DE29521049U1 - Artificial joint, especially a hip joint endoprosthesis - Google Patents

Description

G 8798 EN

Dr. med. Günther Aldinger

Ob dem Viehweidle 22

72076 Tuebingen

Artificial joint, especially hip joint endoprosthesis

The invention relates to an artificial joint, in particular a hip joint endoprosthesis, with a joint socket and a joint head as interfitting joint partners, the joint contact surfaces of which consist of metal or ceramic.

Hip joint endoprostheses, where the aim is not only to relieve pain for the patient and improve mobility, but also to achieve the longest possible lifespan of the implants, are also known with the above-mentioned material combinations of the joint partners. However, clinically common hip systems and other artificial joints mainly consist of a polyethylene/metal pairing. The pairing of a ceramic joint head in a socket made of plastic material has also proven to be successful. Although high-molecular plastic materials are well tolerated by the body and have good sliding properties, it cannot be overlooked that artificial joints such as hip joint endoprostheses are subject to very high load values with a high number of load cycles and changing load rhythms and that the duration of the load should extend over decades. In this case, it cannot always be assumed that the joint is evenly lubricated, so that joint friction also plays a noticeable role, which can also lead to a

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leads to non-negligible abrasion. Once the abrasion volume reaches a certain level, the resulting abrasion particles are no longer tolerated without irritation by the soft tissue surrounding the artificial joint, and in the specialist literature, particularly in recent times, more and more has been written about the formation of foreign body granulomas and bony osteolysis due to abrasion particles.

It is known that contact surface pairs of metal/metal and especially ceramic/ceramic result in significantly less abrasion on the joint partners. Despite these low wear values, ceramic/ceramic and metal/metal pairs have not yet been sufficiently successful in clinical practice. Improved manufacturing methods, which lead to high dimensional accuracy and contact surface quality with very low roughness depth, as well as material improvements, have now further improved the abrasion resistance of the joint parts. In addition, metals and especially ceramic material can be easily wetted with body fluids. The lower impact/bending strength of ceramic material can also be taken into account by a shock-absorbing bearing of the joint socket in a bed made of plastic material. The remaining reluctance to use the above-mentioned material pairings in clinical practice is nevertheless not unfounded, since laboratory test results cannot be simply extrapolated to clinical results, and in fact, explanted ceramic joint heads from artificial joints with ceramic contact surfaces on both sides have shown abrasion patterns that suggest the following wear mechanism: When the free range of motion of the artificial joint is exceeded, i.e. when the joint head is levered out by the joint neck hitting the edge of the joint socket, as well as when the joint head partially slips out of the joint socket with reduced muscle tone, as occurs, for example, during sleep, there is increased friction of the joint head on the hard, sometimes rough shell edge.

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as well as a break in the scratching fluid film.

The invention is based on the object of designing an artificial joint of the type mentioned at the beginning in such a way that even in the event of a subluxation or partial slipping of the joint head out of the joint socket with reduced muscle tone, abrasion on the joint partners cannot occur.

The stated object is achieved according to the invention in that the edge of the socket, which also forms a contact surface for the joint head, consists of another abrasion-resistant and biocompatible material that is softer than the material forming the contact surface of the joint head.

In an artificial joint designed according to the invention, even in the joint positions mentioned above, no abrasion can occur on the joint head, where abrasion would have a particularly detrimental effect. The softer joint socket edge can expediently consist of a high-molecular plastic material, as is known from clinically common artificial joints. Since the joint socket edge in an artificial joint is subjected to less friction overall, a noticeable increase in abrasion volume must not be expected when using plastic material. However, metal alloys are also possible as a comparatively softer material for the joint socket edge in joints with a ceramic/ceramic contact surface pairing to solve the problem.

Advantageously, the softer material forming the rim of the joint socket can be used to form an intermediate body that can be anchored in a holding body of the joint socket, into which the joint socket made of ceramic or metal that forms the joint contact surface is inserted and is secured in its position by an inwardly projecting contact surface edge of the intermediate body. The softer contact surface edge of the

G 8798 EN

The joint socket can be suitably formed by a continuous peripheral edge web. This peripheral edge web can also have interruptions or depressions at least on the contact surface side, which make it difficult for the lubricant film to break off in the edge area and in which any abrasion particles can collect. In any case, it can be advantageous to provide the softer contact surface edge of the joint socket with a broken or rounded outer edge, which forms a stop surface for the joint head or an adjoining joint neck. At the transition point to the rest of the contact surface of the joint socket, the softer contact surface edge can also be specially designed, for example with a slanted, undercut inner edge to improve the positive holding of the actual joint socket. The inner edge can also have a non-undercut bevel, which facilitates subsequent insertion of the actual joint socket into the softer material forming the edge of the joint socket, for example by clipping the socket into a holding body made of this softer material.

An embodiment of the subject matter of the invention is explained in more detail below with reference to the accompanying drawing.

In detail:

Fig. 1 is a schematic overall view of a

a hip joint endoprosthesis with the joint head already anchored in the femur;

Fig. 2 a cross section through the acetabulum

the endoprosthesis;

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Fig. 3 to 5 enlarged partial sectional views of the

in Fig. 2, the differently formed edge area of the acetabulum, designated X.

