IE880524L

IE880524L - Joint prosthesis

Info

Publication number: IE880524L
Application number: IE52488A
Authority: IE
Original assignee: Sheehan James
Priority date: 1988-02-25
Filing date: 1988-02-25
Publication date: 1989-08-15
Also published as: GB8904418D0; GB2216015A; IE60622B1; GB2216015B

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. <IMAGE> [GB2216015A]

Description

The present invention relates to a joint prosthesis with means 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 degeneratedf 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. K 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 and. 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. 3 The prosthesis is in use subjected to great stresses and a conunoa problem which arises is that the cement surrounding the tapered element in the femur often cracks due to the stresses, resulting in loosening 5 of the prosthesis and/or pain for the patient,, and possibly also damage to the femur and the pelvis.

A number of methods have been tried to overcome the above problem and strengthen the cement and prevent cracking. These include incorporating into the cement 10 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 15 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 20 provided a prosthesis to bone interface comprising a sleeve of intersticated material generally conforming to the shape of the stem of a prosthesis, the sleeve having secured thereto,, spacing means to space the interior surface of the sleeve from the prosthesis stem 25 and define a space between the sleeve end the stem within which bone cement may be received.

The invention also provides a method of making a prosthesis to bone interface comprising the steps of: providing a sleeve of intersticated material generally 30 conforming to the shape of the stem of a prosthesis; applying a coating of bone cement to the sleeve; 4 heating the sleeve to bake the coating onto the sleeve; and applying a plurality of ©pacer members comprising bone cement to the sleeve, to in use space the interior surface of the sleeve frosa the prosthesis 5 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 10 complementary prosthesis member and a stem depending from the head element and adapted for Insertion into and fixing in a bone cavity by cement, the prosthesis further including a tapered reinforcing sleeve of intersticated material generally conforming to the 15 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 stem, the sleeve having secured thereto spacing means to space the interior 20 surface of the sleeve from the prosthesis stem aad define a space between the sleeve and the stem within which bone cement may be received.

Embodiments of the invention will now be described, by way of example, with reference to the 25 accompanying drawings, in which: Figure 1 is a' cut-away perspective view of an embodiment of a prosthesis interface in ?ase according to the invent!or?,; Figure 2 is a perspective view of the interface 30 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 35 according to the invention.

Referring to Figures 1 and 2P a hip joint prosthesis includes a first rigid metal member 10 comprising a substantially spherical femurai head 11 for articulated cooperation w?ith 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 loose 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 the 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 polymet'nyl methacrylat® (PMMA). The spheres are preferably of 0.5 to 5 mm in diameter and more preferably 1 mm 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 as shown. hs shown in Figure 1, the spacers 18 abut the stem 12 of the prosthesis 10 and effectively space the sleev® 6 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 greater diameter than the stem 12 of the prosthesis, and of a smaller diameter 5 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 10 a prosthesis stem 12 with which the sleeve 15 is to h& 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 15 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 PMMA. 20 Since the bone cement 23„ as described below, comprises PMMA, the coating of the sleeve 15 with PMMA serves the dual function of rendering the sleeve substantially rigid and also ensures a good bond between the PMMA bone cement and the sleeve.

Fiquife 4 illustrates introducing means for correctly locating the sleeve in the recess 19 of the bone 20. The introducing means comprises a holloa nozzle 24 conforming to the shape ox the prosthesis which is to be used with the sleeve 15. The nossle 24 30 is open at its lower end 25 and is adapted at its upper end 26 to be attached to a standard bone cement gun/syringe system (not shown). Thus, the upper end 26 1 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 5 nozzle 24. The procedure for insertion of the prosthesis 10 and sleeve 15 is as follows: a) fill up the medullary canal 19 with hone cement 23 (PHM) in conventional manner, for example, using a standard syringe and noxsle; b) remove the standard nozzle and place the nozzle 24 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 2,4 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® is illustrated in Figure 3. The sleeve 15® of Figure 3 has a flared circular flange 30 formed at its upper end 17'. The flange 30 is 5 provided so that in us© it is positioned and engaged on the 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 10 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 the spacers 18. In addition, the spacers also serve to space the 15 sleeve from th® inner surface of the 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 20 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 25 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 30 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 k 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 IS is coated with PMMA, this promotes an excellent interface between the .bone cement end the sleeve.

It has been found that a sleeve forming a prosthesis to hone interface having the characteristics defined herein, provides excellent reinforcement of the bone cement mantle» It will be appreciated that the 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 comprise rings or strips of bone cement fixed to the sleeve.

Claims

CLAIMS:

1. A prosthesis to bone interface comrising a sleeve of intersticated materiel generally conforming to the shape of the stem of a prosthesis, the sleeve having 5 secured thereto,, spacing means to space the Interior surface of the sleeve from the prosthesis stem and define a space between the sleev® and the stem within which bone cement may be received.

2. An interface as claimed in Claim 1, wherein the 10 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 snembers ©re generally spherical and project from the inner and outer surfaces of the sleeve. 15

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 and is closed at its lower end,. 20

6. An interface as claimed in any preceding Claim wherein the sleeve is formed from metal wire.

7„ An interface as claimed in Claim 6, wherein the diameter of the metal wire is approximately 0»125 mm.

8. An interface as claimed in any one of Claims 1 to 25 5„ wherein the sleeve is formed from carbon fibres. 11

9. An interface as claimed in any preceding Claim wherein the Interstices of the sleeve are in the range 0.5 sm to 5 mm.

10. An interface as claimed in any preceding Claiia, 5 wherein the sleeve has a flared opening at its upper end.

11. An interface as claimed in any preceding Claim, wherein the sleeve is coated with boras cement.

12- A method of making a prosthesis to bone interface 10 comprising the steps of: providing a sleev® 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; 15 and applying a plurality of spacer members comprising bone cement to the sleeve, to in use space the interior surface of the sleev© fro® the prosthesis stem, and define a space between the sleeve and the stem within which bone ©aaeat may fee received. 20

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 the head element and adapted for insertion into and fixing in a bone cavity by cement, 25 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 30 continuously around the stem, the sleeve having secured thereto spacing means to 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 may be received. it

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 in Claim 13 substantially as described with reference to the accompanying drawings.

16. A method ©f making a prosthesis to bone interface as claimed in Claim 12 substantially as described herein - F. R. KELLY & CO., AGENTS FOR THE APPLICANTS.