WO2012079618A1

WO2012079618A1 - An orthopaedic implant and an orthopaedic implant system incorporating same

Info

Publication number: WO2012079618A1
Application number: PCT/EP2010/069591
Authority: WO
Inventors: Stephanie Regula Margrethe Grassmann
Original assignee: Smith & Nephew Orthopaedics Ag
Priority date: 2010-12-14
Filing date: 2010-12-14
Publication date: 2012-06-21

Abstract

An orthopaedic implant (1, 2) is provided for use with or as part of an orthopaedic implant system. The implant (1, 2) comprises a supporting surface (6, 9) adapted for supporting engagement with a part of die orthopaedic implant system. The implant (1, 2) also comprises an outer surface defining a self-tapping thread (3) adapted for implantation of the implant (1, 2) directly into a bone cavity by screwing. Means (7, 8; 19) adapted for engagement of the implant (1, 2) by a tool are provided to enable the implant to be implanted by screwing. The implant (1, 2) is intended to prevent or to mitigate post-operative displacement (translation and rotation) of an implant system and, therefore, post-operative loosening of the system. The implant (1, 2) is primarily intended for use in long bones in the human or animal body. A set of such implants (1, 2) is also disclosed wherein each of said implants (1, 2) is adapted for supporting engagement with a different portion of the orthopaedic implant system. Likewise, an orthopaedic implant system comprising a first implant in the form of a stem adapted for implantation in a long bone and at least one implant (1, 2) is also disclosed.

Description

AN ORTHOPAEDIC IMPLANT AND

AN ORTHOPAEDIC IMPLANT SYSTEM INCORPORATING SAME

The present invention relates to an orthopaedic implant in particular, but not exclusively, for use in long bones in a human or animal body in combination with or as part of an orthopaedic implant system and to an orthopaedic implant system incorporating such an implant

The loosening of orthopaedic implants in sitti is one of the primary causes of their postoperative failure. This problem can be caused by axial rotation of the implant and/or by translation, which is movement of the implant longitudinally, typically caused by subsidence within the long bone. The problem has been addressed in several ways but typically by the use of projections in the form of fins, wings, spikes, or tines on the stem of the prosthesis proximal to the joint cavity. In US5755805 is described a prosthesis component that has longitudinally stepped ridges which cut into the cortical bone of the diaphysis of a bone canal when the component is implanted and thereafter resist post-operative movement of the prosthesis. In contrast, in EP0715835 is described an anchoring shaft having ribs with cutting surfaces in the form of saw tooth- shaped teeth. The ribs cut into the bone as the shaft is driven into a prepared bone cavity and again resist post-operative movement of the shaft

These conventional methods of minimising post-operative loosening of an implant have been designed by considering only the biomechanical characteristics of the long bone environment. They do not take into account the biological environment, for example the bone characteristics of particular patients. Nor do they offer the surgeon any options with regard to customized size, modularity or the possibility of using visco- clastic or flexible/pliable materials that may be more suitable for use in some patients. Due to severe bone loss or inferior bone quality, some patients require revision orthopaedic implants to prevent early revision due to loosening. Revision implants are noticeably larger, bulkier, have more components and are more complex to implant than orthopedic implants for primary surgery, leading to lengthened surgical time and in some cases requiring the surgeon to remove additional tissue and/or add cement and/or bone grafts to allow for adequate fixation. The proposed implant may used in conjunction with primary surgical implants thereby eliminating in some cases the need foi these revision implants. The proposed implant may also, however, be used in conjunction with a revision implant system to provide additional stability and prevent loosening in severe cases.

It is an object of the present invention to provide an orthopaedic implant for use with or as part of an orthopaedic implant system that obviates or substantially mitigates post-operative loosening of the implant system and that can be adapted to take into account both the biomechanical and the biological characteristics of the environment into which it will be implanted.

According to a first aspect of the present invention there is provided an orthopaedic implant for use with or as part of an orthopaedic implant system comprising a supporting surface adapted for supporting engagement with a part of the orthopaedic implant system, an outer surface defining a self-tapping thread adapted for implantation of the implant directly into a bone cavity by screwing, and means adapted for engagement of the implant by a tool to enable the implant to be implanted by screwing.

