GB2290971A

GB2290971A - Implantable device for removing particulate debris from prosthetic joints

Info

Publication number: GB2290971A
Application number: GB9503295A
Authority: GB
Inventors: Richard John Montgomery
Original assignee: Individual
Current assignee: Individual
Priority date: 1994-02-24
Filing date: 1995-02-20
Publication date: 1996-01-17
Also published as: GB9503295D0; GB9403547D0

Abstract

An implantable device for removing abrasive particulate debris from prosthetic joint surfaces (particularly the hip and knee) and reducing wear associated therewith comprises; two flexible tubular conduits 5, 6, a pump 9 and a filter 8. Bodily fluid and associated particles are pumped down conduit 5 and through filter 8 where the debris (e.g cement particles) are removed. The fluid is then returned to the joint via conduit 6. Alternatively filtration may be replaced or augmented by magnetic separating means or an electrolytic cell. The pump 8 may be located internally or externally and be powered by battery, manual compression or body movement. To prevent occlusion by blood clots formed during installation of this device, conduitS is initially sealed with a hydrolysable plug which disperses within two weeks. Advantages are decreased wear of joint surfaces. <IMAGE>

Description

Device for Use with Joint Prostheses The present invention is a device for use in association with joint prostheses which have been implanted in the human body.

The replacement of human joints by artificial components has been practised for many years now, to the extent that the potential adverse effects of implantation have become apparent and indeed have been studied in depth. Increased clinical success and also the use of such prostheses with younger patients have together resulted in prostheses remaining in position for longer periods, with the result that the consequences of wear occurring in such artificial joints have become more significant. Thus increasing attention is now paid to the degradative effects attributable to the presence of particles of wear debris in the immediate region of the prosthesis and at related sites.

The artificial joints which are most prone to wear in use are the hip and knee joints, although such wear occurs also, but usually to a lesser extent, at shoulder, elbow and ankle joints.

The artificial joint most frequently comprises a metal alloy component bearing upon a surface formed from ultra-high molecular weight polyethylene, although other materials are used or under consideration, for example ceramic materials. While significant research effort is devoted to identifying and adopting combinations of materials designed to reduce the occurrence and extent of wear, nonetheless the effects resulting from wear particles remain an important problem.

The particles in question consist mostly of the polyethylene and metal of which the prosthesis is constructed but particles may also arise from the cement by which the joint components may be retained in place. The particles may vary in size from about 40 micrometres down to small fractions of a micrometre. The presence of the particles can not only aggravate wear which is already occurring but can also lead to serious degradation of the adjacent bone, in particular at the interface between the bone and the prosthesis and/or the interface between the bone and cement.

It is an object of the present invention to provide a device by means of which the adverse results arising from- particulate debris associated .with a joint prosthesis may be reduced or eliminated.

The device according to the invention comprises, all formed in biologically-compatible materials, a first flexible tubular conduit for conveying liquid containing particulate material away from the region of a prosthesis, a separator means for removing particulate material from the liquid, a second flexible tubular conduit for returning liquid from which particulate material has been removed to the region of the prosthesis, and a pump for circulating the liquid and particulate material through said conduits and separator means.

Thus the device of the invention approaches the problem of wear of artificial joints in a novel way, that is, by removing the resultant debris, continuously or discontinuously, from the body. In general, the device is intended to be itself implanted, wholly or partly, into the body, where it is devised to remain over an extended period.

The tubular conduits by which the bodily fluid and associated particles are conveyed from and to the body may be made from any biologically-compatible material which is acceptable for long-term implantation. Such materials include polyethylene, polypropylene and other polymeric materials.

The separator means for removing the particles from the liquid may take various forms, depending to some extent upon the perceived nature of the particles to be removed.

Thus the separator means may be a fine filter, selected to remove particles above a selected size, for example 5 micrometres, 1 micrometre or 0.5 micrometres. The filter may be a simple flat sheet of a perforated material or may be formed of a woven or non-woven fabric or similar material, or ceramic.

In another form, the separator means may be devised to separate metallic particles by magnetic methods. In a further form, the separator means may be an electrolytic cell, by means of which dissolved metal ions may be removed. As yet a further possibility, the separator means may comprise a combination of two or more of the abovedescribed items, for example a filter in combination with a magnetic separator.

