WO2000045749A1 - Hip socket prosthesis with a coupling element between the socket housing and the socket insert - Google Patents

Abstract

The invention relates to hip socket prostheses which consist of a socket housing and a ceramic socket insert which can be introduced into the socket housing. The joint surfaces of the two components have to be processed exactly since imprecision can lead to uneven concentrations of stress in the socket inserts, which in turn can lower the resistance of the component. Operation-related contamination can also impair the durability of the clamped joint. For this reason, elements for homogenising the transmission of force are arranged between the ceramic socket insert and the metal socket housing. A known solution is a layer of plastic, especially polyethylene. However, a polyethylene coupling element has the disadvantage of not being cold flow-resistant. Relative movements between the coupling element and the socket housing can also occur, which can cause friction wear. According to the invention, the elasticity and damping properties of the coupling element (5) between the socket housing (2) and the socket insert (3) of the hip joint prosthesis (1) can be predetermined by its porosity and the structure of its surface.

Description

 Acetabular cup with coupling element between socket housing and

Pan insert

The invention relates to an acetabular cup according to the preamble of the first claim

5 acetabular cups are an integral part of a hip joint endoprosthesis, which generally has a modular structure.For example, the endoprostheses consist of a shaft that is inserted into the femur and a socket that is implanted in the hip bone. A spherical head is attached to the shaft The pan is usually stored in a pan made up of two parts

10 consists of a socket housing, the so-called metal back, and a socket insert, the so-called insert, made of plastic or ceramic. The modular endoprostheses connect implant components of different materials and sizes. The combination of the individual parts is usually determined by the joint dimensions

i ⁴ In the case of acetabular cups, which consist of a socket housing and a socket insert made of ceramic, which can be inserted into the socket housing, the joint surfaces of the two components must be machined precisely because inaccurate stress concentrations can occur in the socket inserts, which can reduce the strength of the component As is already known from DE 43 37 936 A1, means for homogenizing the power transmission between the ceramic insert and the metal socket are arranged for this reason. A layer made of plastic, in particular polyethylene, is known. However, a coupling element made of polyethylene has the disadvantage that it is not resistant to cold flow. In addition, relative movements between the coupling element and the socket housing can occur, as a result of which abrasion can be generated. It is also disadvantageous that the surface in the socket housing, on the the ceramic cup insert rests on it, it is sensitive to contamination caused by surgery, for example bone fragments. Such contamination can significantly reduce the durability of the pan insert in the pan housing.

It is therefore the object of the present invention to present an acetabular cup consisting of a socket housing made of metal and a socket insert made of ceramic with a coupling element arranged therebetween, in which the coupling element causes a homogeneous force flow by controlled deformability and small irregularities in the surface of the interconnected components and contamination between the two components is able to compensate.

The problem is solved with the aid of the characterizing features of the first claim. Further advantageous embodiments of the invention are claimed in the subclaims.

Through a targeted design of the surface structure and the internal structure of the coupling element, in particular its porosity, according to the invention its elasticity and damping properties and thereby the introduction of force into the body coupled to it are predetermined. An embodiment of porous coupling elements can be produced as a winding body. The porosity of the winding body and its surface structure can be controlled by a targeted placement of the threads on a body that has at least approximately the shape that the coupling element is to receive. The porosity of cylindrical or conical bobbins, such as those that can be wound on cores on winding machines, can be specified by setting the crossing angle, the spacing of the threads placed next to each other (thread stroke) and the thread tension during the winding process.

Instead of a winding body, the coupling element can also have a fabric-like structure. Due to the weave, ie the distance between the threads and their interweaving, the porosity and surface quality can Roughness. The construction of a coupling element from several fabric layers also gives the possibility to influence the porosity and thus its deformability.

The surface structure of the bobbins and the fabrics is essentially determined by the thread diameter, the thread shape - flat, round or twisted, and the placement or interlacing of the threads. Because the threads can be processed both with the winding body and with a fabric-like structure with variable distances from one another, elevations arise on the surface of the winding body or the fabric at the crossing points of the threads, while the pores arise due to the spacing between the threads. On the surface, therefore, the crossing points and the spacing of the threads influence the structure, the roughness, of the coupling element.

Although the coupling element between the socket housing and the ceramic insert is essentially shielded from the bone and the body tissue, there is nevertheless the possibility of an interaction between the material of the coupling element and the body tissue due to the body fluid. For this reason, the threads of the bobbin or the fabric are made of a biocompatible material. All materials that are already considered to be biocompatible in prosthetics are suitable as materials. The threads can therefore be made of metal or a metal alloy such as chrome, tungsten chrome, cobalt chrome, and titanium, for example. As particularly effective! threads made of carbon have proven to have a particularly high tensile strength and also consist of an element that is present in the body itself. In particular, with threads made of carbon, it is possible to design a coupling element in such a way that it does not deform in the direction of its surface area when subjected to a load.

In order to facilitate the production of a coupling element in the correspondingly desired shape, it is advantageous if the threads or the thread layers are fixed in their position by a fixing means. As a fixative, for example Epoxy resins are used. Here, too, the fixing agent must consist of a bio-inert or biocompatible material.

In a further embodiment, in addition to winding bodies and fabrics, coupling elements can also be produced as sintered bodies or sponge bodies. For example, coupling elements can be sintered in any desired shape from balls or grains of a biocompatible material, in particular from the known biocompatible metals already mentioned above, the pore size within the sintered body and its surface structure being determined simultaneously by the ball size or grain size. In the case of sponge bodies, which can be produced, for example, by gassing metal melts, the pore content and the pore size can be influenced by appropriate supply of the fumigant.

The coupling element for an acetabular cup can, depending on the expected load and size of the endoprosthesis, have a thickness of up to 6 mm. Its proportion of pores, adjusted to the desired elasticity and damping, can be adjusted to a proportion between 20% and 90%, a proportion of pores of around 40% being regarded as optimal. The higher the proportion of pores, the more elastic the coupling element behaves.

The roughness of the surface of the coupling element also exerts an influence on the elasticity and damping. With a higher surface roughness, the deformability of the surface increases and, as a result, the elasticity of the coupling element and its damping properties increase. The surface roughness is also adapted to the endoprosthesis and can be between 2 μm and 300 μm with a roughness depth Ra. A roughness depth of approximately Ra = 60 μm has proven to be advantageous.

The surface structure, ie the surface roughness, is, as explained above, by the winding process or the weaving process or the sintering technique or Influences pore production. Particularly in the case of the coupling elements sintered from metallic materials and the sponge bodies, the structure and thus the roughness can be influenced in a targeted manner by subsequent processing of the surface, for example by grinding, sandblasting or overturning.

The invention is explained in more detail using exemplary embodiments.

Show it:

1 shows an acetabular cup according to the invention, consisting of a socket housing and a ceramic insert inserted into the socket housing and between the socket housing and the

Pan insert a coupling element, cut,

FIG. 2 shows a segment-shaped section from a coupling element which is formed from a winding body,

FIG. 3 shows a section of a coupling element which has a fabric-like structure,

FIG. 4 shows a segment-shaped section from a coupling element, which is a porous sintered body, and

5 shows a segment-shaped section of a coupling element, which is a sponge body.

In Figure 1, 1 denotes an acetabular cup according to the invention. The pan housing 2, the metal back, consists of a biocompatible metal. The pan insert 3 is the ceramic bearing shell with a hemispherical Recess 4 for receiving the joint partner, not shown here, the spherical head of the femoral head prosthesis. With 5 the coupling element is designated. The socket insert 3 is inserted into the socket housing 2 by means of the known clamp seat. Depending on the size of the acetabular cup and its intended use, the coupling element 5 has a thickness of approximately 1 mm to 6 mm.