The implant according to the invention is designed to act as a 'stopper' implant that is implanted in the cavity of a long bone to prevent or reduce the post-operative loosening or abnormal subsidence/translation of an orthopaedic implant system implanted in conjunction with it by preventing rotation of the implant system and/or by preventing translation of the system caused by subsidence within the bone. With regard to the prevention of translation of the system, it should be appreciated that in some embodiments the supporting surface may not engage any part of the implant system unless abnormal translation of the latter occurs when contact with the supporting surface is designed to prevent further translation occurring. The supporting surface is, therefore, adapted to provide a support without, necessarily having to actual provide this support in all cases.

Preferably, the implant comprises a component with said supporting surface at a proximal end thereof. Preferably also, said supporting surface comprises a transverse end surface adapted to engage a stem forming part of said orthopaedic implant system.

Preferably also, said supporting surface is defined by the surface of an aperture into which said stem is located.

Preferably also, said aperture has a non-rotational transverse profile. Advantageously, the aperture has a rectangular, a square, a triangle, a trapezoidal, or a rhombic profile, or has a circular profile with ribs, or an oval profile with or without ribs.

Preferably also, said aperture extends axialry along the full length of the implant

Preferably also, said aperture tapers in a distal direction.

Preferably also, said means comprises an end recess defining radial cut-outs into which an end of said tool is engageable.

AlternanVery, said means comprises a plurality of longitudinally extending holes into which parts of said tool are engageable.

Preferably also, the self-tapping thread is interrupted by a groove or recess that enables bone chip breaking and/or tissue collection when screwing the implant during implantation.

Preferably also, the implant defines at least one aperture into which a fastener or pin is located to restrict the movement of implant after implantation.

Preferably also, the implant defines a cavity in which is located a spring means adapted to expand after implantation to engage surfaces of said bone cavity. In some embodiments the cavity is cylindrical and a compressed helical spring or a leaf spring is located therein and adapted for manual expansion during implantation. Alternatively or in addition, said leaf spring is part of an elliptical leaf spring arrangement adapted to expand radially until restrained by bands that cooperate with the hook arrangements attached to the springs.

Preferably also, the implant is comprised of bio-compatible materials including any or a mixture of any of the following, namely titanium, titanium alloy, stainless steel, stainless steel alloy, cobalt chrome alloy, a polymer, a polymer composite, a ceramic, a ceramic composite, and a metal composite.

Preferably also, the implant comprises or is comprised of any or a combination of a viscoelastic material, a natural or artificial bone graft or a bioabsorbable material.

Preferably also, the self-tapping thread has a cutting dp made from ceramic or a ceramic composite material or a biocompatible metal or metal composite or a polymer composite.

Preferably also, said implant is comprised of a flexible or pliable or viscoelastic or shape-memory material whereby it may change its shape in response to its biological environment, to its material property, to engagement by the orthopaedic implant system, or by manipulation.

Preferably also, said implant is adapted for use with or as part of an orthopaedic implant system for a long bone.

Preferably also, said implant is adapted for supporting engagement with a stem of a prosthesis for implantation in any of a hip joint, a knee joint, an ankle joint, a toe joint, a shoulder joint, an elbow joint, a wrist joint, a hand joint, and a finger joint

According to a second aspect of the present invention there is provided a set of implants each according to the first aspect of the present invention, wherein each implant is adapted for supporting engagement with a different portion of the orthopaedic implant system. According to a third aspect of the present invention there is provided an orthopaedic implant system comprising

a first implant in the form of a stem adapted for implantation in a long bone; and

at least one second implant comprising a supporting surface adapted for engagement with said stem, an outer surface defining a self-tapping thread adapted for implantation of the second implant directly into a bone cavity by screwing, and means adapted for engagement of the implant by a tool to enable the implant to be implanted by screwing.

Preferably, said implant system comprises a plurality of said second implants each adapted to engage a different portion of said stem.

Preferably also, said second implants each define an aperture through which said stem passes, the dimensions of said aperture conforming to the dimensions of that portion of the stem with which the implant is adapted to engage. Preferably also, said apertures have a non-rotational transverse profile. Advantageously, the apertures have a rectangular, a square, a triangle, a trapezoidal, or a rhombic profile, or have a circular profile with ribs, or an oval profile with or without ribs.

