EP1104269A1

EP1104269A1 - Joint prosthesis and anchoring means

Info

Publication number: EP1104269A1
Application number: EP99938449A
Authority: EP
Inventors: Nicolaas Gerardus Adrianus Van Leerdam; Nicolaas Jacobus Joseph Verdonschot; Hans Rudolf Kriek; Antonius Johannes Bernardus Sanders; Petrus Tarasius Josephus Spierings
Original assignee: Novarticulate Holdings Ltd
Current assignee: Novarticulate Holdings Ltd
Priority date: 1998-08-10
Filing date: 1999-08-10
Publication date: 2001-06-06
Also published as: JP2002522158A; KR20010082116A; WO2000009044A1; AU5295799A; CA2340158A1; NL1009831C2

Abstract

This invention relates to a joint prosthesis. The joint prosthesis has an anchoring means (1, 51, 100) arranged to be placed in a bone to rest against and be supported by an inside surface of the cortical bone layer. The anchoring means (1, 51, 100) may be placed in a bore along an extra medullary axis of a bone, such as the femur (F), and be supported by the cortical bone layer distal from the hip joint. Locking means (2, 2', 3, 3', 52, 106) are provided in order that the anchoring means (1, 51, 100) can be inserted through an inlet opening (Fi) and be supported by the inside surface (C) of the cortical bone wall adjacent the opening (Fi).

Description

JOINT PROSTHESIS AND ANCHORING MEANS

This invention relates to a joint prosthesis and, more particularly, to anchoring means for anchoring a joint prosthesis, and a method of fitting an anchoring means , in a bone .

It is a well known medical technique to replace worn out, damaged or diseased joints in human and animal bodies with artificial joint prostheses . Such prostheses may, for example, comprise a replacement joint articulation, such as a metal ball and socket or other pivotable means. Alternatively, the joint prosthesis may replace only part of the joint. For example, the ball of a ball and socket joint may be replaced with a joint prosthesis comprising an artificial replacement ball designed to sit in the original socket of a natural joint. Specifically, it is intended for the purposes of this application that the term 'prosthesis' or 'joint prosthesis' is not limited to a component which takes the form of a natural joint, but is intended to include any component for replacing part or all of the function of a natural joint.

Regardless of whether a joint prosthesis replaces all or part of a joint, the joint prosthesis, or parts of the joint prosthesis, needs to be anchored in or located on bone adjacent or near to the joint. Joint prostheses therefore generally further comprise means for anchoring the replacement articulation, joint surface or joint part in a bone. For example, a joint prosthesis for replacing a ball and socket joint, such as the human shoulder or hip, often has a replacement articulation comprising a ball and socket. The replacement ball may be located on, or formed integrally with, anchoring means comprising a pin arranged to be inserted in the medullary canal of a bone, such as the femur or humerus, after the natural ball has been removed. Similarly, a replacement socket may be carried in, or formed integrally with, anchoring means comprising a cup which is arranged or shaped to be cemented into the bone surrounding the socket, such as the acetabulum (hip bone) or scapula (shoulder blade) . Alternatively, the replacement socket may be carried on anchoring means comprising a pin which is inserted into an artificial bore in the acetabulum (hip bone) or scapula (shoulder blade) . Many problems arise concerning such fixation of joint prostheses in or to bones. For example, micro- movement of the anchoring means in the bone prevents bone from re-growing around the anchoring means and securing the anchoring means in place. This micro movement may even cause the joint prosthesis to work loose. Also, redistribution of load bearing in the bone, particularly near joints that carry heavy loads, such as the human hip or knee, causes localised deterioration or resorption of bone around the anchoring means and can lead to loosening of the joint prosthesis. In other words, movement of the anchoring means once it is in place, or in vivo erosion or destruction of bone around the anchoring means, results in the joint prosthesis working loose or never achieving stability. It is these problems that often result in large numbers of patients having their implanted joint prostheses replaced or operated on after they are first fitted.

The Applicant has identified that the above mentioned problems arise, at least in part, due to anchoring means being located in Spongiform bone, which is found inside, or in the central core, of human and animal bones. In particular, anchoring means that comprise pins are often inserted deep in a bone, for example in the medullary canal of bones such as the human femur or humerus . Spongiform bone is softer and less resilient than Cortical bone which is found in the outer layer or surface of human or animal bone . Thus , bone erosion, resorption or destruction around a joint prosthesis is more likely when a joint prostheses is fitted or anchored by anchoring means located in Spongiform bone. Another problem is that conventional procedures for fitting joint prosthesis are generally very invasive. Joints are buried deep in the human or animal body, so to replace natural joints with joint prostheses and to insert anchoring means into bone around a joint requires a large amount of tissue, including muscle, ligaments and cartilage which support the joint to be cut or destroyed. This leads to a long recovery time for joint replacement operations and a large failure rate. More recently, however, less or "minimally" invasive surgical techniques have been developed for joint replacements. Such a technique is disclosed in the Applicant's International Patent Application No. 098/34567, where it is disclosed to carry out a joint replacement by inserting the replacement parts through a bore in a bone. Such a bore is made through an incision distal from the joint being replaced and this reduces trauma to the tissue surrounding the joint.

