WO2007016795A1

WO2007016795A1 - Device for the artificial replacement of a joint articulation in humans and animals

Info

Publication number: WO2007016795A1
Application number: PCT/CH2005/000463
Authority: WO
Inventors: Lukas Eschbach
Original assignee: Dr.H.C. Robert Mathys Stiftung
Priority date: 2005-08-09
Filing date: 2005-08-09
Publication date: 2007-02-15

Abstract

The device (1) is for the artificial replacement of a joint articulation in humans and animals, comprising a first sliding component (2), with a first sliding surface (4) and a second sliding component (3), with a second sliding surface (5) which articulates with the first sliding surface (4) such that the first and second sliding components (2,3) form an articulated connection. At least one of the sliding surfaces (4, 5) is made from a composite material (7), with at least one inorganic non-metallic material embedded in a polymer matrix, said inorganic non-metallic material comprising a number of particles with an average diameter of less than 200 nanometres.

Description

Device for the artificial replacement of joint articulation in humans and animals

The present invention relates to a device according to the preamble of claim 1. In particular, it relates to applications in hip, knee and shoulder arthroplasty.

The pairings of polyethylene / metal or polyethylene / ceramics that are most commonly used as sliding partners in joint endoprosthetics are currently being used. In hip joint endoprostheses, for example, polyethylene (PE) as ultrahigh-molecular-weight PE (UHMWPE) forms the socket material, while the ball consists of metal or ceramic, mostly Al ₂ O 3 or ZrO ₂ ceramics.

Although metal-metal and ceramic-ceramic pairings have already been clinically proven, they have better wear and sliding properties than UHMWPE / metal or UHMWPE / ceramic pairings. On the other hand, disadvantageous from a material point of view is the damping behavior, the possibility of destruction of the surface of metal-metal pairings by third particles and, in the case of ceramic-ceramic pairings, additionally the material brittleness, which can lead to the catastrophic breakage of the implant components. Furthermore, the manufacturing costs for these so-called hard-hard pairings are higher than for pairings with UHMWPE.

The excellent wear characteristics of metal-to-metal sliding pairings are based on the fact that the cobalt alloys used consist of a metallic matrix and embedded fine hard carbides. When articulating touch virtually only the hard carbides and the softer matrix is thereby spared. This surface structure also has a positive effect on the lubrication of the system in that the matrix, which is slightly recessed relative to the sliding surface carbides, promotes the formation of a lubricating film.

The advantages of UHMWPE are above all in the good biocompatibility, in a high fracture and impact resistance, in the good damping properties, the deep Friction coefficients and in the low water absorption. However, there are also a number of arguments against UHMWPE. The disadvantages of PE in implanted acetabular cups are seen above all in excessive wear (linear wear rates of 0.3 to 0.5 mm / year are measured). It is known that the wear products of the UHMWPE can lead to a resorption of the surrounding bone via a cascade of reactions and thus bring about aseptic prosthesis loosening in the long term. Further disadvantages must be seen in the too low strength (too strong creep under pressure load, too soft against scratching), in a too low rigidity, especially towards the bone and in the heavy wettability. In addition, the aging resistance in the organism (oxidation) is not sufficient depending on the treatment and leads to a degradation of the mechanical properties.

In order to combine the advantages of the polymeric matrix with the hardness of ceramic, various composite materials have already been proposed as sliding partners for hard (metal or ceramic) components. The inorganic reinforcement phase has a particle size distribution of the order of micrometers. The disadvantage of these concepts is the risk that individual particles are torn out of the sliding surface as the state of wear progresses, scratch the surface and then lead to a catastrophic wear progress with destruction of the sliding surface.

It is an object of this invention to mitigate the disadvantages of the previously known solutions for sliding pairings in joint endoprosthesis and to develop a sliding partner whose special composite material reduces the wear on the articulation partner, and thus counteracts early prosthesis loosening.

According to the invention, this object is solved by the features of claim 1.

