IE60622B1

IE60622B1 - Joint prosthesis

Info

Publication number: IE60622B1
Application number: IE52488A
Authority: IE
Original assignee: Sheehan James
Priority date: 1988-02-25
Filing date: 1988-02-25
Publication date: 1994-07-27
Also published as: GB2216015B; GB2216015A; IE880524L; GB8904418D0

Abstract

A joint prosthesis includes a rigid prosthesis member 10 comprising a head element 11 for articulated cooperation with a complementary prosthesis member (not shown) and an elongate tapered element or stem 12 depending from the head element and adapted for insertion into the fixing in a bone cavity by cement. The prosthesis further includes a reinforcing sleeve 15 surrounding and of slightly greater diameter than the stem 12 and which in use is adapted for embedding in and reinforcing the cement continuously around the elongate element. The sleeve 15 has secured thereto spacing means 18 to space the interior surface of the sleeve from the prosthesis stem 12 and define a space within which bone cement may be received.

Description

The present invention relates to a joint prosthesis with steens for improving the securement of the prosthesis, and is particularly applicable to a hip joint prosthesis but is also applicable to other joints such as knee, elbow, etc.

Prostheses are used in orthopedy for restoring articulation of the joints where the natural articulation components of the joint have degenerated, or ceased to function at all.

A standard joint, e.g. a hip joint prosthesis, comprises a first rigid metal member having an elongate tapered element which is longitudinally received in the upper part of the femur, and a substantially spherical femural head, which is in the position corresponding to the natural one to be replaced. A second member is engaged with the pelvis and includes a seat for the spherical head in the form of an element made of a substantially rigid ©nd self-lubricating synthetic resin.

The first rigid metal_ member is usually secured in the femur with bone cement and the second member is usually screwed or cemented to the pelvis.

The prosthesis is in use subjected to greet stresses end a common problem which arises is that the cement surrounding the tapered element in the femur often cracks due to the stressese resulting in loosening of the prosthesis and/or pain for the patient,, end possibly also damage to the femur and the pelvis.

A number of methods have been tried to overcome the above problem and strengthen th© cement and prevent cracking. These include incorporating into the cement chopped carbon fibre or short metal filaments or fibres to strengthen the cement. However, this is not very successful as one can only include approximately 2% of such chippings into the cement, as any greater amount is likely to promote the development of cracks in the cement.

Thus an object of the present invention is to provide an improved prosthesis which will mitigate the above problems.

According to the present invention, there is provided a prosthesis to bone interface comprising a sleeve of intersticated «Material generally conforming to the shape of the stem of a prosthesis, th© sleeve having secured thereto, spacing means to space the interior surface of the sleeve from the prosthesis stem and define a space between the sleeve and the stem within which bone cement may be received.

The invention also provides a method of making a prosthesis to bone interface compx’ising the steps of: providing a sleeve of intersticated material generally conforming to the shape of the stem of a prosthesis,’ applying a coating of bone cement to the sleeve? heating the sleeve to bake the coating onto the sleeve; and applying a plurality of spacer members comprising bone cement to the sleeve, to in use space the interior surface of the sleeve from the prosthesis stem, and define a space between the sleeve and the { stem within which bone cement may be received.

The invention further provides a joint prosthesis including a rigid prosthesis member comprising a head element for articulated cooperation with a complementary prosthesis member and a stem depending from the head element and adapted for insertion int© and fixing in a bone cavity fey cement, the prosthesis further including a tapered reinforcing sleeve of intersticated material generally conforming to the shape of the stem, the sleeve surrounding and of slightly greater diameter than th® stem and which in use is adapted for embedding in and reinforcing the cement continuously around the stem, the sleeve having secured thereto spacing means to space the interior surface of the sleeve from the prosthesis stem and define a space between the sleeve and th® stem within which bone cement may be received.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a' cut-away perspective view of an embodiment of a prosthesis interface in use according to the invention; Figure 2 is a perspective view of the interface of 25 Figure 1; Figure 3 is a perspective view of another embodiment of interface according to the invention; and Figure 4 is a perspective view of an introducer V according to the invention.

Referring co Figures 1 and 2P a hip joint prosthesis includes a first rigid metal member 10 comprising a substantially spherical femural head 11 for articulated cooperation with a complementary prosthesis member in the form of a seat (not shown) which is fixed to the patient8s pelvis, and an elongate tapered element or stem 12 depending integrally from the head 11 and adapted tor insertion into and fixing in a bone cavity by cement.

