Abstract:
Disclosed herein are systems and methods of patella arthroplasty. A navigated patella clamp used in an arthroplasty procedure includes first and second movable jaw members and an actuation member coupled to the first and second jaw members for moving the first and second jaw members along a plane toward and away from one another. The patella clamp further includes a tracker and adjustable stylus for positioning the clamp on a patient&#39;s patella below a desired resection plane. The adjustable stylus coupled to the clamp is used to check the position and orientation of the clamp with respect to the patella to ensure the correct amount of bone will be resected from the patella corresponding to the thickness of a patella component that will be implanted on the resected patella.

Description:
FIELD OF THE INVENTION 
       [0001]    The present disclosure relates to a device used in aiding patella preparation and in particular relates to a navigated device that engages the patella in a planned position and orientation such that the patella may be resected in a desired manner. 
       BACKGROUND OF THE INVENTION 
       [0002]    Patella preparation in total knee arthroplasty procedures is generally performed manually with the use of sawblades and clamps. Calipers may be used during preparation to contact opposing superior and inferior surfaces of the patella to aid in determining the depth of the cut. However, these conventional tools do not adequately control the depth and orientation of the cut which also results in the medial/lateral translational and rotational position of a patellar component. 
         [0003]    Patella clamps may be used to clamp the anterior and articular surfaces of the patella before resecting the articular surface of the patella. Additionally, some patella clamps may require fixation pegs or keels to engage the patella before everting it to a desired angle. Common methods to remove bone from the articular surface of the patella include saw resection or milling/planar systems. The removal of bone in either of these systems may provide a flat, stable platform to support, but not secure, a prosthetic patellar component. 
         [0004]    The patella includes boney landmarks such as the articular high point, retinaculum and/or the cartilage border. These landmarks may be referenced by a patella clamp to orient the clamp on the non-resected patella in view of a desired final placement of the patellar component. However, these landmarks are generally irregularly shaped, which makes it difficult to orient the clamp below a planned resection level. 
       BRIEF SUMMARY OF THE INVENTION 
       [0005]    Disclosed herein are systems and methods for navigated patella preparation. A preoperative plan may be developed such that the patella may be intraoperatively prepared to receive an implant component in a desired position and orientation. The present invention includes a navigated clamp for use during the intraoperative bone resection. 
         [0006]    In one method, a patella resection plane is preoperatively planned and the size of a patella component is preoperatively chosen as well as its position with respect to the resection plane. A patella and tracker instrument holder or clamp is provided which intraoperatively informs the surgeon where to place the clamp on the native patella such that the position and orientation of the resection plane can be made with either manual instrumentation or via a robotic cutting arm. 
         [0007]    During preoperative planning, the patella resection plane and implant position are determined. Key boney landmarks of the patella are used in planning the patellar resection plane, which establish the coordinate system for positional alignment of the patella component. The component size and placement plan will consider the cartilage borders (both medially-laterally and superiorly-inferiorly), the articular high point and overall thickness of the patella to calculate size and placement of the patella component. The overall goal is to replicate patient patella thickness with the suggested component thickness. A graphics user interface (“GUI”) will suggest a patella resection level based on the preoperative plan. 
         [0008]    There is a correlation between the patella clamp and the registration tracker instrument. During preoperative planning, the positioning of the patella clamp must be determined to ensure its placement is below the resection plane or level. Intraoperatively, the system informs the surgeon of which stylus setting to use when placing and locking the patella clamp (correlated to patella component position). Also during the procedure, the surgeon places the patella clamp around the patella using the suggested stylus setting. The patella clamps houses a tracker for navigation, and the surgeon registers the patella bone by running a navigated probe across the bone to capture key landmarks. For example, the surgeon could surface map the articulating surface of the patella, the articulation high point, the retinaculum, and/or cartilage border. These landmarks preferably correlate back to the preoperative plan. 
         [0009]    Once the patella is registered, the system knows the position of the patella relative to the tracker housed on the patella clamp. The GUI displays the final patella plan on the bone. A computer aided design (“CAD”) model for the clamp is stored in the system software, so if the surgeon clamps above the resection level or there is a risk of machining the clamp, the system will prompt the surgeon to re-clamp and re-register. Once the clamp is sufficiently positioned and registered, the patella may then be resected using a cutting tool. 
