Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1989-11-16
1991-05-14
Isabella, David J.
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
623 23, A61F 230, A61F 232
Patent
active
050152564
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and means for fixing joint prostheses.
2. Related Art and Technology
A common method of anchoring a joint prosthesis is cementing it to bone tissue, i.e. filling a gap between the joint prosthesis and the osseous wall with bone cement. The problem of unsatisfactory long-term fixation of cemented prostheses has resulted in that use is now less frequently made of cement for fixing prostheses. In this context, it is vital that the shape of the prosthesis stem, which is inserted in the cavity reamed in the bone, conforms well with the shape of the cavity, and that the bridging distance between the osseous wall and the surface of the prosthesis stem is as short as possible to allow bone tissue to form and, within a reasonable time, grow onto the prosthesis from all sides to anchore it to the osseous wall. The minimum bridging distance is of course a true physical contact between the prosthesis surface and the osseous wall but, in a joint prosthesis in a bone, it is highly unlikely that such contact can be established other than at points, which is not sufficient. It is difficult to combine the cementless method, consisting in establishing such a physical contact and providing good long-term fixation but poor short-term fixation, with the method using bone cement which provides good short-term fixation but poor long-term fixation, since the bone cement isolates the prosthesis surface from the osseous wall.
BRIEF SUMMARY OF THE INVENTION
According to the invention, the fixation of the joint prosthesis to bone tissue is ensured by means of a biologically compatible, granular material in which the grains have a substantially even particle size distribution and are substantially irregular and/or plastic. After the operation is completed, these grains should be tightly packed and locked relative to each other and to the bone tissue and the prosthesis stem. By using grains as anchoring means, larger tolerances between the prosthesis stem and the osseous wall are permissible as compared with conventional cementless operations, the problems linked with the use of bone cement being at the same time eliminated. Thus, the present invention offers a solution to the problem of achieving good short-term fixation as well as good long-term fixation.
In practice, the fixation of the prosthesis can be achieved in different ways.
Preferably, the method according to the invention is carried out in the following way.
A cavity is reamed in the bone in which the prosthesis is to be applied. Grains of biologically compatible material are placed in the cavity so as to form a bed, whereupon the prosthesis is driven down into the grain bed until substantially the entire prosthesis stem is surrounded by the grains. A device for retaining the grains is applied around the prosthesis stem, and the prosthesis is finally fixed, optionally by striking it with a tool.
More specifically, the mixture of grains is first inserted in the cavity so as to substantially fill the cavity as a bed of grains. The grain bed should reach substantially up to the resection surface. The distal end of the prosthesis stem is thereafter inserted in the bed, and the grains are subjected, by a striking force exerted on the prosthesis, to vibrations of such a frequency that the grains are caused to fluidize. While the grains are fluidized, the stem is driven down into the bed, substantially to its intended final position. The grains in the bed are thereafter subjected to vibrations of such a second frequency that packing, i.e. interlocking and compaction, of the grains with respect to each other, and of the grains with respect to the prosthesis stem and the bone tissue is brought about.
After said interlocking and compaction step, the prosthesis may optionally be finally fixed by strokes exerted on the prosthesis in the longitudinal direction thereof.
According to an advantageous and preferred aspect of the invention, said cavity has as lower boundary a stop plug which i
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Bruce Ingrid
Burce Lars
AB Idea
Isabella David J.
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