Preferably, the device according to the invention is designed as a joint endoprosthesis, typically with a concave and a convex sliding surface. The advantage of the invention is that the amplification phase has a great effect of reducing the rate of wear. Nevertheless, the embedded particles - because of their small size in the nanometer scale - even if they are torn out of the sliding surface, they do not damage. In addition, the advantage according to the invention exists that certain properties of the polymeric matrix-for example, the fracture toughness-are less impaired by the use of nanoparticles as a reinforcing phase in comparison with particles in the micrometer scale.

The tribological properties of the inventive device are comparable to those of metal / metal pairings based on cobalt alloys with embedded carbides. During the articulation of the composite material in the device according to the invention, practically only the ceramic nanoparticles come into contact with the sliding partner made of metal or ceramic and the polymeric matrix of the composite is thereby protected.

Suitable polymer matrix are the proven in vivo long-term stable polymers. Ultra-high molecular weight polyethylene (UHMWPE), polytetrafluoroethylene (PTFE) or a polymer from the family of polyaryletherketones (PAEK), for example PEEK (polyetheretherketone) or PEK or PEKEKK or PEKK, have proved particularly suitable for this purpose. On the one hand, these polymers have a high stability in the body milieu, on the other hand, it is also necessary to exclude questionable degradation products in the case of a slight degradation of these materials in the body, which can not be completely ruled out. They also have very good mechanical properties and have proven themselves in various applications as implant materials.

Reinforcing phases are inert inert inorganic-non-metallic (ceramic) materials. Ceramic materials based on oxides, nitrides or carbides, in particular of the following types: Al ₂ O 3, TiO _2, ZrO _2, SiO ₂ , Al ₂ SiO, SiC, Si 3 N ₄ , BaSO ₄ or a mixture thereof, have proven useful for this purpose. On the one hand, these inorganic-non-metallic materials have a high hardness and wear resistance, on the other hand they do not behave completely Excluded case of release of these materials in the body inert. These materials lead to a further improvement of the tribological properties.

The embedded in the polymer matrix parts of inorganic non-metallic material act primarily as Abrasionspräventoren and preferably have a spherical shape, a ball-like or a roundish shape. The lack of sharp edges or tips lessens the surface of the other metallic or ceramic sliding partner.

The two sliding surfaces may consist of a metallic or ceramic, but also of an unreinforced polymeric material. Especially in prostheses with high mechanical stress, e.g. In hip and knee joint prostheses, metallic or ceramic materials are particularly well suited.

In another embodiment, both sliding surfaces of the

Composite exist. The advantage of this embodiment is found especially in prostheses with low mechanical stress, e.g. for elbows, shoulders or finger prostheses.

The inorganic-non-metallic material is advantageously at least 90 wt .-% of a plurality of particles having an average diameter of less than 200 nanometers.

The particles advantageously have a spherical shape, a spherical or a roundish shape. The size distribution of the individual particles incorporated into the polymer matrix is preferably such that the mean value of the largest diameters of the particles is less than 100 nanometers, preferably less than 60 nanometers. This results in a further improvement of the tribological properties.

In a further embodiment, the size distribution of the individual particles incorporated into the polymer matrix is such that the mean value of the smallest diameters of the particles is above 5 nanometers, preferably above 10 nanometers. The inorganic-non-metallic material is expediently selected from the group of bioinert and / or biocompatible ceramics of high hardness, preferably the oxides, nitrides or carbides, in particular the following types: Al ₂ O ₃ , TiO ₂ , ZrO ₂ , SiO ₂ , Al ₂ SiO ₅ , SiC, Si ₃ N ₄ , BaSO ₄ or a mixture of these compounds.

In a particular embodiment, the particles are homogeneously distributed throughout the polymer matrix. Thus, by avoiding undesirable particle agglomerations, the tribological properties can be further improved.

In another embodiment, the particles are incorporated only to a depth of 2 mm in the polymer matrix.

The particles incorporated in the polymer matrix expediently make up a proportion of between 1 and 25 percent by weight, preferably between 5 and 15 percent by weight, of the composite material. Higher levels of embedded particles can lead to unwanted embrittlement.

The particles incorporated in the polymer matrix expediently have a Mohs hardness of greater than 5, preferably greater than 7.

In a particular embodiment, at least one of the two sliding surfaces is formed on the associated sliding component as a surface layer, and preferably has a maximum layer thickness of 2 mm.

