DE29516473U1 - Artificial acetabular cup - Google Patents

Description

ft * · · ft ft · · · W. Abitz Abitz & Partner &Iacgr; .·*. &Iacgr; Dr.-Ing., European Patent Attorneys * DF Morf
Dr. Dipl.-Chem. Patent attorneys M. Gritschneder Dipl.-Phys. A. Frhr. von Wittgenstein Dr. Dipl.-ChEm. J. Morf Abitz & Partner, PO Box 86 01 09, D - 81628 Munich Dr. DipL-Chera.

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

17 October 1995 2 9788/Hip socket

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 has an outer shell and an inlay which is fixed in the outer shell by conical clamping.

In such two-part hip joint cups, the outer shell is generally made of metal. The outer surface of the shell can be spherical or conical or have different radii of curvature.

&iacgr;&ogr; The inlay can be made of plastic, e.g. polyethylene, or ceramic. If the inlay is made of plastic, a cobalt-chrome cast alloy or ceramic is generally used for the joint ball and shaft that rotate within it. If, on the other hand, the inlay is made of ceramic, ceramic is generally also used for the joint ball and shaft. The ceramic/ceramic sliding pair has proven to be particularly advantageous, since hardly any wear can be detected even after years.

The outer surface of the shell is provided with a thread for anchoring in the bone to enable screwing in the

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bone, or has a porous surface into which the bone grows, thus providing a permanent anchor.

In two-part hip joint cups, the inlay must be fixed in the outer shell in a rotationally stable manner on the one hand, and on the other hand be able to be easily replaced, which may be necessary from a surgical point of view both during the first operation and during a possible second operation. From EP-A 0 655 230 and EP-A-O 649 641 it is known that the rotationally secure anchoring of the inlay can be achieved by means of a conical clamping of the inlay. In order to enable the inlay to be removed using levers or special devices, the cone is not designed to be self-locking.

However, experience with conically clamped parts, e.g. hip joint balls on hip joint shafts, teaches that such clamps are generally difficult to release.

The invention is based on the object of simplifying the removal of the inlay in a bivalve artificial hip joint cup.

This is a particular problem with ceramic inlays. While plastic inlays can be removed using pull-out devices attached to the periphery of the inlay, this is not possible with ceramic inlays, as they easily break or deform the outer shell when attempting to remove them.

According to the invention, this object is achieved in that a radial threaded hole is provided on the pole of the shell, into which a threaded bolt can be screwed, the head of the threaded bolt facing the inlay and a hole is located on the pole of the inlay, the diameter of which is smaller than the head of the threaded bolt and through which a screwdriver can be placed on the head of the threaded shaft.

When the threaded bolt is unscrewed towards the inlay, a force is exerted on the inlay which is directed axially to the clamp, thus preventing breakage or deformation of the inlay or shell.

Preferably, the outer shell is made of metal and the inlay is made of ceramic, whereby the ratio of the diameter of the bore to the wall thickness of the inlay is preferably in the range of about 0.5 to 2 and preferably about 1 μm.

The inlay preferably has a flat surface perpendicular to the bore with a diameter of approximately 30% of the outer diameter of the cup.

The outer shell preferably has a shallow recess around the threaded hole to accommodate the enlarged head of the threaded bolt. The widening of the head can be about 25%.

Preferably, the hole in the inlay has about half the diameter of the threaded hole in the shell and the threaded bolt has an internal square or hexagon for inserting the screwdriver.

The edges of the inlay bore are purposefully broken to avoid increased surface pressure.

An embodiment of the invention is explained below with reference to the drawing.

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

Fig. 2 the inlay of the acetabulum according to Fig. 1 in section and

Fig. 3 the artificial hip joint socket with the threaded bolt partially unscrewed to release the inlay from the shell.

Fig. 1 shows the artificial hip joint socket, which 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. At the periphery of the inlay 2 there is a conical fit with the inside of the outer shell 1.

In the middle, ie at the pole, of the outer shell 1 there is a through-threaded hole 3 M20 × 1 with a flat recess 4 running around the inside. A short threaded bolt 5 can be screwed into this threaded hole 3, which has a widened head 6 that fits into the recess 4.

A hole 7 is provided on the pole of the inlay 2, through which a screwdriver or a similar tool can be inserted into a hexagon socket opening 8 in the threaded bolt 5 to unscrew the threaded bolt 5. The hole in the inlay 2 has approximately half the diameter of the threaded hole 3 of the shell 1. On the outside of the inlay 2, a flat surface 9 is formed around the hole 7, perpendicular to the axis of the hole 7.

To release the conical clamping between the inlay 2 and the shell 1, the threaded bolt 5 is unscrewed in the direction of the inlay 2 so that the head 6 of the threaded bolt 5 rests on the flat surface 9 of the inlay and, as it is unscrewed further, exerts an axially acting and increasing force on the inlay until the inlay 2 separates from the shell 1. In order to avoid excessive surface pressure on the edge of the hole 7 of the inlay 2 and the associated risk of ceramic material splintering, the edge of the hole 7 facing the shell 1 is broken.

Claims (6)

PROTECTION CLAIMS s 1. Artificial hip joint socket, which has an outer shell (1) and an inlay (2) which can be fixed in the outer shell (1) via a conical clamp, characterized in that &iacgr;&ogr; - that in the outer shell (1) approximately in the middle there is a threaded hole (3) into which a threaded bolt (5) can be screwed and that a hole (7) is provided in the inlay through which a screwdriver can be inserted into the Threaded bolt (5) can engage. 2. Hip joint cup according to claim 1, characterized in that the outer shell (1) consists of metal and the 0 inlay (2) of ceramic. 3. Hip joint cup according to claim 2, characterized in that the diameter of the bore (7) to the wall thickness of the inlay (2) is in the range of 0.5 to 2. 4. Hip joint cup according to claim 2 or 3, characterized in that a flat surface (9) perpendicular to the axis of the threaded bore (3) of the shell (1) is formed on the inlay (2) around the bore (7). 5. Hip joint cup according to one of claims 1 to 4, characterized in that a circumferential recess {4) for receiving a widened head (6) of the threaded bolt {5) is provided on the inner edge of the threaded bore {3} of the outer shell (1). 6. Hip joint cup according to one of claims 1 to 5, characterized in that the diameter of the bore (7) in the inlay (2) is approximately half the maximum diameter of the threaded bolt (5).