Preferably also, said aperture of each of the second implants tapers in a distal direction.

Preferably also, said implant system comprises a plurality of said second implants and an additional impknt that is adapted to engage a distal tip of said stem.

Preferably also, said additional implant defines a supporting surface or blind aperture that is adapted to engage the distal tip of said stem.

Preferably also, an additional component is provided that is adapted to engage said second implant and comprises means adapted to restrict movement of said second implant. Preferably also, the additional component has an outer surface adapted to restrict movement of said second implant by the provision of longitudinal cutting ribs or wings.

Preferably also, the additional component is adapted to engage said second implant by the provision of a projection that locates in an end recess defined by said implant Alternatively, the additional component is adapted to engage said second implant by the provision of one or more fasteners that engages said implant or by a spring-holding mechanism.

Other preferred but non-essential features of the various aspects of the present invention are described in the dependent claims appended hereto.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which: Figs. 1 and 2 are respective plan views of first and second embodiments of implants in accordance with the present invention; Fig. 3 is a side view of either of the embodiments shown in Figs. 1 and 2; Fig. 4 is cross-sectional view along the line IV-IV in Fig. 1; Fig. 5 is a cross-sectional view along the line V-V in Fig. 2; Fig. 6 is a cross-sectional view of the first embodiment of implant shown in Figs. 1 and 4 but with modifications; Fig. 7 is a view similar to Fig. 6 but showing slightly different modifications; is a schematic plan view of a spring arrangement for use in combination with cither of the implants shown in Figs. 1 and 2; Fig. 9 is a side view of the spring arrangement shown in Fig. 8 in an unexpended state; Fig. 10 is a plan view of part of the spring arrangement shown in Figs. 8 and 9 when in an expanded state; Fig. 11 is a plan view of an additional component for use in conjunction with either of the first and second embodiments of implants detailed above; and Fig. 12 is a side view of the component shown in Fig. 11.

Implants 1, 2 as shown respectively in Figs, 1, 3 and 4 and in Figs. 2, 3 and 5 are designed for implantation into a cavity of a long bone, typically the femur, to prevent or to limit the movement of a subsequently implanted system such as a hip joint prosthesis or similar in other long bones such as those of a knee joint, an ankle joint, a toe joint, a shoulder joint, an elbow joint, a wrist joint, a hand joint, and a finger joint The implant 1, 2 is screwed into the bone defining the cavity and thereby anchored into place so that it can then engage with the implanted system, which may not incorporate any other means designed to prevent or to limit post-operative axial rotation and/or translation

Both illustrated implants 1, 2 comprise a cylindrical, disc-shaped component but in other embodiments the implant may be conkal. Both have an outer surface defining a self-tapping thread 3, as shown in Fig. 3, adapted for implantation of the implant 1, 2 directly into a bone cavity by screwing. The profile and length of the thread 3 may be customized dependent on the type of bone that the implant 1, 2 will come into contact with during implantation and post-operatively, for example osteoporotic bone. In particular, the design of the thread 3 is such that it enables a surgeon to locate the implant 1, 2 by screwing it directly into a bone cavity using either manual or power tools. The thread 3 therefore engages the inner bone surface, which may be cancellous or corticalis or both, following implantation. Preferably, the thread 3 is interrupted by a groove or recess 4 that enables bone chip breaking and/or tissue collection when screwing the implant 1, 2 during implantation.

Referring now particularly to the first embodiment of implant 1 shown in Figs. 1, 3 and 4, this implant 1 comprises a proximal end 5 that is adapted for supporting engagement with a part of the orthopaedic implant system by means of an aperture 6. In this embodiment the aperture 6 extends axially all the way through the implant 1 but it is envisaged that is some embodiments the aperture 6 could be blind. The aperture 6 need not be axial but in some embodiments could be offset from the longitudinal axis of the implant 1. The aperture 6 has a transverse profile complementary to a the stem of a blade (not shown) of a subsequently implanted system such as a femoral stem of a hip joint prosthesis. The stem is intended to be located into the aperture 6 during implantation. Typically, the stem will have a non-rotational transverse profile, such as a rectangular, a square, a triangle, a trapezoidal, or a rhombic profile, or has a circular profile with ribs, or an oval profile with or without ribs. In the illustrated embodiment, implant 1 is provided with an aperture 6 having a rectangular profile that tapers from the proximal end 5 towards the distal end of the implant 1 to mirror the profile of a stem so that the stem may have a snug fit within the aperture 6. This means that not only will the implant 1 support the stem but it will restrict movement of the stem either intra- or post- opera tively.

