibiofemoral joint; and (iv) the location of the contact between preferably the femur on the sensor; (5) an implant, optionally configured to receive the tibial insert trial assembled with at least one sensor and/or to articulate against the tibial insert trial assembled with at least one sensor and (6) a computing device to display the at least one reported information wirelessly received from the at least one sensor. 
     In one embodiment, the at least one sensor has an elongated shape in the transversal plane; where its dimension along the antero-posterior axis is longer than its dimension along the medio-lateral axis. 
     In one embodiment, the distal aspect of the at least one sensor is configured to allow for assembly with the femoral paddle of the mechanical distractor as well as the plurality of tibial insert trials. 
     In one embodiment, the proximal aspect of the sensor-based device comprises a concave surface; wherein the curvatures are approximately similar to those of the proximal surface of an usual tibial insert trial of the same size. 
     In one embodiment, an individual tibial insert trial assembled with the at least one sensor has a similar proximal geometry as a usual tibial insert trial of the same size. 
     In one embodiment, the at least one sensor reports at least one parameter selected from the group consisting of: load value (available at planning and verification stages), load orientation (available at planning and verification stages), pressure mapping (available at planning and verification stages), joint gap (available at planning stage only) and contact location (available at planning and verification stages). 
     In one embodiment, the at least one parameter defines the location of the contact pattern between the native femur (at the planning stage) and/or or the femoral component (trial) (at the verification stage) against the at least one sensor. 
     In one embodiment, the at least one parameter is used, along with the displacement distance and/or displacement force, to define the stiffness of the soft tissue envelope of the joint. 
     In one embodiment, the at least one sensor reports the at least one parameter wirelessly to a computing device. 
     In an embodiment, a kit includes a distractor, a plurality of trial elements, and at least one sensor, the distractor configured to separate a first bone from a second bone adjacent to the first bone, the distractor having a first member and a second member configured to be positioned between the first bone and the second bone, a distance between the first member and the second member being adjustable to thereby separate the first bone from the second bone, the distractor further configured to receive at least one sensor in the first portion, each of the trial elements corresponding to a corresponding one of a plurality of surgical implants, each of the trial elements being configured to be temporarily coupled to the second bone so as to evaluate suitability of the corresponding one of the plurality of surgical implants for implantation, each of the trial elements further configured to receive at least one sensor, the at least one sensor configured to be selectively received in the distractor or one of the plurality of trial elements, wherein the at least one sensor is configured to record at least one of a magnitude of a force, a direction of application of a force, a pressure mapping, and/or a location of application of a force. 
     In an embodiment, the distractor is configured to receive two of the at least one sensor. In an embodiment, each of the plurality of trial elements is configured to receive two of the at least one sensor. 
     In an embodiment, the first bone is a femur and the second bone is a tibia. In an embodiment, the distractor is configured to receive a first one of the at least one sensor at a location corresponding to a medial condyle of the femur and to receive a second one of the at least one sensor at a location corresponding to a lateral condyle of the femur. In an embodiment, each of the plurality of trial elements is configured to receive a first one of the at least one sensor at a location corresponding to a medial condyle of the femur and to receive a second one of the at least one sensor at a location corresponding to a lateral condyle of the femur. 
     In an embodiment, each of the at least one sensor includes a variable sensor that is configured to provide a linear relationship between an applied force and an output voltage. In an embodiment, each of the at least one sensor is configured to wirelessly transmit data recorded by the each of the at least one sensor to a computing device. In an embodiment, the computing device is a computer-assisted orthopedic surgery system. 
     In an embodiment, the distractor is configured to record the distance between the first member and the second member. In an embodiment, each of the at least one sensor includes a Hall sensor and the second portion of the distractor includes a magnet, the Hall sensor and the magnet configured to cooperate to record the distance between the first member and the second member. 
     In an embodiment, the distance between the first member and the second member is adjustable in a range of between 5 mm and 19 mm. In an embodiment, the kit also includes a computer-assisted orthopedic surgery system. In an embodiment, the distractor includes a first recess configured to receive a first one of the at least one sensor and a second recess configured to receive a second one of the at least one sensor, each of the first and second recesses configured to receive the corresponding one of the first and second ones of the at least one sensor in a plurality of positions, whereby a distance between the first one of the at least one sensor and the second one of the at least one sensor can be adjusted. 
     In an embodiment, each of the at least one sensor has a proximal aspect that is contoured so as to resemble a native articular surface and a distal aspect that is configured to be selectively received in the distractor or one of the plurality of trial elements. In an embodiment, the distal aspect has a shape that is a one of a diamond, a square, a rectangle, an oblong shape, an ellipse, or an elongated freeform shape. 
     In an embodiment, a first one of the plurality of trial elements has a size that differs from a size of a second one of the plurality of trial elements. In an embodiment, the kit also includes a baseplate that is configured to be attached to the second bone. In an embodiment, each of the plurality of trial elements is configured to be removably received in the baseplate that is attached to the second bone. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The present invention will be further explained with reference to the attached drawings, wherein like structures are referred to by like numerals throughout the several views. The drawings shown are not necessarily to scale, with emphasis instead generally being placed upon illustrating the principles of the present invention. Further, some features may be exaggerated to show details of particular components. 
