Title of Invention

JOINT SOCKET FOR A HIP ENDOPROSTHESIS

Abstract

Abstract The joint socket of a hip endoprosthesis consists of a socket shell (18) implantable in the pelvic bone (10) and a socket insert (20) for providing a bearing for the joint head (16). The socket Shell (18) has an accornmodating space having a conical inner surface in which the spherical outer surface of the socket insert (20) is inserted. As a result, the socket insert (20) can be ciamped in self-retaining manner in any desired Position of rotation and tut in the accornmodating space of the socket shell. Figure 1

Full Text

Description Joint socket for a hip endoprosthesis The invention relates to a Joint socket for a hip endoprosthesis according to the preamble of claim t. in the case of total hip endoprostheses, a prosthesis stern having a joint head is inserted into the femur. A joint socket, which serves as a bearing shell for the joint head, is implanted in the pelvic bone. It is known to constmct the joint socket from a socket shell and a socket insert Ths socket shell can be optimised with regard to Implantation in the pefvic bone, whereas the socket insert can be optimised with regard to the bearing properties for the joint head. In that case the socket shell is so formed and so positioned in the pelvic bone as to aliow ingrowth that is as stable as possible by the socket shell in the pelvic bone. The socket insert can be oriented in the socket shell in such a way that the Joint head is accommodated so that the prosthesis stem and accordingly the femur of the patient are as far as possible in the correct orthopaedic pos'rtion. From EP 0 663 193 A1 there is known a joint socket wherein the socket insert has a spherical outer surface and that spherical outer surface is seated in a spherical accommodating space - of the same spherical radius - of the socket shell. Therefore, when the socket insert has been inserted into the socket shell, the socket insert can be rotated at will about its axis of rotation and its axis of rotation can be tilted at will with respect to the axis of rotation of the accommodating space. As a resuit, it is possible for the socket shell to be positioned in the pelvic bone in accordance with the bone structure. The socket insert can be oriented in accordance w'rth the orthopaedic position of the prosthesis stem inserted into the femur. In order to fix the socket insert in its position,within the socket shell, the inner spherical surface of the accommodating space of the socket shell has pointed projecting teeth which engage in the outer surface of the socket insert. Because the teeth have to dig into the outer surface of the socket insert, there are limitations with respect to the choice of material for the socket insert. Pressing the socket insert onto the teeth of the socket shell makes it difficult for the socket insert to be inserted in a preciseiy positioned manner. The problem underlying the invention is to provide a joint socket for a hip endoprosthesis which allows the socket insert to be freely oriented in relation to the socket shell with high precision and nicety. The problem is solved in accordance with the invention by a Joint socket having the features of ciaim 1. Advantageous embodiments of the invention are given in the subordinate Claims. in accordance with the invention, the Joint socket has a socket insert which, by virtue of its spherical outer surface, allows free rotation and tilting in the socket Shell. The socket shell can therefore be implanted in accordance with the anatomy and structure of the pelvic bone, so that Optimum conditions for ingrowth can be achieved. The socket insert can be so rotated in the socket shell and its axis of rotation can be so titted in relation to the axis of rotation of the socket shell that the axis of rotation of the socket insert is aligned with the axis of the shaft neck of the prosthesis stem when the femur with the inserted prosthesis stem is arranged in the optimum orthopaedic posjtion. The spherical outer surface of the socket insert is in contact with the inner surface of the accommodating space along a circumferential line which is concentrically arranged with respect of the axis of rotation of the accommödating space. That line contact makes it possible for the socket insert to be readily rotated and tilted in the accommodating space so that the socket insert can be optimaliy oriented in terms of its posttion. Once the socket insert has been oriented, slight pressure is sufficient to press the socket insert into the narrowing accommodating space, whereupon the socket insert becomes clamped in the accommodating space in self-retaining manner. The self-retaining clamping brings about fixing of the socket insert in the socket shell with a high degree of stabiiity; loading of the Joint causes additional pressing of the socket insert into the socket shell so that fixing of the socket shell is additionally strengthened. Because fixing of the optimaliy oriented socket insert results from its being simply pressed into the accommodating space: this fixing is simple to carry out and does not require any additional instruments or additional fixing means. The self-retaining clamping is established with a minimal amount of displacement of the socket insert into the accommodating space so that unintentional misalignment of the socket insert orientation cannot occur in the course of fixing the socket insert in position. In the case of an impianted prosthesis, the shank neck of the prosthesis stem can7 in unfavourable cases, make contact with the edge of the Joint socket (so-called impingement). As a resuit thereof, the prosthesis stem exerts leverage on the Joint socket, in the case of customary Joint sockets, in which the socket insert is held in the socket shei! with an interlocking fit, that leverage can resuit in the entire joint socket's being levered out from the peivic bone or at least becoming loose in the pelvic borte. Because1 in accordance with the invention, the socket insert is merely pressed into the accommodating space of the socket shell, such leverage in an unfavourable case merely causes ioosening of the socket insert in the socket sheli in the case of the Joint socket according to the invention. When the Joint is subsequently subjected to normal loading, the socket insert is pressed back into the accommodating space of the socket sheli and is again firmly clamped and fixed. In a preferred embodiment, the inner surface of the accommodating space of the socket sheli is, at least in the region of the line of contact, in the form of a cone that narrows towards the pole of the accommodating space. As a resuit thereof, simple manufacture is possible. The conical surface additionally ensures especially effective self-retaining. As the cone angle, that is to say the angle between the mid-axis of the cone and the line of the lateral surface of the cone, there is selected the self-retaining angle corresponding to the material pairing of socket shell and socket insert. Usually, that cone angle is, depending on the