Patent Document

FIELD  
       [0001]     This invention relates to the field of arthroplasty, and particularly to interpositional knee arthroplasty.  
       BACKGROUND  
       [0002]     Arthroplasty involves the surgical reconstruction or replacement of a malformed or degenerated joint. With interpositional arthroplasty, a knee implant is placed between inflamed joint surfaces to keep them apart. Such knee implants are often referred to as knee spacers.  
         [0003]     In one common interpositional arthroplasty procedure, a knee spacer is placed between the tibia and the femur. In particular, the knee spacer is implanted between either the medial or lateral condyle of the femur and the meniscus of the tibia. The knee spacer provides a surface for articulation of the femur relative to the tibia.  
         [0004]     Knee spacers are generally designed to conform to either the femur or the tibia in an attempt to prevent dislocation of the knee spacer within the joint. Various methods have been proposed for conforming the knee spacer within the joint. For example, some knee spacers are formed with a posterior lip that extends distally over the tibia. Other knee spacers are designed to conform to the femur in an attempt to retain the spacer within the joint. However, it has been noted that many of these knee spacers do not prevent in vivo movement of the knee spacer. In vivo movement of the knee spacer is one factor that may significantly contribute to the pain a patient experiences following an interpositional arthroplasty procedure.  
         [0005]     Accordingly, it would be advantageous to provide a knee spacer for an interpositional knee arthroplasty that may be secured in such a manner to prevent in vivo movement of the knee spacer relative to the femur or tibia. It would be of further advantage if such knee spacer could be secured to the tibia in a manner that does not violate the subcondylar plate. It would also be advantageous if the knee spacer could be easily fixed to the femur or the tibia.  
       SUMMARY  
       [0006]     An interpositional knee arthroplasty is disclosed herein. The interpositional knee arthroplasty is configured for attachment to a lateral or medial condyle of a knee, each condyle including articular cartilage and subcondylar bone. The interpositional knee arthroplasty comprises a spacer and at least one fastener extending from the spacer. In one embodiment, the spacer comprises a kidney shaped plate. The fasteners are attached to one side of the spacer. Each fastener comprises a peg with at least one deformable fin attached to the peg. The deformable fins are cup shaped. In one embodiment, the spacer is also deformable such that a surface of the spacer may be contoured against the condyle.  
         [0007]     In operation, a surgeon forms one or more holes in either the femoral or tibial condyle. In one embodiment, the holes do not perforate the subcondylar plate that forms the perimeter portion of the subcondylar bone. In this embodiment, the holes extend through the articular cartilage and into the subcondylar plate, but do not extend completely through the subcondylar plate. In an alternative embodiment, the holes formed by the surgeon extend completely through the subcondylar plate.  
         [0008]     After the holes are formed in the condyle, the surgeon orients the spacer on the condyle with the fasteners directed toward the holes. The surgeon then presses against the spacer, forcing the fasteners into the holes. As the fasteners are forced into the holes, the deformable fins collapse. The collapsed fins act to wedge the pegs in the holes, thus securing the spacer to the condyle. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  shows a top view of an interpositional knee arthroplasty;  
         [0010]      FIG. 2  shows a fastener for the interpositional knee arthroplasty of  FIG. 1 ;  
         [0011]      FIG. 3  shows a bottom view of the interpositional knee arthroplasty of  FIG. 1 ;  
         [0012]      FIG. 4  shows a side view of the interpositional knee arthroplasty of  FIG. 1 ;  
         [0013]      FIG. 5  shows a cross-sectional view of the interpositional knee arthroplasty along line V-V of  FIG. 4 ;  
         [0014]      FIG. 6  shows a perspective view of a femur and tibia with a first interpositional knee arthroplasty of  FIG. 1  attached to the lateral plateau of the tibia and a second interpositional knee arthroplasty attached to the medial plateau of the tibia;  
         [0015]      FIG. 7  shows a proximal view of the tibia of  FIG. 6  showing the first interpositional knee arthroplasty positioned in the lateral plateau and the second interpositional knee arthroplasty positioned in the medial plateau; and  
         [0016]      FIG. 8  shows a cross-sectional view of the tibia of  FIG. 6  showing holes formed in the tibial condyles and the peg members extending into the subcondylar plate of the tibia. 
     
    
     DESCRIPTION  
       [0017]     With general reference to  FIGS. 1-5 , an interpositional knee arthroplasty  10  comprises a spacer  12  and a plurality fasteners  14  extending from the spacer  12 . As explained herein, the arthroplasty  10  is configured for attachment to either the lateral or medial plateau of the tibia.  