FIG. 2 shows a quarter segment of a coupling element 6, which was formed from a winding body. Five thread layers 7a to 7e lying one above the other are clearly visible. The individual threads 8 are placed next to one another. As can be seen from the illustration, their diameter 9 and their distance 10 from one another determine the dimensions of the pores 11. At the same time it can be seen that the diameter 9 of the threads 8 on the surface 12 essentially determines the roughness 13. Furthermore, the diameter and the depth of the pores 11, which are connected to the surface 12 and are thus open, influence the roughness 13 of the surface 12. As can also be seen from FIG. 2, the threads are in their position by means of a Fixing agent 14, for example by means of an epoxy resin, fixed.

FIG. 3 shows the structure of a coupling element 15, which is made up of two fabric layers A and B. Here, too, it can be clearly seen that the diameter 16 of the threads 17 and their distance 18 from one another within the respective fabric layer A or B and between the individual fabric layers A and B, the size of the pores 19 and the structure of the surface 20 and thus the roughness 21st influence.

FIG. 4 shows the segment of a sintered body as a coupling element 22. In the present exemplary embodiment, the sintered body 22 consists of balls 23 of a biocompatible metal that are sintered together. The diameter 24 of the balls 23 determines the dimensions of the pores 25 and the surface structure of the surface 26 and thus their roughness 27. In FIG. 5, 28 denotes the segment of a coupling element, which is a sponge body. In the present exemplary embodiment, the structure of the coupling element 28, in contrast to the previous exemplary embodiment, is determined by the size of the pores 29 which are introduced into the biocompatible metal 30. In the present exemplary embodiment, the pores are irregularly shaped and partially connected and thus form a sponge structure. The pores can be created in the metal by gassing or by so-called placeholders during the sintering process. Placeholders are substances in the shape and size of the pores that burn without residue during sintering. The metal 30 is structured by the pores 29. The roughness 32 is influenced on the surface 31 by the dimensions of the pores 29. The smaller the pores 29, the lower the roughness 32.

Claims

claims 1. acetabular cup with a socket housing which can be inserted into the bone tissue of the hip bone and a socket insert made of ceramic which is inserted into the socket housing, a coupling element for homogenizing the socket between the socket housing and the socket insert Power transmission is arranged, characterized in that the elasticity and damping properties of the coupling element (5, 6, 15, 22, 28) by its porosity (11, 19, 25, 29) and the structure (13, 21, 27, 32) of it Surface (12, 20, 26, 31) can be predetermined. 2. acetabular cup according to claim 1, characterized in that the coupling element (6) is a winding body which consists of threads (8) of a biocompatible material. 3. acetabular cup according to claim 1, characterized in that the coupling element (15) has a fabric-like structure (A, B) which is made of threads (17) made of a biocompatible material. 4. acetabular cup according to claim 2 or 3, characterized in that the threads (8, 17) are metal threads. 5. acetabular cup according to claim 2 or 3, characterized in that the threads (8, 17) are made of carbon. 6. acetabular cup according to one of claims 2 to 5, characterized in that the threads (6) or thread layers are fixed in position by a fixing means (14). 7. acetabular cup according to claim 1, characterized in that the coupling element (22) is a porous sintered body which consists of a biocompatible metal or a biocompatible metal alloy. 8. acetabular cup according to claim 1, characterized in that the 5 coupling element (28) is a sponge body made of a biocompatible Metal or a biocompatible metal alloy (30). 9. acetabular cup according to one of claims 1 to 8, characterized in that the proportion of pores (11, 19, 25, 29) of the coupling element (5, 6, 15, 22, 28) is between 20% and 90%. 10 10. acetabular cup according to claim 9, characterized in that the proportion of pores (11, 19, 25, 29) is about 40%. 11. acetabular cup according to one of claims 1 to 10, characterized in that the roughness (13, 21, 27, 32) of the surface (12, 20, 26, 31) has a roughness depth Ra of about 2 microns to 300 microns. 15 12. acetabular cup according to claim 11, characterized in that the roughness depth Ra is about 60 microns.