Patent Application
20070233268
This invention relates to the field of arthroplasty, and particularly to interpositional knee arthroplasty.
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.
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.
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.
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.
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.
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.
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.
With general reference to
In the embodiment shown in
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
As shown in
With reference to
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.
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
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.
With reference to
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.
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.
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.
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.
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
While
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.