         [0018]     In the embodiment shown in  FIGS. 1 and 3 , the spacer  12  comprises a plate that is generally kidney shaped when viewed from the top and bottom. The spacer  12  is greater in length measured from its anterior side  20  to its posterior side  22  than it is in width measured from its medial side  24  to its lateral side  26 . While the kidney shape of the spacer has advantages with respect to attachment of the spacer to the condyle, one of skill in the art will recognize that other shaped spacers may also be used.  
         [0019]     The spacer  12  is comprised of a biocompatible material, either a polymer or metal such as ultra high molecular weight polyethylene (UHMWPE), polyurethane (PU), cobalt chrome (CoCr), or titanium (Ti). As shown in  FIGS. 1 and 4 , the top surface  18  of the spacer  12  is generally smooth with rolling contours. These rolling contours are designed to mimic the surface of a condyle facing the meniscus of the tibia.  
         [0020]     As shown in  FIGS. 3 and 4 , the bottom surface  28  of the spacer  12  is generally flat with the fasteners  14  extending from the bottom surface  28 . In one embodiment, the spacer  12  is somewhat flexible, allowing the bottom surface  28  to be bent in order to match the curved surface of the condyle when the spacer  12  is attached to the condyle. This distortion of the spacer  12  to match the curved surface of the condyle is more easily achieved because of the kidney shape of the spacer. In particular, the kidney shape of the spacer facilitates spacer distortion such that the bottom surface  28  more closely conforms to the curved surface of the condyle. In an alternative embodiment, the spacer  12  is more rigid, but the bottom surface  28  of the spacer is curved, allowing the bottom surface  28  of the spacer to conform to the curved surface of the condyle.  
         [0021]     With reference to  FIG. 4 , the fasteners  14  may comprises peg members  15  that extend from the bottom surface  28  of the spacer  12 . The plurality of peg members  15  each include a rigid center peg  30  and a plurality of deformable fins  32  attached to the center peg. In the disclosed embodiment, the deformable fins  32  comprise cup structures  33 . Each cup structure  33  is secured at a central location to the center peg  30  and extends from such central location upward toward the bottom surface  28  of the spacer  12 . A first cup structure  33  is positioned at the end of the center peg  30 . A second cup structure is positioned at a midpoint of the center peg.  
         [0022]     The cup structures  33  are secured to the center peg  30  by any of numerous methods. For example, the cup structures  33  may be secured to the center peg using adhesives or fasteners. In one embodiment, the center peg is comprised of a plurality of peg segments which are attached by one peg segment threadedly engaging an adjacent peg segment. In this arrangement, an extending screw portion of one peg segment is inserted through a center hole in a cup member and the adjacent peg sections are screwed together. This action clamps the center hole of the cup member between peg segments. Of course, numerous other methods may be used to secure the cup members  33  to the center peg, as will be recognized by those of skill in the art.  
         [0023]     The center peg member is comprised of an appropriate rigid bio-compatible material, either a polymer or metal such as titanium or cobalt chromium. As shown in  FIG. 5 , each center peg  30  extends into the spacer  12  through the bottom surface  28 , allowing the center peg to be fixed to the spacer. The center peg includes a threaded top portion  34 . The threads on the top portion  34  of the center peg  30  engage threaded holes  36  in the bottom of the spacer to secure the center peg to the spacer. Adhesives may be used in the holes  36  of the spacer  12  to further secure the peg members  14  to the spacer  12 . Of course, various other methods may be used to secure the center posts to the holes in the spacer, such as adhesives, friction fit, or snap fit arrangements, as well as other arrangements as will be recognized by those of skill in the art. Alternatively, the peg members may be integral with the spacer, such as an arrangement where the peg members are molded with the spacer as a one piece construction.  
         [0024]     The deformable fins  32  or cup members  33  are designed in a manner and/or are comprised of an appropriate material that facilitates deformation of the fins. For example, the deformable fins  32  may be comprised of an appropriate deformable biocompatible material having relatively flexible characteristics, such as polyethylene or polyurethane. As explained in further detail below, the deformable cup members  33  are designed to collapse when forced into holes formed in the articular cartilage of the condyle. In alternative embodiments, the deformable fins  32  take different shapes other than that of cup members. For example, the deformable fins may comprise clover structures, spoked structures, circular structures that are not cupped, or numerous other designs. Furthermore, with certain designs, the deformable fins  32  may be comprised of a relatively rigid material instead of a flexible material. For example, in one embodiment, the deformable fins are comprised of a relatively rigid metal material arranged as a clover leaf cup structure. Such rigid metal fin structures will typically have a lesser thickness than fins comprised of more flexible material such as PE or PU.  