The following are some examples of the production of composite materials, which are suitable for the inventive devices.

Example 1 (hip joint)

90% by weight UHMWPE / ultrahigh molecular weight polyethylene) were mixed with 10% by weight nanoparticles of aluminum oxide (Al ₂ O ₃ ) having a size distribution below 40 nm for 30 minutes in a ball mill. Thereafter, the resulting mixture was precompressed at 18 MPa and 180 ⁰ C for 15 minutes and finally pressed for a further 15 minutes at 26 MPa and 180 ⁰ C. The resulting blank, in which the nanoparticles were finely dispersed in the polymer matrix was cooled slowly.

From the blank were made by cutting acetabular cups, which were used as a sliding partner in a Totalhüftendoprothese.

Example 2 (hip joint)

The composite consisted of a polyetheretherketone matrix (PEEK) with 15% by weight finely dispersed nanoparticles of titanium oxide (TiO ₂ ) with a size distribution between 40 and 60 nm. This composite material was mixed by known processes of polymer processing, eg by melting the polymer produced with the nanoparticles, extrusion, granulation and processing of the granules by injection molding and processed into a final product, eg an artificial acetabulum.

Example 3 (knee component)

The composite consisted of a polyaryletherketone matrix (PAEK) with 10% by weight finely dispersed embedded nanoparticles of aluminum oxide (Al ₂ O ₃ ) with a size distribution between 60 and 90 nm. This composite material was prepared by known processes of polymer processing, eg by melting of the polymer , Mixing with the nanoparticles, extrusion, granulation and processing of the granules by injection molding and processed into a component for a knee joint prosthesis.

Example 4 (shoulder component)

The composite consisted of a polytetrafluoroethylene matrix (PTFE) with 5% by weight finely dispersed embedded nanoparticles of zirconium oxide (ZrO _Σ ) with a size distribution between 80 and 100 nm. This composite material was mixed by known processes of polymer processing, eg by melting the polymer manufactured using the nanoparticles, extrusion, granulation and processing of the granules by injection molding and processed into a component for a shoulder joint prosthesis. The invention and further developments of the invention will be explained in more detail below with reference to the partially schematic representations of several embodiments.

Show it:

1 shows a schematic cross section through a hip joint endoprosthesis.

FIG. 2 shows a schematic cross section through a shoulder joint endoprosthesis; FIG.

3 shows a schematic cross section through a knee joint endoprosthesis;

Fig. 4 is a schematic cross-section through another embodiment of a

Acetabulum; and

5 shows a schematic cross section through a further embodiment of a

Acetabulum.

FIG. 1 shows the schematic structure of a joint endoprosthesis 1 using the example of a hip prosthesis. The first, anchored in the acetabulum sliding component 2 consists of a material 7 which has been prepared according to one of the above examples 1 or 2. Its concave (hollow spherical) sliding surface 4 is polished smooth. The corresponding to the acetabular component second sliding component 3 is formed as a femoral component, made of metal or ceramic and has a polished convex (spherical) sliding surface 5 of the ball head 6.

In Fig. 2 a shoulder joint endoprosthesis with a joint shell and a ball head having humeral component is shown. The first sliding component 2 is designed as a joint shell with a concave (spherical) first sliding surface 4 and anchored in the scapula 13 according to one of the known surgical techniques, for example by means of bone screws 10 and bone cement. The second sliding component 3 comprises a ball head 6, which has a second, with the first sliding surface 4 articulating sliding surface 5, and a shaft 11 which is inserted into the drilled medullary space in the humerus 12 and fixed there by means of a bone cement in the bone. The trained as a joint shell first sliding component 2 and the ball head 6 here consist both of a material 7 which was prepared according to the above example. The first, concave and the second, convex sliding surface 4, 5 are polished smooth. The shaft 11 of the humeral component is preferably made of a metal and on the ball head 6 attached axially and stable to rotation.