According to a first aspect of the present invention there therefore provided a hip prosthesis comprising a first fastening assembly intended for being mounted in the hip bone and an anchoring means for being mounted in the top end of the femur, wherein the first fastening assembly and the anchoring means are interconnected by means of a pivotable connection, wherein all parts of the hip prosthesis are so small and/or slender that they can each be arranged in the intended end position thereof via a bore in the femur, said bore extending from an inlet opening in the cortical bone on the lateral outer side of the femur through the femoral neck substantially in the direction of the imaginary longitudinal centre line of the femoral neck to the femoral head, wherein the anchoring means comprises, adjacent a lateral end thereof, locking means movable from a first position into a locked position, wherein said locking means can pass the inlet opening of the femoral bore in the first position, wherein said locking means cannot pass the inlet opening of the femoral bore in the locked position, wherein in a mounted condition of the anchoring means the locking means is in the locked position and engage a side, facing a femoral inner space, of the lateral cortical bone wall of the femur bounding the inlet opening.

Thus, the anchoring means, and indeed the whole hip prosthesis, may be fitted using a minimally invasive technique, in which all access to the joint is gained through the bore in the bone. This vastly reduces trauma to area of the joint, and therefore shortens recovery time and reduces failure rate. Furthermore, the anchoring means is smaller than those of the conventional type as it extends across rather than along the bone. Thus, less bone is destroyed with the result that the procedure is less traumatic and may be recovered from more quickly.

An anchoring means or joint prosthesis that is supported by the inside surface of cortical bone wall is, however, more widely applicable. The bore may, for example, extend in a different direction through a bone and the anchoring may be used to support various other joint prostheses for replacing joints in the human and animal body, such as the human shoulder joint for example . According to a second aspect of the present invention there is therefore provided a joint prosthesis having an anchoring means arranged to be placed in a bore in a bone via an inlet opening of the bore distal to the intended position of the prosthesis, the anchoring means having locking means movable from a first position, in which it may be inserted through the inlet opening, into a locked position when mounted in the bore, the locking means in the locked position preventing the anchoring means from passing back out through the inlet opening and supporting the anchoring means by resting against the inside surface of the cortical bone wall adjacent the inlet opening.

Also, according to a third aspect of the present invention there is provided a method of anchoring a joint prosthesis in a bore in a bone, comprising inserting the anchoring means through an inlet opening of the bore distal to the intended position of the prosthesis, and moving a locking means into a locked position when the anchoring means is mounted in the bore, which position prevents the anchoring means from passing back out through the inlet opening and supports the anchoring means by resting against the inside surface of the cortical bone wall adjacent the inlet opening .

A minimally invasive surgical technique may therefore still be used as the anchoring means is inserted from a position distal from the joint.

However, the invention may be applied to a variety of different joint replacements and the whole joint may not even be replaced. For example, the anchoring means may support a replacement ball for a humerus, the ball being adapted to fit with the socket of the scapula (shoulder blade) .

The locking means of the above aspects of the invention rests against and is supported by an inside surface of the cortical bone wall. As cortical bone is stronger, more rigid and more resilient than Spongiform bone, the anchoring means is supported with more stability and there is less chance of micro-movement causing erosion of bone around the anchoring means in position. Furthermore, as cortical bone generally carries the largest load in a bone, there is a more natural load distribution in the bone, which decreases the chance of resorption of bone due to load redistribution .

Considering the application of this type of anchoring or fixation in bones more widely, it will also be appreciated that an anchoring means that rests against the inside surface of the cortical bone wall can be used to fix not only joint prostheses in position but other components for fitting in or to bones, such as plates that are fitted to the outside of broken or fractured bones for support. In other words, an anchoring means of this type can be used in place of conventional screws and the like which are used to attach artificial components to bones.

According to a fourth aspect of the present invention there is therefore provided an anchoring means arranged to be mounted in a bore in a bone through an inlet opening, the anchoring means having locking means movable from a first position, in which it may be inserted through the inlet opening, into a locked position when mounted in the bore, the locked position preventing the anchoring means from passing back out through the inlet opening by resting against the inside surface of the cortical bone wall adjacent the inlet opening .