         [0025]     With reference to  FIG. 3 , the plurality of peg members  15  are placed on the bottom surface  28  of the spacer  12  in an arrangement that promotes a secure attachment of the spacer  12  to the condyle. In the arrangement of  FIG. 3 , four peg members  15  are provided on the bottom surface  28  of the spacer  12 . However, depending on numerous factors such as the size of the patient and particular shape of the spacer, different numbers of peg members may be used in different configurations.  
         [0026]     In order to secure the interpositional arthroplasty to either a femoral or tibial condyle, the surgeon first prepares the condyle by forming holes in the condyle.  FIGS. 6-8  show an exemplary embodiment where an interpositional arthroplasty  10  is secured to each tibial condyle  43  and  44 .  FIG. 8  particularly shows a cross-sectional view of the tibia  40  with holes  60  formed in the tibial condyles  43  and  44 .  
         [0027]     Before the holes  60  are formed in the condyles  43  and  44 , the surgeon first clears the interior portion of the meniscus  46 . With the interior of the meniscus  46  cleared, the medial tibial condyle  43  and lateral tibial condyle  44  are open to receive an arthroplasty  10 . In one embodiment, the surgeon may also smooth the exterior articular cartilage  47  to prepare a surface for the spacer  12 .  
         [0028]     Once the interior portion of the meniscus  46  is cleared, holes  60  are formed in the condyles  43  and  44  using a drill and guide arrangement. Such arrangements are common in prosthetic procedures. In this case, the drill and guide arrangement is configured to create a hole  60  in the condyle that extends to the subcondylar plate  48 . In one embodiment, the depth of the hole extends through the articular cartilage  47 , but does not extend completely through the subcondylar plate  48 . The actual depth of such a hole will depend upon the patient, but the typical depth of such a hole in the condyle that does not extend through the subcondylar plate  48  is less than eight mm. In an alternative embodiment, the hole created by the surgeon in the condyle extends completely through the subcondylar plate  48 , thus perforating the subcondylar plate. In any event, the diameter of the hole that is created in the condyle is slightly larger than the diameter of the center peg of a peg member, but smaller than the diameter of deformable a cup member  33 . This allows the peg member to be inserted into the hole while causing the cup members  33  to collapse.  
         [0029]     After the holes are formed in the condyles, the surgeon aligns the peg members  15  with the holes in the condyle and manually presses against the spacer  12  to force the peg members  15  into the holes.  FIG. 8  shows the peg members  15  inserted in the holes  60 . When the deformable cup members  33  are forced into the holes in the condyle along with a peg member  15 , the deformable cup members  33  collapse since the diameter of the hole  60  is less than the diameter of the cup members  33 . The deformed cup members  33  are collapsed into excessive space in the hole and wedge the center peg in the hole in a friction fit arrangement. The deformed cup members are represented in  FIG. 8  by the rectangular portions positioned between the holes  60  and the peg members  15 . The wedging action of the deformed cup members effectively secures the arthroplasty to the associated condyle.  
         [0030]     Following implantation, the spacer  12  of each arthroplasty  10  is secured to a condyle  43  or  44  and covers a substantial portion of the exterior surface of the condyle. In particular, each spacer  12  is configured to cover the articular cartilage  47  surface portion of the condyle that would normally contact the meniscus  46  of the tibia  44 . Thus, as shown in  FIG. 6 , the top surface  18  of each spacer  12  is exposed to the femur  50 , with each top surface  18  directly opposed to a femoral condyle  51 ,  52 . With the spacers  12  in place, inflamed joint surfaces on the femur and tibia are separated, thus relieving pain encountered by the patient. Furthermore, with the arthroplasty secured to the condyle, in-vivo movement of the arthroplasty is restricted, and less pain is encountered by the patient following the procedure. Also, because the arthroplasty may be secured without perforating the subcondylar plate, the patient may experience less pain following surgery along with a faster recovery time.  
         [0031]     While  FIGS. 6-8  shown an interpositional knee arthroplasty  10  attached to both the medial tibial condyle  43  and the lateral tibial condyle  44 , some surgeries may only call for the use of a single arthroplasty secured to a single condyle, depending on the needs of the patient. Furthermore, as mentioned above, the interpositional knee arthroplasty may be secured to either the tibial condyles or the femoral condyles.  
         [0032]     Although the present invention has been described and shown with respect to certain preferred embodiments, it will be appreciated by those of skill in the art that other implementations and adaptations are possible. For example, although the pegs have been shown in the figures extending in a perpendicular fashion from the spacer, the pegs may also be positioned at an acute angle, such that the pegs enter the condyle at an associated angle. As another example, different shaped or different numbers of fins may be attached to each peg. Moreover, in addition to alternative embodiments, there are advantages to individual advancements described herein that may be obtained without incorporating other aspects described above. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred embodiments contained herein.

Technology Category: 1