GB2162753A

GB2162753A - Sleeve for metal implant into bone

Info

Publication number: GB2162753A
Application number: GB08515964A
Authority: GB
Inventors: Professor J R Shearer; Dr P Shelley
Original assignee: Chas F Thackray Ltd
Current assignee: SSL CC Services Ltd
Priority date: 1984-06-22
Filing date: 1985-06-24
Publication date: 1986-02-12
Also published as: GB8515964D0

Abstract

A sleeve 2 for location within a bone has a longitudinal bore for receiving a stem of a metal bone implant to prevent direct implant stem to bone contact and to aid removal of the implant after failure. The outer surface of the sleeves is shaped to provide good keying with the bone, and may be coated with a suitable porous material to encourage tissue fixation. <IMAGE>

Description

SPECIFICATION Prosthetic device This invention relates to prostheses and in particular to bone implants and more particularly to bone implants in the form of joint implants. Examples of joint implants are those for the knee, the hip, the shoulder, finger or thumb.

Typically a joint implant includes two or more separate parts, at least one of which has a stem or other portion for location within and anchoring to one of the bones adjacent the joint. For instance, in one type of hip joint, one part is in the form of a metal femoral implant having a head portion intended to replace at least part of an actual joint and a stem part for location within and anchoring to the femur. Such an artificial joint is subject to failure which can arise as a result of shearing movement between the implant and the bone and the very great difference in elastic modulus between the metal of the implant and the bone.This difficulty can be alleviated by the use of an acrylic bone cement located between the stem of the implant and the bone and the use of an implant shaped mechanically to lock with the bone which may itself be reshaped to accommodate the shaped implant.

Also, in the case of an inter-phalangeal joint such as a finger, the implant comprises a first stem for location within and anchoring to one of the phalangeal bones adjacent the joint, and possibly also a second stem for location within and anchoring to the opposite phalangeal bone, with an artificial articulation joint being located between the two stems.

In either case, associated with the use of acrylic bone cement, are problems arising from thermal necrosis of the bone, the toxicity of the material and the variability of the material as prepared by the surgeon. As to the special shaping of the implant and the bone there is a conflict between the shape desired for the implant to achieve a locking configuration with the bone and that desired for the necessary functional requirements of the implant. Furthermore the difference in elastic modulus between the metal and the bone still lead to somewhat patchy fixation and the presence of a soft tissue layer between the implant and the bone.

Furthermore with such a shaped arrangement, the implant is difficult to remove after failure.

According to the present invention there is provided a prosthetic device comprising a sleeve for location within a bone between the stem of a metal bone implant and the bone itself whereby any substantial direct contact between the implant stem and the bone is avoided.

Accordingly the present invention envisages the use of an intermediate prosthetic device located between the normal load bearing metal implant and the bone thereby allowing implant stem to bone contact to be substantially avoided.

Preferably the sleeve is shaped to provide good keying or locking to the bone and the bone itself may be reshaped internally provide a corresponding keying or locking surface.

The sleeve may be inserted into the bone in a separate stage of the operation to insertion of the metal implant within the sleeve.

In a preferred arrangement in accordance with the invention, the fit between the metal implant and the sleeve is such that to at least some extent sliding movement between the sleeve and the metal implant is permitted, whether to accommodate for subsidence after the initial operation or after some extensive use by the patient, or alternatively or in addition to allow for a greater degree of flexibility of movement by the patient.

The anchoring of the sleeve to the bone may be assisted by the used of bone cement.

In one particular embodiment of the present invention the sleeve is provided with an outer screw thread and the corresponding inner surface of the bone is tapped to provide a corresponding screw thread. The sleeve can then be screwed into position within the bone whereby it is then securely locked into position.

Alternatively, the outer surface of the sleeve may be provided with a number of longitudinal and/or circumferential ribs.

In addition to the advantages mentioned above for the case where the metal implant is permitted to slide within the sleeve, there may be achieved as a result an improved load distribution by the use of, for example, a calcar collar.

It would be appreciated that use of an intermediate prosthetic device in the form of a sleeve will allow the easy removal of the metal implant in the case of failure and the subsequent easy removal of the sleeve after first removing any hindering proximal cement.

The outer surface of the sleeve may be coated with a suitable material to present a mechanically compatible surface to the bone and reduce the possibility of particles of the stem material produced as a result of wear coming into contact with the endosteal surface of the bone.