         FIG. 1  shows the elements of an exemplary kit. 
         FIG. 2A  shows a side view representation of an exemplary mechanical distractor according to some embodiments of the present invention, the exemplary mechanical distractor being shown in a closed configuration. 
         FIG. 2B  shows a side view representation of the exemplary mechanical distractor of  FIG. 2A  in an open configuration 
         FIG. 2C  shows a perspective view of the exemplary mechanical distractor of  FIG. 2A . 
         FIG. 2D  shows a detailed view of a femoral paddle of the exemplary mechanical distractor of  FIG. 2A . 
         FIG. 3  shows individual tibial trials in a plurality of tibial trials according to some embodiments of the present invention. 
         FIG. 4A  shows side views of various sensors according to some embodiments of the present invention. 
         FIG. 4B  shows a top perspective view of an exemplary embodiment of a sensor. 
         FIG. 4C  shows a bottom perspective view of the sensor of  FIG. 7A . 
         FIG. 5  shows a representation of a computer-assisted orthopedic surgery system to aid a surgeon to place components of a joint implant in connection with some embodiments of the present invention. 
         FIG. 6  shows an exemplary screenshot taken during use of the computer assisted orthopedic surgery system of  FIG. 5  according to some embodiments of the present invention. 
         FIG. 7  shows the main dimensions of the native femur to be used for the selection of the sensor and their position on the distractor. 
         FIG. 8A  shows a femoral paddle of an exemplary distractor with exemplary sensors positioned in a in a wide position. 
         FIG. 8B  shows the femoral paddle of  FIG. 8A  with the exemplary sensors positioned in a in a central position. 
         FIG. 8C  shows the femoral paddle of  FIG. 8A  with the exemplary sensors positioned in a in a narrow position. 
         FIG. 9  shows a femur and tibia of a knee joint after the tibia has been prepared. 
         FIG. 10  shows the exemplary distractor of  FIG. 2A  as positioned in the knee joint after the tibia has been prepared. 
         FIG. 11  shows various flexion angles of the knee while the exemplary distractor is positioned as in  FIG. 10 . 
         FIG. 12  shows data that may be recorded by the exemplary sensor while installed in the exemplary distractor as positioned in  FIG. 10 . 
         FIG. 13  shows a femur and tibia of a knee joint after the tibia and femur have been prepared. 
         FIG. 14  shows the knee joint of  FIG. 13  after a femoral component trial and tibial baseplate trial have been installed. 
         FIG. 15A  shows a top view and cross-sectional view of an exemplary embodiment of a tibial trial insert prior to receiving sensors therein. 
         FIG. 15B  shows a top view and cross-sectional view of the tibial trial insert of  FIG. 15A  after receiving sensors therein. 
         FIG. 15C  shows a top perspective view of an exemplary embodiment of a tibial trial insert and two exemplary sensors, prior to assembly of the sensors with the tibial trial insert. 
         FIG. 15D  shows a cross-sectional view of the tibial trial insert and sensors of  FIG. 15C . 
         FIG. 15E  shows the cross-sectional view of  FIG. 15D , after the sensors have been assembled with the tibial trial insert. 
         FIG. 16  shows the knee joint of  FIG. 14 , after an assembled tibial trial insert with sensors has been placed in the tibial baseplate trial. 
     
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Among those benefits and improvements that have been disclosed, other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying figures. Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely illustrative of the invention that may be embodied in various forms. In addition, each of the examples given in connection with the various embodiments of the invention which are intended to be illustrative, and not restrictive. 
     The present invention will be further explained with reference to the attached drawings, wherein like structures are referred to by like numerals throughout the several views. The drawings shown are not necessarily to scale, with emphasis instead generally being placed upon illustrating the principles of the present invention. Further, some features may be exaggerated to show details of particular components. 
     The figures constitute a part of this specification and include illustrative embodiments of the present invention and illustrate various objects and features thereof. Further, the figures are not necessarily to scale, some features may be exaggerated to show details of particular components. In addition, any measurements, specifications and the like shown in the figures are intended to be illustrative, and not restrictive. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
     Throughout the specification and claims, the following terms take the meanings explicitly associated herein, unless the context clearly dictates otherwise. The phrases “in one embodiment” and “in some embodiments” as used herein do not necessarily refer to the same embodiment(s), though it may. Furthermore, the phrases “in another embodiment” and “in some other embodiments” as used herein do not necessarily refer to a different embodiment, although it may. Thus, as described below, various embodiments of the invention may be readily combined, without departing from the scope or spirit of the invention. 
     In addition, throughout the specification, the meaning of “a,” “an,” and “the” include plural references. The meaning of “in” includes “in” and “on.” 
