Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1986-07-23
1988-09-13
Apley, Richard J.
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
A61F 238
Patent
active
047706635
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a knee joint endoprosthesis consisting of a femur part provided with two skid surfaces leaving between each other a free space, said surfaces being connected with each other in front and having their curvature increasing from the front towards the rear and being curved also on planes perpendicular to said curvature, and of a tibia part having two surfaces on which the skid surfaces ride in a sliding manner, with an elevation being disposed between said two surfaces, and of artificial connecting means for keeping together the two parts of the prosthesis.
In a known prosthesis of said type (DE-PS No. 25 49 819), each of the two surfaces of the tibia part is highly concave from the front to the rear on a center sectional plane, i.e., the sliding surfaces of the femur part are fitted congruently. The slopes from the elevuation to the two surfaces are the same, and the parts of the prosthesis are kept together by way of two lugs in the elevation and two grooves in the skids, said grooves being engaged by said lugs. The drawback of said joint is that the conditions of motion are very imperfectly conforming to the conditions of motion in a natural joint.
The invention is based on the problem of developing the above prosthesis in a way such that the conditions of motion are more closely conforming to the natural conditions of motion as compared to the known case, and that phenomena of wear are avoided.
According to the invention, said problem is solved in that the outer surface of the tibia part is largely plane on a center sectional plane from the front to the rear; that the inner surface of the tibia part is slightly concave on a center sectional plane from the front to the rear; that the slope of the elevation to the outer surface is flatter than the slop of the elevation to the inner surface; and that the parts of the prosthesis are kept together by two ending, non-elastic bands, of which a first band extends from the center of the front of the tibia part upwardly, on the outside and inclined rearwardly to the femur part, and of which bands a second band extends from the center in the rear of the tibia part upwardly, on the inside and inclined to the front to the femur part, whereby the bands are taunt when the knee is stretched, and slightly relaxed in the unstressed state when the knee is bent.
In said way, the following is achieved: when bending the joint, the zone of contact of the inner skid sweeps a small arc on the surface associated with it, whereas the zone of contact of the outer skid sweeps a large arc on the surface associated with it, which conforms to the natural conditions.
The following applies with respect to the tension of the bands: The bands are taut when the knee is stretched, and slightly relaxed in the unstressed state when the knee is bent. In the stressed, bent state, both bands are taunt. When the knee is bent in the unstressed state from the stretched position, the tension of the bands decreases gradually.
Of course, the points where the bands are connected with the parts of the prosthesis have to be disposed in a way such that the possible motions are not interfered with. For example, the band extending from the front bottom upwardly and on the outside may not be connected to the tibia part too far in front. Owing to the fact that the curvatures of the skids of the femur part decrease rearwardly, trouble-free bending of the joint is assured.
According to another feature of the invention, two elevations are provided between the surfaces, whereby the outer elevation is disposed slightly to the rear of the inner elevation, and said elevations are connected with each other by way of a saddle surface. In this way, the center part of the tibia part is adapted to the different positions of the bands in the different angular positions of the knee.
It is proposed, furthermore, that the slope to the outer surface gradually changes into the surface with a conical shape.
According to another feature of the invention, the inner and outer surfaces slope off rearwardly wit
REFERENCES:
patent: 3748662 (1973-07-01), Helfet
patent: 4267608 (1981-05-01), Bora, Jr.
Hanslik Lothar
Henssge Joachim E.
Apley Richard J.
Davis IV F. Eugene
Isabella David
Stone Mark P.
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