DE4142920A1 - Screwed bush for socket of hip joint prosthesis - has hand of screw thread chosen so that bush tends to tighten in use - Google Patents

Abstract

The hip joint endoprosthesis has a socket (2,7) which is screwed into the pelvic bone (1). The hand of the screw thread is so chosen that the turning moment exerted on the bush, during use, tends to tighten the bush. That is when the patient is walking and the endoprosthesis bears the weight of the patient and the femur rotates relative to the pelvis. This effect is achieved by providing the right leg bush with a right-hand screw thread and providing the left leg bush with a left-hand thread. ADVANTAGE - The bush is prevented from becoming loose in its socket.

Description

The invention relates to an endoprosthesis socket, which can be fixed in the bone by means of a thread and in which a rod end can be inserted.

In DE-AS 24 11 617 such a socket is described as an acetabular cup. The external thread of the The pan is used to screw the socket into the Acetabulum of the pelvic bone. As an anti-twist device notches are provided on the end face of the socket. These notches can then only counter the socket prevent twisting when the bone grows into it. This anti-rotation device is unsatisfactory.

DE 38 04 310 C1 is also one Acetabular cup with external thread described. Spaces in the threads should be one Prevent the pan from rotating. It also hangs here Protection against rotation from the ingrowth of the socket. In practice, waxing is sufficiently safe uncertain. At least additional measures are needed to to promote ingrowth.

Another hip joint socket is in EP 01 79 736 A2 provided with an external thread. To loosen the Avoid pans are depressions or roughening provided a non-rotating ingrowth of the pan should guarantee. It also hangs here Protection against rotation depends on how fixed sooner or later the pan grows in.  

Another type of joint socket works without External thread. According to EP 01 69 978 B1 Outside of the pan a variety of pins for Fixation of the pan in the bone is provided. Similar Anchoring pins are also shown in DE 36 20 460 C1. To DE 29 11 754 C2 grooves are provided on the pan, to achieve a twist-proof seat.

The object of the invention is to provide an endoprosthesis To propose a socket of the type mentioned at the beginning, which can not be loosened even without additional funds tends under stress.

According to the invention, the above task is for an acetabular cup of the type mentioned in that the Thread of the socket is designed so that its Direction of screwing into the bone in the same direction has like a torque that the joint head under the functional loading of the joint on the socket exercises.

This ensures that the socket at usual load on the joint head in their Screwing direction is loaded. So that's it avoided that the joint socket when loading the Bone against their screwing direction, d. H. the Unscrewing direction of the thread is loaded. The Stress on the joint therefore does not have the tendency to Loosen the socket. Special additional funds are not to be used for this. It just has to Threads can be designed as left-hand threads if that through the torque arising in the left direction of rotation works. With an effect of the load on the right The external thread is designed so that it turns Right-hand thread is, as is usual.

Further advantageous embodiments of the invention result from the following description of  Embodiments. The drawing shows:

Fig. 1 is a partial view of a pelvic bone with right and left hip, from the front,

Fig. 2 is a side view of the left hip,

Fig. 3 is a side view of the right hip and

Fig. 4 shows another embodiment in a Fig. 1 corresponding view.

A joint socket ( 2 ) is screwed into the left, possibly milled, acetabulum ( 1 ). For this purpose, the joint socket ( 2 ) has an external thread ( 3 ). The external thread ( 3 ) is a left-hand thread. It is therefore screwed into the acetabulum ( 1 ) of the left hip in the left direction of rotation (E1).

The joint socket ( 2 ) is designed to receive a joint head ( 4 ) of the left femur ( 5 ). The joint head ( 4 ) is rotatably seated in the joint socket ( 2 ). The socket can be made in one piece from metal or ceramic. It can also be constructed with two shells, the inner shell being seated against rotation in the outer shell and consisting, for example, of plastic, ceramic or other materials.