     Various embodiments of the present invention relate to methods and systems to optimize the position and orientation of components in order to decrease the occurrence of joint instability after total joint arthroplasty. In particular, various embodiments of the present invention relate to methods and systems to optimize the position and orientation of components in order to decrease the occurrence of joint instability after total knee arthroplasty. 
     Without intending to be limited to any particular theory, joint instability can be prevented by using a proper surgical technique that aims to balance the medial &amp; lateral gaps in the implant joint (i.e., rectangular gaps) as well as the flexion &amp; extension gaps in the implant joint. 
     Without intending to be limited to any particular theory, achieving a balanced knee joint and a proper alignment of the leg is expected to demonstrate proper ligament tension through the full range of motion, which provides a natural acting joint and minimizes pain and discomfort. Further, properly balanced ligaments reduce stress, wear and tear on the prosthesis and extend its life. 
     The present invention is directed to a method and kits intended to reduce the incidence of joint instability while maintaining a proper alignment of the joint. The method relates to the possibility of planning a bone cut based on both alignment and soft-tissue considerations (planning stage) and to then verify the achieved alignment and soft-tissue tension with the final or provisional implants in place (verification stage). 
     According to some embodiments, the same sensor device is used for both the planning stage and the verification stage. 
     In some embodiments, the present invention provides a kit, comprising: (1) an alignment guide for preparing the distal aspect of the femur and the proximal aspect of the tibia for receiving a femoral implant and a tibial implant; respectively; (2) a distractor comprising a tibial member engageable with the tibia and a femoral member engageable with the femur, and a sensor, wherein the distractor is configured to move the femur away from the tibia, wherein the sensor is configured to record (at the planning stage) at least one of (i) the force required to separate the femur from the tibia; (ii) the orientation of the force required to separate the femur from the tibia; (iii) the pressure mapping resulting from the contact of the femur against the sensor surface; (iv) the distance between the femur and tibia; and (v) the location of the contact of the femur against the sensor surface; (3) a plurality of tibial insert trials configured to be selected by a surgeon to assess the proper thickness of the final tibial insert component, wherein the tibial insert trials are further configured to receive at least one sensor; (4) at least one sensor configured to be integrated into an individual tibial insert trial within the plurality and measure and report (at the verification stage) at least one of (i) the loading of the tibiofemoral joint; (ii) the direction of the load; (iii) the pressure mapping of the tibiofemoral joint; and (iv) the location of the contact between preferably the femur on the sensor; (5) an implant, optionally configured to receive the tibial insert trial assembled with at least one sensor and/or to articulate against the tibial insert trial assembled with at least one sensor and (6) a computing device to display the at least one reported information wirelessly received from the at least one sensor. 
     Referring to  FIG. 1 , in some embodiments, a kit  100  includes a distractor  200 , a set of tibial insert trials  300 , and at least one sensor  400 . The elements of the kit  100  will be discussed in detail hereinafter. 
     Referring to  FIGS. 2A-2D , an embodiment of a distractor  200  is shown.  FIG. 2A  shows a side view of the distractor  200  in a closed position,  FIG. 2B  shows a side view of the distractor  200  in an open position,  FIG. 2C  shows a perspective view of the distractor  200 , and  FIG. 2D  shows a detailed view of a femoral member of the distractor  200 . In some embodiments, the distractor  200  comprises a tibial member  210  engageable with the tibia and a femoral member  220  engageable with the femur. In some embodiments, the tibial member  210  includes a magnet. In some embodiments, a distraction mechanism is configured to move the femoral member  220  away from the tibial member  210  (and, thereby, move the femur away from the tibia) under a manually applied load, or, alternatively, through a force-applying mechanism. In some embodiments, the femoral member  220  features recesses  222  intended to receive sensors  400  according to some embodiments of the present invention. In some embodiments, the recesses  222  are diamond-shaped. In some embodiments, the femoral member  220  is configured to receive two of the sensors  400 . In some embodiments, the femoral member  220  includes a first portion  224  having a recess  222  that is configured to receive a first one of the sensors  400  and a second portion  226  having a recess  222  that is configured to receive a second one of the sensors  400 . In some embodiments, the first and second portions  224 ,  226  are configured such that, when the distractor  200  is in use, the recesses  222  are positioned along the mediolateral axis. In some embodiments, the femoral member  220  of the distractor  200  is configurable so as to adjust the mediolateral spread between the medial and the lateral sensors. In some embodiments, the spread between the medial sensor and the lateral sensor is adjustable so that the spread can be similar to the distance between the lowest aspects of the medial and lateral condyles of the native femur.  FIG. 2D  shows a detailed view of the femoral member  220 . In the embodiment shown in  FIG. 2D , each of the first and second portions  224 ,  226  of the femoral member  220  includes a plurality of the recesses  222 , each of which is configured to receive one of the sensors  400 . In some embodiments, each of the first and second portions  224 ,  226  of the femoral member  220  includes an overlapping plurality of the recesses  222 , each of which is configured to receive one of the sensors  400 . In some embodiments, by placing a first sensor  400  in a selected one of the recesses  222  in the first portion  224  of the femoral member  220 , and by placing a second sensor  400  in a selected one of the recesses  222  in the second portion  226  of the femoral member  220 , the distance between the sensors  400  (e.g., in a mediolateral direction) may be adjusted so as to be similar to the distance between the lowest aspects of the medial and lateral condyles of the native femur. 