The prosthesis to bone interface comprises a knitted mesh sleeve 15 of a cobalt chrome wire the wire having a diameter of approximately 0.125 mm which is knitted on a standard 10 guage knitting maching. The sleeve 15 is closed at its lower end 16 and tapers outwardly to the top end 17 which is open. The sleeve 15 is preferably flexible which results from loos© knitting and is therefore somewhat floppy along its longitudinal axis. The interstices of the sleeve 15 are preferably in the range 0.5 mm to 5 mm when th© sleeve is stretched to its maximum length. The interstices of the sleeve thus enable ready penetration of the sleeve by bone cement as will be described below.

The sleeve 15 has fixed thereon a plurality of spacer members comprising spheres 18 of bone cement for example polymethyl methacrylate (PMMA). The spheres are preferably of 0.5 to 5 mm In diameter and more preferably 1 m In diameter and are arranged such that they project about 0.5 mm from the inner and outer surfaces of the sleeve. The spheres 18 are arranged In a plurality of rows or columns ©s shown.

As shown in Figure 1, the spacers 18 abut the stem of the prosthesis 10 snd effectively space the sleeve from the stem 12 so that there is no contact between the stem 12 and sleeve 15. It will be appreciated that the sleeve 15 is of a slightly greeter diameter than the stem 12 of the prosthesis, end of a smaller diameter than the recess 19 (medullary canal) which is formed in the cortical bone 20 of the upper part of the femur 21 of a recipient patient.

Once a knitted sleeve 15 is produced, it is located on a mandrel (not shown) corresponding to the shape of a prosthesis stem 12 with which th® sleeve 15 is to be used. The sleeve 15 is then coated with a PMMA powder in the form of a fine spray which is baked onto the surface of the sleeve. This PMMA spray does not block the interstices 22 of the sleeve and when baked the sleeve is substantially rigid and conforms to the shape of the prosthesis stem 12 with which the sleeve 15 is to be used,.

The spacer spheres 18 are preferably fixed to the sleeve 15 after the sleeve has been coated with ΡΜΜΆ. Since the bone cement 23, es described below, comprises PMMA, the coating of the sleeve 15 with ΡΜΜΆ serves the dual function of rendering the sleeve substantially rigid and also ensures a good bond between the PMMA bone cement and the· sleeve.

Fiqufe 4 illustrates introducing means for correctly locating- th® sleeve in the recess 19 of the bone 20. The introducing means comprises a hollow nozzle 24 conforming to the shape of the prosthesis which is to be used with the sleeve 15. The nozzle 24 is open at its lower end 25 and is adapted at its upper end 26 to be attached to a standard bone cement gun/syri.nge system (not shown). Thus, the upper end 26 has fixed thereon a screw cap 27 by which the nozzle may be connected to a standard cement syringe (not shown). The cap 27 is attached to the nozzle by a cylindrical tube 28 which conveys cement from the syringe to the nozzle 24. The procedure for insertion of the prosthesis 10 and sleeve 15 is as follows: a) fill up the medullary canal 19 with bone cement (PMMA) in conventional manner, for example, using a standard syringe and nozzle; b) remove the standard nozzle and place th© nozzle onto the syringe with the sleeve 15 located on the nozzle 24; c) the nozzle 24 is pushed into the medullary canal 19 and more cement is forced into the medullary canal through the hollow nozzle 24; d) while continuing to force cement into the medullary canal through the nozzle 24, the nozzle 24 is removed leaving the sleeve IS in the medullary canal filled with cement; e) the prosthesis 12 is then pushed into the interior of the sleeve 15 to a position as shown in Figure 1.

It is envisaged that it may be necessary in some instances to hold the top 17 of the sleeve 15 to prevent it from being pushed down into the medullary canal. Any suitable form of retaining means may be employed for this purpose, for example, a string attached to the top 17 may be held while the prosthesis stem 12 is pushed into the medullary canal. Alternatively, another embodiment of the sleeve 15,J is Illustrated in Figure 3.

The sleeve 15’ of Figure 3 has a flared circular flange formed at its upper end 17'. The flange 30 is provided so that in us© it is positioned and engaged on (, th® upper surface of the cortical bone 20 with the flange 31 of the prosthesis engaged on top of it. The flange 30 may be held manually, to prevent the sleeve 15s from being pushed too far down into the medullary canal. Alternatively, the flange 30 may be formed as a PMMA collar.

