Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1996-03-21
1998-04-07
Brittingham, Debra S.
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
A61F 230
Patent
active
057359008
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/GB94/02284 filed Oct. 19, 1994.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is directed to bone implants and in particular to prosthesis for total joint replacement.
2. Discussion of Related Art
Total joint replacement is now becoming a commonplace method of treating disorders, such as acute arthritis, where the diseased joint is removed surgically and replaced with an artificial joint. As such operations have become more common, problems arising from long-term wear of such joints have become apparent. In a number of instances, it is found that bone resorption occurs in the region of the implant which leads to the loosening of the implant in the bone canal, and the breakdown of any cement mantle between the implant and the bone canal.
Various suggestions have been made as to the cause of such degeneration. It is believed that a primary reason for this loosening is the ingress of wear particles, generated by prolonged movement of the articulating surfaces of the joint and that such particles migrate from the area of articulation into the junction between the implant and the bone. It is believed that wear particles generated in this way at the articulating surfaces migrate along the cement/metal interface (or between the bone and the implant), and cause endosteal erosion. Progressive erosion ultimately causes breakdown of the cement mantle or sufficient loosening of a cement-less stem such that it can become displaced from the bone canal or socket.
OBJECTS AND SUMMARY
It is a primary object of the present invention to provide a means for overcoming this problem and to enable total joint replacement prostheses to have a longer effective life.
According to one aspect of the present invention, there is provided a method of sealing the interface between a prosthesis and a bone, in which the prosthesis is implanted, which method comprises applying a membrane over the junction between the prosthesis and the bone, said membrane having a microporous structure whereby liquids are able to pass through the membrane but wear particles generated by articulation of the prosthesis are excluded.
Preferably, the microporous membrane has openings which are sized so as to exclude connective tissue cells, whereby bone regeneration under the membrane is also encouraged.
Since the membrane is installed essentially permanently in the area of the prosthesis, the membrane should be one which is highly bio-compatible and essentially inert to body fluids. Examples of suitable polymer materials include silicone polymers, polyurethane, polyethylene, polyesters, polypropylene, polyacrylates and methacrylates and fluorinated olefins, especially perfluorinated olefins, e.g. perfluorinated ethylene and propylene. Polytetrafluoroethylene is currently preferred. Methods of producing microporous polymer membranes of this type are known and are described, for example, in U.S. Pat. Nos. 3,953,566 & 4,187,390. An example of one commercially available product is the microporous polytetrafluoroethylene material manufactured by W. L. Gore & Associates Limited, under the trade mark "GORE-TEX ePTFE". This material has been used successfully in the past as a suture material and also for periodontal material, to encourage bone growth in the area of tooth roots where the gums are regressed. The wear particles produced by articulation of the joint are generally small particles of metal or plastics material of micron or sub-micron size and the pore size in the membrane material should be selected so as to exclude particles of such sizes. The above cited U.S. Patents give details of how such microporous materials can be manufactured and its disclosure is specifically incorporated herein. The membrane may be a single sheet material or a laminate.
The invention will now be illustrated with reference to the accompanying drawings, describing the application of the invention to a total hip replacement prosthesis, although it will be appreciated that the invention may also be applied to other joints,
REFERENCES:
patent: 4731088 (1988-03-01), Collier
patent: 4822368 (1989-04-01), Collier
patent: 5514182 (1996-05-01), Shea
Barrett David
Blunn Gordon
Muirhead-Allwood William
Walker Peter Stanley
Brittingham Debra S.
University College London
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