The anchoring means can therefore be used to secure prostheses or components to the surface of bones, for example adjacent to the inlet opening, such that the prosthesis or component cannot be pulled away from the bone. Advantageously, the locking means may distribute the load exerted on the cortical bone wall by the anchoring means over a wider area than a conventional screw type fitting and this increases strength and durability.

The form of the locking means may vary. For example, the locking means may comprise one or more deformable bridges which are displaced outwardly in the locked position to rest against the inside surface of the cortical bone. Thus, the locking means can be inserted through the inlet opening and the bridges subsequently displaced to a locking condition. This provides a convenient locking means for resting against the cortical bone_. wall. The bridges may extend between two sleeves formed around the anchoring means, and the locked position may be achieved by moving the sleeves toward one another, such that the bridges flex or extend outwardly. This provides a simple way to extend and retract the bridges. The outward flexation may be made more reliable by providing a weak point or hinge along the length of the bridges. This ensures the bridges have the desired shape in use as the bridges will always bend at their weak point . Preferably two or more bridges are provided, at least one bridge longer than the other. More specifically, the longer bridges may have weak points or hinges provided at a position that causes them to extend in use, further toward the cortical bone wall than the shorter bridges. Thus where the anchoring means in use is not perpendicular to the cortical bone wall, the longer and shorter bridges may still be arranged to contact the cortical bone wall evenly. This provides more stable support as the force exerted on the cortical bone wall may be evenly spread.

Long and short bridges may also be used to accommodate the particular shape of the cortical bone wall of a femur or other bone in which the anchoring means is to be fitted. In particular, where the anchoring means does not extend perpendicularly from the cortical bone wall, the longer bridge (s) may be provided on a side of the anchoring means that extends obtusely from the cortical bone wall, and the shorter bridge (s) may be provided on a side of the bridge that extends acutely from the cortical bone wall.

Alternatively, the locking means may comprise a peg that is rotatably connected to the anchoring means such that it can be rotated out of a first position substantially within the radial dimensions of the anchoring means to a locked position extending beyond the radial dimensions of the anchoring means. Another alternative is for the locking means to comprise a peg that can be moved from a first position outside the anchoring means to a locked position in which it extends between and through two radially opposing holes in a cylindrical wall of a tubular anchoring means. In this embodiment it is preferable that the peg is entirely separate from the anchoring means in the first position.

The locking means may not, however, be movable in the bore, but some other provision may be made for engaging the cortical bone wall.

Thus, according to a further aspect of the present invention there is provided a joint prosthesis having an anchoring means arranged to be mounted in a bore extending through a bone via an inlet opening on the side of the bone distal from the intended position of the prosthesis, the anchoring means being provided with locking means effective when mounted in the bore, to prevent the anchoring means from passing back out through the inlet opening by resting against the inside surface of the cortical bone adjacent the inlet opening. The locking means may comprise a bulb of cement which is located e.g. in a recess on an outer wall of the anchoring means and which, when set, cooperates between the cortical bone wall and the anchoring means. This has the advantage that the cement may take the exact form of the cavity and therefore can abut the cortical bone wall in a very stable manner.

Considering the advantages of the anchoring means more generally, it will be understood that an anchoring means that rests against the inside surface of the cortical bone wall opposite a joint that is being replaced may be inserted using conventional surgical techniques. In this case, a movable or separate locking means may not be required but the anchoring means may simply have a shape suitable for resting against the cortical bone wall, either side of the anchoring means. Thus, according to a further aspect of the present invention there is provided a joint prosthesis having an anchoring means arranged to be placed in an extra medullary bore in a bone, the anchoring means arranged to rest against and be supported by an inside surface of the cortical bone wall remote from the intended position of the prosthesis.

Also, according to a further aspect of the present invention there is provided a method of anchoring a joint prostheses in a bone comprising placing an anchoring means in an extra medullary bore in a bone such that it rests against and is supported by an inside surface of the cortical bone wall remote from the intended position of the prosthesis.

By extra medullary, it is intended that the bore may extend in any direction in a bone other than along the medullary canal. For example, the bore may extend across the bone or, more specifically along the imaginary centre line of a femoral neck for example. Unlike prior art arrangements, therefore, the anchoring means is firmly supporting the inside surface of the cortical bone wall.

