GB2029229A

GB2029229A - Hip joint endoprosthesis

Info

Publication number: GB2029229A
Application number: GB7840338A
Authority: GB
Original assignee: MEDICINSKA AKADEMIA
Current assignee: MEDICINSKA AKADEMIA
Priority date: 1978-03-17
Filing date: 1978-10-12
Publication date: 1980-03-19
Also published as: GR66558B; DE2839661A1; PL209835A1; TR20171A; DD236853A3; RO85055A; JPS54127195A; IT7851238A0; CH636261A5; GB2029229B; FR2419717A1; SU980709A1; CS223355B1; YU218678A; RO85055B; BG27580A1

Abstract

The acetabulum component of a hip-joint endoprothesis comprises an acetabulum cup 6, a non-metallic shell member 1 and a retaining nut 10. The shell member defines therewithin a volume 8 which is greater than hemispherical and less than spherical, having an opening around which the wall of the shell member is formed with radial slots 9. The nut 10 serves to hold the head portion of a femur shank in the volume 8 and simultaneously lock the shell member 1 in the acetabulum cup 6. In accordance with requirements, the shell member may be used with an acetabulum cup which is of self-anchoring type or to be cemented in the natural acetabulum and with a shank which is self-anchoring or to be cemented in the medullary canal of the thigh. <IMAGE>

Description

SPECIFICATION Hip-joint endoprothesis This invention relates to a total hip-joint endoprothesis for use in orthopaedic surgery and traumatology for the replacement of injured or diseased hip joints. A variety of forms of total hip-joint prothesis are known. These are generally of either divisible design with the component parts being separable or locking design in which the component parts when assembled cannot be separated. These protheses are joined to existing bones by use of bone cement or by mechanical anchoring.

One design of prothesis is known having a shank portion which is tapered and which is to be mechanically anchored in the medullary canal of the femur and an acetabulum cup portion which is to be fastened mechanically to the hip bone by means of two screws terminating in L-shaped nuts. With a known variant of this prothesis having the same shank, the acetabulum cup ends with a screw, which is screwed up in to the hip bone. With another design of prothesis, the shank is flat, having smooth walls, while the acetabulum cup is formed with three sharp projecting pins by means of which it is driven into a prepared seat in the natural acetabulum. These hipjoints may be considered to be of the divisible design type.

A locking design of hip-joint is known comprising a tapered shank formed with two elongate holes, which shank is to be wedged into the medullary canal, while a ball-shaped portion of the shank is fastened rigidly in a metal seat. This seat is riveted into another metal cup which is toothed around its periphery so that it may be anchored in the seat in the natural acetabulum. A variant on this design comprises a non-replaceable plastics seat and tightening nut to permit disassembiy of the joint during implantation, although such disassembly is not possible afterwards.

Several other designs of total hip-joint prothesis are known, in which the shank, as well as the acetabulum cup are fastened to the bones by means of bone cement.

In addition, a unipolar hip-joint prothesis is known, in which the femural shank is transversely toothed, with round holes being provided in the bases of the teeth.

Each of the aforementioned total hip-joint prothesis designs has its own characteristic disadvantages.

The divisible designs with their separable components permit an arbitrary dislocation of the joint when subject to comparatively small non-functional stresses, while the locking designs in which the component parts are non-divisible can cause breaking of the femur or the hip bone to occur when the joint is subject to high non-functional stresses. In contrast, when such stresses act on natural joints, they may simply cause dislocation without fracture.

Another substantial drawback of the non-divisible designs is the difficult implantation operations required and the necessity of cutting off a large portion of the trochanter.

A major problem with hip-joint protheses having a tapered shank is the frequent tendency for loosening of the shank in the medullary canal to occur, thereby resulting in rotation and instability of the joint, leading to sharp pains limiting totally movement of the lower limb.

Further problems encountered hitherto with total hip-joint endoprotheses have been the lack of flexibility and choice of implantation technique available in accordance with a particular indicated clinical condition. Moreover, it is generally necessary to effect replacement of the complete endoprothesis or a component thereof by secondary bone fragmentation in reoperation if failures occur in the postoperative period. Thus, for example, with a total endoprothesis comprising a metal ball and nonmetallic cup, abrasion of the cup is frequently observed. This requires reoperation to replace the whole acetabulum cup by a new one and leads to a secondary traumatizing of the hip bone.