         [0010]    The clamp is designed to accommodate all size and shape patellae since there are two teeth per jaw which bite into the patella. The stylus has some built-in tolerance to ensure the patella is clamped below the level of resection and not in the machining path. 
         [0011]    One aspect of the present invention is a patella clamp comprising first and second jaw members; an actuation member coupled to the first and second jaw members for moving the first and second jaw members along a plane toward and away from one another; a tracker; and an adjustable stylus. 
         [0012]    In one embodiment of the first aspect, the first and second jaw members of the patella clamp each have at least one tooth for engaging a patella. 
         [0013]    In another embodiment of the first aspect, the patella clamp further comprises first and second parallel support members coupled to the first and second jaw members respectively and the actuation member. 
         [0014]    In yet another embodiment of the first aspect, the tracker is coupled to one of the first and second parallel support members. 
         [0015]    In still yet another embodiment of the first aspect, the tracker is capable of receiving and transmitting digital information, the digital information relating to positing the patella clamp with respect to a patella. 
         [0016]    In yet another embodiment of the first aspect, the adjustable stylus is coupled to one of the first and second jaw members. 
         [0017]    In still yet another embodiment of the first aspect, the adjustable stylus is coupled to one of the first and second jaw members via a post, the stylus being adjustable about the post. In another embodiment, the post includes a plurality of grooves for adjust the stylus about the post, each of the plurality of grooves relating to a height of the stylus. 
         [0018]    A second aspect of the present invention is a method of determining a position of a patella implant on a resected patella of a patient comprising displaying a three-dimensional model on a graphics user interface of an unresected patella of the patient; selecting a plurality of landmarks on the three-dimensional model including peripheral cartilage borders and an articular high point of the model; and determining a patellar resection plane on the model and a position of the patella implant with respect to the patellar resection plane. 
         [0019]    In one embodiment of the second aspect, the peripheral cartilage borders include medial, lateral, superior and inferior borders. In another embodiment, the peripheral cartilage borders and articular high point are used to determine a thickness for the patellar implant. 
         [0020]    In another embodiment of the second aspect, the peripheral cartilage borders and articular high point establish a coordinate system for positional alignment of the patellar implant. 
         [0021]    In still yet another embodiment of the second aspect, the plurality of landmarks are used to calculate and suggest a location and an orientation of the patellar resection plane on the model. 
         [0022]    In still yet another embodiment of the second aspect, the method further comprises positioning a patella clamp with respect to the determined patella resection plane, the navigated patella clamp having a tracker and a stylus. In another embodiment, the method further comprises engaging the unresected patella with first and second jaws of the patella clamp and a contact surface of the stylus. 
         [0023]    In yet another embodiment, the first and second jaws engage the unresected patella adjacent the peripheral cartilage borders below the patellar resection plane. The contact surface of the stylus engages the articular high point of the unresected patella. 
         [0024]    In still yet another embodiment of the second aspect, the method further comprises resecting the patella along the patellar resection plane and positioning the patella implant on the resected patella. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]    Other objects and advantages of the present invention will be apparent from the following detailed description of the present preferred embodiments, which description should be considered in conjunction with the accompanying drawings in which like reference indicate similar elements and in which: 
           [0026]      FIG. 1  is a perspective view of a navigated patella clamp of the present invention including a clamp, a tracker and an adjustable stylus. 
           [0027]      FIG. 2  is a perspective view of the clamp shown in  FIG. 1 . 
           [0028]      FIG. 3  is a top view of the clamp shown in  FIG. 2 . 
           [0029]      FIG. 4  is an enlarged side view of a jaw portion of the clamp shown in  FIG. 2 . 
           [0030]      FIG. 5  is a perspective view of a tracker post of the clamp shown in  FIG. 1 . 
           [0031]      FIG. 6  is a perspective view of the tracker shown in  FIG. 1 . 
           [0032]      FIG. 7  is an enlarged side view of an intermediate portion of the clamp shown in  FIG. 1  in which the adjustable stylus is shown in at a certain setting. 
