Prosthesis for attachment without bone cement

Abstract: A prosthesis having attachment portion (4) for insertion into or attachment to a patient's bone without bone cement, characterised in that the parts of said attachment portion (4,62) which are to be attached to said bone are covered with a mantle of (7,63) synthetic resin material and which has a roughened outer surface (10) and which is preformed as a separate component before fitting to said attachment portion.

Description: This invention relates to a bone joint replacement prosthesis assembly for location in a bone cavity without bone cement. United States Patent Specification 3 918 100 proposes the use of sputtering to apply a layer of coating material directly onto a metal prosthesis. The process requires a complicated and expensive equipment and it is not clear whether it was ever used successfully. The intention appeared to be to coat the prosthesis and then place it in the bone relying on the coating of bone particles to promote bone growth and attachment to the living bone. United States Patent Specification 4 168 326 proposed a prosthesis covered with an enamel or enamel-like coating to which bio-active material was applied. Once again the intention was to use the prosthesis without bone cement. This construction also called for expensive and complicated procedures. United states Patent Specification 4 650 489 proposed a prosthesis which was provided with a metallic external sheath. The prosthesis member is attached to the sheath by elastomeric material so that there is a shock absorbing effect. In this construction the sheath is said to have an outer irregular surface to provide for regrowth of bone. It is stated that in the growing process the bone integrates with the sheath resulting in a cancellous or spongy bone. Once again no cement was used but the whole intention of this device is to provide shock absorbing. The use of roughened surfaces on metallic components in prostheses is of course well known in itself. It is also known, for example as shown in European Patent Application No. 91303958.2 (EP 0 457 464 A1), to provide a prosthesis with a sheath in the form of a preformed cement layer which can be fitted to the implant as a separate component. The purpose of the layer provided by the sheath is to guarantee that there is a minimal cement thickness separating the implant from the bone; and to produce a better implant cement interface for in-service taper re-engagement. In this arrangement the device is assembled to the preformed cement sheath and he surgeon implants the assembly using freshly mixed bone cement. It is important that there is an effective engagement at the bone cement/bone interface in total joint replacement. If the engagement becomes loose internal damage occurs to the bone which rapidly accelerates the loosening effect to such an extent that the joint becomes inoperable. GB 2 162 753 also shows the use of a sleeve to receive the stem of a metal bone implant and with the outer surface shaped to provide keying with the bone and which may be coated with a porous material to encourage tissue fixation, but in this construction the anchoring of the sleeve to the bone is assisted by bone cement or relies upon a mechanical fixation such as a screw thread. It is also proposed to provide a surface which produces bio-mechanical compatibility. The features of the preamble of Claim 1 are known from DE-A-3802214. It has been found by experiment that a prosthesis can be implanted but with the inside of the opening in the bone filled with bone chips rather than bone cement. A very thin layer of bone cement is provided which separates the implant from the compacted internal bone graft. It has been found that the results are excellent and there is immediate adhesion between the thin layer of bone cement and the adjacent and contacting bone chips. The present invention is intended to take advantage of the technique referred to above so as to provide a prosthesis which eliminates the time consuming and messy operation of handling fresh bone cement during an operation but new bone cement also has some toxic characteristics; there is a release of methyl methacrylate monomer and it is usual for the patient's blood pressure to drop for a short period when the bone cement is first introduced; there is a small risk of intra-operative death associated with the use of bone cement. Moreover, there is an emission of monomer vapour while the bone cement is being mixed and there is a suspicion that this could be linked with some long term health hazard for those who mix it regularly. According to the present invention therefore a bone joint replacement prosthesis assembly for location in a bone cavity comprises a prosthesis component having an attachment portion for location in a bone cavity in the patient's bone without bone cement, and a tapered mantle which surrounds said attachment portion and made of synthetic resin material which has a roughened outer surface formed of discrete projections and which is preformed as a separate component for fitting to said attachment portion characterised in that said roughened outer surface of the mantle has a coating of or is formed by a bio-active material, bone fragments or a combination thereof, and is surrounded by and co-operates with a layer of compressed bone fragments. Thus, the invention provides a prosthesis with a mantle to which the compressed bone chips can easily engage. It has been found that when used with internal bone grafting, that is the use of bone chips, it seems as if the bone remodelling process is accelerated. The bone chips are, of course, dead and the body often replaces these with living structures remarkably quickly. A detailed analysis of the bone structure of patients on which bone chips have been used shows how the orientation of the trabecular bone structures have regenerated, not in a normal physiological way, but rather in a direction that responds to the new ay in which the load is transferred from the implant to the bone, which of course is different from the original passage or route of load transfer in the original normal joint. The depth of the roughened outer surface can be between .5 to 5 mm and is preferably between 1 and 3 mm. The roughened outer surface can have a coating of a bio-active material, for example hydroxyapatite or bioglass. Such a bio-active material will tend to combine with the bone chippings used for the internal bone grafting. The mantle can be made from any suitable material which is biocompatible and thus it can be made from an acrylic material, for example bone cement. As referred to above the mantle can be secured or not secured to the attachment portion of the prosthesis. Preferably the mantle is dimensioned to enclose said attachment portion from either the distal or proximal extremity of the implant away from the articulating surfaces to a point where it emerges from the bone when in use and is constructed to allow said attachment portion to move further into it under load. With the above arrangement the end of the mantle away from the articulatory surfaces of the implant can be in the form of a cup, the inner surface of which is spaced away from the adjacent end of the attachment portion, to provide a void when initially located in position to accept subsequent movement between the mantle and the attachment portion after fitting. The invention can be performed in numerous ways and some embodiments will now be described by way of example and with reference to the accompanying drawings in which : Figure 1 is a part cross-sectional diagrammatic side elevation of a prosthesis according to the invention and showing different forms of construction for the mantle; Figure 2 is a diagrammatic cross-section showing a desired installation of a total hip prosthesis of known kind in a femur; Figures 3 to 15 are diagrammatic part cross-sectional representations showing how a hip prosthesis of the kind shown in Figure 2 can come loose and be replaced by a prosthesis assembly according to the present invention; and, Figure 16 is a part cross-sectional side elevation of another form of total hip prosthesis embodying the invention in different forms. Figure 1 shows the mantle of the invention applied in various forms to a prosthetic intramedullary femoral prosthesis 1 which has a head 2 of known type connected through a neck 3 to an intramedullary tapered stem 4. The stem 4 is enclosed from its distal end 5 to a point 6 where it will emerge from the femur in which it is implanted by a tapered mantle 7 which is in the form of an enveloping sheath. The mantle can be made from any suitable material which is biocompatible and can, for example, be made from an acrylic material such as polymethylmethacrylate which is similar to bone cement material. A filler can be added to make it more flexible. It will be seen that the distal end 8 of the mantle is somewhat longer than the distal end 5 of the stem 4 and is in the form of a cup the inner surface of which is spaced away from the distal end 5 of the stem 4 to provide a void 9. The thickness of the mantle can be about 1 mm and although it can initially be moulded on the prosthesis itself and removed before use in the embodiments being described it is provided as a preformed separate component. The prosthesis is of the shoulderless type and if there is a tendency for it to move further into the mantle this is accommodated by movement within it by movement into the void 9. From the above it will be appreciated that the mantle is not fixed to the stem 4, but the stem can move within it. In a first construction to be described the whole of the outer surface of the mantle is covered with a roughening of discrete projections as indicated by reference numeral 10. The roughening can be patterned or irregular and is between .5 and 5 mm deep. The depth of the roughening can vary over the area of the mantle if desired. The roughening is provided with a bio-active coating, as indicated by reference numeral 11. Thus a hydroxyapatite coating is provided or the coating could, for example, be bioglass In an alternative construction particles of hydroxyapatite or tricalcium phosphate or some other calcium phosphate can be embedded into the bone fixation surface provided by the roughening. Reference numeral 12 indicates another alternative surface in which the surface roughening is covered in bone chips 13. These bone chips can be natural or synthetic bone. In the above examples of the surface construction the roughness is at least partly provided by a roughening of the surface of the material from which the mantle 7 is made but reference numeral 14 indicates a surface in which the roughness is provided by chips or fragments (24) of any suitable bio-active material such as a calcium phosphate, for example hydroxyapatite. Again, this surface could be provided by imbedded bone fragments. Any one or a combination of the surfaces described above can be used. The depth of roughness can be between .5 and 5 mm but preferably is between 1 and 3 mm although, as mentioned above, it can vary over the area of the mantle. The method by which a prosthesis with its mantle according to the invention is assembled and used will now be described with reference to Figures 2 to 15. Figure 2 shows an idealised primary hip intramedullary femoral prosthesis 1 of the straight tapering collarless polished design concept located in a femur 15. The prosthesis has a head 2, neck 3 and stem 4 and is held in place by bone cement indicated by reference numeral 16. The cortical bone 17, of the femur 15, retains some cancellous bone 18. The stem 4 is centralised in the canal by a centraliser 19 of known type and the canal is plugged by a bone plug 20. Figure 3 illustrates what can happen when an implant as shown in Figure 2 fails. The stem 4 together with the cement 16 bred away from the bone and a pendulum effect is produced as shown by arrows 21. This causes severe damage within the bone so that all that is left is a thin cortex 22. A space 23 is created which becomes filled by fluids and fibrous tissues. The present invention however provides an implant assembly with which the damaged joint can be repaired. The revision procedure commences as shown in Figure 4 by removing the original implant complete with cement and the fibrous tissue and first fitting a bone plug 30 and guide wire 31. Bone chips 32 are now added and compressed using an impactor/ram 33. The bone chips are built up layer by layer to a point about 8 cm below the greater trochanter as shown in Figure 6. At this point, as shown in Figure 7, a stem phantom 34 is applied down the guide wire and under impaction dislodges bone chips radially and proximally around the phantom, the movement of the bone chips is indicated by reference numeral 35. This movement initiates a cavity for the prosthesis. When the cavity has been formed as shown in Figure 8 the stem phantom 34 is withdrawn. The arrows 36 indicate how the bone chips 32 have been radially compressed to leave a cavity 37. Packing of bone chips now continues as shown in Figure 9, the additional bone chips being indicated by reference numeral 38. These added chips 38 are now rammed with a ram 40 to which handforce is applied to cause compression. The stem phantom 34 is now reintroduced, as shown in Figure 10, to again radially compress the bone chips as indicated by arrows 39, the arrows 40 indicating bone chips which are dislodged proximally. Impaction to the stem phantom is applied mechanically. The actions of filling and compressing are repeated until the bone chip level 41 is 2 cm below the greater trochanter tip 42 as shown in Figure 11. The space 23 is now filled with bone chips 32. A cannulated trial implant 44 is now inserted into the bone chips, as shown in Figure 12, as a trial prosthesis and the proximal exposed bone chips are tamped by a tamper 45 to compress them. If desired extra bone chips can be added proximally. The trial implant 44 is now removed along with the guide wire 31 and a trial prosthesis is inserted. This prosthesis (not shown) is oversized to allow for mantle thickness. The trial prosthesis is removed and the guide wire replaced to guide an introducer 50 carrying a preformed mantle 7 as shown in Figure 13. The introducer acts to place the preformed mantle 7 in the bone chips, a guide wire 31 acting to accurately centralise it. The introducer 50 and guide wire are removed leaving the preformed mantle in situ as shown in Figure 14. The final stage, shown in Figure 15, is to implant the femoral prosthesis 1 add further bone chips 51 and tamp them into place with tamper 45. The bone chips can, for example, be 1 to 2 mm cubed and they can be provided in a variety of shapes and sizes after a pestal and mortar crushing operation. At the small end of the spectrum chips of approximately 1 mm cubed can be found. Long splinters, approximately .5 mm by 1 mm by 4 or 5 mm in length can also be produced. It is felt however that the chips should not be produced such that a boney slurry is formed. The bone graft, when it is compacted on the inside of the femoral canal, must be mechanically stable and reasonable well consolidated. When the stem with mantle is then pressed into the bone graft the bone chippings will manoeuvre slightly as a response to the roughness on the mating surface of the preformed cement mantle. Thus, when the bone chips are later replaced by vital bone, a mechanical lock will result. In the method described above any of the constructions described with regard to Figure 1 can be used. Bone chips which are grafted to the bone before the mantle is introduced can either be taken from the patient or from another subject, for example obtained from a bone bank, allografting. Where bone chips are embedded in the surface of the mantle prior to introduction into the patient this can be allograft bone which is embedded in the cement mantle