In another embodiment of the present invention the sleeve is of a length so that, with the metal implant in position, it extends some distance below the distal surface or base of the implant to provide a space or void below the implant into which there may collect any wear particles of the stem material and/or metal which may result from movement of the metal prosthesis within the sleeve. The distal end of the sleeve may be closed as a result of which any wear particles are retained wholly within the sleeve and do not make contact with the surrounding bone.

In a preferred aspect of the present invention the proximal or upper portion of the sleeve may include a deformable portion. This deformable portion may be in the form of a thin, closely contouring membrane made of plastics material.

While the sleeve is being inserted into the bone, this upper plastics portion is gathered together so there is defined between this upper portion of the sleeve and the bone an endosteal void which may be packed with bone cement. Subsequent insertion of the metal implant then displaces the gathered portion of the plastics sleeve to compress the cement and to diminish the endosteal void. As a result the upper portion of the metal implant is supported by a thinner continuation of the sleeve which in turn is grouted into a load bearing position by the bone cement. The metal implant is still able to slide or subside within the body of the sleeve.

In the case of a sleeve for the stem of a finger joint implant (and equally for a thumb joint implant), the stem of the implant may be fully restrained within the sleeve, so that no movement of the stem is possible, but preferably it is either partially restrained or unrestrained within the sleeve.

For instance, partially restrained could mean that axial sliding only of the stem within the sleeve is permitted, or alternatively that rotation only is permitted, whereas unrestrained could mean that a combination of both these types of movement is permitted.

Thus, by limiting the restraint on the joint implant, the transmission of forces which could loosen the fixation of the implant within the bone is prevented.

In the case of a finger joint, the stem of the joint implant may be curved and the sleeve would also be curved accordingly.

As with other applications of this invention, the sleeve may be made wholly of metal, or alternatively of plastics coated on its outer surface with a suitable material.

In cases where the sleeve is coated, a so-called "biological fixation" of the sleeve within the bone can be achieved by coating the sleeve with a material of a type and physical composition which will permit tissue fixation. Examples of suitable materials for the coating are porous metal, sintered metal fibre or beads, or porous plastic.

Embodiments of the present invention will now be described, by way of examples only, and with reference to the accompanying drawings, in which: Figure 1 illustrates a prosthetic device in accordance with the present invention; Figure 2 shows the device of Figure 1 located within the bone; Figure 3 shows a second embodiment of a prosthetic device in accordance with the present invention; Figure 4 shows the device of Figure 3 located within the bone; Figure 5 illustrates the use of a deformable upper portion to a plastics sleeve forming a prosthetic device in accordance with the present invention; Figure 6 is similar to Figure 5 but shows the deformable portion in a different position; Figure 7 illustrates the coating with metal of a plastics sleeve forming a prosthetics device in ac cordance with the present invention;; Figure 8 illustrates a particular type of metal implant located in position in a bone together with an embodiment of the present invention; Figure 9 illustrates a particular shape of outer surface of a sleeve forming a prosthetic device in accordance with the present invention; and, Figure 10 shows a third embodiment of a prosthetic device in accordance with the present invention.

Referring to the drawings, Figure 1 shows a prosthetics device in accordance with the present invention in the form of a plastics sleeve having an external screw threaded surface. The upper portion of the plastics sleeve is flared outwardly and the top of the sleeve is provided with diametrically opposed notches 1 whereby the blade of a screwdriver can be located in order to screw the sleeve into the tapped cavity of a bone.

Figure 2 shows the use of the plastics sleeve of Figure 1 in conjunction with a metal femoral implant 3.

Referring to Figure 3, another embodiment of a prosthetic device in accordance with the present invention is again in the form of a plastics sleeve similar to that shown in Figure 1 but having a closed distal end 5 and being of such a length that, having regard to the length of the stem of the metal implant with which it is used, there is provided a space or void 7 between the proximal end of the metal implant and the end of the plastics sleeve. This void 7 will collect wear particles below the metal implant. Figure 4 illustrates such a plastics sleeve in use together with a metal femoral implant 9.

Referring to Figures 5 and 6, the upper portions of a prosthetic device in accordance with the present invention is shown. This prosthetic device is in the form of a plastics sleeve similar to those described above but having an integral thin proximal or upper portion which is readily deformable. Figure 5 illustrates this upper portion with the deformable part in its open position and Figure 6 shows the deformable part gathered together and retained by means of a suitable retaining clip. The plastics sleeve is inserted into the bone with the upper deformable part gather together. Cement can then be inserted between the upper deformable part and the bone. The retaining clip is removed and the metal implant inserted into the plastics sleeve thereby expanding outwardly the deformable part of the plastics sleeve and compressing the bone cement between said part and the bone.