           [0033]      FIGS. 8A-8D  are perspective views of the tracker of the navigated patella clamp of  FIG. 1  in four orientations at least 90 degrees different that one another about a longitudinal axis of the tracker post. 
           [0034]      FIG. 9A  shows the jaw end of the clamp of  FIG. 2  oriented with respect to a patella in a medial to lateral direction in which the jaws are separated a maximum distance from one another. 
           [0035]      FIG. 9B  shows the jaw end of the clamp of  FIG. 2  oriented with respect to a patella in a superior to inferior direction in which the jaws are separated a maximum distance from one another. 
           [0036]      FIG. 9C  shows the jaw end of the clamp of  FIG. 2  oriented with respect to a patella in both medial to lateral and superior to inferior directions in which the jaws are separated a minimum distance from one another. 
           [0037]      FIG. 10  is a front view of the jaws of a navigated patella clamp engaged to medial and lateral portions of a patella showing a resection level and an articular high point representing a corresponding high point of a patella component that will be implanted on the resected patella. 
       
    
    
     DETAILED DESCRIPTION 
       [0038]    In describing preferred embodiments of the disclosure, reference will be made to the directional nomenclature used in describing the human body. It is noted that this nomenclature is used only for convenience and that it is not intended to be limiting with respect to the scope of the invention. When referring to specific directions in relation to a device, the device is understood to be described only with respect to its orientation and position during an exemplary application to the human body. 
         [0039]    As used herein when referring to bones or other parts of the body, the term “proximal” means closer to the heart and the term “distal” means more distant from the heart. The term “anterior” means toward the front part or the face and the term “posterior” means toward the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body. 
         [0040]      FIG. 1  is a perspective view of a navigated patella clamp  100  of the present invention including a clamp  200 , a tracker  300  and an adjustable stylus  400 . Clamp  200  is shown engaged to an exemplary patella bone  10 . 
         [0041]      FIG. 2  is a perspective view of clamp  200  shown in  FIG. 1 . Clamp  200  includes a handle portion  220 , a parallel motion body portion  240  and a jaw portion  260 . Handle portion  220  includes first and second pivotable handle members  222 ,  224 . Each handle member  222 ,  224  includes first and second pin members  222   a ,  222   b  and  224   a ,  224   b , respectively that allow the handle members  222 ,  224 . A pin member  226  is coupled to both first and second handle members  222 ,  224 . Pin members  222   a ,  222   b ,  224   a ,  224   b , and  226  allow handle members  222 ,  224  to pivot toward and away from one another during use. 
         [0042]    Parallel motion body portion  240  includes first and second arm portions  242 ,  244 . Handle portion  222  is coupled at a distal portion of first arm portion  242  by first pin member  222   a , while handle portion  224  is coupled at a distal portion of second arm portion  244  by first pin member  222   b . Handle portion  222  is coupled to second arm portion  244  by second pin member  222   b  which may translate about a slot  254  in second arm portion  244 , while handle portion  224  is coupled to first arm portion  242  by second pin member  224   b  which may translate about a slot  252  in first arm portion  242 . First and second pin members  222   b ,  224   b  may translate in both linear proximal and distal directions within slots  254 ,  252  respectively. As handle portions  222 ,  224  are brought closer to one another, pin members  222   b ,  224   b  generally translate in a proximal direction about slots  252 ,  254  respectively. As handle portions  222 ,  224  are allowed to move away from one another, pin members  222   b ,  224   b  generally translate in an opposite distal direction about slots  252 ,  254  respectively. 
         [0043]    Clamp  200  further includes a thumbwheel  256  with a threaded shaft  258 . Threaded shaft  258  is threaded at least partially into opposing apertures in first and second arm portions  242 ,  244 . As thumbwheel  256  is rotated in a clockwise direction, first and second parallel arm portions  242 ,  244  are brought closer together. As thumbwheel  256  is rotated in a counterclockwise direction, first and second parallel arm portions  242 ,  244  may be separated further away from one another. 