The aperture 6 is a through-hole that extends through the full length of the implant, which allows some tolerance regarding the relative implanted position of the implant 1 with regard to the stem. However, a major reason for the through-hole is that a plurality of implants 1 may be implanted in a spaced series into a single bone cavity in order to support a stem of an implant along the whole or a major part of its length. As the transverse size of the stem of the impknt may vary along its length and in particular may taper towards the distal tip, a set of implants 1 may be provided with apertures 6 which similarly vary in size. The diameter of the implants 1 may also vary as required. Also, the implant 1 used at the distal end of the stem, may be provided with a blind aperture 6 in the form of a socket to support the distal end of the stem. In older to enable implantation of the implant 1, a means is provided whereby the implant is adapted for engagement by a tool to enable it be implanted into a bone cavity by screwing. This means comprises a proximal end recess 7 that defines radial cut-outs 8 into which an end of the tool is engageable. Typically, the tool will comprise a clutch with a cross-brace that fits into the recess 7 and cut-outs 8 whereby the implant 1 can be screwed into position within the cavity in a long bone. Once located, the surgeon can then proceed with the implantation of the orthopaedic system that is to engage with the implant 1.

It will be appreciated that after implantation of the orthopaedic system, the implant 1 will resist translational movement of the system longitudinally within the bone cavity as the threads 3 firmly engage the inner bone surface and the tapering aperture 6 will prevent significant translational movement of the stem of the implant system relative to the implant 1. Similarly, the component implant 1 will resist rotational movement of the system 1 owing the non-rotational profile of the aperture 6. The implant 1 therefore resists both forms of movement to reduce the likelihood of post-operative loosening of the implant system.

Turning now to the second embodiment of implant 2 shown in Figs. 2, 3 and 5, this has a different design of a proximal end that is adapted only for supporting engagement with a part of the orthopaedic implant system and that comprises a recess 7 and a simple transverse supporting surface 9 against which the distal tip of a stem (not shown) of a subsequendy implanted system such as a femoral stem of a hip joint prosthesis is able to engage. Hence, this embodiment of implant 2 is only designed to resist movement or abnormal subsidence of the system longitudinally within the bone cavity. The implant 2 may be used in conjunction with the implant 1 or a ribbed/winged additional component as part of a set, the implant 2 being implanted in a cavity in a long bone beneath the distal tip of an implant system and one or more implants 1 being implanted part way along the cavity to support portions of the stem of an implant system at one or more positions intermediate its length. In this case, the additional component has an aperture large enough for the stem to travel through it The aperture may be tapered. In addition, both of the implants 1 and 2 may be adapted by the addition of an external geometry or other components in the form of one or more radial projections such as fins, pins, tines or the like so that they will resist rotational movement after implantation. Both implants 1 and 2 may have apertures 10 (see Fig. 4) for fasteners which would enable the fasteners to connect implants 1 and 2 to the bone. Such fasteners may comprise screws or pins that are driven into the immediate osseous walls to further restrict the movement of the implant 1, 2 ox the whole implant system. These rotation limiting design features may be customized to take into account the implant system with which the implant 1, 2 is to be used as well as the planned position of the implant 1, 2.

The implants 1 and 2 may also be modified by the addition of one or more springs to further stabilize the implant system within a bone cavity. As shown in Figs. 6 to 10, the implant 1 may comprise a cylindrical cavity 11 in which is located a compressed helical spring 12 (Fig. 6) or a leaf spring 13 (Fig. 7) or a leaf spring arrangement 15 (Fig. 8, 9, 10). The springs 12, 13 and the leaf spring arrangement 15 expand out of the cavity 11 to provide a fit and fill mechanism within the bone cavity after implantation. Alternatively, these springs 12, 13, 15 may reside within the recess 7 of the implant In another variation, the implant 1, 2 may have define a cavity with one or more grooves on its exterior profile in which is compressed the leaf spring arrangement 15 that comprises an elliptical leaf spring 15a retained by bands 14 and hook arrangements 15b, as shown in Figs. 8 to 10. These springs 12, 13, 15a are pushed against and compressed within the inner cylindrical wall of the grooves of the implant 1 prior to implantation. Following fixation of the implant, the surgeon via one or more radial slots can manually push the springs 12, 13, 15a so that they expand to extend out of the implant and press against the inner walls of the bone cavity. In the case of the spring arrangement 15, the springs 15a expand radially until restrained by the bands 14 that cooperate with the hook arrangements 15b attached to the springs 15a as shown in Fig. 10. The surgeon can also pull springs 12, 13 and the spring arrangement 15 via access through one or mote radial slots or through aperture 6. The implant 2 may also be provided with similar spring mechanisms. An additional component 16, as shown in Figs. 11 and 12 may also be provided. This component 16 has a projection 17 at one end that is dimensioned to fit into the recess 7 of the implants 1 and 2, the outer diameter of the component 16 being dimensioned to correspond closely with that of implant 1, 2, being in some cases slightly smaller or larger to correspond to the bone cavity geometry. The outer surface of the component 16 is provided with cutting longitudinal ribs or wings 18, for example like a Wagner or ADR stem, to engage the walls of the bone cavity, and serves to further restrict axial rotation. The cutting ribs 18 may run the whole length of the component 16, as shown in Fig. 12, or run only partially along the length of the component 16. They may also be continuous or interrupted on their length. The component 16 is in the form of a disc or a cylinder, which may be hollow or partially hollow. Its inner geometry enables manual implantation or implantation through existing instrumentation or power tools and if necessary the inner geometry also enables this component to be removed during revision surgery. The inner geometry may also match closely the implant 1 and the implant 2 so that there is a snug fit between the components. Both the component 16, the implant 1 and the implant 2 may have more than one aperture to secure the components together with one or more fasteners after implantation. The component 16 may be implanted by being hammered into the bone cavity prior to or following the implantation of implants 1, 2. It is attached to the implant 1 or 2 either above or below (distal or proximal to the joint space) through one or more means, namely one or more fasteners; a press-fit into the contacting profile of implant 1, 2 as described above; or a spring-holding mechanism that is actuated when the components come into contact, for example when the component 16 is hammered into the implant 1, 2. A combination of these means may also be used.

Mote generally, therefore, an implant 1, 2 in accordance with the invention may be positioned proximal or immediate to an orthopaedic implant system. It may surround a part of the implant system with or without contact therewith, the contact or engagement only arising should the implant system suffer post-operative loosening or abnormal subsidence/translation when the implant 1, 2 will act to limit movement of the system and to prevent worsening of its loosened state. It will be appreciated that the degree to which the implant 1, 2 will do this can be predetermined by a surgeon when the implant 1, 2 is initially located in a cavity of a long bone relative to the intended location of the implant system itself.

In order to enable implantation of the implant 2, a means is provided whereby the implant is adapted for engagement by a tool to enable it be implanted into a bone cavity by screwing. This means could be similar to that described above with reference to the implant 1, the surface 9 comprising the bottom of the recess 7. Alternatively, as shown in Figs. 2 and 5, the means comprises a plurality of longitudinally extending holes 19 into which parts of the tool are engageahle to enable the implant 2 to be implanted into a bone cavity by screwing. Such a means 19 could be also used with the first embodiment of implant 1 in preference to the recess 7 and cut-outs 8 in some embodiments.

The implants 1 and 2 are manufactured from bio-compatible materials, which may include any or a mixture of any of the following, namely titanium, titanium alloy, stainless steel, stainless steel alloy, cobalt chrome alloy, a polymer, a polymer composite, a ceramic, a ceramic composite, and a metal composite. The thread 3 may comprise or have a cutting tip made from the same or a different material from the rest of the implant 1, 2 and may comprise any hard biocompatible material enabling the implant to have self-cutting properties to cut bone.

