This invention relates to a femoral prosthesis for use in an artificial hip joint, and to a method of making a femoral prosthesis.

A femoral prosthesis for use in an artificial hip joint is disclosed in GB-1510968. The prosthesis comprises a stem at its distal end for insertion into the medullary cavity of the femur of a patient, and a part-spherical head at its proximal end for engaging the acetabulum of the patient, the stem and head being connected by a neck. Adjacent the neck, the stem has a curved portion which has two laterally extending flanges, one on each side of the stem, by which escape of acrylic cement, provided in the medullary cavity around the stem of the prosthesis, is controlled when the stem is inserted into the cavity, and through which the weight of a patient can be transferred onto cement in the upper half of the medullary cavity.

The prosthesis is generally introduced into the medullary cavity after removal of the trochanter from the femur, and after the cavity has been packed tightly with an acrylic cement. It is common for the two flanges to be symmetrical with respect to the stem of the prosthesis in order that each prosthesis might be considered for use in either left or right hip, in order to minimise the number of parts which it is necessary to manufacture and to stock. However, the cavity within which the stem of the prosthesis is received is not symmetrical when viewed laterally, so that the posterior flange on the prosthesis tends to cause the prosthesis to be forced forward during installation and subsequent use.

It is essential for an osteoprosthesis to have precisely the right configuration to be engage other existing joint components of a patient. In the context of prostheses for hip joints, it is necessary to provide a range of components in order to accommodate variations in the configurations of femurs. The required large inventory of components increases

the cost and complexity of providing suitable prostheses, and inventory is minimised in some part by use of flanged components in which the flanges provided on the stem are symmetrical.

The present invention provides a femoral prosthesis which comprises modular components; a primary component is for insertion into the medullary cavity of a femur, and a secondary component slidingly engages the primary component by means of a cooperating rib and groove.

Accordingly, in one aspect, the invention provides a femoral prosthesis which comprises:

(a) a primary component comprising a proximal portion through which the component engages the acetabulum, and a distal portion for insertion into the medullary cavity of a femur, and

(b) a secondary component which engages the first component between the proximal and distal portions thereof;

one of the first and second components bearing a rib which is narrower at its base than at a point above its base when viewed in cross-section, and the other bearing a groove which has a cross-sectional configuration corresponding to that of the rib, the rib or groove on the primary component extending in a direction from the distal.portion thereof towards the proximal portion so that the primary and secondary components can be attached to one another by sliding the components relative to one another in the said direction to locate the rib in the groove.

The technique of the invention has the advantage that prostheses can be constructed easily and conveniently from a range of components to suit accurately the requirements of a

particular patient, or to be suitable for use in a surgical technique selected by the surgeon. For example, the primary component of the prosthesis of the invention may adapted for use with cement by use of a secondary component which incorporates flanges, or for use in a cementless technique by use of a secondary component which includes a collar to fit around the stem of the primary component, and then to fit on the cut upper end of a femur. The present invention therefore allows prostheses to be adapted to suit individual requirements, without the need to provide a large inventory of separate prostheses.

The primary component will generally have a curved portion. The convex curved surface of the component will generally be the superior surface. The component will generally have flat surfaces on each side of the curved surface as its anterior and posterior surfaces. The rib or groove, as the case may be, provided on the primary component preferably extends along a shoulder on that superior surface between the distal and proximal portions of the component. It may be generally linear, for example as a result of being cut into the surface, or it may be curved following the contours of the surface.

The use of a cooperating rib and groove, with the rib or groove on the primary component extending in a direction from the distal portion towards the proximal portion, allows the two components of the prosthesis to be attached to one another securely, in such a way that force can be transmitted between the components generally without risk of the connection between the components working loose during use of the prosthesis. It has been found that the provision of a rib or a groove on a shoulder on the superior surface of the primary component of the prosthesis does not detract from the load bearing abilities of the finished prosthesis compared with existing conventional prostheses. Furthermore, it has been found particularly significantly that the provision of a rib or groove on a shoulder on the superior surface of the primary component

ensures that that component is not weakened by the formations provided for engagement with the secondary component.

For ease of manufacture, it will generally be preferred for the rib to be formed on the primary component, and for the groove to be formed in the secondary component.

The primary component of the prosthesis may comprise a part spherical head which engages the acetabulum of a patient (or a prosthetic liner located within the acetabulum) directly, or it may be arranged to receive a part such as such a head, for example by means of a spigot and socket arrangement, and to engage the acetabulum indirectly through that part.

The secondary component of the prosthesis may provide at least one flange which extends anteriorly or posteriorly of the primary component. The flange or flanges can serve to control flow of cement in the medullary cavity of a femur when fitting the prosthesis, and can serve to transmit weight of the patient onto cement in the upper half of the medullary cavity. It has been found to be particularly attractive for the secondary component to provide a pair of flanges which extend anteriorly and posteriorly respectively of the primary component when the components are attached to one another. Preferably, the anteriorly extending flange extends from the primary component, when the two components are attached to one another, to a greater extent than the posteriorly extending flange. In this way, the asymmetry of a femur can be accommodated in the prosthesis to avoid the. prosthesis assuming an incorrect position in the cavity. The prosthesis of the invention can therefore be fitted accurately and used in either left or right hip joints, simply by selecting an appropriate secondary component.

