Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
523115, 523457, 524436, 501 70, 501109, 264 6, 623 18, 623 19, 623 20, 623 23, A61L 2700, C08K 322
FIELD OF THE INVENTION
The invention pertains to the use of glassy crystalline materials in the field of joint endoprosthetics by an elastic embedment of suitable ceramic bodies in physiologically harmless addition-polymerization synthetics in the socket, and by the minimization of frictional and abrasive forces through a combination with highly polished ceramic bodies in the ball, as well as by an optimal design of the sliding surfaces with respect to one another. The composite material thus serves as a sliding counterpart in artificial joints (e.g., hip, knee, elbow, shoulder, wrist and ankle joint prostheses, etc.) in which the other sliding counterpart consists of a molded body made of an Al.sub.2 O.sub.3 ceramic. Prostheses such as these are used in various disciplines within bone replacement surgery, orthopedics and traumatology.
BACKGROUND OF THE INVENTION
Although progress has been made in the field of synthetic joint replacement by making one sliding counterpart consist of an Al.sub.2 O.sub.3 ceramic and the other consist of a synthetic material, sufficient examples of prosthesis failures have become known.
The state of this technology which had been attained by approximately the year 1987 has been described by P. Eyerer (in Zeitschrift fur Werkstofftechnik [Materials Technology Journal] 17 (1986), pp. 384-91, 422-28, 444-48).
DD-PS 272603 further explained the disadvantages of the various forms of polyethylene (e.g., PS-D 2129832), which have been used extensively until now. However, the same document also explained why one should not dispense with the damping effect of an organic polymer against shock loading (e.g., in a hip joint endoprosthesis). The use of a socket and joint head consisting of an Al.sub.2 O.sub.3 ceramic thus becomes theoretically questionable (DE-PS 2305333).
To be specific, in the case of implants of bioinert materials based on ceramics, there is a large modulus difference between the implant and the bone. This often represents the cause of implant failure.
The associated failure mechanisms are attributable on one hand to undamped stress peaks at the sliding interface and the resulting pressure on one of the sliding counterparts, and on the other hand to constant local irritation in the osseous implant bearing and the resulting disintegration of the bone.
A composite material was therefore introduced as a solution to these problems. This composite material is based on a polyurethane or epoxy resin component and a filler material.
Patent specifications pertaining to this subject explain that materials of the CaO--P.sub.2 O.sub.5 --SiO.sub.2 type with apatite and wollastonite crystal phases prove advantageous.
On the other hand, these very materials are known to possess excellent bioactive properties--that is, they form a direct bond with the bone (without connective tissue), as a result of their superior surface reactivity.
Although these substances are apparently also suitable for the manufacture of the composite material as a sliding counterpart in the interface between a composite and an Al.sub.2 O.sub.3 ceramic, the surface reactivity itself is the justification for suspecting that the hydrolysis stability is inadequate for this application (without direct bone contact). Prevention of an implant failure caused by this insufficient hydrolysis stability is sufficient reason to search for a material which on one hand at least maintains (or even improves) the excellent sliding properties, and on the other hand clearly displays hydrolysis stability in comparison with known bioactive materials (e.g., DD 248351 A1, JP-P 57/191252).
The goal of the invention is to develop wear-resistant joint endoprostheses with long-term stability.
SUMMARY OF THE INVENTION
The invention is based on the task of improving the hydrolysis stability of known joint endoprostheses with a socket consisting of a polymer matrix containing an inorganic component with apatite and/or wollastonite crystal phases.
The task of the invention is accomplished by attaining a nonwearing operation of the conve
patent: 3803279 (1974-04-01), Bailey, Jr. et al.
patent: 3939497 (1976-02-01), Heimke et al.
patent: 4652534 (1987-03-01), Kasuga
patent: 4714721 (1987-12-01), Franek et al.
patent: 4731394 (1988-03-01), Vogel et al.
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Chemical Abstract Service Abstract No. 112:165028j for East German Patent No. DD 248,351, Sep. 1984.
English titles and abstracts for the following patents (written by Derwent): JP 57191252, EP 0315795/US 4969910, EP 0216016/US 4731394, DD 248351, DD 272603/DE 3917035, DE 2129832, DE 2305333 (English title only), and DE 2365022/US3939497.
P. Eyerer, Zeitschrift fuer Werkstofftechnik, 17, pp. 384-391, 422-428 and 444-448 (1986) untranslated Jul. 9, 1993.
Eska Medical Luebeck Medizin Technik GmbH
Merriam Andrew E. C.
Michl Paul R.
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