         [0044]    Extending from body portion  240  of clamp  200  is jaw portion  260 . Extending from first and second arm portions  242 ,  244  of body portion are respective first and second jaws  262 ,  264  of jaw portion  260 . Jaws  262 ,  264  each have respective superior surfaces  266   a ,  266   b  and inferior surfaces  268   a ,  268   b . Each jaw  262 ,  264  includes one or more respective teeth portions  270   a ,  270   b . Jaws  262 ,  264  move toward and away from one another as either handle members  222 ,  224  are moved toward and away from one another and/or thumbwheel is rotated in a clockwise or counterclockwise direction respectively. 
         [0045]    Handle members  222 ,  224  and jaws  262 ,  264  move toward and away from longitudinal axis L 1  of clamp  200  shown in  FIG. 3  as clamp  200  is actuated either via handles  222 ,  224  and/or thumbwheel  256 . Clamp  200  engages a patella bone such as patella  10  in  FIG. 1 , for example, such that teeth portions  270   a ,  270   b  of jaws  262 ,  264  engage outer surface portions of patella  10  about longitudinal axis L 2 . Depending on the orientation of clamp  200  with respect to the patella, teeth portions  270   a ,  270   b  may engage respective medial and lateral portions or proximal and distal portions of patella  10 . In reference to patella  10 , the term “superior” is used to reference an upper or outer portion of the bone while the term “inferior” is used to reference a bone contacting, articulating or inner portion of the bone. In this context, the terms “superior” and “anterior” are generally synonymous while “inferior” and “posterior” are generally synonymous. 
         [0046]      FIG. 4  shows an enlarged side view of jaw portion  260  of clamp  200 . A tracker post  440  is shown coupled to clamp  200  with at least a portion thereof received in an aperture  278   a ,  278   b  in the parallel motion body portion  240 . A release mechanism  280  is shown located on each jaw  262 ,  264  of jaw portion  260 . Release mechanism  280  has a neutral locked position. A user can pull-back on contact surface  282  to move release mechanism  280  in a distal direction. Release mechanism is moved into an unlocked position when moved distally. Any known mechanism to provide force on release mechanism  280  proximally or into the neutral locked position can be used such as a spring, for example. When release mechanism  280  is a neutral position, apertures  288   a ,  288   b  on jaw portion  260  are slightly closed or a portion of release mechanism  280  is located within these apertures such that a post within these apertures would be captured and unable to move unless release mechanism  280  was moved distally. 
         [0047]      FIG. 5  is a perspective view of tracker post  440  having a body portion  442 , arm portions  444  and a head portion  446 . Body portion  442  is configured to be received at least partially within either one of apertures  278   a ,  278   b  of clamp  200 . Arm portions  444  and head portion  446  are configured to engage corresponding recesses  462  within tracker  460  shown in  FIG. 6 . Tracker  460  may be engaged to tracker post in at least four positions with respect to a longitudinal axis L 3  of tracker post  440 . Each of the four positions are separated preferably 90° about the longitudinal axis of tracker post  440 . In some embodiments, tracker  460  may rotate together with tracker post  440  with respect to apertures  278   a ,  278   b . The location of tracker post  440  and the size of tracker  460  is such that movement of tracker  460  does not interfere with stylus  400  and vice versa.  FIGS. 8A-8D  are perspective views of tracker  460  in four orientations at least 90° different that one another about longitudinal axis L 3  of tracker post  440 . In each configuration, there is clearance between an outer surface of tracker  460  and stylus  400 . 
         [0048]    As shown in  FIG. 7 , a stylus post  480  is coupled to aperture  288   b  of clamp  200 . Stylus post  480  includes a body portion  482  and a cap portion  484 . Body portion  482  includes a plurality of teeth portions  486  along a length thereof. Stylus  400  has a bore  402  including a plurality of grooves  404  corresponding to the plurality of teeth portions  486  of stylus post  480 . A release button  408  can activated to release the engagement between plurality of grooves  404  corresponding to the plurality of teeth portions  486  of stylus post  480 . When release button  408  is activated, stylus  400  can be slid up and down the length of body portion  482  of stylus post  480  until the release button  408  is released to re-engage the grooves  404  and teeth portions  486 . 
         [0049]      FIGS. 9A-9C  show various positions of jaws  262 ,  264  with respect to patella  10 . In  FIG. 9A , jaws  262 ,  264  of clamp  200  are shown oriented with respect to patella  10  in a medial to lateral direction in which jaws  262 ,  264  are separated a maximum distance from one another about L 2 .  FIG. 9B  shows jaws  262 ,  264  oriented with respect to patella  10  in a superior to inferior direction in which jaws  262 ,  264  are separated a maximum distance from one another.  FIG. 9C  shows jaws  262 ,  264  fully engaged to patella  10  in both medial to lateral and superior to inferior directions such that jaws  262 ,  264  are separated a minimum distance from one another. It should be understood that patella  10  in reference to these maximum and minimum distances is only exemplary and that the location of jaws  262 ,  264  with respect to a patella being operated on will ultimately be based on the size and shape of that patella. 
         [0050]      FIG. 10  is a front view of jaws  262 ,  264  of a navigated patella clamp engaged to medial and lateral portions  12 ,  14  of patella  10  showing a resection level  16  and a articular high point  18  representing a corresponding high point of a patella component (not shown) that will be implanted on the resected patella. The patella includes boney landmarks such as articular high point  18 , retinaculum and/or the cartilage border. These landmarks are generally used in what may be referred to as a bony landmark patella positioning plan. During the pre-operative planning of patella positioning, these landmarks help in determining a position and orientation of the patella implant based on the alignment methodology used for orienting other implants in a TKA procedure, such as a femoral and/or tibial implant. These landmarks may also be used to orient patella clamp  200  on the non-resected patella  10  in view of a desired final placement of the patellar component. Patella clamp  200  positioning preferably utilizes stylus  400  for setting depth and the actual cartilage boarders for setting the angle of the clamp  200 . These reference points help to ensure clamp  200  is not placed where the planned resection plane is, mitigating the need to reposition clamp  200  and re-register. 
         [0051]    During preoperative planning, the size and orientation of a patellar component is taken into consideration when defining resection level  16 . The position of jaws  262 ,  264  with respect to patella  10  is defined such that superior surfaces  266   a ,  266   b  of jaws  262 ,  264  will be oriented such that each is parallel to resection level  16 . The position of superior surfaces  266   a ,  266   b  below resection level preferably takes into account the cutting tool that will be used to resect patella  10  such that there is sufficient clearance that the cutting tool can function without contacting superior surfaces  266   a ,  266   b  while also allowing teeth  270   a ,  270   b  of jaws  262 ,  264  to sufficiently purchase bone of patella  10  and stabilize clamp  200  with respect to bone during patella resection. 
         [0052]    A linear distance D 1  as shown in  FIG. 10  between a bottom surface  410  of stylus  400  and superior surfaces  266   a ,  266   b  is defined in the preoperative plan. Once this linear distance is calculated, the distance preferably corresponds to a specific tooth portion  486  and groove  404  of stylus  400 . A viewing window  412  allows a user to see the position of stylus  400  with respect to the teeth portions  486  of stylus post  480 . Stylus  400  is positioned along stylus post  480  according to the determined position from the preoperative plan. Stylus  400  is designed to not only move linearly about stylus post  480  but also rotationally in order to position with respect to articular high point  18 . Stylus  400  is preferably rotated about a longitudinal axis of stylus post  480  until bottom surface  410  lies just above articular high point  18 . Jaws  262 ,  264  are then oriented into position via tracker  460  and into contact with patella  10  such that superior surfaces  266   a ,  266   b  of jaws  262 ,  264  are oriented parallel to resection level  16 . The patella clamp  200  is now oriented in place with respect to patella  10  according to the preoperative plan and resection of patella about resection level  16  can commence. Once patella  10  is resected a resection may be further made through the planar resected surface to receive a corresponding peg, for example of the patellar component. 
         [0053]    Although the devices and methods described herein are generally described in relation to patella arthroplasty systems, it should be understood that the devices and methods are not intended to be so limited and could be used with other bone and joints, such as other ball and socket joints, including the ankle, shoulder or hip, for example. 
         [0054]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention.