DE19904436A1 - Hip joint socket with coupling element between socket housing and 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

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

Acetabular cups are a component of hip joint endoprostheses that are used in the Are generally modular. The endoprostheses consist of, for example a shaft that is inserted into the thigh bone and one in the Hip bone implanted pan. A ball head is attached to the shaft is usually stored in a pan made up of two parts. The pan consists of a pan housing, the so-called metal-back, and one Pan insert, the so-called insert, made of plastic or ceramic. Both modular endoprostheses become implant components different materials and sizes combined. The combination the individual parts are usually specified by the joint dimensions.

In acetabular cups, which consist of a socket housing and one in the The pan insert can be made of ceramic, the Joining surfaces of the two components can be machined precisely because at Inaccuracies in uneven stress concentrations in the Pan inserts can occur, leading to a reduction in the strength of the Lead component. As is already known from DE 43 37 936 A1, from this Basic means of homogenizing the transmission between the Pan insert made of ceramic and the pan housing made of metal. A layer of plastic, in particular polyethylene, is known. On Coupling element made of polyethylene has the disadvantage that it is not is cold flow resistant. In addition, relative movements between the Coupling element and the socket housing occur, which creates abrasion can be. It is also disadvantageous that the surface in the pan housing on the  the ceramic cup insert rests, is sensitive to surgery-related Soiling, for example bone fragments. Such contaminants can significantly reduce the durability of the pan insert in the pan housing.

It is therefore the object of the present invention to provide an acetabular cup, consisting of a metal pan housing and one inserted in it Ceramic insert with a coupling element arranged between them to introduce, in which the coupling element through controlled deformability causes a homogeneous flow of force and small irregularities in the surface the interconnected components and contaminants between the is able to balance two components.

The task is solved with the help of the characteristic features of the first Claim. Further advantageous embodiments of the invention are in the Claimed claims.

Through a targeted design of the surface structure and the internal structure of the Coupling element, in particular its porosity, will be his Elasticity and damping properties and thereby the introduction of force into it coupled body specified. An execution of porous coupling elements is as Winding body producible. Through a targeted placement of the threads on a body that is at least approximately the shape that the coupling element is to receive Porosity of the winding body and its surface structure controllable. The porosity can be in the case of cylindrical or conically shaped packages, such as can be wound on spools on cores by adjusting the Crossing angle, the distance between the threads placed next to each other (thread stroke) as well as the thread tension during the winding process.

Instead of a winding body, the coupling element can also be a fabric-like one Have structure. By the weave, d. H. the distance between the threads and  their intertwining, the porosity and the surface texture, the Roughness. Also the construction of a coupling element Several layers of fabric give the opportunity to look at the porosity and thus on its Deformability.

The surface structure is in the winding form and in the fabrics in essentially by the thread diameter, the thread shape - flat, round or twisted, and the filing or interlacing of the threads determined. Because the Threads with the winding body as well as with a fabric-like structure variable distances to each other can be processed in the Crossing points of the threads elevations on the surface of the winding body or of the tissue, while due to the spacing between the threads the pores arise. Therefore, the intersection points and the influence on the surface Spacing of the threads the structure, the roughness, the coupling element.

Although the coupling element between the socket housing and the ceramic insert in the is essentially shielded from the bone and the body tissue due to the body fluid the possibility of an interaction between the Material of the coupling element and the body tissue. Because of this, are the threads of the winding body or the fabric from a biocompatible Made of material. All materials in prosthetics are already suitable as materials biocompatible materials. The threads can therefore, for example Metal or a metal alloy such as chrome, tungsten chrome, cobalt Chrome, and titanium. Threads made of carbon have proven particularly effective proven that have a particularly high tensile strength and also from one There is an element that is present in the body itself. Especially through threads made of carbon, it is possible to design a coupling element so that it is a load is not deformed in the direction of its surface area.  

To manufacture a coupling element in the desired shape To facilitate, it is advantageous if the threads or the thread layers through a Fixing agents are fixed in their position. As a fixative, for example Epoxy resins are used. It also applies here that the fixing agent consists of one bio-inert or biocompatible material must exist.

In a further embodiment, in addition to winding bodies and fabrics Coupling elements are produced as a sintered body or sponge body. For example, balls or grains of a biocompatible material, in particular from the known biocompatible metals already listed above, Sintering coupling elements in any desired shape, due to the ball size or grain size simultaneously the pore size within the sintered body and its Surface structure determined. For spongy bodies, for example, by Fumigation of molten metals can be produced by appropriate supply of fumigant the pore content and pore size to be influenced.

The coupling element for an acetabular cup can, depending on what is to be expected Load and size of the endoprosthesis, have a thickness of up to 6 mm. His Porosity can, depending on the desired elasticity and damping, on one Proportion between 20% and 90% can be set, with a pore proportion of about 40% is considered optimal. The higher the proportion of pores, the more elastic the coupling element behaves.

The roughness of the surface of the coupling element also influences the Elasticity and cushioning. With higher surface roughness, the Deformability of the surface increases and this increases the elasticity of the Coupling element and its damping properties. The surface roughness is also adapted to the endoprosthesis and can have a roughness between Ra  2 µm and 300 µm. A roughness of about Ra = 60 µm has been found to be advantageous proven.

The surface structure, i.e. H. the surface roughness, as explained above, by the Winding process or the weaving process or the sintering technology or the Influences pore production. Especially with those made of metallic materials sintered coupling elements and the sponge bodies can by a subsequent processing of the surface, for example by grinding, Sandblasting or overturning, the structure and thus the roughness continue to be targeted to be influenced.

The invention is explained in more detail using exemplary embodiments.

Show it:

Fig. 1 an acetabular cup according to the invention, comprising a socket housing and a socket insert inserted into the socket housing made of ceramic, and between the socket housing and the socket insert a coupling member, cut,

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

Fig. 3 shows a detail of a coupling member having a web-like structure,

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

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

In Fig. 1, 1 denotes an acetabular cup according to the invention. The pan housing 2 , the metal back, consists of a biocompatible metal. The socket 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.

In FIG. 2, a quarter segment of a coupling member 6 is shown, which has been formed from a wound body. Five thread layers 7 a to 7 e 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 therefore open, influence the roughness 13 of the surface 12 . As can also be seen from FIG. 2, the threads are fixed in their position by means of a fixing means 14 , for example by means of an epoxy resin.

Fig. 3 shows the structure of a coupling element 15 which is composed of two tissue layers A and B. It can also be clearly seen here 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 21 influence.

In FIG. 4, the segment is shown 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 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 is referred to with the segment 28 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 (12)

1. acetabular cup with a socket housing that can be inserted into the bone tissue of the hip bone and a socket insert made of ceramic that is inserted into the socket housing, a coupling element being arranged between the socket housing and the socket insert for homogenizing the power transmission, characterized in that the elasticity and damping properties of the coupling element ( 5 , 6 , 15 , 22 , 28 ) due to its porosity ( 11 , 19 , 25 , 29 ) and the structure ( 13 , 21 , 27 , 32 ) of its 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 coupling element ( 28 ) is a sponge body, which consists 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. 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 µm to 300 µm. 12. acetabular cup according to claim 11, characterized in that the Roughness depth Ra is about 60 µm.