Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1992-01-31
1994-05-24
Isabella, David
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
623 16, 623 18, A61F 238
Patent
active
053144805
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an improved metal-backed patellar component for implantation in a patient during a total knee replacement operation.
Recent studies suggest that existing designs of metal backed patellar components lead to failures occurring in which the component is not only destroyed but can also cause other problems such as severe pain, abrasion of the femoral component, metal induced synovitis and severe inflammation.
Such conventional designs commonly comprise a metal base plate embedded within a dome of polyethylene, and these failures have been attributed to one or both of two factors. One factor is the cracking of the polyethylene over the sharp edge of the rectangular cross-section of the metal plate, and the other factor is a shearing dislocation either of the polyethylene from the metal base plate or the shearing of the entire patellar component, including the metal base plate, from the anchoring pegs which remain firmly embedded in the cancellous bone of the natural patella.
It is therefore the aim of the present invention to provide an improved patellar component which eliminates or at least reduces the above-mentioned disadvantages.
According to a first aspect of the present invention there is provided a patellar component for use in conjunction with a prosthetic knee joint of the type which comprises a femoral component and a tibial component, the patellar component comprising a first member having a substantially flat bearing surface for bearing against the femoral component, a second member having means for fixing said second member to the natural patella, and means for holding said first and second members together.
Preferably, the first member is manufactured from a plastics material such as ultra-high molecular weight polyethylene, and the second member is manufactured from metal such as stainless steel.
Conveniently, both first and second members take the form of flat discs, one of which (the first member) has a recess in one surface thereof for receiving the other disc (the second member).
Preferably, the first and second members each have a central aperture therein for receiving a central peg which serves to retain the two members together.
Conveniently, said central peg also includes a fixation device to be driven into the bone of the natural patella.
In addition to the central peg, further means for fixing the second member to the natural patella comprises a series of spikes spaced equally around the circumference of the second member. These spikes are also preferably of metal, and may be separate from or continuous with the second member.
According to a second aspect of the present invention, there is provided an endoprosthetic assembly of components for use in total knee replacement, the assembly including a femoral component for attachment to the femur, a tibial component for attachment to the tibia and patellar component for attachment to the natural patella, in which the patellar component is formed with a substantially flat bearing surface and the femoral component is formed with a substantially cylindrical bearing counterface, the flat surface of the patellar component bearing against the cylindrical surface of the femoral component.
The bearing interengagement between the flat patellar component and the cylindrical counterface on the femoral component of the knee prosthesis guarantees line bearing contact between the patellar and femoral components. Contact stress is reduced in comparison to domed or other contoured patellar components which conventionally run in tracks on the femoral component. With these conventional designs, a combination of variable track geometry, practical manufacturing tolerances and practical surgical inaccuracies may result in there being only point contact between the bearing surfaces of the patellar and femoral components. By way of contrast with the flat patellar component of the present invention, proper tracking and line bearing contact is independent of surgical inaccuracy. The cylindrical patellar bearing surface of the femor
REFERENCES:
patent: 3878566 (1975-04-01), Bechtol
patent: 3927423 (1975-12-01), Swanson
patent: 4007495 (1977-02-01), Frazier
patent: 4285070 (1981-08-01), Averill
patent: 5019104 (1991-05-01), Whiteside et al.
Elloy Martin A.
Johnson Robert
Brittingham Debra S.
DePuy International Ltd.
Isabella David
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