AU2005251427A1

AU2005251427A1 - Hip joint endoprosthesis having a sleeve from a biocompatible plastic

Info

Publication number: AU2005251427A1
Application number: AU2005251427A
Authority: AU
Inventors: Anton Cotting; Wilfried Glien; Thomas Oberbach; Dirk Salomon
Original assignee: Mathys AG Bettlach
Current assignee: Synthes Bettlach GmbH
Priority date: 2004-06-07
Filing date: 2005-04-12
Publication date: 2005-12-22
Also published as: WO2005120596A1; DE502005004202D1; DE102004027658A1; EP1753477B1; EP1753477A1

Description

IN THE UNITED STATES PATENT AND TRADEMARK OFFICE DECLARATION I, Malcolm Gesthuysen, BSc., translator to Messrs. Taylor and Meyer of 20 Kingsmead Road, London SW2 3JD, England, do solemnly and sincerely declare as follows: 1. That I am well acquainted with the English and German languages; 2. That the following is a true translation made by me into the English language of the accompanying International Patent Application PCT/EP2005/003845; 3. That all statements made herein of my own knowledge are true and that all statements made on information and belief are believed to be true; and further that these statements were made with the knowledge that willful false statements and the like so made are punishable by fine or imprisonment, or both, under Section 1001 of Title 18 of the United States Code and that such willful false statements may jeopardise the validity of the application or any patent issued thereon. Signed, this day of b-.,o- 2006 Edgware, Middesex HA8 8PG, United Kingdom WO 2005/120596 PCT/EP2005/003845 1 Hip-joint endoprosthesis with sleeve made of biocompatible plastic 5 The invention relates to a hip-joint endoprosthesis for the prosthetic care of the human or animal hip joint. A joint ball for a hip-joint endoprosthesis is known from DE 101 56 610 A1, for example. Said joint ball exhibits an 10 interior metallic reinforcing body on which a coating is formed by way of sliding partner for its counterpart in the joint. A conical clamping sleeve for receiving a hip-shank cone is arranged in the metallic reinforcing body. 15 A disadvantageous aspect of the joint ball known from DE 102 56 610 Al is, in particular, the fact that the clamping sleeve serves merely for fixing the hip-shank cone, and deviations of the hip-shank cone from the optimal shape as a result of damage to or contaminations of the 20 surface cannot be compensated. Furthermore, a joint endoprosthesis is known from CH 676 922 A5 having a cone-type plug-and-socket connection between a ceramic joint part and a metallic joint part, in 25 which prosthesis the cone-type plug-and-socket connection is relocated into a metallic adapter sleeve which is firmly pre-assembled in the ceramic joint part. Only the second plug-and-socket connection is then joined together during the operation. 30 A disadvantageous aspect of the joint endoprosthesis known from CH 676 922 A5 is, in particular, the fact that a metallic adapter sleeve is only very inadequately suitable for compensating for deformations in the region of the 35 conical plug-and-socket connection that are brought about, WO 2005/120596 PCT/EP2005/003845 2 for example, by damage to the conical faces or by contaminations. Accordingly, the object underlying the invention is to 5 create a hip-joint endoprosthesis that is designed in such a way that surface irregularities as a result of damage and contaminations can be compensated, and the possibility is thereby offered for exchanging the joint ball without making a total operation necessary. 10 The object is achieved by the features of Claim 1. According to Claim 1, the invention provides for arranging a sleeve, which is produced from a biocompatible plastic, 15 between an inner wall of the joint ball and the hip-shank cone. Further advantageous configurations of the invention are characterised in the dependent claims. 20 It is advantageous that a sleeve made of a polymer such as polyethylene or polyether ether ketone is thermoplastic and at the same time impact-resistant and, as a result, offers excellent preconditions for compensating for damage and 25 contaminations on one of the surfaces of the conical plug and-socket connection. In advantageous manner the sleeve exhibits a peripheral bead which is in engagement with a groove of the joint 30 ball, as a result of which the sleeve can be delivered pre assembled with the joint ball without there being any risk of slipping out in the course of transportation and during the operation.