In this aspect of the invention the cortical bone wall may be unapertured and hence intact, with the anchoring means being inserted from the opening of the bore facing the joint, as in conventional prosthesis. The anchoring means may having at least two generally opposed elements extending radially therefrom, each of which elements is arranged to rest against and be supported by the inside surface of te cortical bone wall. Thus, the anchoring means is supported in at least two locations, either side of a central axis of the bore. These elements may be spaced apart around the axis of the bore, or may be part of a continuous element extending around the anchoring means and engaging the bone wall in at least two locations to provide firm support . As mentioned above, it is desirable to distribute load bearing of loads exerted by a joint through an anchoring means in a way that mirrors the way in which load is born by the bone when a natural joint is still in place. In the human hip joint, for example, a large load is born by the bone wall adjacent the femoral neck. Preferably, the anchoring means therefore further comprises a radially extending lip for resting against a resected bone surface proximal to the joint. The bone surface may be the resection plane of the bone, for example at a femoral neck of a femur. Thus the load distribution of the load exerted, in use, through the anchoring means is close to the natural load distribution in the bone. This decreases the chance of bone resorption and subsequent loosening of the anchoring pin in the bone.

Preferred embodiments of the present invention are now described, by way of example only, with reference to the accompanying drawings, in which:

Fig. 1 is a front view of a sleeve forming part of an anchoring means according to the invention;

Fig. 2 is a sectional view taken on the line II-II of Fig. 1;

Fig. 3 is a rear view of the sleeve shown in Fig.

1; Fig. 4 is a sectional view of the sleeve taken on the line IV-IV of Fig. 3 ;

Fig. 5 is a sectional view of a coupling sleeve forming part of the anchoring means taken on the line V- V of Fig. 6; Fig. 6 is a view of the lateral end face of the coupling sleeve shown in Fig. 5;

Fig. 7 shows a longitudinal section of the anchoring means, with a locking means being in a second position;

Fig. 8 shows the sleeve in a femur in a first position; Fig. 9 shows the sleeve with an associated clamping tool, the locking means being in a position between the first and the second position;

Fig. 10 shows the anchoring means mounted in the femur; Fig. 11 is a sectional view of a femur containing a second exemplary embodiment of an anchoring means according to the invention;

Fig. 12 is a sectional view of a femur containing a third exemplary embodiment of an anchoring means according to the invention in an unlocked condition; and Joint prostheses may be used to replace virtually all joints in the human and animal body. Likewise, this invention may be used in the replacement of any joint in the human and animal body. However, it is particularly applicable to the replacement of hip and shoulder joints and, for convenience, preferred embodiments will be described with reference to the replacement of the human hip joint. The preferred embodiments relate in particular to a hip prosthesis in accordance with that described in International Patent Application No. 098/34567.

As is described in detail in W098/34567, the parts of such a hip prosthesis are designed such that they can all be placed into their end positions through a bore in the femur Fo, which bore extends from the lateral outer side Fo of the femur F through the femoral neck Fn substantially in the direction of the imaginary longitudinal centre line of the femoral neck to the femoral head (see Figure 8) . During the positioning of the hip prosthesis, a relatively small incision is made in the leg, providing access to the lateral outer side of the femur F. Next, a bore is made in the femur F for example as described in 098/34567. Via this bore, the femoral head is removed with a special tool, for example also as described in the above-cited International patent application. Next, a first fastening assembly can be mounted in the hip bone via the bore in the femur F. After the positioning of the first fastening assembly and any other components of the joint prosthesis, an anchoring means in accordance with the present invention, can be mounted. Referring to Figures 1 to 11, the anchoring means

1, 51 comprises, adjacent a lateral end thereof, locking means 2, 2', 3, 3', 52, movable from a first position into a second position. In the first position, these locking means 2, 2', 3, 3', 52 can pass the inlet opening Fi of the femoral bore. In the second position, these locking means 2, 2', 3, 3', 52 cannot pass the inlet opening Fi of the femoral bore . In a mounted position of the anchoring means 1, 51, the locking means

2, 2', 3, 3', 52 are in the second position and engage a side C, facing a femoral inner space I, of the lateral cortical bone wall C of the femur F bounding the inlet opening Fi . The axially directed forces exerted on the anchoring means 1,51, for instance when the carrier of the hip prosthesis is walking or standing, are transmitted, by means of the locking means, to the firm lateral cortical bone wall C of the femur F, which bone wall C bounds the inlet opening. The locking means 2, 2', 3, 3', 52 press against the inside C of the cortical bone wall and can be of such design that a relatively large pressure area is created.

Such locking of the anchoring means 1, 51 is much stronger than anchoring means of the prior art which were, for example, screwed down with an end plate on the lateral outer side of the cortical bone wall of the femur at the location of the inlet opening. In that case, all axial forces exerted on the anchoring means were taken up by means of the screws screwed into the cortical bone wall.

