Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Patent
1998-03-11
1999-12-28
Willse, David H.
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
623 18, A61F 242
Patent
active
060075805
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a joint prosthesis intended to be mounted between two bones to be joined together, wherein the joint prosthesis comprises a spacer part intended to be placed between the joint surfaces of the bones to be joined, and which is manufactured of biodegradable polymer, copolymer, polymer mixture and/or composite, and fixation parts which are arranged to fix the spacer part to the bones to be joined.
In surgery, it is previously known to use synthetic, elastic joint implants made of non-biodegradable plastics to replace joints between small bones in hands and feet. A typical biostable elastic joint prosthesis is composed of (a) a spacer part placed between the bones to be joined, and (b) a proximal and distal elongated fixation part both of which are placed inside the bones to be joined. This type of artificial joint includes for example, Silastic.RTM. implants made of silicon elastomer (Manufacturer: Dow Corning S.A., Valbourne Cedex, France).
When inserting an artificial joint, one or both, for example, of rheumatism damaged joint surfaces are customarily removed partially or totally, and inside the joint capsule, an elastic implant is placed to function as joint prosthesis for keeping the bones to be joined at a desired distance from each other, and allowing the joint to be bent by muscular powers. Artificial joint operations in hand, wrist and feet areas are described, for example, in the book "Surgery for Rheumatoid Arthritis," Eds. M. Clayton and C. Smyth, Churchill Livingstone, New York, 1992.
However, the use of joint prostheses manufactured of biostable polymers, polymer mixtures and elastomers may cause problems to the patient. A permanent strain limit for the operated limb has to be set. For example, when Silastic.RTM. joint prostheses are used, the operated hand may be strained only with a burden of 5 kg. Overstraining may lead to breaking or wearing of the implant which forms the joint prosthesis.
Furthermore, wearing and/or corrosion may cause that particles come loose of the biostable implant operating as joint prosthesis, which particles effect a chronic inflammation reaction, i.e., a synovitis, and/or osteological changes in the bone. Further, the inflammation reaction may cause tumefaction and pain in the joint even to the degree that the joint prosthesis has to be removed.
It is the surprising discovery of the present invention that by manufacturing an elastic joint prosthesis, mainly according to the manner described in the characterizing part of the claim 1, it is possible to eliminate the above described disadvantages related to prior art solutions and to substantially improve the level of technology applied in the field of surgically inserted joint prostheses, particularly the functionality and strength of the joint provided with a joint prosthesis, and to avoid harmful and chronic foreign substance reactions. It is possible to eliminate the above presented problems typical for biostable joint protheses by means of a joint prosthesis according to the invention, which joint prosthesis is manufactured of biodegradable polymer, co-polymer, polymer mixture or polymer composition in a manner that it is composed of (a) a porous interposition spacer part, and (b) a proximal fixation part fixed in the bones to be joined to each other, and (c) a distal fixation part.
A joint prosthesis in accordance with the invention can be inserted in the hand, wrist or feet areas to replace the damaged joint entirely or partially. The porous spacer part of the prosthesis keeps the bones to be joined at a desired distance from each other. The spacer part is fixed in the bones to be joined by using a proximal and distal fixation part. The strength and ductility values of the fixation parts have been chosen to allow the bending of the operated joint shortly after the insertion operation.
It is characteristic to the joint prosthesis of the present invention that, because the spacer part is porous and biodegradable, a fibrous tissue is induced to form on its surface and inside it. Earl
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Lehtimaki Mauri
Lehto Matti
Paasimaa Senja
Tormala Pertti
Bionx Implants Oy
Jackson Suzette J.
Willse David H.
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