Fig. 1 shows a hip joint endoprosthesis 10 with a holding body 11 for the joint socket, designed as a screw body and provided with an external thread 12, and the spherical joint head 13, which interacts with the joint socket as a joint partner and is already anchored in a femur 14 with a shaft (not shown). Both joint partners, the joint shell 15 shown in Fig. 2 and the joint head 13 , are made of so-called bioceramic material, e.g. zirconium oxide, and their contact surfaces 15.1 and 13.1 are ground and polished to a precise shape and with a very low roughness depth. The fit of the joint head 13 in the joint socket 15 is such that a lubricating film of body fluid can form and remain between the joint partners.

As can be seen from the sectional view of Fig. 2, the joint shell 15 is inserted into an intermediate body 16, which is fastened in the holding body 11 and consists, for example, of a high-molecular plastic material. This intermediate body 16, on the one hand, ensures a limited elastic support of the ceramic joint socket 15 in the holding body 11 and, on the other hand, forms, with an inwardly projecting ring web 17, the joint socket edge 15.2, which still forms part of the contact surface of the joint socket 15. The ceramic contact surface 15.1 of the joint socket 15 thus transitions seamlessly into the contact surface edge 15.2 made of the softer material.

The inwardly projecting ring web 17 of the intermediate body 16 can have a different cross-sectional profile, as shown in Figs. 3 to 5. In all embodiments of Figs. 3 to 5, the dimensions are selected so that the spherical shape

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steering socket 15 including the ring web 17 is slightly smaller than a hemisphere, i.e. it extends over a spherical angle range of slightly less than 180". In the embodiments according to Fig. 3 and 4, the ring web 17 has a broken outer edge to form a stop surface 18 for a joint head neck. In the embodiment according to Fig. 5, the outer edge is provided with a rounding ^18. In all cases, the ring web 17 forms a spherical contact surface edge 15.2 and merges with the inner edge 19 of the ring web 17 into the contact surface 15.1 of the ceramic joint shell 15. The difference in the embodiments is that in the embodiment according to Fig. 3, the inner side 20 of the ring web 17 and the front surface of the joint socket 15 resting against this inner side 20 run in a spherical sector plane, that in the embodiment according to Fig. 4, the inner side 20' defines an undercut into which the correspondingly shaped front end of the joint socket 15 fits and that in the embodiment according to Fig. 5 the inner side 20*' runs diagonally without forming an undercut. In all three embodiments the joint socket 15 is anchored in the softer intermediate body 16 in a form-fitting manner. The embodiment according to Fig. 5 makes it easier to clip the prefabricated joint socket 15 into a prefabricated intermediate body 16. For this purpose the inner side 20'' and accordingly also the front surface of the joint socket 15 can also run in a ball diameter plane.

The ring web 17 can also be profiled in the area of its outer edge, for example in such a way that individual rounded elevations or depressions in the edge area only provide small contact surfaces for the joint head in the event of subluxation.

Claims (8)

G 8798 DE - 7 - Protection claims: 1. Artificial joint, in particular a hip joint endoprosthesis, with a joint socket (15) and a joint head (13) as interfitting joint partners, whose joint contact surfaces (15.1, 13.1) consist of metal or ceramic, characterized in that the socket edge, which also forms a contact surface (15.2) for the joint head (13), consists of another abrasion-resistant and biocompatible material that is softer than the contact surface (13.1) of the joint head (13). 2. Artificial joint according to claim 1, characterized in that the softer joint socket edge (ring web 17) consists of a high molecular plastic material. 3. Artificial joint according to claim 1 or 2, characterized in that an intermediate body (16) which can be anchored in a holding body (11) of the joint socket is formed from the softer material forming the joint socket edge (17), into which intermediate body the joint socket (15) made of ceramic or metal forming the joint contact surface (15.1) is inserted and is positively secured in its position by an inwardly projecting contact surface edge (ring web 17) of the intermediate body (16). 4. Artificial joint according to one of claims 1 to 3, characterized in that the softer contact surface edge (15.2) of the joint socket (15) is formed by a continuous circumferential edge web (17). • a G 8798 EN - 8 - 5. Artificial joint according to one of claims 1 to 3, characterized in that the softer contact surface edge (15.2) of the joint socket (15) is formed by a peripheral edge web having interruptions or depressions at least on the contact surface side. 6. Artificial joint according to one of claims 1 to 5, characterized in that the softer contact surface edge (15,2) of the joint socket (15) is provided with a broken outer edge forming a stop surface (18). 7. Artificial joint according to one of claims 1 to 6, characterized in that the softer contact surface edge (15.2) is provided with an undercut inner side (20*) at the transition point (inner edge 19) to the remaining contact surface (15.1) of the joint socket (15) (Fig. 4). 8. Artificial joint according to one of claims 1 to 7, characterized in that the contact surface (15.1) of the articular socket (15) extends over a spherical angle range which is smaller than 180", i.e. smaller than a hemisphere.