According to the present invention, there is provided an acetabulum cup arrangementfor receipt of a substantially spherical head portion of a femur shank in providing a replacement hip, said arrangement comprising an acetabulum cup whose outer surface is adapted for fitting in a natural acetabulum and which is formed at its base with a circular aperture or recess, a non-metallic shell member sized to enter and occupy substantially completely the acetabulum cup and having a projecting portion shaped to enter and engage said circular aperture or recess when the shell member occupies said cup, the shell member defining therewithin a volume which is greater than hemispherical and less than spherical and having a pole at said projecting portion, a peripheral portion of the wall of the shell member opposite said pole being formed with radial slots, and a fastening not internally tapered in accordance with the outer contours of said peripheral portion of the shell member, the exterior of the fastening nut and the interior of the acetabulum cup being adapted to enter into separable engagement with each other with the shell member held thereby in the acetabulum cup.

This invention allows flexibility in the choice of implantation techniques in accordance with clinical conditions which prevail, so that for a particular shell member adapted to a prescribed dimensioned head portion of a femur shank, it is possible to employ an acetabulum cup of a self-anchoring type or an acetabulum cup which is to be held in place in a natural acetabulum by use of bone cement. Furthermore, insofar as the cooperating femur shank is concerned, it is possible to employ, irrespective of the method of fixing the acetabulum cup, a femur shank which is either of self-anchoring type or intended for bonding using bone cement.

Thus, if a surgeon has available a complete assemblage of parts comprising acetabulum cups of the two types as aforesaid, femur shanks of the two types as aforesaid and a shell member and associated fastening nut as aforesaid, four possible operating procedures become available in accordance with the prevailing clinical conditions.When a total endoprothesis has been provided from a suitable selection of such components, in the event that one of the components subsequently becomes worn out or loosened, easy and non-traumatizing replacement thereof can be effected in a subsequent reoperation because of the separability of the acetabulum cup and femur shank components which may be achieved by separation of the fastening nut from the acetabulum cup, which will usually be in screw threaded engagement, thereby allowing removal of the femur shank head portion from the shell member and if required, removal of the shell member from the acetabulum cup.

When forming the total hip joint endoprothesis from these components, stable fixing of the prothesis components in the corresponding bones is achieved in a manner which allows normal operation of the joint connection with the joints having the normal resistance to dislocation characteristic of a natural joint. The prothesis is divisible so that it can be easily manipulated during operation and is so constructed that conditions which lead to increase of the internal pressure in the medullary canal are not created during the driving in of the shank.

The shell member is formed of non-metallic, and preferably plastics material, so that when the spherical head portion of the femur shank which will generally be metallic is rotating therein, minimum friction will be set up and there will be no bimetallic corrosive effect. The volume defined within the shell member will preferably be approximately three quarters spherical and the radial slots formed around the peripheral portion opposite the pole allow the embracement of, in such a case, three quarters of the rotating head when emplaced therein in forming the total joint replacement. Locking together of the joint components is achieved by means of the nut with a force corresponding to the antidisplacement capability of a natural hip-joint.

Thus,the risk of breaking off of the acetabulum cup from the hip bone or breakage of the femur will be minimised. The separability of the joint components, that is the acetabulum cup with non-metallic shell member and the femur shank make it possible to achieve the required easy manipulation during implantation. The femur shank employed preferably has smooth wall portions formed with longitudinal oval grooves extending therealong in order to avoid an increase of pressure in the medullary canal during driving in of the shank in the femur.

For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which there are illustrated diagrammatically components in accordance with this invention for forming total hip endoprotheses.In the drawings:~ Figure 1 shows partly in elevation and partly in actual cross-section a non-metallic shell member for use in an acetabulum cup in forming an acetabulum cup arrangement according to the invention; Figure la is an underside plan view of the shell member of Figure 1; Figure 2 shows partly in elevation and partly in axial cross-section a fastening nut for securing the shell member of Figures 1 and 1a in an acetabulum cup in forming an acetabulum cup arrangement according to the invention; Figure 2a is a plan view from above of the fastening nut of Figure 2; Figures 3 and 4 are axial cross-sections through two acetabulum cups, that of Figure 3 being selfanchoring and that of Figure 4 being for cementing in a seat prepared in the natural acetabulum; Figures 3a and 4a are plan views from above of the acetabulum cups of Figures 3 and 4 respectively; and Figures 5 and 6 are elevational views of two femur shanks, that of Figure 5 being self-anchoring and that of Figure 6 being for cementing in the medulary canal of the femur.

