Prosthesis (i.e. – artificial body members) – parts thereof – or ai – Implantable prosthesis – Bone
Reexamination Certificate
2000-09-28
2001-11-20
McDermott, Corrine (Department: 3738)
Prosthesis (i.e., artificial body members), parts thereof, or ai
Implantable prosthesis
Bone
C623S022210
Reexamination Certificate
active
06319285
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a hip-joint socket of a hip-joint endoprosthesis in accordance with the preamble of the first claim.
Hip-joint endoprostheses as a rule are build up in a modular fashion. They consist, for example, of a shaft which is inserted into the femur. Plugged onto the shaft is a ball head which is mounted in a socket that is constructed from two parts. The socket consists of a socket housing, the so-called metal back, and a socket insert, the so-called insert. Furthermore, there are also systems which permit even more possibilities of combination and variation, for example in order to lengthen the shaft. With the modularly built up endoprostheses, implant components of different materials and sizes are connected together. For example, ball heads made of cobalt chromium are plugged onto a shaft of titanium alloy, or a socket insert of polyethylene or a ceramic material is inserted into a socket housing, as known, for example, from DE 196 112 48 A1. The combination of the individual parts is, as a rule, predetermined by the dimensions of the joint.
As known from the publication “Frettingkorrosion, ein Problem bei Hüftendoprothesen” by G. Willmann, Praktische Orthopädie, Rheumatologie-Endoprothetik, Volume 27, 1997, the disadvantage of the modular construction of endoprostheses is that, after having been assembled, instances of loosening can occur as a result of strains in the body that result in the relative movement between the individual parts of the prostheses and thus give rise to wear. In addition, on account of the plurality of possible components and possibilities for the assembly thereof, there is also a risk of confusion with regard to the sizes or a combination of prosthesis components that is not as prescribed. This can result in defective functioning of the prosthesis and thus ultimately in failure.
SUMMARY OF THE INVENTION
The object of the present invention is to put forward a hip-joint socket of a hip-joint endoprosthesis in which not only is incorrect assembly of the socket insert and socket housing precluded, but loosening of the two components caused by strain is also prevented.
The object is achieved with the aid of the characterising features of the first claim. Advantageous developments of the invention are claimed in the subclaims.
The invention gives rise to a one-piece hip-joint socket as an implant. As a result of coating the ceramic material of the socket with a biocompatible metal or a biocompatible metal alloy in the region in which the socket is inserted into the hip bone, a non-detachable connection results between the part of the prosthesis that functions as an insert in accordance with the prior art for the purpose of mounting the ball head and the so-called socket housing, this establishing the connection between the bone and the bearing shell for the ball head. Only one part is thus made available to the surgeon for the implantation of a socket, with the coating being matched in an optimum manner to the size and assembly of the ceramic bearing shell. The risk of incorrect assembly of the socket insert and socket housing is precluded. Furthermore, the risk that the connection between the insert and the housing will loosen on account of the strains in the prosthesis joint and that the prosthesis will wear as a result of the relative movement of the two components in relation to each other is precluded.
In an advantageous development of the invention, the surface of the bearing shell of the hip-joint socket that is to be coated is roughened. As a result, an intimate and solid mechanical connection of the coating with the ceramic body is guaranteed, since the coating neither reacts with the ceramic material chemically nor does it react therewith metallurgically. The surface of the ceramic body can be roughened, for example, by blasting with particles of hard material, by rough-grinding or etching.
In particular, two known and tested methods are available for the application of the coating. According to the first method, the coating is vapour-deposited thereon. The vapour-deposition can be effected, for example, by sputtering. In this connection, the metal that is to be applied is pulverized under high vacuum and is precipitated from the vapour phase onto the surface of the substrate. It is possible to produce a coating that is of the required layer thickness by means of repeated vapour-deposition.
The coating can also be sprayed thereon. Plasma-spraying is suitable for spraying on metals or metal alloys, in particular high-melting metals or metal alloys of titanium.
Plasma-spraying also presents the possibility of producing a coating to the required thickness. When a coating is of sufficient thickness, it is possible to roughen the surface of the coating. The roughness can be brought about by means of the method of application or by means of appropriate finishing in such a way that the bone tissue is offered the possibility of growing together with the surface and thus effecting reliable anchorage of the implant in the bone. The surface quality can already be achieved by means of the spraying technique, in particular in the case of plasma-spraying, so that no finishing is required.
Particularly good anchorage of the implant in the bone tissue is achieved if the coating is porous. In this case, the bone tissue can grow into the pores and thus provide the implant with a particularly good hold.
The thickness of the coating must be selected so that, on the one hand, it presents the bone tissue with a sufficiently large working surface to grow together therewith, but not so that, on the other hand, it is subject to the risk of fracture, something which can be the case, for example, with a porous coating that is too thick. A layer thickness which is thinner than 1 mm has therefore proved to be advantageous. A layer thickness of 50 micrometers to 150 micrometers, on the one hand, presents a sufficient level of thickness in order to form a structure that is favourable for ingrowth of the bone tissue and, on the other hand, presents sufficient stability of the coating per se.
All biocompatible metals and metal alloys are suitable for coating purposes. On account of their thermal and mechanical properties, titanium-based alloys, for example TiAl6V4 and TiAl6Nb7, have proved to be particularly advantageous.
All ceramic materials that have been applied successfully in prosthetics can be used as ceramic materials for the bearing shell of the hip-joint socket. Aluminium oxide with an appropriate level of purity has proved to be particularly advantageous for reasons of wear resistance, mechanical stability and medical compatibility.
In order to facilitate and accelerate the ingrowth of the implant into the bone, the coating can be provided with a bioactive covering. A covering that is known for these purposes is, for example, hydroxyapatite. The coating is applied in the same way and to the same level of thickness, as, for example, in the case of the coating of the shafts which are inserted into the femur.
REFERENCES:
patent: 5222984 (1993-06-01), Forte
patent: 5338771 (1994-08-01), Neumann et al.
patent: 5549700 (1996-08-01), Graham et al.
patent: 5571193 (1996-11-01), Kampner
patent: 5879404 (1999-03-01), Bateman et al.
patent: 6066176 (2000-05-01), Oshida
Chamier Wilfried Von
Kalberer Kartmut
Pfaff Hans-Georg
Antonelli Terry Stout & Kraus LLP
CeramTec AG Innovative Ceramic Engineering
McDermott Corrine
Phan Hieu
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