DE2621123A1 - Carbon prosthesis reinforced by carbon fibres - and pref. impregnated with antifriction resins, for use in replacing joints - Google Patents

Abstract

A prosthesis of C fibre-reinforced C is used to replace a similarly shaped joint in a living body. In multi-axially loaded prostheses, e.g. for hip joints, parallel C fibres are pref. arranged as several inclined strips. Frictional forces and abrasion are reduced by impregnating the C body with a synthetic resin, e.g. PTFE, polyethylene or a silicone rubber. Layers of C fluoride, e.g. applied by direction fluorination, also have good anti-friction properties. Prosthesis pref. contains a shank fitted with a screw thread, to facilitate anchoring in bone tissue. C bodies have average pore dia. >=0.4mm. No special bone cement is needed to fix prosthesis. Elasticity modulus of C fibre-reinforced C prosthesis corresponds to the modulus of the bones, averaging 10-20 kN/mm2. C fibre reinforcement improves impact resistance. Tissues are not damaged.

Description

Joint prosthesis

The invention relates to a prosthesis for replacing a joint in a living body which has the shape of the too. replacing joint is similar.

The replacement of stressed and unencumbered with degenerative, inflammatory, traumatic or other causes significantly impaired in their functionality Joints caused by artificial joint parts is known. For the satisfactory operation of the implanted joint replacement, it is important that the implant is facing each other is inert to human body tissue, i.e. good tissue compatibility having. Other prerequisites are resistance to the diverse mechanical forces acting on the joint and the uniform dissipation of the Forces on the body's own bone tissue. Finest For example, particles not only roughen the sliding surfaces and thus increase them the coefficient of friction, but trigger harmful connective tissue reactions. Instabilities, i.e. loosening of the implant is caused by chemically and mechanically induced Tissue changes and resorptions, whereby according to Wolff's law of transformation the material composition and the Structure of the bone den respective stress stimuli changed accordingly.

Metals such as stainless steels are particularly suitable as materials for joint prostheses and iron-free alloys, synthetic resins such as polytetrafluoroethylene and polyethylene and combinations of these substances have been proposed.

For stressed joints, such as the hip joint, is favorable because of the Abrasion and sliding properties and sufficient mechanical strength Combination of metal / plastic widely used. The prosthetic restoration through Cementing the metal parts, e.g.

of the prosthesis stem, however, could not yet be solved satisfactorily because the metallic prosthesis stems are loosening and due to their great rigidity Can induce degradation phenomena in the bone.

Other possible causes of loosening are those related to the attachment of the stem used bone cement itself and foreign body reactions that lead to a Lead connective tissue encapsulation of the plastic material.

All factors limit the functional time of the Joint replacement, so that, for example, the half-life for hip joint prostheses is only about 5 years. Since, increasingly, younger patients are also getting joint prostheses are cared for, the proportion of patients who visit one several times is growing steadily need to undergo surgery. It grows with each new intervention the complication rate and the chances of success are significantly lower.

According to German Offenlegungsschriften 1 902 700 and 2 138 146 is It is finally known to be artificial limbs, joints and similar parts for the human body from a synthetic resin reinforced with carbon fibers and strength and power flow in the prosthesis due to a special orientation of the Adapt carbon fibers to the respective geometric conditions. According to the German Offenlegungsschrift 2 142 820 is a prosthetic member for replacing a joint with a carbon fiber-coated carrier coated with pyrocarbon known. However, the proposals are elastic because of the different Behavior of bones and prosthesis not likely to solve the problem of loosening To solve joint prostheses.

It is an object of the invention to loosen joint prostheses by resorption of the bone or connective tissue changes and to prevent the Increase survival rate of artificial joints. It's another job of the invention, the joint replacement without the use of a bone cement in the undamaged Anchor bones.

According to the invention, the object is achieved with a prosthesis of the type mentioned at the beginning Type solved, which consists of carbon reinforced with carbon fibers.

