Implantable prosthetic patellar components

Details Implantable prosthetic patellar components Implantable prosthetic patellar components

1995-11-17

1998-03-03

Shay, Randy C.

Prosthesis (i.e., artificial body members), parts thereof, or ai

Implantable prosthesis

Bone

612 18, A61F 238

Patent

active

057230161

DESCRIPTION:

BRIEF SUMMARY
This invention concerns prosthetic patellar components for implantation in the knee joint of a patient.
A number of different knee prostheses have been developed for surgical treatment of the disabling effects of knee joint deterioration, such as results from arthritis, injury or disease. A fairly common operation nowadays is total knee replacement, where the femoral facets of the proximal tibia as well as the patellar and tibial facets of the distal femur are replaced with prosthetic components. It is also recognised that replacing the articulating surface on the posterior aspect of the patella improves the result of such operations, and prosthetic patellar elements for such a purpose have been developed.
More recently study has been carried out directed to investigation of contact stresses between the patella and the femoral components in three common designs of knee prostheses. At different angles of flexion under a load of 500 newtons contact stresses across the patello- femoral interface were monitored. It was determined from these tests that the contact stress areas move outwards towards the periphery of the interface and the contact stress values increase at increases in knee flexion, for all the designs tested. patellar implants retrieved at revision of the designs tested confirmed wear and deformation in the areas of measured maximum contact stress. All the designs showed poor congruency at all angles of knee flexion.
Examples of prosthetic patellar components are disclosed in DE-U-9116507.5, WO-93/00871 and U.S. Pat. No. 4,041,550. None of these teachings provides a device which suitably accommodates the conditions referred to above.
To improve this situation the present invention provides a novel implantable prosthetic patellar component, comprising a patellar part having one side adapted to be secured to the inner surface of a natural patella, and a femoral part having one side defining an articulation surface to replace the femoral facet of the patella, the opposite sides of said parts being mutually engageable to afford sliding movement therebetween in a medio-lateral direction.
The invention therefore provides an implantable prosthetic patellar component of two-part form, these two parts of the component referred to herein as the patellar part and the femoral part. When in place in a patient the component according to the invention allows sliding movement between the two parts in the medio-lateral direction to accommodate naturally occurring relative movement in this direction. Considerable variation in the quadriceps-patellar ligament angle from subject to subject produces variations in the magnitude of the medio-lateral force acting on the patella, and such variations are allowed for by the component of the present invention. This improves congruency throughout flexion and at various loading of the joint, which has the effect of considerably reducing wear and deformation by reducing contact stresses during movement of the joint.
In a preferred form, the engagement between the two parts allows translational sliding movement only in a substantially medio-lateral direction. In this way, sliding displacement of the whole of one part relative to the other part is limited to that in a substantially medio-lateral direction.
Preferably, either the patellar part or the femoral part has an elongated dovetail slot, the other part having a complementary projection, such as a dovetail rib or a flared stud, the slot and the projection being dimensioned for engagement to afford the sliding movement between the two parts. In this way, the mutually interfacing sides of the parts are held in contact and the risk of dislocation of one part from the other is reduced. The provision of a flared stud accomplishes this whilst at the same time allowing relative rotation about an axis in the anterio-posterior direction.
Certain embodiments of the invention will now be described by way of example with reference to the accompanying drawings, in which:
FIGS. 1a and 1b illustrate a patellar part of a prosthetic patella

REFERENCES:
patent: 4007495 (1977-02-01), Frazier
patent: 4041550 (1977-08-01), Frazier
patent: 4151615 (1979-05-01), Hall
patent: 5246460 (1993-09-01), Goodfellow et al

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