material pairing, about from 4° to 10°. In order to bring about reliabie clamping of the socket insert in the socket Shell, the socket insert and the socket shell are made from a hard material. The socket shell is preferably manufactured from a biocompatible material, for example a titanium alloy. For the socket insert there can be selected a material corresponding to the siiding characteristics pairing of socket sheli and Joint head, for example a metallic or ceramic material or a plastics material, The invention is explained in greater detail hereinbelow with reference to an exempiary embodiment shown in the drawings, in which: Figure 1 shows a total hip endoprosthesis, and Figure 2 is an axial section through the joint socket of that prosthesis. The total hip endoprosthesis consists of a Joint socket, which is implantable in the peivic bone 10, and a prosthesis stem 12, which is inserted into the femur 40. The prosthesis stem 12 has a shaft neck 14, on which a Joint head 16 sits, which will be held in the Joint socket. The Joint socket separately shown in Figure 2 consists of a socket sheli 18 and a socket insert 20. The socket shell 18 is inserted in the peivic bone 10 in a manner known per se. For that purpose, the socket sheil 18 can be fixed in the peivic bone 10 by means of additional screws. The socket sheli 18 can be in the form of a screw socket, which has a thread on its outer surface, in the form of a press-in socket, which is formed having a suitable structure 22 on its outer surface, as shown by way of example in Figure 2, or in the form of a re-operation socket, as is described, for example, in EP 0 663 193 A1. The substantially hemispherical socket shell 18 is recessed by means of an accommodating space 24, which is open to the equatoriai plane. The accommodating space 24 has rotationai symmetry with respect to the mid-axis 26 of the socket shell 18. The accommodating space 24 has an internal surface 28 in the form of a straight circular cone which becomes narrower from the opening located in the equatoriai plane towards the pole of the socket Shell 18. The base 30 of the accommodating space 24 in the pole region is flattened off. The cone angie of the conical inner surface 28, that is to say the angle inciuded between the axis of rotation 26 and the lateral line of the inner surface 28, is so selected in dependence on the materia! pairing of socket Shell 18 and socket insert 20 that self-retaining will come about. That angle is preferably about from 4° to 10°. .In the case of a metallic socket sheli 18, for example, a self-retaining cone angle of about 4.5° is established for a metallic socket insert 20 and a self-retaining cone angle of about 9.5° for a ceramic socket insert 20. The socket insert 20 is likewise of substantially hemispherical shape, The outer surface 32 of the socket insert 20 is sphericaliy shaped at least in the region in which that outer surface 32 comes into contact with the inner surface 28 of the accommodating space 24. The diameter of the outer surface 32 corresponds to the diameter of the inner surface 28 at a line of contact 34, which extends, spaced somewhat (about from 5 mm to 15 mm) away from the equatorial opening plane, inside the accommodating space 24 concentrically with respect to the axis of rotation 26. The socket insert 20 has a recessed spherical bearing surface 36, which serves to accommodaie, and provide a bearing for, the Joint head 16. The spherical outer surface 32 and the spherical bearing surface 36 are rotationally symmetrical with respect to an axis of rotation 38 of the socket insert 20. The socket shell 18 is inserted in the pelvic bone 10, as shown in Figure 1, the arrangement of the socket Shell 16 in the pelvic bone 10 being selected in accordance with the anatomy and structure of the pelvic bone 10. The socket insert 20 is then looseiy inserted in the accommodating space 24 of the socket shell 18. The outer surface 32 of the socket insert 20 comes into contact with the conical inner surface 28 of the accommodating space 24 along the line of contact 34. The socket insert 20 can then be rotated at will about its axis of rotation 38 and the axis of rotation 38 of the socket insert 20 can be tiited at will with respect to the axis of rotation 26 of the socket shell 18. The prosthesis Stern 12 is hammered into the cleared marrow cavity of the femur 40, the prosthesis stem 12 possibiy adapting very slightly, in terms of its rotational position, to the bone structure of the femur, As a result» the position and orientation of the shaft neck 14 together with the joint head 16 become fixed in relation to the femur. The joint head 16 is then inserted into the bearing surface 36 of the socket insert 20, and the femur 40 together with the prosthesis stem 12 is brought into the Optimum orthopaedic position. The socket insert 20 can then be oriented in accordance with that positioning. As soon as the socket insert 20 has been optimally oriented, the socket insert 20 is pressed axially into the accommodating Space 24 so that it is clamped in self-retaining manner in that orientation position. List of reference numerals 10 peivic bone 12 prosthesis siem 14 shaft neck 16 joint head 18 socket sheli 20 socket insert 22 strudure 24 accommodating space 26 mid-axis of sockst Shell 28 inner surface 30 base in pole region 32 outer surface 34 line of contact 36 spherical bearing surface 38 axis of rotation of socket insert 40 femur Patent Claims 1. Joint socket for a hip endoprosthesis, having a socket stiel! (18) implantable in the pelvic bone (10) and a socket insert (20) for providing a bearing for the Joint head (16), a spherical outer surface (32) of the socket insert (20) sitting in an accommodating space (24) of the socket Shell (18), characterised in thatthe outer aurface (32) of the socket insert (20) contacts the inner surface (28) of the accommodating space (24) in a line of contact (34) which is concentric with respect to the axis of rotation (26) of the accommodating space (24); in that the inner surface (28) of the accommodating space (24) in the region of that line of contact (34) narrows towards the pole of the accommodating space (24) in such a manner that the radius of curvature in that region is always greaterthan the sphericai radius of the outer surface (32) of the socket insert (20); and in that the socket insert (20) is arranged to be clamped in self-retaining manner in the accommodating space (24). 2. Joint socket according to claim 1, characterised in that the inner surface (28) of the accommodating space (24) is of conical shape (infinite radius of curvature) in the region of the line of contact (34). 3. Joint socket according to ciaim 2, characterised in that the cone angle of the oonicalty narrowing inner surface (28) of the accommodating space (24) is the self-retaining angle of the material pairing of socket Shell (18) and socket insert (20). 4. Joint socket according to c!aim 3, characterised in that the cone angle of the conical inner surface (28) is between about 4° and 10°. Dated this 21 day of June 2006