The invention is based on the knowledge that the main disadvantage of the physiologically inert and tissue-compatible carbon, namely the brittleness against shock loads by reinforcing the carbon with carbon fibers completely repealed and a tissue compatible one suitable for implants and at the same time mechanically strong material is obtained. The main advantage compared to the known materials used for joint prostheses, their compatibility and mechanical stability is also more or less satisfied, consists in that the modulus of elasticity that consists of carbon fiber reinforced carbon Prosthesis corresponds to the module of bone, which on average is about 10 to 20 kN / '»2 amounts to. The matching or nearly matching elastic behavior of bone and prosthesis causes uniform excessive loads on the bone exclusive application of force from the bone to the prosthesis and vice versa and eliminated thus disruptive stimuli that result in permanent fusing of the prosthesis in the bone tissue impede.

For multi-axis loaded prostheses it is advantageous to use the reinforcing To arrange carbon fibers in several mutually inclined piles, with the Longitudinal extension of the fibers within a group with a main load direction coincides. Such structures, which are similar to natural bones, make it possible a targeted introduction and discharge of forces. After all, it's for mitigation the frictional forces and the wear advantageous, the carbon body with a Synthetic resin such as polytetrafluoroethylene, polyethylene or a silicone rubber impregnate.

Layers of carbon fluoride also have favorable sliding properties, which are expediently applied by direct fluorination.

The prosthesis has a stem-shaped design for anchoring it in the bone tissue Part that engages in a corresponding recess in the undamaged bone.

The stem-shaped part and the recess are useful with one Provided a thread that facilitates an exact fixation of the prosthesis.

In the context of the invention, carbon is exclusively or to understand moldings consisting almost exclusively of the element carbon, thus also moldings made of graphite. Carbon and graphite are physiologically inert Materials, which inter alia due to their porous structure with the bone tissue can enter into a permanent connection. Are particularly suitable for this purpose Bodies with a mean pore diameter of at least 0.4 mm. The usage a special bone cement to fix the prosthesis is therefore not necessary. To create a permanent connection with great mechanical strength Rather, it is sufficient to use parts of the prosthesis that are, for example, stem-shaped or peg-shaped are to be let into corresponding recesses in the bone and the joint for to calm the duration of the overgrowth. Screw connections behave particularly well, wherein the threads are cut into the pin or into the recess. By Larger thread areas can increase the adhesion area and thus the pressure be reduced accordingly in the critical interface. Tensions and relative movements between implant and bone are because of the mismatched or almost mismatched elastic behavior of the implant and bone or just in one for the resorption of bone substance and thus the loosening of the prosthesis insignificant amount possible For the production of carbon fibers it is known Threads made of an organic material such as rayon or polyacrylonitrile in the Usually after a previous thermal or catalytic stabilization to carbonize by heating to about 10000C. Through the choice of raw materials and manufacturing parameters, it is possible to elasticity and strength of carbon fibers to vary over a wide range. Fibers suitable for reinforcement purposes are available in the form of filaments, ropes, staple fibers or woven fabrics.

A method of making carbon fiber reinforced carbon consists in impregnating fabric layers with pyrocarbon, including one Temperature above about 1000 0C hydrocarbon-containing gases on the fiber surfaces be decomposed.

A second suitable manufacturing process is impregnation of laid-out fiber layers, of fabrics or of staple fibers with a synthetic resin, which is first hardened and then carbonized by further heating. The at Excess porosity formed by carbonization can be increased by one or more times Impregnating the body with a synthetic resin or even a pitch can be reduced. Each impregnation step is followed by a carbonization step, to the desired mechanical parameters and also an advantageous porosity and pore size distribution are achieved. The breaking strength of the Carbon body should be at least 50 - 100 N / mm2, the modulus of elasticity preferably 10 - 40 kN / mm . For certain prostheses, such as a hip joint prosthesis, it is because of the different directions of load advantageous, the fibers parallel to the respective To design the direction of force application. Tissue or fiber layers become this Purpose inclined to one another and arranged one above the other.

Carbon, especially in the form of graphite, has a relatively high small coefficient of friction even under dry running conditions. To avoid of superficial abrasion, it is advantageous under certain conditions to use the Impregnate carbon bodies themselves with a synthetic resin - the impregnating agent expediently only fill part of the pores - or the sliding surface of the To provide the prosthesis with a lubricant. Suitable resins are, for example Polytetrafluoroethylene or phenol formaldehyde. Layers have proven to be particularly advantageous of carbon fluoride proven by direct fluorination on the carbon surface are formed. With this surface layer, there is a particularly small coefficient of friction achieved and the wear and tear significantly reduced.