In the drawings, like reference numerals denote like parts.

Referring to the drawing, Figure 1 shows a replaceable non-metallic shell member 1 into which a ball 2 of a femur shank3 (Figure 5 or 6) is to be fitted to rotate therein. The shell member 1 is provided with a journal portion 4 which is to enter so as not to undergo rotation therein a hole Sin an acetabulum cup 6 (Figure 3 or 4). To avoid any dislocation of the joint to be produced, the shell member 1 defines a spherical volume 8 which lies between half spherical and complete spherical so that a peripheral portion 7 thereof extends below the equator of ball 2. Radially extending slots 9 are cut in the peripheral portion 7 of the shell member 1 so as to allow the ball 2 to enter the shell member 1 and be seated therein by application of light pressure.Locking of the ball 2 within the shell member 1 will then be achieved by means of a fastening nut 10 (Figures 2 and 2a) which will be drawn over the femur shank in the end thereof opposite to the ball 2 and caused to engage with the acetabulum cup 6 by engagement with screw threading 13 thereon. The fastening nut 10 has an internally tapered wall 11 which will press against the correspondingly tapered peripheral portion 7 of shell member 1 and thereby secure the joint against arbitrary dislocation. The pressure involved will be such as to allow freedom of rotation of the ball within the shell member and will yet allow disengagement of the ball with the shell member to be achieved when the joint is subjectto stresses of the type which with a natural joint would cause dislocation thereof. In this way, the possibility of breakage of the femur or breaking off of the acetabulum cup will be avoided.

The acetabulum cups 6 are formed internally with a seat 12 to be occupied by the non-metallic shell member 1 and with a hole 5 for driving in of the journal 4 of the shell member. The acetabulum cup 6 of Figures 3 and 3a is formed with specially shaped teeth 14 for wedging the cup in a previously prepared seat in a natural acetabulum thereby to achieve mechanical fixing of the acetabulum cup.

The outer surface of the acetabulum cup of Figures 4 and 4a and which may be formed of metal or plastics material is formed with grooves 15 for enhancing the bond achieved between the acetabulum cup and a natural acetabulum using bone cement.

The femur shanks of Figures 5 and 6 are provided with a collar portion 16 by means of which they are to be seated in the cortical contour in the base of the collumfemuris, having an elongate portion connecting the collar 16 with the ball 2. In this way, the shank is able to carry stably the weight of the body without sinking into the soft spongy tissue of the bone marrow. The self-anchoring shank 3 of Figure 5 is wide and rectangular in transverse cross-section in order to avoid any rotation taking place with respect to the femur. In its upper portion, the shank 3 of Figure 5 is formed with teeth 17 and has holes 18 passing therethrough. The teeth serve to enlarge the passage in the femur into which the shank is inserted, which hole will previously have been bored using special files.The bored holes 18 in the shank serve to accommodate bone shavings produced by means of the files, which shavings also occupy the voids between the teeth and the bones and serve, in the post-operating period, to achieve a stable fixation of the shank to the femur. The bottom portion of the rectangular shank of Figure 5 is smooth but provided with longitudinally extending oval grooves 19 in each of its four sides for minimising increases in pressure in the medullary canal when driving the shank into the bone.

The femur shank 3 of Figure 6 is narrower than the self-anchoring shank3 of Figure Sto allow for filling of the hole in the femur with the necessary quantity of cement. The illustrated femur shank in Figure 6 has the cross-sectional shape of a flattened hexagon formed with rounded edges and having longitudinally extending oval grooves 19 in edge regions thereof. The faces of the shank are otherwise smooth and the functions of the oval grooves 19 are the same as those of the grooves 19 of the femur shank of Figure 5.

A total hip-joint endoprothesis embodying this invention is implanted as follows. An acetabulum cup and a femur shank are selected in accordance with the prevailing clinical requirements indicating whether self-anchoring or cementing is to be employed for fixing the respective parts. Thus, depending upon the particular situation, four different combinations of acetabulum cup and femur shank can be used, namely fully cemented joint, fully mechanically anchored joint, cemented acetabulum cup and mechanically anchored shank and mechanicallyfas- tened acetabulum cup and cemented shank. Both components of the joint are fitted in position separately in the relevant bone. The ball 2 of the shank 3 is then inserted into the spherical chamber 8 of the nonmetallic shell member 1 and is locked therein by means of the fastening nut 10 being brought into engagement with the screw threading 13 on the acetabulum cup 6. In the event that reoperation is required, the joint is unlocked by unscrewing the nut 10 and the unsatisfactory component is replaced by a new one without the need to remove the part which remains satisfactorily fixed. The joint is then relocked.

Claims

1. An acetabulum cup arrangement for receipt of a substantially spherical head portion of a femur shank in providing a replacement hip, said arrangement comprising an acetabulum cup whose outer surface is adapted for fitting in a natural acetabulum and which is formed at its base with a circular aperture or recess, a non-metallic shell member sized to enter and occupy substantially completely the acetabulum cup and having a projecting portion shaped to enter and engage said circular aperture or recess when the shell member occupies said cup, the shell member defining therewithin a volume which is greater than hemispherical and less than spherical and having a pole at said projecting portion, a peripheral portion of the wall of the shell member opposite said pole being formed with radial slots, and a fastening nut internally tapered in accordance with the outer contours of said peripheral portion of the shell member, the exterior of the fastening nut and the interior of the acetabulum cup being adapted to enter into separable engagement with each other with the shell member held thereby in the acetabulum cup.

2. An arrangement as claimed in claim 1, wherein the acetabulum cup is formed of metal and externally toothed for mechanical fixing thereof in a natural acetabulum.

3. An arrangement as claimed in claim 1 or 2, wherein the shell member is formed of synthetic plastics material.

4. An arrangement as claimed in any one of claims 1 to 3, wherein said volume is approximately three quarters spherical.

5. An acetabulum cup arrangement as claimed in claim 1, substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

6. A separable total hip-joint endoprothesis which comprises an acetabulum cup arrangement as claimed in any one of the preceding claims and an associated femur shank comprising a substantially spherical head portion adapted to enter said volume and be held therein by means of said fastening nut and an elongate portion for entering the medullary canal of a femur.

7. An endoprothesis as claimed in claim 6, wherein the femur shank is formed with a collar portion for seating the cortical contour in the base of the collumfemuris, which collar is separated from the spherical head portion by means of an elongate neck portion.

8. An endoprothesis as claimed in claim 6 or 7, having smooth surface portions extending towards the end thereof remote from the spherical head portion provided with longitudinally extending oval grooves therein.

9. An endoprothesis as claimed in any one of claims 6 to 8, wherein the femur shank is adapted for self-anchoring in a medullary canal, the femur shank being formed with a toothed zone thereon.

10. A separable total hip-joint endoprothesis as claimed in claim 6, substantially as hereinbefore described with reference to and as shown in the accompanying drawing.

11. An assemblage of parts for use in the con struction of a separable total hip-joint endoprothesis in accordance with prevailing clinical requirements, which assemblage comprises an acetabulum cup arrangement as claimed in any one of claims 1, 3 and 4, an associated second acetabulum cup, one acetabulum cup being adapted for self fixing and the other being intended for fixing using bone cement in a natural acetabulum cup, and a pair of femur shanks, one being adapted so as to be self-anchoring and the other being intended for fixing using bone cement in the medullary canal of the femur.

12. An assemblage as claimed in claim 11, wherein the self-anchoring acetabulum cup is formed on its external periphery with teeth for wedging the cup into a previously prepared seat in the natural acetabulum.

13. An assemblage as claimed in claim 11 or 12, wherein the acetabulum cup intended for fixing with bone cement has a grooved outer surface for enhancing the fixing thereof with bone cement.

14. An assemblage as claimed in any one of claims 11 to 13, wherein the acetabulum cup for fixing with bone cement is formed of plastics or metal.

15. An assemblage as claimed in any one of claims 11 to 14, wherein the self-anchoring acetabulum cup is formed of metal.

16. An assemblage as claimed in any one of claims 11 to 15, wherein the femur shanks each comprise a collar portion for seating onto the cortical contour in the base of the collumfemuris separated from the spherical head portion thereof by an elongate neck portion.

17. An assemblage as claimed in any one of claims 11 to 16, wherein the self-anchoring acetabulum cup is of rectangular cross-section and formed with teeth therearound.

18. An assemblage as claimed in any one of claims 11 to 17, wherein the femur shanks comprise smooth portions extending towards the end thereof remote from the spherical head portions thereof formed with longitudinally extending oval grooves.

19. An assemblage of parts for use in the construction of a separable total hip-joint endoprothesis in accordance with prevailing clinical requirements, substantially as hereinbefore described with reference to and as shown in the accompanying drawing.