DE29614342U1 - Artificial acetabular cup - Google Patents

Description

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European Patent Attorneys *· »· ·· Dr. Dipi.-chem.

Patent Attorneys _M . Gritschneder

Dipl.-Phys.

A. Frhr. von Wittgenstein

Dr. Dipl.-Chem.

J. Morf

Abitz & Partner, PO Box 86 01 09, D - S1628 Munich ^Dr - Dipi-o™.

Postal Address / Postal Address PO Box 86 01 09 D - 81628 Munich

19 August 19 3 0331/Asymmetr. Inlay

KERAMED Medical Technology GmbH

At the Trillers Bushes 2

07646 Mörsdorf/Thuringia Federal Republic of Germany

Artificial hip joint socket

The invention relates to an artificial hip joint socket, which consists of an outer metal shell and an inlay made of metal, ceramic or plastic. The outside of the shell and the outside of the inlay are rotationally symmetrical about a first or second longitudinal axis and the inlay can be inserted into the shell, e.g. by means of a conical clamp.

Such artificial hip joint sockets are known in different designs (DE-GM 295 16 473) and are anchored in the natural pelvis either by means of a self-tapping thread or by a so-called press-fit effect (DE-GM 94 08 200). The outer metal shell and the inlay made of metal, ceramic or plastic are connected to each other in axial alignment, i.e. their longitudinal axes coincide.

A crucial problem with these joint implants is the permanent anchoring in or on the natural bone. The bond between the implant and the bone depends on various factors. There are a number of inert materials that

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whose surface the bone grows directly onto. These materials include primarily metallic titanium and alloys of this metal as well as oxide ceramic materials such as aluminum oxide ceramic.

Plastics such as polyethylene are less suitable for this purpose. However, high molecular weight low-pressure polyethylene is used as a sliding partner for joint sockets in hip endoprosthetics. Such sockets consist of a metal shell with a polyethylene inlay. This construction is used in many cases, but has the disadvantage that the polyethylene inlay can wear at a rate of 0.1 - 0.3 mm/year.

This wear creates a highly dispersed abrasion material that is deposited in the living tissue around the implant. Over a very long period of time, these deposits damage the reproducing biological processes in the living tissue and lead to the adjacent bone being less or no longer able to support the implant, thus loosening the implant-bone connection. This can lead to the artificial joint not functioning properly. This is known as aseptic loosening of the artificial joint.

In order to counteract this mechanism, functional principles were sought for artificial joints that show more favorable sliding and wear behavior. One possibility for this is the ceramic/ceramic sliding pair.

If a hip joint head made of aluminum oxide ceramic and the hip joint socket made of the same material are used, very little wear material is produced. This small amount of wear material can easily be deposited in the surrounding bone and soft tissue without disturbing the natural growth processes of the living organism.

This creates the possibility of significantly increasing the service life of artificial hip joints. However, with all joint pairs used to date, complications have occurred in a few isolated cases, which can be caused by misalignment, especially of the hip joint socket. With such misalignments, especially steep positioning of the hip joint socket, a so-called edge run can occasionally occur, i.e. the hip joint head is only in contact with the upper edge of the hip joint socket and

&iacgr;&ogr; does not fit as desired with the entire inner surface of the hip joint socket. This creates such high surface pressures that all previously known materials produce high levels of abrasion, which damages the surrounding tissue and, for this reason, the artificial joint stops functioning within a relatively short period of time.

This case cannot be ruled out with the current design of hip joints, even with ceramic/ceramic pairing.

The invention is based on the task of designing the artificial hip joint sockets in such a way that edge running is excluded or at least very unlikely.

The task is solved by the fact that the longitudinal axis of the shell and the longitudinal axis of the inlay enclose an angle of 1 to 15° in the assembled state of the acetabulum.

The inlay is therefore fitted asymmetrically in the metal casing, 0 in such a way that the equator of the inlay and the equator of the metal casing are at an angle of 1-15° to each other. The metal casing is inserted into the acetabulum in the conventional way. Due to the offset orientation of the inlay in the metal casing, the shoulder or edge of the ceramic inlay is positioned in such a way that the edge of the hip joint head against the upper edge of the inlay is counteracted. The implantation

By using the hip joint cup according to the invention with a tilted inlay, luxation and edge running can be prevented.

An embodiment of the invention is explained in more detail using the drawing. They show:

Fig. 1 the artificial hip joint socket in cross section.

The artificial hip joint socket consists of an outer shell 1 and an inlay 2. The outer shell 1 is made of metal and the inlay 2 is made of ceramic. In the middle, i.e. at the pole, of the outer shell 1 there is a continuous threaded hole 3 with a recess running around the inside. A short threaded bolt can be screwed into this threaded hole 3 in order to release the inlay 2 from the shell 1, as is known from DE-GM 295 16 473.

The shell 1 is approximately hemispherical. The outer side 5 of the shell 1 is rotationally symmetrical about the longitudinal axis 6, i.e.

the outside 5 of the shell 1 lies on a surface of rotation. The inside 7 of the shell 1 is also rotationally symmetrical, but about a second longitudinal axis 8, which encloses an angle of up to about 15° with the first longitudinal axis 6. The inside 7 has a truncated cone-shaped main area 9, which extends from the open underside to about half the height of the shell 1. Further truncated cone-shaped areas follow upwards up to the recess 4. The main area 9 and the other areas are all rotationally symmetrical to the second longitudinal axis 8.

The inlay 2 is also approximately hemispherical in shape, with the outside of the inlay 2 essentially corresponding to the inside of the shell 1 and having a truncated cone-shaped area to form a clamping fit with the main area 9 of the inside 7 of the shell. The outside of the inlay 2 is rotationally symmetrical to the longitudinal

axis of the inlay, which coincides with the second longitudinal axis 8 when inserted.

Because the inlay 3 sits at an angle in the shell 1, it protrudes on the underside of the shell 1 on one side, in Fig. 1 on the left side. The lower edge of the shell 1 is pulled down so far in this area that the otherwise protruding edge of the inlay 3 is covered. In the embodiment shown in the drawing, the inner side 7 of the shell 1 is extended to the lower edge of the inlay 2 and there is a bevel 10 between the inner side 7 and the outer side 5 of the shell 1. The lower edge 11 of the outer side 5 lies in a plane normal to the first longitudinal axis 6.

The hip joint socket according to the invention can be provided on its outside with a self-tapping thread for anchoring in the natural pelvis or can be anchored by the press-fit effect mentioned above.

Claims (3)

PROTECTION CLAIMS 1. Artificial hip joint socket with a shell (1), the outside (5) of which is rotationally symmetrical about a first longitudinal axis (6), and with an inlay (2), the outside of which is rotationally symmetrical about a second longitudinal axis (8) and which can be inserted into the shell (1), characterized in that the first longitudinal axis (6) and the second &iacgr;&ogr; Longitudinal axis (8) may enclose an angle of up to approximately 15° when the inlay (2) is inserted into the shell (1). 2. Hip joint cup according to claim 1, characterized in that the inner side (7) of the shell (1) has a conical main region (9) into which the inlay (2) can be inserted by means of a conical clamp. 3. Hip joint cup according to claim 1 or 2, characterized in that the lower edge (11) of the inner side (7) of the shell (1) on the side towards which the inlay (2) is tilted in the inserted state is extended downwards so that the inlay (2) does not protrude downwards from the shell (1).