A joint socket ( 7 ) is screwed into the acetabulum ( 6 ) of the right hip and has a right-hand external thread ( 8 ). The joint socket ( 7 ) is thus screwed into the acetabulum ( 6 ) in the right direction of rotation (Er).

The joint socket ( 7 ) serves to receive a joint head ( 9 ) of the right femur ( 10 ). The two joint sockets ( 2 , 7 ) are the same. They differ only in that the left socket ( 2 ) is provided with a left-hand external thread (3), whereas the right joint socket ( 7 ) is equipped with a right-hand external thread ( 8 ).

In FIGS. 2 and 3, the loads occurring when walking are shown schematically. Between the front (v) and the rear (h) position of the leg there is the greatest load on the leg in the area of the middle position (m). With the left leg, this load on the joint head ( 4 ) of the left socket ( 2 ) results in a loading torque (B1) in the left direction of rotation (see FIG. 2). Since the left socket ( 2 ) is screwed in with a left-handed external thread ( 3 ), the loading torque (Bl) therefore acts in the screwing direction (El). The loading torque (Bl) therefore does not have the tendency to turn the socket ( 2 ) against its screwing direction (El).

Accordingly, there is the greatest load between the front (v) and the rear (h) leg position of the right leg in the area of the middle position (m). This load leads to a clockwise rotating load torque (Br) on the right joint head ( 9 ) or the right joint socket ( 7 ). Since this socket ( 7 ) is screwed in with the right screw-in direction (Er), the screw-in direction (Er) and the load torque (Br) are in the same direction of rotation in this case too. The loading torque (Br) therefore does not tend to loosen the socket ( 7 ).

In the exemplary embodiment according to FIG. 4, the joint sockets ( 2 , 7 ) are not provided with external threads, but instead each carry a screw pin ( 11 or 12 ). The screw pin ( 11 ) of the left socket ( 2 ) is provided with a left-hand thread. The screw pin ( 12 ) of the right socket ( 7 ) is provided with a right-hand thread. The load torque (Bl) acting in the left-hand direction of rotation therefore also acts in the left-hand screwing direction (El) of the left-hand screw pin ( 11 ). Correspondingly, the right-turning load torque (Br) of the right femur ( 10 ) acts in the same direction as the right-hand screwing direction (Er) of the screw pin ( 12 ).

The screw pins ( 11 , 12 ) can be made in one piece with the relevant socket ( 2 , 7 ). However, it is also possible to screw in the screw pins ( 11 , 12 ) only after the socket has been inserted.

Overall, the adapted choice of thread (right-hand thread or left-hand thread) ensures that neither the left joint socket ( 2 ) nor the right joint socket ( 7 ) can loosen due to the respective loading torques. In practice, right-hand threads have been used for both the left hip joint socket and the right hip joint socket, which can lead to loosening of the joint socket in the left hip.

Claims (4)

1. Endoprosthesis socket, which can be fixed by means of a thread in the bone and into which a joint head can be inserted, characterized in that the thread ( 3 , 8 ; 11 , 12 ) of the socket ( 2 , 7 ) is designed so that its The screwing direction (El, Er) into the bone has the same direction of rotation as a torque (Bl, Br) which the joint head ( 4 , 9 ) exerts on the joint socket ( 2 , 7 ) under the functional load on the joint. 2. Endoprosthesis joint socket according to claim 1, characterized in that the thread of the joint socket ( 7 ) for the right hip is a right-hand thread ( 8 , 12 ) and that the thread of the joint socket ( 2 ) for the left hip is a left-hand thread ( 3 , 11 ) is. 3. Endoprosthesis socket according to claim 1 or 2, characterized in that the thread is an external thread ( 3 , 8 ) of the socket ( 2 , 7 ). 4. Endoprosthesis socket according to claim 1 or 2, characterized in that the thread on a socket ( 2 , 7 ) holding screw pin ( 11 , 12 ) is provided.