by the manufacturer. However, it is also possible that the mantle can be made in the operating theatre during the course of the bone joint replacement operation by the surgeon or by a theatre technician and the patient's own bone (autografting) can be pulverised and embedded in the mantle. Where particles of hydroxyapatite or tricalcium phosphate or some other calcium phosphate are embedded into the roughened bone fixation surface or where the roughness has a thin bioactive layer, for example bioglass, hydroxyapatite or tricalcium phosphate, but no chips or particles are embedded in the surface, these materials will assist in giving adequate fixation at the interface. The overall effect of the roughened surface is to provide some degree of immediate fixation to the surrounding bone graft. From the above it will be appreciated that the operation can be carried out without the use of additional bone cement apart from that which might be used for forming the mantle. The material from which the mantle is made must be mouldable and such that the bone mantle interface is protected and the movement between the implant and the mantle is permitted, in arrangements where this is desirable. It is important that the mantle completely covers the attachment portion of a prosthesis so that any debris generated by movement between the implant and the preformed mantle cannot find its way to the boney interface and become a site for osteolysis (bone death). In the method described above the implant is to replace an earlier implant which has failed but it will be appreciated that the method can also be used to implant a prosthesis initially. When the implant is an original one the space in the bone will of course be smaller in size but the same technique can be applied. Figure 16 shows a construction similar to Figure 1 and the same reference numerals are used to indicate similar parts. In this construction however the stem 4 is provided with a collar 55 which prevents its sinking into the sheath 7 or the bone when installed. With the construction shown in Figure 16 the same technique for application of the prosthesis to the bone can be used as that described above.

Claims: A bone joint replacement prosthesis assembly for location in a bone cavity comprising a prosthesis component having an attachment portion (4) for location in a bone cavity in the patient's bone without bone cement, and a tapered mantle (7) which surrounds said attachment portion (4) and made of synthetic resin material which has a roughened outer surface (10) formed of discrete projections and which is preformed as a separate component for fitting to said attachment portion (4) characterised in that said roughened outer surface (10) of the mantle (7) has a coating of or is formed by a bio-active material (11)(24), bone fragments (13)(24) or a combination thereof, and is surrounded by and co-operates with a layer of compressed bone fragments (32). A prosthesis as claimed in claim 1 characterized in that the depth of the roughened outer surface (10) is between 0.5 and 5 mm. A prosthesis as claimed in claim 1 or claim 2 characterised in that said coating of bio-active material (11) on the roughened surface (10) is hydroxyapatite or bioglass. A prosthesis as claimed in claim 1 or claim 2 characterized in that a coating of particles of hydroxyapatite or calcium phosphate are embedded into the roughened outer surface (10). A prosthesis as claimed in claim 4 characterised in that the calcium phosphate is tricalcium phosphate. A prosthesis as claimed in claim 1 characterised in that the bio-active material (24) which forms the roughened surface is provided by chips or fragments of calcium phosphate. A prosthesis as claimed in claim 6 characterised in that said bio-active material is hydroxyapatite. A prosthesis as claimed in any one of the proceeding claims characterised in that said mantle (7,63) is made of an acrylic material. A prosthesis as claimed in claim 8 characterised in that said mantle (7,63) is made from bone cement. A prosthesis as claimed in any one of the preceding claims characterised in that said mantle (7,63) is not secured to said attachment portion (4,62). A prosthesis as claimed in any one of the preceding claims characterised in that said mantle (7,63) is dimensioned to enclose said attachment portion (4,62) from either the distal (5) or proximal extremity of the implant away from the articulating surfaces to a point where it emerges from the bone when in use and is constructed to allow said attachment portion (4) to move further into it under load. A prosthesis as claimed in claim 11 characterised in that the end (8) of the mantle away from the articulating surfaces is in the form of a cup, the inner surface of which is spaced away from the distal end (5) of the attachment portion (4), to provide a void (9) when initially located in position to accept subsequent movement between the mantle and the attachment portion after fitting.

Inventors: GIE GRAHAM ALLAN, LAWES PETER DR, LINDER LARS DR, LING ROBIN SYDNEY MACKWOOD, SLOOFF TOM JOHANES PROF DR, GIE, GRAHAM ALLAN, LAWES, PETER, DR., LINDER, LARS, DR., LING, ROBIN SYDNEY MACKWOOD, SLOOFF, TOM JOHANES, PROF. DR.
Applicants: HOWMEDICA, HOWMEDICA INTERNATIONAL INC.
Application year: 1993
Main classification: A61F2
IPC codes: A61F2