     Referring to  FIG. 3 , in some embodiments, the kit  100  includes a set of tibial insert trials  300  that are configured for use to assess the proper thickness of the final tibial insert component.  FIG. 3  illustrates a set of tibial insert trials  300  that includes the tibial insert trials  300  in at least three (3) different sizes (e.g., small, medium, and large), but it will be apparent to those of skill in the art that this is only exemplary and that any number of different sizes may be included in other exemplary sets. In some embodiments, the tibial trials  300  include recesses  310  at the level of each condylar dish of the tibial trials  300 , the recesses  310  being configured to receive one of the sensors  400 . In some embodiments, the recesses  310  are diamond-shaped. 
     In one embodiment, the tibial trials  300  are similar to those described in U.S. Patent Application Publication No. 2003/0069644A1 other than as described herein. In one embodiment, the tibial trials  300  are similar to those described in U.S. Pat. No. 7,097,662 other than as described herein. In some embodiments, an individual one of the tibial trials  300  that has been provided with one of the sensors  400  has a similar proximal geometry to that of a usual tibial insert trial (i.e., a tibial insert trial lacking a sensor) of the same size. 
     Referring to  FIGS. 4A and 4B , in some embodiments, the kit  100  includes at least one sensor  400 .  FIG. 4A  shows side views of sensors  400  from a kit  100  that includes sensors  400  in at least three (3) different sizes (e.g., small, medium, and large), but it will be apparent to those of skill in the art that this is only exemplary, and that other embodiments of a kit  100  may include sensors of a single size or sensors of any other number of sizes.  FIGS. 4B and 4C  show top and bottom perspective views, respectively, of an exemplary sensor  400 . In some embodiments, the kit  100  includes two (2) of the sensors  400  in a single size. In some embodiments, the kit  100  includes two (2) of the sensors  400  in each of a plurality of sizes. In some embodiments, the sensors  400  are configured to be received in the recesses  222  of the distractor  200  and in the recesses  310  of the tibial trials  300 . In some embodiments, the at least one sensor  400  has a distal aspect  410  that is configured to allow for assembly selectively with either the femoral member  220  of the distractor  200  or with one of the plurality of tibial insert trials  300 . In some embodiments, the distal aspect  410  is diamond-shaped. In some embodiments, the distal aspect  410  has a different shape (and, correspondingly, the recesses  222  of the distractor  200  and the recesses  310  of the tibial trials  300  have a different shape as well). In some embodiments, the distal aspect  410  has a shape that is configured to prevent rotation of the sensor  400  with respect to the distractor  200  and to the tibial trials  300 . In some embodiments, the distal aspect  410  has a shape that is either a square, a rectangle, an oblong shape, an ellipse, or an elongated freeform shape. In some embodiments, the at least one sensor  400  has a proximal aspect  420  that is shaped concavely such that, when the at least one sensor  400  is assembled to one of the plurality of tibial insert trials  300 , the resulting curvature is approximately similar to the curvature of the proximal aspect of a usual tibial insert trial (e.g., a tibial insert trial that lacks a sensor) of the same size. 
     In some embodiments, the at least one sensor  400  is similar to that described in U.S. Patent Application Publication No. 2007/0233267 A1 other than as described herein. In some embodiments, the at least one sensor  400  is similar to that described in U.S. Pat. No. 7,587,945 other than as described herein. In some embodiments, the at least one sensor  400  is similar to that described in U.S. Pat. No. 7,097,662 other than as described herein. In some embodiments, the at least one sensor  400  includes a Hall sensor. 
     In some embodiments, the at least one sensor  400  includes a variable resistor which is set up in an amplification circuit to create a linear relationship between load input and voltage output or any other known technology able to record at least one parameter. In some embodiments, the at least one sensor  400  includes an array of force sensitive aspects. In some embodiments, a force is recorded at each position within the array by interpreting a change in impedance (e.g. resistive, capacitive, or inductive), or deformation (e.g., piezoelectric, magneto-elastic, optical, or change in resonance). In some embodiments, the data output by the sensor  4000  is interpreted by a processing module, which calculates a data array consisting of forces and/or spatial data. 
     In some embodiments, the at least one sensor  400  includes a piezoelectric sensor configured such that, when a load is applied to the sensor, an electrostatic charge proportional to the load is generated. In some embodiments, the at least one sensor  400  includes a strain gauge configured such that, when the strain gauge deforms in response to deformation (i.e., in response to a load), a change in electrical resistance results. In some embodiments, the at least one sensor  400  includes a plurality of layers. In some embodiments, the at least one sensor  400  includes three or more layers. In some embodiments, the resistance of an inner layer (e.g., of a sensor  400  including a plurality of layers) changes proportionally in response to deformation (i.e., in response to a load). In some embodiments, the capacitance between two layers (e.g., of a sensor  400  including a plurality of layers) changes proportionally in response to deformation (i.e., in response to a load). 
     In some embodiments, the at least one sensor  400  is configured to record at least one of (i) a force (e.g., when the at least one sensor is received in the distractor  200 , the force required to separate the femur from the tibia); (ii) an orientation of a force (e.g., when the at least one sensor is received in the distractor  200 , the orientation of the force required to separate the femur from the tibia); (iii) a pressure mapping resulting from a force (e.g., when the at least one sensor is received in the distractor  200 , the pressure mapping resulting from the contact of the femur against the sensor surface); and (iv) a location of contact (e.g., when the at least one sensor is received in the distractor  200 , the location of the contact of the femur against the sensor surface). In some embodiments, the at least one sensor  400  is configured to wirelessly transmit sensed data to an external device (e.g., a CAOS system, as will be described hereinafter). 
     In some embodiments, the at least one sensor  400  has an elongated shape in the transversal plane; that is, when the at least one sensor  400  is received in either the distractor  200  or one of the tibial insert trials  300 , and the distractor  200  or the one of the tibial insert trials  300  is positioned in its normal manner with respect to a patient&#39;s body, the dimension of the at least one sensor  400  along the antero-posterior axis is longer than the dimension of the at least one sensor  400  along the medio-lateral axis. 
     Referring to  FIG. 5 , in some embodiments, the kit  100  is used in connection with an alignment guide for preparing bone elements at a joint for receiving an implant. In some embodiments, the alignment guide includes a conventional mechanical instrumentation. In some embodiments, the alignment guide includes a computer-assisted orthopedic surgery (CAOS) system. In some embodiments, CAOS systems are configured to assist surgeons in placing the knee components relative to the acquired patient&#39;s anatomical landmarks. In some embodiments, a CAOS system includes a computer, a display unit, and a tracking system. In some embodiments, the CAOS system is similar to that disclosed in U.S. Pat. No. 8,403,934. 
     CAOS systems are widely recognized as an effective tool to provide surgeons with guidance in terms of accuracy and precision of knee implant alignment. They allow surgeons to plan for the tibial and femoral resection parameters based on their preference relative to the acquired anatomical landmarks. This ensures proper alignment of the components relative to the mechanical axis.  FIG. 6  shows an graphical user interface that may be generated by a CAOS system to this end. While achieving proper alignment is of paramount importance, it does not ensure proper balance of the soft-tissue envelope over the range of flexion. In other words, the knee joint may be perfectly aligned relative to the mechanical axis but still presents some instability over the range of flexion. 
     In some embodiments, the CAOS system is configured to wirelessly receive data from the at least one sensor  400 , to treat the data, and to display the data to the surgeon. In some embodiments, a different type of monitoring device is configured to wirelessly receive data from the at least one sensor  400 , to treat the data, and to display the data to the surgeon. 
     In some embodiments, the distractor  200  is configured to record (at the planning stage) the displacement of the femoral member  220  relative to the tibial member  210  during the distraction of the knee joint by tracking the position of the at least one sensor  400  attached to the femoral member  220  of the distractor relative to the tibial member  210  of the distractor  200  placed against the proximal tibial cut and wirelessly transmit the information (i.e., displacement) to a computing device. In some embodiments, the computing device is a CAOS system. In some embodiments, the computing device is another type of device (e.g., computer, tablet, smartphone, . . . ) able to wirelessly receive data from the sensor  400 . Regardless the nature of the computing device, it is configured to treat the data and then display them to the surgeon. 
     In some embodiments, the displacement is evaluated by a Hall sensor encapsulated inside the sensor  400  attached to the femoral member  220  of the distractor  200  relative to a magnet attached to the tibial member  210  of the distractor  200 . In some embodiments, the displacement can also be directly measured by the CAOS system by tracking the motion of the tracker attached to the femur relative to the tracker attached to the tibia. In some embodiments, the displacement is evaluated by another known technique for determining a displacement between two objects. 
     In some embodiments, the at least one sensor is used in multiple applications during a surgical procedure. For example, in some embodiments, the at least one sensor is configured to record at least one of (i) the force required to separate the femur from the tibia; (ii) the orientation of the force required to separate the femur from the tibia; (iii) the pressure mapping resulting from the contact of the femur against the sensor surface; (iv) the distance between the femur and tibia; and (v) the location of the contact of the femur against the sensor surface. In some embodiments, the at least one sensor is configured to be attached to a joint tensing apparatus (at the planning stage, before the preparation of the femoral cuts), or to be attached to trial implants (at the verification stage, after the preparation of the femoral cuts) so as to assess intraoperative loads, or to be attached to the selected prosthetic insert to allow load sensing post operatively. In some embodiments, the proximal aspect of the sensor is configured to contact the native femur (at the planning stage) or the femoral component (at the verification stage). In some embodiments, the proximal aspect of the sensor is flat. In some embodiments, the proximal aspect of the sensor has a geometry that matches the articulation being evaluated. While the knee is shown as the preferred embodiment, and may include the femoral-tibial articulation(s) and the patella articulation, the at least one sensor, and the kits described herein have application in other joints, including but not limited to the shoulder, ankle, wrist and other articulating joints of the body. 
     Consequently, in some embodiments, the present invention provides a kit, comprising: (1) an alignment guide for preparing bone elements at a joint for receiving an implant; (2) a distractor comprising a member configured to engage with a first bone member, a member configured to engage with a second bone member, and a sensor, wherein the distractor is configured to move the first bone member away from the second bone member, wherein the sensor is configured to record (at the planning stage) at least one of (i) the force required to separate the first bone member from the second bone member; (ii) the orientation of the force required to separate the first bone member from the second bone member (iii) the pressure mapping resulting from the contact of one of the bone member against the sensor surface; (iv) the distance between the first and second bone members; and (v) the location of the contact of one of bone member against the sensor surface; (3) a plurality of trial members configured to receive at least one sensor; (4) at least one sensor configured to be integrated into an individual trial within the plurality and record (at the verification stage) at least one of (i) the loading of the joint; (ii) the orientation of the load of the joint; (iii) the pressure mapping of the joint; and (iv) the location of the contact between one of the bone member on the sensor; and (5) an implant. In some embodiments, the implant is configured to receive the trial member assembled with at least one sensor and/or to articulate against the trial member assembled with at least one sensor. 
     In some embodiments, the at least one sensor is configured to record at least one parameter selected from the group consisting of: load value, load orientation, pressure mapping, and contact location. In some embodiments, the at least one parameter defines the location of the contact pattern between the native femur (at the planning stage) and/or the femoral trial component (at the verification stage) against the at least one sensor. 
     In some embodiments, the at least one parameter is used, along with the displacement distance and/or displacement force, to define the stiffness of the soft tissue envelope of the joint. In some embodiments, the at least one sensor reports the at least one parameter wirelessly. 
     In some embodiments, the distractor  200  provides overall guidance regarding the soft-tissue in extension and/or flexion and/or at any degree of flexion of the knee. Distractors include, for example, simple laminar spreaders to complex tensors able to quantify the joint gap(s) as well as the load. However, distractors are typically used in extension and/or in flexion, so the status of the soft-tissue envelope between these two discrete and pre-defined angles of flexion or above 90° of flexion is unknown. While achieving balanced and equal gaps in extension and/or at 90° of flexion is a desired outcome, a substantial amount of cases are associated with instability occurring between 30° and 60° of flexion (aka. mid flexion instability); which is a range of flexion angles not tested by usual distractors. Further, when using such instrument, the knee joint balancing is performed under a distraction load usually ranging from 20 lbs. to 60 lbs. Unfortunately, there is no consensus regarding the optimum load to be used. Because of the absence of consensus regarding the inputs (i.e., the distraction load), the output (i.e., joint gap) is questionable. 
     In some embodiments, the mechanical distractor  200  further comprises at least one additional sensor beyond the sensor  400 . In some embodiments, the additional sensor included in the mechanical distractor  200  is the sensor is the sensor described in U.S. Pat. No. 4,066,082. In some embodiments, each tibial insert trial  300  further comprises at least one additional sensor beyond the sensor  400 . In some embodiments, the additional sensor included in each tibial insert trial  300  is the sensor described in U.S. Patent Application Publication No. 2007/0233267 A1. 
     In some embodiments, an exemplary system (e.g., a system including the kit  100 ) is employed in a surgical method, such as the method described below. For the purpose of this proposed description, the alignment guide for preparing the proximal tibia and distal femur for receiving an implant comprises a computer-assisted orthopedic surgery (CAOS) system. In some embodiments, at the beginning of the procedure, the CAOS system is initiated. Next, in some embodiments, the surgeon exposes the knee joint according to his/her preferred surgical technique and attaches tibial and femoral trackers to the tibia and femur, respectively. In some embodiments, once the trackers have been attached to the bones, the surgeon performs the acquisitions of the femoral and tibial anatomical landmarks using a navigated probe. In some embodiments, based on the computation of the acquisitions, the CAOS system provides information in term of leg alignment, anteroposterior size of the distal extremity of the native femur (e.g., measurement A shown in  FIG. 7 ), and spread between the condyles (e.g., measurement B shown in  FIG. 7 ). 
     In some embodiments, from the kit  100  including at least one of the sensors  400  (e.g., from a kit that includes small, medium, and large sensors as shown in  FIG. 4A ), the surgeon selects the sensors  400  that approximately matches the computed femoral size (e.g., measurement A shown in  FIG. 7 ) and connects the selected sensors  400  with the computing device of the CAOS system using a wireless type of communication. 
     In some embodiments, based on the knowledge of the spread between the condyles of the native femur (i.e., measurement B shown in  FIG. 7 ), the surgeon assembles the selected sensors  400  with femoral member  220  of the distractor  200  by placing the sensors  400  at the proper mediolateral spread (e.g., in ones of the recesses  222  selected so as to provide the proper mediolateral spread).  FIG. 8A  shows the femoral member  220  of the distractor  200  with sensors  400  positioned in the most lateral ones of the recesses  222 .  FIG. 8B  shows the femoral member  220  of the distractor  200  with sensors  400  positioned in centrally positioned ones of the recesses  222 .  FIG. 8C  shows the femoral member  220  of the distractor  200  with sensors  400  positioned in the most medial ones of the recesses  222 . In some embodiments, as a result, the distance between the lowest point of the proximal articular surface of the selected ones of the sensors  400  is similar to the spread between the two condyles of the native femur (e.g., measurement B shown in  FIG. 7 ); which is helpful for the planning stage. Similarly, in some embodiments, the size of the selected one of the tibial insert trials  300  (e.g., small, medium, large, etc.) matches the size of the femoral component, and, as a result, the size of the sensor  400  (e.g., small, medium, large, etc.) is the same as the size as the femoral component (i.e., size A), which is helpful during the verification stage. 
     In some embodiments, the surgeon performs the proximal tibial cut (or a preliminary proximal tibial cut) using the guidance from the CAOS system. In some embodiments, the tibial cut is at least 5 mm thick.  FIG. 9  shows a femur and tibia after the proximal tibial cut has been made. In some embodiments, once the proximal tibial cut has been checked and confirmed to be in accordance with the plan from the CAOS system, then the surgeon inserts the assembled distractor  200  (i.e., the distractor  200  with the selected sensors  400  in place) between the proximal tibial cut and the native femur.  FIG. 10  shows the distractor  200  as positioned in this manner. As noted above with reference to  FIG. 2 , the anticipated opening distance of the distractor  200 , which is measured as the minimum distance between the distal aspect of the tibial member to the lowest point of the concave surface of the sensors  400  may typically range from 5 mm (i.e., the size of the distractor  200  when in its closed configuration) to 19 mm (i.e., the size of the distractor  200  when in its open configuration). 
     In some embodiments, at this point, the surgeon places the leg at different angles of flexion, preferably ranging from extension (i.e., 0° of flexion) to the full passive flexion allowed by the patient (e.g., 140° of flexion). In some embodiments, the leg is moved at various angular increments depending on the number of acquisition points desired by the surgeon. In some embodiments, the angular increments are in the range between 10° and 45° depending of the number of acquisition points requested by the surgeon.  FIG. 11  shows the leg during this process, positioned at approximately 105° of flexion. In some embodiments, at each degree of flexion measured by the CAOS system, the surgeon manually actuates the distractor  200  to separate the femoral member  220  from the tibial member  210 . In some embodiments, because the tibial member  210  contacts the proximal tibial cut and the sensors  400  attached to the femoral member  220  contact the native femur, such separation of the femoral member  220  from the tibial member  210  results into a separation of the native femur from the proximal tibial cut. In some embodiments, during the distraction, the sensors  400  record at least one of (i) the force required to separate the femur from the tibia; (ii) the orientation of the force required to separate the femur from the tibia; (iii) the pressure mapping resulting from the contact of the femur against the surface of the sensors  400 ; (iv) the distance between the femur and tibia; and (v) the location of the contact of the femur against the surface of the sensors  400 . In some embodiments, the surgeon configures the sensors  400  (e.g., via the CAOS system) to recorded a selected one or more of the parameters noted above. In some embodiments, the recorded information is wirelessly transmitted to the CAOS system so it can be displayed to the surgeon.  FIG. 12  shows data recorded by the at least one sensor  400  as configured to record force, at four different flexion angles. 
     In some embodiments, based on the acquisition of the recorded information, the CAOS system may provide a feedback loop. For example, in some embodiments, the CAOS system is configured alert the surgeon or stop the distraction when the recorded load is above a threshold (e.g., 300 N) previously defined by the surgeon. In some embodiments, the CAOS system is configured to alert the surgeon or stop the distraction when the recorded stiffness (e.g., ratio of load to displacement) is above a threshold previously defined by the surgeon. In some embodiments, the CAOS system is configured to alert the surgeon or stop the distraction when the recorded displacement (or distraction) is above a threshold (e.g., 19 mm) previously defined by the surgeon. In some embodiments, such alerts are intended to ensure that the acquisition process does not damage the soft-tissue envelope. 
     In some embodiments, based on the load/displacement curves obtained at discrete angles of flexion and the alignment data from the CAOS system (e.g., the curves shown in  FIG. 12 ), the surgeon plans the position and orientation of the femoral component relative to the native femur. This use of the sensors  400  and the data recorded thereby is referred to herein as the “planning stage”. In some embodiments, the planned target is based on information from both the CAOS system (e.g., the alignment and sizing of the components) and the sensors (e.g., the data recorded by the sensors, which may be referred to as the “soft-tissue signature”) in order to achieve both a mechanically aligned and balanced knee. In some embodiments, the definition of the proper soft-tissue tension to be used for the plan is a parameter up to the choice of the surgeon. Generally, the surgeon leverages the load/displacement curves in order to define the joint gap (i.e., the distance between the femur and the tibia) under a defined load. In some embodiments, from the knowledge of these gaps, the surgeon is able to leverage the CAOS system in order to position and orient the femoral component. In some embodiments, the surgeon selects the femoral component based on the change of slope of the load-displacement curve in order to define the optimal tension of the soft-tissue envelope, as described in European Patent No. EP 1304093. 
