DE9416881U1 - Endoprosthesis for insertion into the body to replace a joint, in particular a hip or knee joint - Google Patents

Description

Endoprosthesis for insertion into the body to replace a joint, in particular a hip or knee joint

The invention relates to an endoprosthesis of the type mentioned in the preamble of claim 1.

A known hip joint prosthesis of the type in question has a base body that is elongated and is inserted over most of its length into a corresponding cavity in a long bone, while its protruding end has a cone that serves to hold a ball. When implanted, the ball moves in a bearing socket of a bearing part inserted into the hip bone.

In order to avoid relative movements of the elongated base body, it is known to insert this base body with cement. This is complex and has the disadvantage that the base body is difficult to separate from the surrounding bone tissue, with which it has since grown together, in order to replace it.

It is therefore generally desirable to implant the base body without cement. However, there is always the risk that an intermediate layer of connective tissue will form between the prosthesis and the bone, which is then the result of relative movements.

The invention is based on the object of providing an endoprosthesis for insertion into the body to replace a joint

9 ·

which can be implanted without cement and in which the risk of relative movements between the prosthesis and the bone is reduced.

The problem underlying the invention is solved by the teaching specified in the characterizing part of claim 1.

The basic idea behind this teaching is to provide knife-like projections on the base body that not only cut into the spongiosa, but also into the inner cortex, thus supporting the base body of the endoprosthesis on the firmer parts of the bone tissue. At the same time, there is the advantage that the knife-like projections increase the overall surface area, which enables bone to grow over a large area. The knife-like projections can be roughened or coated in a known manner to improve the growth behavior, for example with hydroxylapatite. Since the knife-like projections do not result in a form-fitting embedding, as is the case with cementing, such an implant can be loosened and removed more easily later for the purpose of replacement.

A further development of the invention consists in that the base body is essentially round and that the knife-like projections extend in a star shape away from the base body. This embodiment is particularly easy to manufacture, in particular according to a further development of this embodiment in which the base body is essentially hemispherical. This embodiment is particularly suitable for the formation of a joint socket of a hip joint.

Another development of this embodiment consists in that the sharp edges are each curved, preferably circular. This embodiment is also particularly easy to manufacture. Another embodiment of the invention consists in that the base

body is elongated so that the knife-like projections have the shape of ribs that run parallel to each other and in the direction of the longitudinal extension of the base body. This base body, which is part of a hip joint prosthesis, can then be inserted into a suitably prepared cavity in the femur, whereby the ribs with their sharp outer edges cut not only into the spongiosa, but also into the inner corticalis, depending on the dimensions.

One embodiment of the invention consists in that the base body is curved, has the sliding surface on its outside and the knife-like projections on its inside. The base body is thus part of a knee joint. The knife-like projections are expediently arranged in two planes that run at a distance and parallel to one another and cut the curved base body essentially perpendicularly.

The invention will be explained in more detail using an exemplary embodiment in the drawing. 20

Fig. 1 shows a section I-I according to Fig. 2 through

a joint socket for a hip joint, Fig. 2 is an axial view from above in Fig. 1, Fig. 3 shows an embodiment of the invention for holding a ball of a hip joint in a first view, Fig. 4 shows the embodiment according to Fig. 3 in

the drawing from the left,

Fig. 5 shows a third embodiment in connection with a knee joint, mounted on

a bone,

Fig. 6 shows the implant according to Fig. 5 in perspective view and

Fig. 7 is a perspective view of Fig. 6 rotated by 90°.

The embodiment shown in Fig. 1 and 2 has a hemispherical base body 1 with a dome-shaped bearing shell 2. Protruding from the base body 1 are essentially star-shaped, knife-like projections 3, which are sector-shaped and point with their sharp edges 4 in the implantation direction, i.e. downwards in Fig. 1.

Fig. 1 is a section I-I through Fig. 2, in which the star-shaped alignment of the projections 3 can be clearly seen.

When implanting the endoprosthesis according to Fig. 1 and 2, a spherical recess corresponding to the outer contour of the base body 1 is created in the bone in which a joint socket is to be made. The implant is then pressed or hammered in, whereby the knife-like projections 3 with their sharp edges 4 dig into the adjacent bone tissue and thus secure the base body 1 against movements, in particular against rotational movements. Bone tissue grows onto the projections 3, which improves the holding of the implant.

Fig. 3 and 4 show, in two representations rotated by 90° to one another, an embodiment of an endoprosthesis according to the invention for holding a ball 5 on a tubular bone (not shown). The ball 5 engages as a result in a bearing shell 2 of a base body 1 according to Fig. 1 and 2, although the representation in Fig. 3 and 4 is reduced in size compared to that according to Fig. 1 and 2. The ball 5 sits firmly on a cone 6 at one end of a base body 7, which is shaped in such a way that it can be inserted into a prepared cavity in a tubular bone. Ribs 8 are located on the base body 7, which have sharp edges 9 on the outside and taper to a point in the direction of insertion. When the base body 7 is inserted into a cavity created in a complementary manner in a raw

In the case of renal bones, the ribs 6 dig into the firmer areas of the bone, whereby the base body 7 is held firmly, in particular also against rotational movements.

Fig. 6 shows a further embodiment of an endoprosthesis according to the invention with a base body 10, which is curved and surrounds the end of a bone 11. On the outside, the base body 10 forms a sliding surface for a knee joint, while on its inside knife-like projections 12 are provided, which penetrate into the bone 11 in a cutting manner when the base body 10 is placed on it.

Fig. 6 shows the base body 10 with its projections 12, which are slightly modified compared to the embodiment according to Fig. 5, in a perspective view. It can be seen that two groups of projections 12 and 13 are provided, which are arranged in two planes that run at a distance and parallel to one another and cut the arched base body 10 essentially perpendicularly.

Fig. 7 shows a perspective view of the embodiment according to Fig. 6 in a view from the right in Fig. 6.

Claims (7)

Protection claims 1. Endoprosthesis for insertion into the body to replace a joint, in particular a hip or knee joint, with a base body to be attached to a bone or to be placed in a cavity in a bone, in or on which sliding surfaces to replicate the joint and projections to improve the hold on and/or in a bone are provided, characterized in that the projections (3) are designed like a knife and each have a preferably sharp edge (4) which points away from the base body (1) and runs in the direction of the insertion or attachment of the base body (1) in or on a bone. 2. Endoprosthesis according to claim 1, characterized in that the base body (1) is substantially round and that the knife-like projections (3) extend in a star shape away from the base body (1). 3. Endoprosthesis according to claim 2, characterized in that the base body (1) is substantially hemispherical. 4. Endoprosthesis according to claim 2, characterized in that the sharp edges (4) each extend in an arc shape, preferably in a circular arc shape. 5. Endoprosthesis according to claim 1, characterized in that - 2 — the base body (7) is elongated and that the knife-like projections have the shape of ribs (8) which run parallel to each other and in the direction of the longitudinal extension of the base body (7).
5 6. Endoprosthesis according to claim 1, characterized in that the base body (10) is arcuate, has the sliding surface on its outer side and the knife-like projections (12, 13) on its inner surface. 7. Endoprosthesis according to claim 6, characterized in that the knife-like projections (12, 13) are arranged in two planes which run at a distance from and parallel to one another and cut the arcuate base body (10) essentially vertically.