To attach the joint prosthesis, it is useful to use the bone thread itself or the medullary canal. For hip joint prostheses is for example after resection of the femoral head and the femoral neck in the Cut a thread into the compact bone from the medullary canal and the stem-like threaded portion of the prosthesis in screwed this thread. The anchoring of the pan is done, for example, by cones extending in recesses in the iliac, seat and pubic bones.

The invention is illustrated below with the aid of examples.

Example 1 Carbon yarn was used to produce a hip joint prosthesis With the following properties - tensile strength - 1.6 kN / mm2 modulus of elasticity - 0.16 MN / mm2 continuously through a 10% solution of phenol-formaldehyde resin in ethanol drawn and the solvent by storing the yarn in the temperature range between 20 and 30 ° C for the most part removed. The yarn was cut into sections of equal length cut up into a semi-cylindrical, stem-like tapering mold are inserted, with the threads in the vicinity of the mold wall following its contours and with increasing distance from the wall increasingly parallel to the central plane of the Form oriented. The arrangement was then closed under a pressure of 0.5 bar a body with a fiber content of approx. 50%.

The composite body 30 was used to cure the phenol-formaldehyde resin min to 1000 ° C. and then a further 30 min to 150 ° C. and for carbonizing the resin in a nitrogen atmosphere with a temperature gradient from about 20 ° C / h heated to 9000C. The composite body was then connected with a coal tar pitch, whose softening point was 750, impregnated and used in an autoclave for this purpose, the pressure of which is initially reduced to about 0.3 bar and then increased after the tar pitch has been added about 2 bar was increased. The total residence time was about 30 minutes, the temperature 150 0C. The impregnated body was then heated to 900 ° C. as described above.

The prosthesis with a detached ball head and a stem-shaped extension with an incised thread and the ball head was impregnated with polytetrafluoroethylene wax in the surface zone, the viscosity of which at a temperature of 360 ° C. was approx. 80 Pa s.

The spherical prosthetic head was then polished.

The properties of the joint prosthesis were as follows: -2 flexural strength - approx. 80 take modulus of elasticity - approx. 20 kN / mm2 bulk density - approx. 0.8 g / cm3 avg. Pore diameter - approx. 0.4 mm The fracture and especially the elastic behavior the prosthesis corresponds to the average properties of human bones.

Example 2 For a knee joint prosthesis, they were stacked one on top of the other Sections of a carbon fabric in a satin weave in a reaction chamber heated to 11500C and propane under a partial pressure of about 0.4 bar through the Chamber headed. After a reaction time of 24 hours, the spaces between the individual threads filled with pyrocarbon and the compact body became the Carved out prosthesis with a convex sliding surface. For better anchoring In the thigh bone, the back was provided with several grooves and the convex one Sliding surface was polished smooth and by reaction with fluorine, the small proportions Contained a thin layer of hydrogen fluoride at a temperature of about 380 ° C Carbon fluoride produced.

The properties of the knee joint prosthesis were -2 flexural strength - approx. 100 take modulus of elasticity - approx. 22 kN / mm2 bulk density - approx. 1.3 g / cm3 7 claims

Claims (7)

Claims prosthesis for the replacement of a joint in a living one Body which is similar to the shape of the joint to be replaced, thereby g e k e n n -z e i c h n e t that the prosthesis is made of carbon reinforced with carbon fibers consists. 2. Prosthesis according to claim 1, characterized in that it is e k e n n -z e i c h n e t that the modulus of elasticity of the carbon fiber reinforced carbon corresponds to the Module of bone corresponds. 3. Prosthesis according to claim 1 and 2, characterized g e -k e n n z e i c h n e t that several inclined families of parallel carbon fibers in the prosthesis are arranged. 4. Prosthesis according to Claim 1 to 3, characterized in that it is -k e n nz e i c h n e t that the mean pore diameter is at least 0.4 mm. 5. Prosthesis according to claim 1 to 4, characterized in that it -k e n nz e i c h n e t that the prosthesis is impregnated with a synthetic resin. 6. Prosthesis according to Claim 1 to 4, characterized in that it is -k e n n z e i c h n e t that the sliding surfaces are provided with a layer of carbon fluoride are. 7. Prosthesis according to claim 1 to 5, characterized in that it is -k e n n z e i c h Not that the prosthesis includes a stem-shaped threaded portion.