Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1993-07-23
1994-12-27
Isabella, David
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
623 22, A61F 228
Patent
active
053761251
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to an endoprosthesis, in particular for a hip joint, having an anchoring component which can be anchored to the bone and which is connected to a joint component. Endprostheses are implanted when a satisfactory therapeutic effect can no longer be achieved by operations performed to preserve the joint. This is particularly the case where hip joints are concerned when advanced arthropathy, necrosis of the head of the femur or a medial fracture of the neck of the femur are present.
One disadvantage of all known endoprostheses is that, although these are initially immovably joined with the bone, they can become loose after a certain amount of time. Living bone is constantly undergoing changes which may vary considerably from location to location. If, in the course of such changes, individual sections of the bone should become weakened in the peripheral area of the prosthesis, the bone at this point will give way and the prosthesis will move. Even if such movements occur only in the micro-range, the original stability is no longer guaranteed. Under unstable conditions, the force flows and load distributions on the bone are constantly changing and the bone cannot start any reparative reactions because the conditions for oriented growth are lacking. Instead, at the points where excessive stress builds up (stress reaction) the bone will react by locally atrophying as it does at points where the stress is too low (stress protection). This leads to a progressive loosening of the prosthesis.
Such restructuring of the bone must be expected to occur even years after the prosthesis has successfully healed into place, because bone is a living organ and it reacts to changes in lifestyle, diet and other circumstances. Conventional endoprostheses do not take account of this situation.
A loosening process of this kind is one of the major problems encountered in orthopaedic surgery and it frequently necessitates replacement of the prosthesis. The corrective operations required in this case are, however, much more problem-ridden than the primary interventions because not only is the bone tissue which was removed for the primary implantation now missing, but also usually as a result of the interventions because not only is the bone tissue which was removed for the primary implantation now missing, but also usually as a result of the loosened implant or because of the resulting abrasion, additional serious defects are created which make it extremely difficult or indeed impossible to re-fix the implant.
In the case of hip endoprostheses sometimes only the head and neck of the femur are removed and replaced by a head prosthesis.
In the prior art head prostheses the anchoring component consists usually of a metal spike, for example of titanium, which is fixed in the medullary cavity of the femur and it is fitted with a laterally projecting pin whose free end bears a head section. In order to implant such a prosthesis it is necessary to remove the head and neck of the femur as well as most of the sponglous bone at the proximal end of the femur. The spike is then cemented into the femoral medullary cavity using polymethylmethacrylate, or it is driven into the bone without any cement; in this latter case it is primarily necessary to achieve optimal contact between the bone and the implant, and this may be reinforced by secondary growth of new bone tissue.
German Patent Application DE-A 28 45 231 describes a joint prosthesis in which a joint component is provided with a shaft which is attached to the bone by means of a tension bolt.
German Patent Application DE-A 28 54 334 describes an endoprosthesis of complicated design for a hip joint. The prosthesis consists of a shaft running longitudinally in the medullary cavity of the bone, and a neck part running in the direction of the neck of the femur and carrying the head of the joint. In this design, the shaft in the medullary cavity is rigidly connected to the femoral neck part.
German Patent Application DE-A 30 17 953 reveals an endopros
REFERENCES:
patent: 2668531 (1954-02-01), Haboush
patent: 2682265 (1954-06-01), Collison
patent: 3740769 (1973-06-01), Haboush
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