Such screwed connection is not stable for a long period, in particular in the case of changing loads. Indeed, the contact area between the bone screws and the cortical bone wall is considerably smaller than the contact area that can be created by means of locking means 2, 2', 3, 3', 52 engaging a side C of the lateral cortical bone wall of the femur F, which side C faces the femoral inner space I . The anchoring means 1 of the first exemplary embodiment is shown in assembled condition in Figs. 7 and 10. The anchoring means 1 comprises a sleeve 4 and a coupling sleeve 8. The anchoring means 1 further comprises a pin 15 whose medial end comprises at least a number of pivot parts for forming a pivotable connection between the first fastening assembly and the anchoring means 1. In Figs. 1-10, these pivot parts are not shown. However, the pivot parts may for instance be formed by a ball of a ball joint, as shown in Fig. 11. Other possible pivotal connections are described in the above-cited International Patent Application 098/34567. The pin 15 is mounted in the sleeve 4 within a cylindrical lining 24. Adjacent a lateral end, the sleeve 4 comprises a deformation zone 2, 2', 3, 3' or plurality of bridges constituting the locking means. For clarity's sake, some elevations of the sleeve 4 are shown in Figs. 1-4. In these elevations, the locking means 2, 2', 3, 3' are in the first, not yet deformed position. The first position of the locking means corresponds to a not yet deformed condition of the deformation zone 2, 2', 3, 3'. The position of the locking means corresponds to a deformed condition of the deformation zone 2, 2', 3, 3'.

In the not yet deformed condition of the deformation zone 2, 2', 3, 3', the transverse dimensions of the sleeve 4 at the location of the deformation zone 2, 2', 3, 3' substantially correspond to the sleeve diameter D₀ on the other parts of the sleeve 4. In the deformed condition of the deformation zone 2, 2', 3, 3' (Figs. 7 and 10), the deformation zone has obtained transverse dimensions D_x which are enlarged in at least one direction relative to the other parts of the sleeve. As is clearly demonstrated in the Figures, the sleeve 4 comprises a medial sleeve part 5 and a lateral sleeve part 6. The deformation zone 2, 2', 3, 3' interconnects the medial and lateral sleeve parts 5, 6. In the present exemplary embodiment, the deformation zone comprises some ribs 2, 2', 3, 3', each having three local weakenings 7. The weakenings 7 are provided such that when a pressure force is exerted on the end faces of the medial sleeve part 5 on the one hand and the lateral sleeve part 6 on the other, the ribs 2, 2', 3, 3' fold together outwards, as shown in Fig. 7. Viewed over the circumference of the sleeve, the deformation zone 2, 2', 3, 3' is asymmetrical, such that the parts of the deformation zone 2, 2', 3, 3' which, in deformed condition, extend radially outwards, substantially abut against the cortical bone wall C bounding the inlet opening Fi . This abutment must be realized in a condition in which the sleeve 4 has the desired angular position relative to the femur F, i.e. a condition in which the centre line of the sleeve substantially coincides with the centre line of the femoral bore in the femur F.

To provide that the deformation zone 2, 2', 3, 3' retains its shape, in particular when the anchoring means 1 is subjected to a load, the anchoring means 1 also comprises a coupling sleeve 8 having medial engagement means 9 intended for cooperation with the medial sleeve part 5. The coupling sleeve 8 further comprises lateral engagement means 10a intended for cooperation with the lateral sleeve part 6. In the present exemplary embodiment , the medial engagement means 9 are designed as external screw thread mating with internal screw thread 11 provided in the medial sleeve part 5. At its lateral end, the coupling sleeve 8 comprises means 12 for engaging a tightening tool therewith. In the present exemplary embodiment, these means are formed by a hexagonal socket which can be engaged by a socket wrench.

In the present exemplary embodiment, the lateral engagement means 10 are designed as a locking bore 10a directed perpendicularly to the longitudinal axis of the coupling sleeve 8, and two locking pins (not shown) insertable into this locking bore. The lateral sleeve part 6 is provided with a transverse bore 13 which, in a deformed condition of the deformation zone 2, 2', 3, 3', registers with the locking bore 10a of the coupling sleeve 8. The two locking pins extend through both the locking bore 10a and the transverse bore 13. Hence, the locking pins provide the connection of the lateral sleeve part 6 to the lateral end of the coupling sleeve 8. As is already described herein above, the anchoring means 1 is provided with a pin 15 connected to pivot parts of the pivotable connection between the first fastening means and the anchoring means 1, and with a lining 24. The pin 15 with the lining 24 are accommodated in a bore 14 in the coupling sleeve 8, which bore 14 extends from the medial end 8M in longitudinal direction of the coupling sleeve 8. Provided in the coupling sleeve 8 is a set screw bore (not shown) accommodating a set screw (not shown) which abuts against a free end of the pin 15 remote from the pivotable connection. By means of the set screw, the axial position of the pin 15 relative to the coupling sleeve 8 and, accordingly, relative to the sleeve 4 and the cortical bone wall C can be set. For positioning the anchoring means 1, the sleeve 4 is inserted into the femoral bore until the stops 26 of the sleeve 4 abut against the outwardly facing side of the lateral cortical bone wall. The medial end of the sleeve 4 extends into or beyond the opening at the femoral neck Fn created due to the fact that the femoral head has been removed from the femur F. This situation is shown in Fig. 8. Next, the deformation zone 2, 2', 3, 3 ' is brought into the deformed condition by means of a clamping tool 17. To that end, the clamping tool 17 comprises a cylindrical clamping pin or bush 22. The clamping pin 22 has its medial end provided with engagement means 18 arranged for engagement with the medial sleeve part 5. In the present exemplary embodiment, the engagement means 18 are designed as external screw thread 18 suitable for mating with the internal screw thread 11 in the medial sleeve part 5 of the sleeve 4. The clamping pin 22 has a lateral end thereof provided with external screw thread 21 suitable for mating with internal screw thread 20 of a pressure element 19. The pressure element 19 comprises lever means 23 for exerting a considerable tightening moment. For deforming the deformation zone 2, 2', 3, 3', the clamping pin 22 is screwed into the medial sleeve part 5 by means of the engagement means 18. Next, the pressure element 19 is screwed onto the lateral end of the clamping pin 22 by means of the screw thread 20 until the pressure element 19 abuts against the lateral end face of the lateral sleeve part 6. By screwing the pressure element 19 further onto the clamping pin 22 with increased force, the ribs 2, 2', 3, 3' of the deformation zone will be compressed in the manner shown, due to the fact that the clamping tool draws the medial sleeve part 5 towards the lateral sleeve part 6. The degree of deformation can for instance be observed by means of X-ray images. It is also possible that the clamping tool is provided with markings or like means, by means of which the degree of deformation can be determined. When the desired deformation of the deformation zone 2, 2', 3, 3' has been effected, the locking means have assumed the position and the clamping tool can be unscrewed. Fig. 9 shows the sleeve 4 in a partially deformed condition which occurs during the deformation of the deformation zone by means of the clamping tool 17.

After the deformation as shown in Fig. 7 has been accomplished, the clamping tool 17 can be removed. To ensure that the sleeve 4 retains its deformed condition, the coupling sleeve 8 is subsequently secured in the screw thread 11 of the medial sleeve part 5 by means of the screw thread 9. The coupling sleeve 8 is rotated into the medial sleeve part 5 so far that the locking bore 10 in the sleeve 8 registers with the transverse bore 13 in the medial sleeve part 6. Next, the two locking pins can be arranged, to establish a connection between the lateral sleeve part 6 and the coupling sleeve 8. This connection does not merely prevent an axial displacement of the lateral sleeve part 6 relative to the coupling sleeve 8, but also a rotation of the coupling sleeve 8 relative to the medial sleeve part 5. It is readily understood that before the coupling sleeve 8 is positioned, the pin 15 and the lining 24 must first be provided in the sleeve 4. Then, by means of the set screw, the axial position of the pin 15 relative to the coupling sleeve 8 and the sleeve 4 can be set. The further fixation of the anchoring means 1 will be created through the growth of bone material around the sleeve 4. If necessary, the sleeve 4 may for this purpose be provided with a coating or the sleeve 4 may be manufactured from porous material enabling bone ingrowth. Fig. 10 shows the fastening assembly 1 in a condition in which it is completely mounted in the femur F.

A further exemplary embodiment of the invention is shown in Fig. 11. In this exemplary embodiment, an anchoring means 51 comprises a pin 53 which is receivable in the femoral bore. . A locking means comprises an anchor 52 pivotally connected to a lateral end 53L of the pin 53. In longitudinal direction, the anchor 52 has a dimension L greater than the diameter Dp of the pin 53. When the anchor is in the first position, the anchor has its longitudinal axis extending parallel to the longitudinal axis of the pin 53. In a position, the anchor 52 is swivelled relative to the pin 53 such that the free ends of the anchor 52 extend beyond the circumferential contour of the pin 53. In Fig. 11, the first position of the anchor 52 is shown in dotted lines. The position of the anchor 52 is shown in full lines. To enable the swivel movement of the anchor 52, the anchor is pivotable about a pivotal axis 54 extending perpendicularly to the pin 53, and provided in the pin 53 is a slot 55 in which the anchor 52 in the first position is at least partially accommodated. When the anchoring means 51 is being positioned, the anchor 52 is brought into the dotted position and the pin 53 is temporarily inserted slightly too far into the femoral bore. Next, the anchor 52 can be swivelled into the position indicated in full lines, after which the pin 53 can be withdrawn slightly in lateral direction, causing the anchor 52 to abut against the side C of the cortical bone wall which side faces the femoral inner space I . Referring to Figure 12, a third exemplary embodiment of the present invention has an anchoring means 100 comprising a hollow body 101, such as a cylindrical metal tube, in which an elongate cylindrical supporting pin 102 carrying a joint articulation (not shown) is housed. The cylindrical body of the supporting pin 102 can be fitted in the hollow body 101, for example, by a frictional fit or by a screw thread, or the two components may be formed integrally.

