Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1995-08-30
1998-05-26
Isabella, David J.
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
A61F 238
Patent
active
057558027
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a knee-joint endoprosthesis with a femoral part, a tibial part and a bearing element made of plastic, in particular polyethylene, which is disposed between the femoral and tibial parts in such a way that the bearing element is slidably seated on a bearing surface of the tibial part that faces the femoral part and is spherically concave in shape.
BACKGROUND OF THE INVENTION
A knee-joint endoprosthesis of this kind has been disclosed in U.S. Pat No. 4,224,696. This knee-joint endoprosthesis permits both a rotational movement and a sliding movement of the bearing element on the tibial bearing surface, with the consequence that the knee joint can continue to move in a nearly natural manner. The known knee-joint endoprosthesis does not, however, comprise structural features to ensure precise rotational and longitudinal guidance of the bearing element. Furthermore, there is a risk that the bearing element will "rock out" beyond the tibial bearing surface or tibial plate, toward either the front or the back.
Other knee-joint endoprostheses are known that enable only rotation of the bearing element relative to the tibial bearing surface, and do not allow transverse displacement (T.A.C.K. knee-joint prosthesis system of the firm Waldemar Link GmbH & Co., Hamburg, Prospectus 736 d-en 3.92). This knee-joint prosthesis does achieve a relatively uncomplicated structure, but because the bearing element can merely rotate, the natural movement of the knee joint is imitated to only a limited extent. On the other hand, means are provided to keep the bearing element seated on the tibial bearing surface. However, if the rotational movement should be excessive, here too there is a danger that the femoral part will be lifted away from the bearing element with the possible consequence of undesired luxation.
SUMMARY OF THE INVENTION
It is the object of the present invention to develop a knee-joint endoprosthesis of the kind described at the outset in such a way as to guarantee precise rotational and longitudinal guidance. Moreover, the bearing element is to be reliably prevented from "rocking out" beyond the tibial plate.
At the same time, however, the prosthesis is designed to ensure that, as in the natural knee, the resistance to flexion does not increase as the knee is flexed or bent by greater amounts.
This object is achieved in accordance with the invention by a knee-joint endoprosthesis including a femoral part, a tibial part, and a bearing element made of plastic, in particular polyethylene, which is disposed between the femoral and tibial parts. The bearing element is slidably supported on a spherically concave bearing surface of the tibial part which faces the femoral part. Advantageously, a stopping device projects above the tibial bearing surface and enters an elongated opening in the supporting and sliding surface of the bearing element that faces the tibial bearing surface. The stopping device and opening cooperate in such a way that the bearing element can rotate on the tibial bearing surface and also, to a limited degree, be displaced longitudinally in the plane of knee flexion. Also, the geometrical median long axis of the bearing surface of the tibial part is tilted backward from the median long axis of the extended knee-joint endoprosthesis, so that the tibial bearing surface in the implanted state is correspondingly inclined downward toward the back. In a particularly worthwhile feature, the stopping device is peglike or rodlike and comprises a cap screw with a head that can be screwed into the tibial bearing surface to hold the bearing element onto the tibial bearing surface. Another advantageous detail is the prevention of the bearing element from "rocking out" beyond the tibial bearing surface, while simultaneously the inclination of the tibial bearing surface in accordance with the invention keeps the resistance to flexion relatively small even in the end phase of knee bending or flexion, particularly in combination with a femoral part having a radius t
REFERENCES:
patent: 4016606 (1977-04-01), Murray et al.
patent: 4224696 (1980-09-01), Murray et al.
patent: 4936853 (1990-06-01), Fabian et al.
patent: 4950297 (1990-08-01), Elloy et al.
patent: 5271747 (1993-12-01), Wagner et al
patent: 5395401 (1995-03-01), Bahler
T.A.C.K. Knee-joint Prosthesis system, Waldemar Link GmbH & Co., Hamburg, Prospectus 3/92.
Gerber Bruno E.
Isabella David J.
LandOfFree
Knee-joint endoprosthesis does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Knee-joint endoprosthesis, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Knee-joint endoprosthesis will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1955417