WO 2005/120596 PCT/EP2005/003845 3 Furthermore, it is advantageous that the sleeve is of cup shaped design and exhibits in a bottom a recess through which air that is trapped between the sleeve and the joint ball in the course of pre-assembly is able to escape. 5 An exemplary embodiment of the invention will be elucidated in more detail in the following on the basis of partially schematic representations in the drawing. Shown in the drawing are: 10 Fig. 1 a schematic view of an exemplary embodiment of a hip-joint endoprosthesis configured in accordance with the invention, and 15 Figs. 2A-C various enlarged views of the joint ball, configured in accordance with the invention, of the hip-joint endoprosthesis according to Fig. 1. 20 Fig. 1 shows, in a schematic representation, a view of a femur component 1 for a hip-joint endoprosthesis. The hip joint endoprosthesis represented in the exemplary embodiment is also designated as a total hip-joint endoprosthesis, since both the femoral joint component and 25 the pelvic joint component are replaced. The femur component 1 exhibits a shank 2 which, depending on the structural shape of the femur component 1, is cemented in the medullary cavity of a femoral bone, or anchored in cement-free manner. Formed on the shank is a neck portion 30 3, at the end of which a hip-shank cone 4 for receiving a joint ball 5 is formed. The measures according to the invention that are described in more detail in the following are to be regarded as being 35 independent of the shape of the shank 2 and are also to be WO 2005/120596 PCT/EP2005/003845 4 viewed in combination with a joint socket, not represented in any detail, or with a prosthesis-head system articulated directly within the joint socket. The shape of the joint socket is arbitrary. The shape of the neck portion 3 can 5 also be chosen freely. Various materials may be used for the sliding pairings between the joint ball 5 and the joint socket. These may be, for example, polyethylene (PE) with a metal alloy such 10 as cobalt-chromium (Co-Cr) or with ceramic; however, this pairing has the disadvantage of severe abrasion and, associated therewith, insidious degeneration as a result of inclusions of the abrasion in the fundus of the socket and loosening of the socket. Sliding pairings consisting of 15 two metallic components are likewise not uncritical, since the abrasion and the subsequent diffusion of heavy ions into the body leads to increased heavy-metal values in the haemogram and, in addition, particularly in the case of nickel, may have an allergenic effect. 20 Ceramic plain bearings, on the other hand, display very little abrasion, which in addition is biologically inert, and enable high-precision surface machining within the nano range. The use of joint balls 5 made of ceramic has 25 therefore gained acceptance, thanks to their good tribological properties in hip endoprosthetics. One disadvantage here, however, is the risk of a sudden case of damage as a result of fracture of the joint ball 5, since the load-bearing capacity of ceramic in reaction to tensile 30 stresses is poor. Tensile stresses may already arise as a result of deformations of the hip-shank cone 4 that lie within the micrometer range. If the hip-shank cone 4 is not free from 35 particles (bone remnants, blood, fat, soft tissue, etc.) WO 2005/120596 PCT/EP2005/003845 5 prior to the mounting of a joint-head system 5 made of ceramic, or if the surface of the hip-shank cone 4 does not conform, or no longer conforms, to the defaults, undesirable tensile stresses may arise in the joint ball 5 5 and may result locally in stress peaks which may lead to the fracture of the joint ball 5. In this connection it is to be noted that it is not a question of a dynamic process, as for example in the case of severe localised loads in the course of sporting activity or the like, but rather a 10 question of a damage picture resulting from constant static loading. Furthermore, in the course of the revision of the joint ball 5, during which the shank 2 might remain in situ, a 15 joint ball 5 made of ceramic might not be chosen again, since the hip-shank cone 4 was possibly damaged as a result of the removal of the joint ball 5, and exhibits a cone geometry deviating from the original geometry, which may lead to the aforementioned problems in a manner analogous 20 to contaminations. Security against a case of damage as a result of fracture of the joint ball 5 by reason of deviating geometry of the hip-shank cone 4 can consequently only be guaranteed by a 25 total operation, in the course of which not only the joint ball 5 but also the entire femur component 1 is exchanged, which, however, entails serious disadvantages. On the one hand, the shank 2 is often well integrated into the femoral bone and can only be removed with great effort, in the 30 course of which, in addition, bone tissue of the femur is lost. Furthermore, the duration of the operation in the case of a total operation is considerably longer than in the case of the exchange of the joint ball 5. In addition, the tissue incision required for a total operation is 35 larger, and accordingly the risk of post-operative WO 2005/120596 PCT/EP2005/003845 6 infection is also higher and the probability of scarring is higher. The object of the present invention is accordingly to 5 design the joint ball 5 in such a way that the ceramic parts of the hip-joint endoprosthesis become capable of revision, as a result of which a total operation is unnecessary and a new ceramic joint ball 5 can be attached onto the existing shank 2. 10 According to the invention, provision is therefore made, as represented on an enlarged scale in various views in Figs. 2A to 2C, to insert a sleeve 6 into the ceramic joint ball 5, which sleeve increases the error tolerance and 15 reduces the risk of a fracture of the joint ball 5. The sleeve 6 takes the form, in particular, of a conical or cup-shaped sleeve 6 which has a bottom 8. The sleeve 6 bears against an inner wall 7 of the ceramic joint ball 5 and is supplied to the operating surgeon firmly pre 20 assembled with said joint ball. During the operation the operating surgeon then only has to fit the joint ball 5 with the inserted sleeve 6 onto the hip-shank cone 4. By virtue of the material properties of the sleeve 6, which are elucidated in more detail further below, there is no 25 longer any reason to fear stress peaks occurring which may lead to a sudden case of damage. With a view to facilitating the pre-assembly, the cup shaped sleeve 6, as evident from Fig. 2C, exhibits in the 30 bottom 8 a recess 9 which enables the air trapped between the sleeve and the inner wall of the joint ball 5 in the course of assembly to escape, so that the sleeve 6 bears over its full surface against the inner wall 7 of the joint ball 5 and against an external surface 12 of the hip-shank WO 2005/120596 PCT/EP2005/003845 7 cone 4. This is an essential precondition for the correct functioning of the sleeve 6. In order to prevent the sleeve 6 from becoming detached 5 from the joint ball 5 during transportation or during the operation, on the inner wall 7 the joint ball 5 exhibits a peripheral groove 11 which is in engagement with a peripheral bead 10 formed on the sleeve 6. In the exemplary embodiment the bead 10 and the groove 11 are 10 formed in the region of the bottom 8 of the cup-shaped conical sleeve 6. However, since production here is particularly easy, it is also possible to place the bead 10 and the groove 11 in another position, or to introduce the sleeve 6 directly without an additional groove. 15 The sleeve 6 preferably consists of a biocompatible material having lower stiffness and higher fracture toughness than the ceramic of the joint ball 5; in particular, it consists of a polymer such as polyether 20 ether ketone (PEEK) or polyethylene (PE) or any biocompatible plastic that by virtue of its thermoplastic, impact-resistant properties enables a pseudo-elastic connection between the components of the prosthesis. 25 The choice of the material for the sleeve 6 has two significant advantages: on the one hand, contaminations of or damage to one of the surfaces of the conical plug-and socket connection can be compensated very effectively, so that cases of damage as a result of fracture of the ceramic 30 joint ball 5 are avoided. On the other hand, it is no longer necessary to machine the surfaces of the plug-and socket connection in highly precise manner, since slight deviations from the ideal surface are likewise compensated, lowering the manufacturing costs considerably. 35 WO 2005/120596 PCT/EP2005/003845 8 The invention is not restricted to the exemplary embodiment represented and may also be used for other shapes of femur components 1. In particular, application of the sleeve 6 is not restricted to ceramic joint balls 5 but is also 5 suitable for application, for example, with a hip-shank cone 4 formed from ceramic.