In some embodiments the implants 1, 2 may be made from biocompatible flexible or pliable material whereby it may change its shape during or after implantation in response to its biological environment and to fit the geometry of an inner bone cavity by allowing the impknt 1, 2 or part of it to change its shape and/or diameter. In particular, such an implant 1, 2 may adopt a non-circular profile after implantation that will act to prevent or reduce loosening of the implant 1, 2 by post-operative rotation. In this case, the thread 3 may have a cutting tip made from ceramic or a ceramic composite material or a biocompatible metal or metal composite or a polymer composite.

The implant 1, 2 may also comprise or be comprised of a viscoelastic material, in particular such a material that has similar viscoelastic properties to the osseous environment into which the implant 1, 2 is intended to be used. This material may be coated with a biocompatible hard material Le. ceramic or metal

It is also possible to adapt the implant 1, 2 so that it can expand following implantation by means of intrinsic or extrinsic influences, for example when contacted by part of a orthopaedic implant system. Such an implant 1, 2 may have at least a part made from a shape memory material so that it will adopt a different shape when triggered to do so after implantation, for example by the application of heat

It will be appreciated that an implant 1, 2 in accordance with the present invention is not limited only to the illustrated forms of implant and the principles described above can be adapted for use in implants designed for implantation in any long bone such as leg, arm, finger and toe bones. It may also be possible to adapt the implants for use in other bones in die same way.

The implants 1, 2 either individually or as components of a set or a modular implant system may be made available in different lengths and geometries including thickness and cross-sectional shape, according to the characteristics of the patient, the patient bone or the requirements of the surgical procedure. Any of the following external geometries are possible, namely disc shaped or cylindrical ( as illustrated), egg shaped, conical, hour-glass shaped, funnel shaped, toroidal, spherical, spiral. Similarly, the implant may have any of a variety of internal geometries and define apertures, spokes, planar resections and the like as appropriate. In particular, the external geometry of the implant can be adapted to match that of the cavity into which it is to be implanted whereas the internal geometry of the implant can be adapted to match that of the implant system with which it is designed to co-operate.

It is also expected that components which respectively resist translational and rotational movement after implantation may be used in conjunction with the implants 1, 2 as part of an orthopaedic implant system. These other components may, fox example, take the form of screws and the like, such as described above, that are connected to the implants 1, 2 after implantation to engage the immediate osseous walls in addition to components such as the component 16 described above. The implants 1, 2 may, therefore, be provided with slots ot apertures to enable connection to or engagement by these other components.

In some embodiments, the implant may have, at least in part, a spiral or tubular design and/or be hollow or partially hollow. In particular, the implant may be adapted for the intra -operative or post-operative drainage of collected materials or the introduction of fluent materials, for example fluent materials that can be pumped through the implant 1, 2 for therapeutic purposes, the implant defining at least one channel for this purpose. Alternatively, the therapeutic materials, either in a fluid or solid state, may be located within or on the surface of the implant 1, 2 to aid healing and prevent infection after implantation.

The implant 1, 2 may also be designed for use in combination with cement or other implant fixation materials adapted to limit translational and/or rotational movement In particular, the implant 1, 2 may be used with implant systems for cement application, e.g. as a distal centralizer for cemented hip stems. The implant 1, 2 would then be used to hold the stem in position during curing of the cement

The surfaces of the implant 1, 2 and those of the implant system as a whole may be surface treated or surface roughened to assist the osteointegration of the implant This treatment may include, for example, adding surface layer(s) of titanium, hydroxyapatite, biocompatible phase-transforming material or other, pressure or grit blasting with zirconium oxide or other grit material(s). Alternatively, the surfaces of the implant 1, 2 may be produced with rapid prototype manufacturing procedures, Le. laser sintering.

In some embodiments, therapeutic material, either in fluid or solid state may be present within or on the surface of the implant 1, 2.

The implant 1, 2 may comprise or be at least parti ally comprised of a radiographic material or comprise a radiographic marker.