Shown in FIG. 3 is a knee joint endoprosthesis with a femoral component, which has convexly curved sliding surfaces 5, and a tibial component, which has concave sliding surfaces 4. The first sliding component 2 is designed as a tibial component and comprises a plate 17 lying on the resected tibial plateau, on whose surface adjacent to the condyles two concave, first sliding surfaces 4 are arranged as depressions. The second sliding component 3 is designed as a femoral component and comprises two convex second sliding surfaces 5 corresponding to the condyles, which articulate with the first sliding surfaces 4 on the femoral component. The femoral component is anchored according to one of the known surgical techniques, for example by means of two pins 16 cemented in the distal femoral head, while the tibial component is fastened to the proximal tibia by means of bone screws 10. The formed as a plate first sliding component 2 consists of a material 7 which was prepared according to the above example. The first, concave sliding surfaces 4 are polished smooth. The second sliding component 3 is made of metal or ceramic, and the convex second sliding surfaces 5 are also polished.

FIG. 4 shows a first sliding component 2 designed as an acetabular component, which consists entirely of a material 7 which has been produced according to one of the examples given above.

FIG. 5 shows a first sliding component 2 designed as an acetabular component, which is assembled from an outer spherical shell 8 and an inner shell 9, which has the concave spherical first sliding surface 4. In this case, the inner shell 9 is made of a material 7, which was prepared according to one of the above examples, while the outer shell 8 is made for example of ultra-high molecular weight polyethylene (UHMWPE).

Claims

claims

1. Device (1) for the artificial replacement of joint articulation in humans and animals with

A) a first sliding component (2) having a first sliding surface (4); and

B) a second sliding component (3), which has a second sliding surface (5) articulating with the first sliding surface (4), so that

C) the first and second sliding components (2, 3) form an articulated connection; characterized in that

D) at least one of the two sliding surfaces (4,5) consists of a composite material (7), which comprises at least one, embedded in a polymeric matrix, inorganic non-metallic material, wherein

E) the inorganic-non-metallic material comprises a plurality of particles with an average diameter of less than 200 nanometers.

2. Device (1) according to claim 1, characterized in that one of the two sliding surfaces (4,5) consists of a metallic, ceramic or unreinforced polymeric material (6).

3. Device (1) according to claim 1, characterized in that both sliding surfaces (4,5) consist of the composite material (7).

4. Device (1) according to one of claims 1 to 3, characterized in that the inorganic-non-metallic material consists of at least 90 wt .-% of a plurality of particles having an average diameter of less than 200 nanometers.

5. Device (1) according to one of claims 1 to 4, characterized in that the particles have a spherical shape, a ball-like or a roundish shape.

6. Device (1) according to one of claims 1 to 5, characterized in that the size distribution of the individual, embedded in the polymer matrix particles is such that the mean value of the largest diameter of the particles is below 100 nanometers, preferably below 60 nanometers ,

7. Device (1) according to one of claims 1 to 6, characterized in that the size distribution of the individual, embedded in the polymer matrix particles is such that the mean value of the smallest diameter of the particles is above 5 nanometers, preferably above 10 nanometers ,

8. Device (1) according to one of claims 1 to 7, characterized in that the inorganic-non-metallic material from the group of bio-inert and / or biocompatible ceramics of high hardness is selected, preferably the oxides, nitrides or carbides, in particular of the following types : AI2O3, TΪO2, ZrO 2, SiO 2, AbSiOs, SiC, SJ ₃ N _4, BaSO ₄ or a mixture of these compounds.

9. Device (1) according to one of claims 1 to 8, characterized in that the particles are homogeneously distributed throughout the polymer matrix.

10. Device (1) according to one of claims 1 to 9, characterized in that the particles are incorporated only to a depth of 2 mm in the polymer matrix.

11. Device (1) according to one of claims 1 to 10, characterized in that the particles incorporated in the polymer matrix account for a proportion of between 1 and 25 percent by weight, preferably between 5 and 15 percent by weight of the composite material (7).

12. Device (1) according to one of claims 1 to 11, characterized in that the particles embedded in the polymer matrix have a Mohs hardness of greater than 5, preferably greater than 7.

13. Device (1) according to one of claims 1 to 12, characterized in that at least one of the two sliding surfaces (4; 5) on the associated sliding component (2; 3) is formed as a surface layer, preferably with a maximum layer thickness of 2 mm ,