The pump, by means of which the materials for separation are circulated, may be located within the body or externally. In general it is preferred to locate it within the body but the power source may be located either internally or externally. For example, the pump may be battery-powered, in which case the battery is preferably carried internally, or it may be operated by induction from an external source. As one alternative, the pump may be in the form of a compressible member, located within the body and operated either by natural muscle movement or alternatively by manual pressure from the body surface. As yet a further alternative, power for the pump may be derived from a mechanism which converts movement into electrical or mechanical power (as in a self-winding watch).

When the pump is powered from an electrical source, for example a battery, that same source may provide the necessary power for a magnetic separator or electrolytic cell, if used.

When the device according to the invention is being installed, it is desirable to take steps to ensure that the flexible conduit by which the fluid is conveyed from the joint does not become blocked with clotted blood. To that end, the first conduit may be sealed at its input end with a plug of a hydrolysable material. The plug may then hydrolyse within a short time of the operation, say within two weeks, and thereby open the conduit to its intended use.

The design of the device, and its location upon or within the body, may be such as to allow replacement of at least a part of the device at appropriate infrequent intervals. For example the filter medium may be readily replaceable or the separator means and pump may be designed together as a replaceable unit.

The device according to the invention may be designed to operate continuously or only when made to do so by the provision of an appropriate electrical, manual or other stimulus.

The invention will now be further described with reference to the accompanying drawing, which illustrates, schematically and by way of example only, one form of the device according to the invention, as applied to a hip replacement prosthesis.

The illustrated prosthesis comprises an elongated, round-headed spike 1, of a cobaltchromium alloy for example, engaging in a socket 2 of ultra-high molecular weight polyethylene.

The spike 1 is inserted in the upper end of the femur 3 and retained there by a biologicallycompatible cement 4, for example of polymethyl methacrylate. Pivotting of the rounded end of the spike 1 in the socket 2 simulates the normal ball-and-socket action of the hip joint.

However wear of the mating surfaces of the spike and the socket leads, over a period of months and years, to the formation of small particles of polyethylene and of metal alloy. Those particles can give rise to degradation of the bone at its interface with the spike 1 and/or with the cement 4.

A pair of flexible tubular conduits 5, 6 are secured, each at a first end, to opposite sides of the spike 1 by means of a metal circlip 7. The other ends of the conduits 5, 6 are connected to a filter 8 and a circulation pump 9, by means of which bodily fluid and associated particles are drawn down the conduit 5, filtered via the filter 8 and returned to the region of the prosthesis by the conduit 6. In this way, particulate matter is removed, continuously or intermittently, from the area of the artificial joint and collected in the filter 8, for subsequent disposal.

While, in the illustrated embodiment, the flexible conduits 5, 6 extend all the way from the region of the joint to the filter 8 and pump 9, a part of the path for the circulated fluid may be constituted by channels formed directly in the components of the joint itself.

Claims

1. A device for use with a joint prosthesis comprising, all formed in biologicallycompatible materials, a first flexible tubular conduit for conveying liquid containing particulate material away from the region of the prosthesis, a separator means for removing particulate material from the liquid, a second flexible tubular conduit for returning liquid from which particulate material has been removed to the region of the prosthesis, and a pump for circulating the liquid and particulate material through said conduits and separator means.

2. A device as claimed in Claim 1, wherein said tubular conduits are of polyethylene, polypropylene or another polymeric material.

3. A device as claimed in Claim 1 or Claim 2, wherein said separator means is a filter.

4. A device as claimed in Claim 3, wherein said filter is of a perforated material, a woven or non-woven fabric or ceramic.

5. A device as claimed in Claim 3 or Claim 4, wherein said filter is sized to remove particles greater than 1 micrometre.

6. A device as claimed in Claim 1 or Claim 2, wherein said separator means is a magnetic separator.

7. A device as claimed in Claim 1 or Claim 2, wherein said separator means in an electrolytic cell.

8. A device as claimed in any of the preceding claims, wherein said pump is battery-powered.

9. A device as claimed in any of Claims 1 to 7, wherein said pump is operated by induction.

10. A device as claimed in any of Claims 1 to 7, wherein said pump is in the form of a compressible member, operated by natural muscle movement or by manual pressure.

11. A device as claimed in any of Claims 1 to 7, wherein said pump is powered by a mechanism which converts movement into electrical or mechanical power.

12. A device as claimed in any of the preceding claims, wherein said first conduit is sealed at its input end with a plug of a hydrolysable material.

13. A device as claimed in any of the preceding claims, wherein said separator means and said pump form together a replaceable unit.

14. A device for use with a joint prosthesis, which device is substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawing.