Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1995-05-19
1998-03-03
Isabella, David
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
A61F 240
Patent
active
057230188
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a shoulder-joint endoprosthesis.
DESCRIPTION OF THE PRIOR ART
In nature the shoulder joint has the form of a ball joint, comprising on one side a shallow socket in the shoulder blade and on the other side, connected to the socket, a large head at the end of the humerus. To make the shoulder joint highly mobile, the joint capsule is wide and the ligaments are weakly developed. The forces that arise are thus transmitted into the humerus by way of the outer layers of the bone etc., with no stepwise change in force. The shoulder joint is held together and prevented from dislocation exclusively by muscles. For example, the tendon of origin of the long head of the biceps itself passes through the shoulder joint and under pressure becomes displaced against the humerus.
In the past, in cases of destruction or severe structural alteration of the shoulder joint or glenohumeral joint, i.e. the joint between the shoulder blade and the upper bone of the arm, a great variety of complete joint replacement systems has been proposed for implantation in humans. For example, in German patent Specification DE 32 16 111 C2 a shoulder-joint endoprosthesis is described that comprises a humerus shaft to be anchored in the humerus and a scapula shaft to be anchored in the scapula, each with a round head at its exposed end. The two heads in turn are functionally engaged with one another by way of a ball joint in the form of a spherical, rotatable bearing element. There is a very similar arrangement in the shoulder-joint endoprosthesis described in German Patent Specification DE 27 14 387 C3. All these shoulder-joint endoprostheses have proved to be clearly disadvantageous with respect both to their elaborate construction and to the transmission of forces. In particular, the forces are transmitted by way of the ball heads and the associated shafts directly onto the shoulder blade or the humerus, or directly into the shoulder blade or the humerus. This results in an enormous stepwise change in force and hence a stepwise moment of force, which applies a high load to the shoulder blade and/or the humerus. Not uncommonly a relative movement is induced between the shoulder blade and the scapula shaft on one side and/or the humerus and the humerus shaft on the other, which in turn causes the durability of the whole shoulder-joint endoprosthesis to be low and can also delay the process of osteointegration between the shoulder blade or humerus and the foreign body.
The present invention is directed to the problem of providing a shoulder-joint endoprosthesis that is simple in construction, that has a favorable transmission of forces, and that is highly compatible with the bone.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a shoulder-joint endoprosthesis comprising a glenoid joint socket for attachment to a shoulder blade, a humeral joint socket with an intramedullary prosthesis stem, by means of which it can be attached to a humerus and a joint ball for disposition between the glenoid joint socket and the humeral joint socket so that it is freely movable.
The artificial glenoid joint socket has a rearward part for attachment to the shoulder blade. With this construction, it is possible to replace, for example, a completely shattered glenoid joint. Further, within the scope of the invention, the rearward part or the like is made with a pore diameter greater than or equal to 100 .mu.m to promote ingrowth of the bone of the shoulder blade. This improves the stability of the glenoid joint socket within the shoulder blade.
Although the design of the shoulder-joint endoprosthesis in accordance with the invention represents a departure from nature in that the shoulder-joint endoprosthesis consists of three parts, namely a glenoid joint socket, a humeral joint socket and freely movable central joint ball disposed between the glenoid joint socket and the humeral joint socket, this arrangement provides additional degrees of freedom so that especially great
REFERENCES:
patent: 3879767 (1975-04-01), Stubstad
patent: 3916451 (1975-11-01), Bucchel et al.
patent: 4550340 (1985-10-01), Kinnett
patent: 4846840 (1989-07-01), Ledercq et al.
patent: 4976738 (1990-12-01), Frey et al.
patent: 5108440 (1992-04-01), Grundei et al.
International Publication WO 89/07917 by Bioconcepts, Inc. entitled "Frangible Modular Joint Prosthesis".
Cyprien Jean-Maxwell
Gerber E. Bruno
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