Figure 7 illustrates the use of a metal coating on the outer surface of a plastics sleeve forming a prosthetics device in accordance with the present invention. This metal outer skin provides an improved bio-mechanical compatibility.

Referring to Figure 8, there is here illustrated a flanged metal femoral prosthesis 11 located with its stem lying within a femur 13. Located between the stem of the metal implant and the bone is a plastics sleeve 15 forming an embodiment of the present invention. This plastics sleeve 15 is screwthreaded on its outside and is inserted by screwing into the correspondingly threaded inner surface of the bone cavity. The plastics sleeve extends below the distal end of,the metal implant and terminates in a closed integral plastics end thereby leaving a void 17 to accommodate and trap wear particles.

The plastics sleeve is provided on its outer surface with a coating or a thin sleeve of porous metal or other suitable material such as sintered material fibre or beads, or porous plastic metal for increased tissue fixation and bio-mechanical compatibility. At its proximal end the plastics sleeve is provided with an integral thin, deformable portion of plastics material and between this thin deformable portion and the bone, acrylic bone cement is provided in order to give sound load bearing of the implant. The prosthesis is provided with a flange 19 and the flanged prosthesis is such that it can take advantage of the sliding effect within the plastics sleeve as a result of, for instance, subsidence, Figure 9 shows a sleeve of the present invention which has multiple circumferential ribs 21 around the outside of the sleeve to enable the sleeve to be fixed within the bone.

Figure 10 shows an arrangement using a sleeve of the present invention with a finger joint implant.

The implant comprises two stems 22, 23 for location within each of the two phalangeal bones adjacent the joint, an articulation joint 24 being provided between the two stems. The sleeve 25 surrounding the stem 22 has a flange 26, the flange 26 engaging with the articulation joint 24 in such a way as to partially restrain the movement of the stem 22 within the sleeve 25, allowing only axial sliding movement.

Alternatively, the sleeve 27 does not have a flange, so that the stem 23 contained therein is unrestrained and can rotate as well as slide axially.

Within the scope of the present invention there is also provided a prosthetic arrangement comprising a metal implant and the device of the invention.

Also within the scope of the present invention there is provided a method of locating a metal implant within a bone comprising providing between the metal implant and the bone a prosthetic device in accordance with the invention.

Claims

1. A prosthetic device comprising a sleeve for location within a bone between the stem of a metal bone implant and the bone itself whereby any substantial direct contact between the implant stem and the bone is avoided.

2. A prosthetic device according to Claim 1 wherein the sleeve is shaped to provide good keying or locking to the bone.

3. A prosthetic device according to Claim 1 or Claim 2 wherein the fit between the metal implant and the sleeve is such that axial sliding movement is possible between the implant and the sleeve.

4. A prosthetic device according to Claim 3 wherein the fit between the metal implant and the sleeve is such that rotational movement of the implant as well as axial sliding is possible.

5. A prosthetic device according to Claim 1 or Claim 2 wherein the fit between the metal implant and the sleeve is such that only rotational movement of the implant is possible.

6. A prosthetic device according to any of the preceding Claims wherein the outer surface of the sleeve is coated to present a mechanically compatable surface to the bone and reduce the possibility of wear particles of the stem coming into contact with the endosteal surface of the bone.

7. A prosthetic device according to any of the preceding Claims wherein there is a void between the base of the implant, when in position in the bone, and the base of the sleeve into which any wear particles may collect.

8. A prosthetic device according to any of the preceding Claims wherein the upper portion of the sleeve includes a deformable portion, the deformable portion being gathered together so that there is defined between the upper portion and the bone a void which may be packed with bone cement, so that when the implant is inserted into the sleeve the bone cement is displaced to partially fill the void and grout the sleeve into a load bearing position.

9. A prosthetic arrangement comprising a metal bone implant and a prosthetic device as claimed in any of the preceding Claims.

10. A method of locating a metal implant within a bone comprising providing between the metal implant and the bone a prosthetic device in accordance with the present invention.

11. A prosthetic device according to Claim 1 and substantially as herein described.

12. A prosthetic device substantially as herein described with reference to the accompanying drawings.

13. A method of locating a metal implant within a bone according to Claim 10 and substantially as herein described.

14. A method of locating a metal implant within a bone substantially as herein described with reference to the accompanYing drawings.