The supporting pin 102 only extends part way along the hollow body such that an empty space 103 is provided at the end of the hollow body distal from the joint articulation. The hollow body 101 has two radially opposing holes 104,105 in its circumferential wall, also at the end of the body distal from the joint articulation such that the holes 104,105 are adjacent the empty space 103. A locking pin 106 is provided which can be inserted through the distal end of the hollow body 101, into the empty space 103 and into a position in which it extends between the holes 104,105 and protrudes through each of the holes 104,105 beyond the outer surface of the hollow body 101. The locking pin 106 must therefore be narrow and short enough to fit in the hollow space 103 and be manipulated into a position extending through the holes 104,105, yet be long enough to extend through each of the holes and outside of the hollow body when in place. The anchoring means 100 is inserted into a bore in a bone, such as the femur F, such that the holes 104,105 are located adjacent to the inside surface of the cortical bone wall distal from the joint articulation. The pin is then inserted into the hollow body and into a locked position in which it extends through both of the holes 104,105. The pin therefore rests against the inside surface of the cortical bone wall distal from the joint articulation and the anchoring pin is supported in the direction of its main axis away from the joint articulation by the holes abutting the locking pin 106. Still referring to Figure 12, in this embodiment the anchoring means 100 has a proximal support section 107 which comprises a lip 108 which is arranged to abut the surface of the cortical bone wall, in this case proximal to the femoral neck below the joint articulation. This enables the anchoring means 100 to be supported at its proximal end by resting on a surface of the femur or femoral neck left after the femoral head has been resected, which may be referred to as the 'resection plane'. This may comprise substantially cortical bone or part cortical bone, part spongiform bone dependant on the positioning of the bore. In the femur in particular, this is an area of high natural loading and supporting the anchoring means 100 in this way reduces unnatural redistribution of the load in the bone which in turn reduces resorption. In all of the above exemplary embodiments the anchoring pin or fastening means is inserted in a bore in a bone. The locking means is then positioned in the inner space of the bone, such as the femoral inner space I, such that it abuts or rests against the inside surface of the cortical bone wall. The procedure for fitting such an the anchoring means is as follows.

Firstly, an incision is made in the flesh such that access to the bone may be achieved. A bore is then made through the bone from an inlet opening in the intended position of the anchoring means. In the case of a hip joint being replaced in accordance with the method described in W098/34567, the bore may be from the outer surface of the femur, the lateral outer side Fo, through the femoral neck Fn. Regardless of how the bore is made, after the bore has been made, a portion of the inner space of the bone adjacent the inside surface of the cortical bone wall distal from the joint articulation or adjacent the inlet opening is resected to provide a cavity in which the locking means can be located when locked. In the case of an anchoring pin for a femur F in accordance with the devices described in W098/34567, the cavity Ca is generally a space above and below the Femoral inlet opening Fi .

In a fourth exemplary embodiment of the present invention (not shown in the drawings) the locking means comprises a bulb of cement filling a cavity next to the inside surface of the cortical bone wall distal from the joint articulation. When set the cement therefore rests against the inside surface of the cortical bone wall distal from the joint articulation and the cortical bone wall supports the anchoring pin.

It is understood that the invention is not limited to the exemplary embodiments described, but that various modifications are possible within the framework of the invention.

Claims

1. A hip prosthesis comprising a first fastening assembly intended for being mounted in the hip bone and an anchoring means (1, 51) intended for being mounted in the top end of the femur (F) , wherein the first fastening assembly and anchoring means (1, 51) are interconnected by means of a pivotable connection, wherein all parts of the hip prosthesis are so small and/or slender that they can each be arranged in the intended end position thereof via a bore in the femur (F) , said bore extending from an inlet opening (Fi) in the cortical bone on the lateral outer side (Fo) of the femur (F) through the femoral neck (Fn) substantially in the direction of the imaginary longitudinal centre line of the femoral neck (Fn) to the femoral head, wherein the anchoring means (1, 51) comprises, adjacent a lateral end thereof, locking means (2, 2', 3, 3', 52) movable from a first position into a locked position, wherein said locking means (2, 2', 3, 3', 52) can pass the inlet opening (Fi) of the femoral bore in the first position, wherein said locking means (2, 2', 3, 3', 52) cannot pass the inlet opening (Fi) of the femoral bore in the locked position, wherein in a mounted condition of the anchoring means (1, 51) the locking means (2, 2', 3, 3', 52) is in the locked position and engages a side (C) , facing a femoral inner space (1) , of the lateral cortical bone wall of the femur (F) bounding the inlet opening (Fi) .

2. A joint prosthesis having an anchoring means (1) arranged to be placed in a bore in a bone via an inlet opening (Fi) distal to the intended position of the prosthesis, the anchoring means (1) having locking means (2) movable from a first position, in which it may be inserted through the inlet opening, into a locked position when mounted in the bore, the locking means in the locked position preventing the anchoring means (1) from passing back out through the inlet opening (F) and supporting the anchoring means (1) by resting against the inside surface of the cortical bone wall adjacent the inlet opening (Fi) .

3. The prosthesis of claim 1 or claim 2, wherein the locking means (2) comprises one or more deformable bridges (2, 3) which flex outwardly in the locked position to rest against the inside surface of the cortical bone.

4. The prosthesis of claim 3, wherein the bridges (2, 3) extend between two sleeves (5, 6) formed around the anchoring means.

5. The prosthesis of claim 3 or claim 4, wherein each bridge (2, 3) has a weak point (7) along its length at which it flexes in use.

6. The prosthesis of any one of claims 3 to 5, the locking means comprising two or more bridges (2, 3), at least one bridge (2) being longer than another bridge (3) .

7. The prosthesis of any one of claims 3 to 6 , the locking means comprising two or more bridges, the bridges (2,3) extend asymmetrically from the anchoring means (1) to rest against the cortical bone wall adjacent the inlet opening (Fi) .

8. The prosthesis of claim 1 or claim 2, in which the locking means comprises a peg (52) that is rotatably connected to the anchoring means (1) such that, in use, it can be rotated out of a first position substantially within the radial dimensions of the anchoring means (1) to a locked position extending beyond the radial dimensions of the anchoring means (1) .

9. The prosthesis of claim 1 or claim 2, in which the locking means comprises a peg (106) that can be moved from a first position outside the anchoring means into a locked position in which it extends between and through two opposing holes (104, 105) in a wall of the anchoring means (1) .

10. The prosthesis of claim 9, wherein the peg is entirely separate to the anchoring means in the first position.

11. A joint prosthesis having an anchoring means (1) arranged to be placed in an extra medullary bore in a bone, the anchoring means (1) arranged to rest against and be supported by an inside surface of the cortical bone wall remote from the intended position of the prosthesis .

12. The joint prosthesis of claim 11, the anchoring means (1) further comprising at least two generally opposed elements extending radially therefrom, each of which elements is arranged to rest against and be supported by an inside surface of the cortical bone wall remote from the intended position of the prosthesis.

13. The prosthesis of any one of claims 1 to 11, the anchoring means (1) further comprising a lip (107) arranged to rest against a resected bone surface proximal to the joint.

14. A joint prosthesis having an anchoring means (1) arranged to be mounted in a bore extending through a bone via an inlet opening (Fi) on the side of the bone distal to the intended position of the prosthesis, the anchoring means (1) being provided with locking means (2) when the anchoring means is mounted in the bore, the locking means preventing the anchoring means (1) from passing back out through the inlet opening (Fi) by resting against the inside surface of the cortical bone adjacent the inlet opening (Fi) .

15. A joint prosthesis as claimed in claim 14, wherein the locking means comprises cement .

16. The joint prosthesis of claim 14, wherein the locking means comprises a peg insertable into two opposing holes in a body of the anchoring means (1) such that portions of the peg that extend through the holes rest against the inside surface of the cortical bone adjacent the inlet opening.

17. An anchoring means arranged to be mounted in a bore in a bone (F) through an inlet opening (Fi) , the anchoring means having locking means movable from a first position, in which it may be inserted through the inlet opening (Fi) , into a locked position when mounted in the bore, the locked position preventing the anchoring means from passing back out through the inlet opening (Fi) by resting against the inside surface of the cortical bone wall adjacent the inlet opening (Fi) .

18. A method of anchoring a joint prosthesis in an extra medullary bore in a bone, comprising inserting the anchoring means (1) through an inlet opening (Fi) distal to the intended position of the prosthesis, and moving a locking means from a first position to a locked position when the anchoring means (1) is mounted in the bore, which locking means prevents the anchoring means (1) from passing back out through the inlet opening and supports the joint prosthesis by resting against the inside surface of the cortical bone wall adjacent the inlet opening (Fi) .

19. A method of anchoring a joint prosthesis in a bone comprising placing an anchoring means (1) in an extra medullary bore in a bone such that it rests against and is supported by an inside surface of the cortical bone wall remote from the intended position of the prosthesis .