Claims

1. A hip-joint endoprosthesis with a femur component (1) 5 which comprises a shank (2), which is capable of being anchored in a medullary cavity of a femoral bone, and a neck portion (3) formed thereon with a hip-shank cone (4) for receiving a ceramic joint ball (5), a sleeve (6) being arranged between the hip-shank cone (4) and an inner wall 10 (7) of the joint ball (5), characterised in that the sleeve (6) is produced from a biocompatible plastic.

2. Hip-joint endoprosthesis according to Claim 1, 15 characterised in that the biocompatible plastic is a polymer.

3. Hip-joint endoprosthesis according to Claim 2, characterised in that 20 the polymer is polyethylene (PE), polyether ether ketone (PEEK) or polymethyl methacrylate (PMMA).

4. Hip-joint endoprosthesis according to one of Claims 1 to 3, 25 characterised in that the sleeve (6) is conically shaped in the form of a cup.

5. Hip-joint endoprosthesis according to Claim 4, characterised in that 30 the sleeve (6) exhibits a bottom (8) facing towards the inner wall (7) of the joint ball (5).

6. Hip-joint endoprosthesis according to Claim 5, characterised in that WO 2005/120596 PCT/EP2005/003845 10 a recess (9) is provided in the bottom (8).

7. Hip-joint endoprosthesis according to one of Claims 4 to 6, 5 characterised in that the sleeve (6) exhibits a peripheral bead (10).

8. Hip-joint endoprosthesis according to Claim 7, characterised in that 10 the peripheral bead (10) is in engagement with a groove (11) which is formed on the inner wall (7) of the joint ball (5).

9. Hip-joint endoprosthesis according to one of Claims 1 15 to 8, characterised in that the sleeve (6) bears over its full surface against the inner wall (7) of the joint ball (5) and against an external surface (12) of the hip-shank cone (4).