In another embodiment, the implant 1, 2 may enable an arthrodesis (fixed joint). The implant 1, 2 may comprise part of an implant system which is a short-term implant system, a long-term implant system or a trauma implant system. Mote generally, the design and geometry of the implant 1, 2 may be such as to enable the implant 1, 2 to be attached to various types of instrumentation during surgery, for example to retrieve or move the implant 1, 2 intra-operatively, for example during revision surgery, or to remove the implant 1, 2, for example for replacement

Hence, an orthopaedic implant in accordance with the invention obviates or substantially mitigates post-operative displacement (translation and rotation) of an implant system and thereby obviates or substantially mitigates post-operative loosening of the implant system. In addition, the self-tapping thread 3 of the implant has the further advantage that it enables bone to be conserved during the surgical implantation procedure.

Claims

Claims . An orthopaedic implant (1; 2) for use with of as part of an orthopaedic implant system comprising a supporting surface (6; 9) adapted for supporting engagement with a part of the orthopaedic implant system, an outer surface defining a self-tapping thread (3) adapted for implantation of the implant directly into a bone cavity by screwing, and means (7, 8; 19) adapted for engagement of the implant (1; 2) by a tool to enable the implant to be implanted by screwing. . An implant (1; 2) as claimed in Claim 1, comprising a component with said supporting surface (6; 9) at a proximal end thereof. . An implant (2) as claimed in Claim 1 or Claim 2, wherein said supporting surface (9) comprises a transverse end surface adapted to engage a stem forming part of said orthopaedic implant system. . An implant (1) as claimed in Claim 1 or Claim 2, wherein said supporting surface is defined by the surface of an aperture (6) into which said stem is located. . An implant (1) as claimed in Claim 4, wherein said aperture (6) has a non- rotational transverse profile. . An implant (1) as claimed in Claim 4 or Claim 5, wherein said aperture (6) has a rectangular, a square, a triangle, a trapezoidal, or a rhombic profile, or has a circular profile with ribs, or an oval profile with or without ribs. . An implant (1) as claimed in any of Claims 4 to 6, wherein said aperture (6) extends axially along the full length of the implant. . An implant (1) as claimed in any of Claims 4 to 7, wherein said aperture (6) tapers in a distal direction. An implant (1; 2) as claimed in any of Claims 1 to 8, wherein said means composes an end recess (7) defining radial cut-outs (8) into which an end of said tool is engageable. An implant (1; 2) as claimed in any of Claims 1 to 8, wherein said means comprises a plurality of longitudinally extending holes (1 ) into which parts of said tool are engageable. An implant (1; 2) as claimed in any of Claims 1 to 10, wherein the self-tapping thread (3) is interrupted by a groove or recess (4) that enables bone chip breaking and/or tissue collection when screwing the implant during implantation. An implant (1, 2) as claimed in any of Claims 1 to 11, that defines at least one aperture (10) into which a fastener or pin is located to restrict the movement of implant (1, 2) after implantation. An implant (1, 2) as claimed in any of Claims 1 to 12, that defines a cavity (11) in which is located a spring means (12, 13, 15) adapted to expand after implantation to engage surfaces of said bone cavity. An implant (1, 2) as claimed in Claim 13, wherein said cavity (11) is cylmdrical and a compressed helical spring (12) or a leaf spring arrangement (15) or springs (13, 15a) is located therein and adapted for manual expansion during implantation. An implant (1, 2) as claimed in Claim 13 or Claim 14, wherein said leaf springs (15a) are part of a leaf spring arrangement (15) and are adapted to expand radially until restrained by bands (14) that cooperate with hook arrangements (15b) attached to the springs (15a). An implant (1; 2) as claimed in any of Claims 1 to 15, that is comprised of biocompatible materials including any or a mixture of any of the following, namely titanium, titanium alloy, stainless steel, stainless steel alloy, cobalt chrome alloy, a polymer, a polymer composite, a ceramic, a ceramic composite, and a metal composite. An implant (1; 2) as claimed in any of Claims 1 to 16, that comprises or is comprised of any or a combination of a viscoelastic material, a natural or artificial bone graft or a bioabsorbabk material. An implant (1; 2) as claimed in any of Claims 1 to 17, wherein the self-tapping thread (3) has a cutting tip made from ceramic or a ceramic composite material or a biocompatible metal or a metal composite or a polymer composite. An implant (1; 2) as claimed in any of Claims 1 to 18, that is comprised of a flexible or pliable or viscoelastic or shape-memory material whereby it may change its shape in response to its biological environment, to its material property, to engagement by the orthopaedic implant system, or by manipulation. An implant (1; 2) as claimed in any of Claims 1 to 19, that is adapted for the intra -operative or post-operative drainage of collected materials or for the introduction of fluent materials. An implant (1; 2) as claimed in Claim 20, that defines at least one channel through which fluent materials is pumpable for therapeutic purposes. An implant (1; 2) as claimed in Claim 20 or Claim 21, wherein therapeutic materials, either in a fluid or solid state, are located within or on the surface of the implant 1, 2 to aid healing and/or prevent infection and/or fight off infection and/or cancer after implantation. An implant (1; 2) as claimed in any of Claims 1 to 22, that is adapted for use with or as part of an orthopaedic implant system for a long bone. An implant (1; 2) as claimed in any of Claims 1 to 23, that is adapted for supporting engagement with a stem of a prosthesis for implantation in any of a hip joint, a knee joint, an ankle joint, a toe joint, a shoulder joint; an elbow joint, a wrist joint, a hand joint, and a finger joint A set of implants (1; 2) each as claimed in any of Claims 1 to 24, wherein each of said implants (1; 2) is adapted for supporting engagement with a different portion of the orthopaedic implant system. An orthopaedic implant system comprising