Thus, when in place the sleeve 15 is completely spaced from the surface of the stem 12 by th© spacers 18. In addition, the spacers also serve to space the sleeve from the inner surface of th® cortical bone 20. defining the medullary canal.

The spacers thus ensure that the sleeve 15 is located within, and completely surrounded and embedded in the eventual mantle formed by the PMMA bone cement 23. This ensures that the sleeve 15 provides the optimum reinforcing of the bone cement. It has been found that if the sleeve 15 is in contact with either the cortical bone surface, or the stem 12 of the prosthesis, this can substantially reduce the reinforcing effect of the sleeve and could during normal usage, encourage or promote the development of crack sites in the bone mantle. Further, since the spacers 18 are of the same material as the bone cement, the spacers effectively become part of the bone cement mantle and do not produce an additional interface. It is also highly desirable that the sleeve 15 does not contact the stem 12 of the prosthesis as this could potentially give rise 0 to an electro-chemical reaction, or possibly small particles becoming eroded from either the stem or the sleeve which could possibly Initiate cracks in the mantle.· Further, as the sleeve 15 is coated with PMMA, this promotes an excellent interface between the .bone cement and the sleeve.

It has been found that a sleeve forming a prosthesis to bone interface having the characteristics defined herein, provides excellent reinforcement of the bone cement mantle.

It will be appreciated that th® sleeve 15 may comprise any suitable material, for example, metal or carbon fibre. If the sleeve 15 is of metal it preferably comprises chrome-cobalt, titanium or steel matching that of the prosthesis..

In an alternative embodiment of the invention the spacer members 18 may compx-ise rings or strips of bone cement fixed to the sleeve.

Claims

CLAIMS:

1. A prosthesis to hone interface comrising a sleeve of intersticated material generally conforming to the shape of the stem of a prosthesis, th® sleeve having V, secured thereto, spacing means to space the interior surface of the sleeve from the prosthesis stem and define a space between the sleeve and th® stem within which bone cement may be received.

2. An interface as claimed in Claim 1, wherein the spacing means comprises a plurality of spaced apart spacing members fixed on the sleeve.

3. An interface as claimed in Claim 2, wherein the spacing members are generally spherical and project from the inner and outer surfaces of the sleeve.

4. An interface as claimed in any preceding Claim, wherein the spacing means comprises bone cement. 5. An interface as claimed in any preceding Claim wherein the sleeve is tapered snd Is closed at its lower end. δ. An interface as claimed in any preceding Claim wherein the sleeve is formed from metal wire. 7. An interface as claimed in Claim β, wherein the diameter ox the metal wire is approximately 0.125 mm. 8. An interface as claimed In any one of Claims 1 to 5„ wherein the sleeve is formed from carbon fibres. £ il 9. An interface as claimed in any preceding Claim wherein the interstices of the sleeve are in the range 0.5 mm to 5 mm. 10. An interface as claimed in any preceding Claim, wherein the sleeve ha© a flared opening at its upper end. 11. An interface as claimed in any preceding Claim, wherein the sleeve is coated with bone cement. 12» A method of making a prosthesis to bone interface comprising the steps of: providing a sleeve of intersticated material generally conforming to the shape of the stem of a prosthesis; applying a coating of bone cement to the sleeve; heating the sleeve to bake the coating onto the sleeve; and applying a plurality of spacer members comprising hone cement to the sleeve, to in use space the interior surface of the sleeve fro® the prosthesis stem, and define a space between the sleeve and the stem within which bone cement laay fee received. 13. A joint prosthesis including a rigid prosthesis member comprising a head element for articulated cooperation with a complementary prosthesis member and a stem depending from th© head element and adapted for insertion into and firing in a bone cavity by cement, the prosthesis further Including a tapered reinforcing sleeve of intersticated material generally conforming to the shape of the stem, the sleeve surrounding and of slightly greater diameter than the stem and which in use is adapted for embedding in and reinforcing the cement continuously around the stew,, the sleeve having secured thereto spacing means to space the Interior surface of the sleeve from the prosthesis stem and define a space between the sleeve and the stem within which bone cement may be received. 14. ' A prosthesis to bone interface claimed in Claim 1, substantially as described with reference to the accompanying drawings. 15. A joint prosthesis as claimed ia Claim 13

5. Substantially as described with reference to the accompanying drawings. Ιό- A method ©f making a prosthesis to bone interface as claimed in Claim 12 substantially as described herein -