Documents:

2242-CHENP-2006 AMENDED CLAIMS 21-11-2011.pdf

2242-CHENP-2006 AMENDED PAGES OF SPECIFICATION 21-11-2011.pdf

2242-CHENP-2006 CORRESPONDENCE OTHERS 03-02-2012.pdf

2242-CHENP-2006 EXAMINATION REPORT REPLY RECEIVED 21-11-2011.pdf

2242-CHENP-2006 FORM-1 21-11-2011.pdf

2242-CHENP-2006 FORM-13 21-11-2011.pdf

2242-CHENP-2006 FORM-3 21-11-2011.pdf

2242-CHENP-2006 OTHER PATENT DOCUMENT 21-11-2011.pdf

2242-CHENP-2006 POWER OF ATTORNEY 03-02-2012.pdf

2242-CHENP-2006 CORRESPONDENCE OTHERS 02-09-2011.pdf

2242-CHENP-2006 CORRESPONDENCE PO.pdf

2242-CHENP-2006 FORM-18.pdf

2242-chenp-2006-abstract image.jpg

2242-chenp-2006-abstract.pdf

2242-chenp-2006-claims.pdf

2242-chenp-2006-correspondense others.pdf

2242-chenp-2006-discription complete.pdf

2242-chenp-2006-drawings.pdf

2242-chenp-2006-form 1.pdf

2242-chenp-2006-form 3.pdf

2242-chenp-2006-form 5.pdf

2242-chenp-2006-pct.pdf