at least one second implant (1; 2) comprising

a supporting surface (6; 9) adapted for engagement with said stem, an outer surface defining a self-tapping thread (3) adapted for implantation of the second implant directly into a bone cavity by screwing, and means (7, 8; 19) adapted for engagement of the implant by a tool to enable the implant to be implanted by screwing. An implant system as claimed in Claim 26, comprising a plurality of said second implants (1; 2) each adapted to engage a different portion of said stem. An implant system as claimed in Claim 26 or Claim 27, wherein said second implants (1) each define an aperture (6) through which said stem passes, the dimensions of said aperture (6) conforming to the dimensions of that portion of the stem with which the implant (1) is adapted to engage. An implant system as claimed in Claim 28, wherein said apertures (6) have a non-rotational transverse profile. An implant system as claimed in Claim 28 ox Claim 29, wherein the apertures (6) have a rectangular, a square, a triangle, a trapezoidal, or a rhombic profile, or has a circular profile with ribs, or an oval profile with or without ribs. An implant system as claimed in any of Claims 28 to 30, wherein the aperture (6) of each of the second implants (1) tapers in a distal direction. An implant system as claimed in any of Claims 26 to 31, comprising a plurality of said second implants (1) and an additional impknt (1; 2) that is adapted to engage a distal dp of said stem. An implant system as claimed in Claim 32, wherein said additional impknt (1; 2) defines a supporting surface (9) or blind aperture (6) that is adapted to engage the distal dp of said stem. An implant system as claimed in any of Claims 26 to 33, that enables an arthrodesis. An implant system as claimed in any of Claims 26 to 34, that comprises an arthroplasty implant or a part thereof. An implant system as claimed in any of Claim 26 to 35, adapted for implantation in a long bone. An implant system as claimed in Claim 36, wherein the first implant comprises a stem of a prosthesis for implantation in any of a hip joint, a knee joint, an ankle joint, a toe joint, a shoulder joint, an elbow joint, a wrist joint, a hand joint, and a finger joint An implant system as claimed in any of Claims 26 to 37, comprising an additional component (16) adapted to engage said second implant (1, 2) and comprising means adapted to restrict movement of said second implant (1, 2). An implant system as claimed in Claim 38, wherein the additional component (16) has an outer surface adapted to restrict movement of said second implant (1, 2) by the provision of longitudinal cutting ribs or wings (18). An implant system as claimed in Claim 38 or Claim 39, wherein the additional component (16) is adapted to engage said second implant (1, 2) by the provision of a projection (17) that locates in an end recess (7) defined by said implant (1, 2). An implant system as claimed in Claim 38 or Claim 39, wherein the additional component (16) is adapted to engage said second implant (1, 2) by the provision of one or more fasteners that engage said implant (1, 2) and/or by a spring- holding mechanism.