     Next, in some embodiments, the surgeon prepares the distal femur per the previously defined planning as discussed above.  FIG. 13  shows the femur and tibia after the distal femur has been prepared in this manner. Next, in some embodiments, the surgeon places the properly sized tibial baseplate trial and femoral component trial (e.g., sized based on the size of the tibia and the femur).  FIG. 14  shows the femur and tibia after receiving the tibial baseplate trial and the femoral component trial. 
     Next, in some embodiments, the surgeon selects one of the tibial insert trials  300  from the kit  100 . In some embodiments, the surgeon selects one of the tibial insert trials  300  that is compatible with the size of both the tibial baseplate trial and the femoral component trial, and which has a thickness compatible with the joint gap defined at the planning stage. As noted above with reference to  FIG. 3 , the selected tibial insert trial  300  includes recesses  310  configured to receive the selected sensors  400 , which were previously used with the distractor  200  as described above. In some embodiments, the surgeon assembles the sensors  400  with the selected tibial trial insert  300 .  FIG. 15A  shows a top view and cross-sectional view of one of the tibial insert trials  300  before assembly.  FIG. 15B  shows a top view and cross-sectional view of one of the tibial insert trials after having two of the sensors  400  assembled therewith.  FIG. 15C  shows a perspective rendering of one of the tibial insert trials  300  and two of the sensors  400  before assembly.  FIG. 15D  shows a cross-sectional rendering of the one of the tibial insert trials  300  and sensors  400  of  FIG. 15C .  FIG. 15E  shows the view of  FIG. 15D  after the sensors  400  have been assembled with the one of the tibial insert trials  300 . 
     Next, in some embodiments, the surgeon places the assembled tibial insert trial  300  (i.e., including the at least one sensor  400 ) into the space in the tibial baseplate trial in order to verify the proper balancing of the knee joint as well as the preferred thickness of the tibial insert implant to be used.  FIG. 16  shows the assembled tibial trial  300  and the at least one sensor  400  as inserted into the tibial baseplate trial. This use of the sensors  400  and the data recorded thereby is referred to herein as the “verification stage”. In some embodiments, if the load recorded by the at least one sensor  400  during this stage is lower than expected, then the surgeon may select a thicker one of the tibial insert trials  300  and repeat the verification stage. Similarly, in some embodiments, if the load recorded by the at least one sensor  400  during this stage is higher than expected, then the surgeon may select a thinner one of the tibial insert trials  300  and repeat the verification stage. In some embodiments, in case of slight discrepancy in term of balancing (e.g., the load recorded by the at least one sensor  400  that is to the medial side of the tibial insert trial  300  higher than the load recorded by the at least one sensor  400  that is to the lateral side of the tibial insert trial  300 ), then surgeon may elect to perform a slight ligament release. 
     Next, in some embodiments, the surgeon places the final femoral component and tibial baseplate implants. In some embodiments, the surgeon may elect to perform a secondary verification stage with the final implants in place. In order to do so, the surgeon places the assembled tibial insert trial (i.e., the selected one of the tibial insert trials  300  assembled with the at least one sensor  400 ) into the knee joint in order to verify the proper balancing of the knee joint as well as the preferred thickness of the tibial insert to be used. In some embodiments, the information from the sensor can be used to manage the thickness of the cement mantle during the cementation polymerization. Last, in some embodiments, surgeon places the final tibial insert implant and closes the knee joint. 
     While the present document discloses an application of the proposed method and instrumentation kit to a TKA, it will be apparent to those of skill in the art that this approach can be applied to other applications. In some embodiments, a third sensor-based device can be used in the patella-femoral joint in order to provide guidance regarding the level of soft-tissue tension. In some embodiments, the exemplary method and kit can be applied to a unicondylar knee arthroplasty. In such an embodiment, the mechanical distractor may be be configured to only distract one compartment of the knee joint, and only one sensor may be used (instead of two sensors as discussed above). The exemplary embodiments described herein are described with specific reference to the knee joint. However, the broader principles of this disclosure can apply to any other joints (e.g., ankle, hip, elbow, shoulder) that may benefit from the proposed improvements by, for example, changing “tibia” and “femur” to “first bone” and “second bone”, respectively. 
     While a number of embodiments of the present invention have been described, it is understood that these embodiments are illustrative only, and not restrictive, and that many modifications may become apparent to those of ordinary skill in the art. Further still, the various steps may be carried out in any desired order (and any desired steps may be added and/or any desired steps may be eliminated). All publications and other references mentioned herein are incorporated by reference in their entirety, as if each individual publication or reference were specifically and individually indicated to be incorporated by reference. 
     Publications and references cited herein are not admitted to be prior art.