The prosthesis of the invention has the further advantage that components of it can be formed from different materials, so that the characteristics of the components can be optimised for

the purposes which they have to serve. For example, the primary component of the prosthesis must be capable of transmitting loads from the acetabulum to the femur, without fracturing or bending. Preferred materials for the primary component include titanium alloys, cobalt-chrome alloys, certain stainless steels, and certain composite materials. The secondary component, on the other hand, can be required to fulfil any of a number of purposes, depending for example on the surgical technique which is selected by the surgeon, and materials will be selected accordingly. For example, it can be preferable for the secondary component to be formed from a polymeric material. The use of such a material has the advantage that the component can be formed by techniques which are applicable to the manufacture of polymeric components, which are significantly less expensive and more convenient to operate than techniques which are applicable to the formation of components from metallic materials. For example, components can be formed by moulding techniques, for example by injection moulding. Furthermore, it can be arranged by use of a suitable material for the second component for the surgeon to adapt the second component to suit a particular patient by trimming the component to a desired shape prior to use.

It can be preferred for some applications to fabricate at least one of the components from a shape memory alloy which exhibits a shape memory effect. A shape memory alloy article can be supplied in a first configuration in which it remains until the temperature of the article exceeds that at which the alloy begins to transform from the martensite phase to the austenite phase. As a result of appropriate working of the article, the phase change can be accompanied by a change in configuration of the article. Shape memory alloys can be based on, for example, alloys of nickel and titanium, optionally with other elements such as copper, iron, niobium and vanadium.

It can be particularly preferred for the secondary component to be made from a shape memory alloy. The component can be

supplied in a first configuration in which it can be engaged with the primary component. The temperature of the secondary component can then be increased to a temperature at which the phase of the alloy changes from the martensite phase to the austenite phase, to cause the configuration of the component to change to one in which the attachment is made more secure. For example, when the rib is provided on the primary component and the groove on the secondary component, the secondary component may be made to recover on heating so that the groove closes, to engage the rib more securely.

One of the primary and secondary components of the prosthesis may be provided with formations for fixation thereto of tissue. Generally, the component which is provided with the formations will be the secondary component. For example, the secondary component may be provided with formations such as apertures or notches to which tissue such as ligaments or muscle tissue can be attached by means of sutures. In this way, a prosthesis can be provided which obviates the need to reattach the trochanter, with its attached muscles, to the femur after location of the prosthesis in the medullary cavity of the femur; the muscles can be attached directly to the prosthesis.

One of the first and secondary components may be provided on its outer surface with a porous material which facilitates the ingrowth of tissue to form a connection between the tissue and that component. Generally the component which is provided with the porous material will be the secondary component. For example, a coating may be-provided on a component formed from an alloy such as a cobalt-chrome alloy by a layer of a metallic material which is applied by means of a plasma spray or by sintering metal beads or wires. Products to which a porous layer has been applied by sintering metal beads are sold under the trade mark Porocoat. Other materials which can be used to form the porous layer include hydroxylapatite. The formation of the prosthesis of the invention from two components, which can be formed from different materials, allows prostheses to be

made conveniently with such surface layers.

The secondary component may include a collar, which extends at least partially around the primary component, for engaging the cut end of a femur to locate the prosthesis on the femur. The collar may be provided on a secondary component which also has one or more flanges extending from it, for use in a medullary cavity which contains cement. However, the use of a secondary component which includes a collar allows the prosthesis to be used in applications without cement.

The cross-section of the rib and the groove will generally correspond to the extent that the rib can fit into the groove by sliding the rib into the groove, so that the rib cannot be removed from the groove other than by reversing the sliding action, at least when fully inserted into the groove. To this end, the rib is narrower at its base than at a point above its base when viewed in cross-section and the groove has a corresponding cross-section which may be substantially identical. A preferred example of such a cross-section is a dove-tail cross-section, in which the rib (and preferably also the groove) flares gradually outwardly from a point at or towards its base towards a point above its base. Another suitable rib might be one with a T-shaped cross-section.

It is important that there is no movement between the components of the prosthesis during use, since such movement can cause fretting, leading to the creation of small particles which can cause wear of -the joint, and therefore interfere significantly with movement of the joint. Such movement may be prevented by means of a cotter positioned between the rib and the groove, which is contacts the rib and the groove when the components are assembled. An assembly of components of a prosthesis which are assembled in this way is disclosed in the application which claims priority from UK patent application no. 9122936.9, filed with the present application, bearing agents' reference P21249. Subject matter disclosed in the

specification of that application is incorporated in the specification of the present application by this reference.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a side elevation of a primary component of a prosthesis according to the invention;

Figures 2 (a) to (c) are cross-sections through the component shown in Figure 1, along the lines a-a, b-b and c-c respectively;

Figure 3 (a) is an isometric view of a secondary component of a prosthesis according to the invention, and Figures 3 (b) and (c) are an end elevation and a view from below of that component ;

Figure 4 is a side elevation of a prosthesis which comprises the primary component shown in Figure 1 and the secondary component shown in Figure 2;

Figure 5 is a cross-section through the prosthesis shown in Figure 4;

Figure 6 is a cross-section through an additional embodiment of prostheses; and

Figures 7 (a) and (b) are respectively a side elevation of and a cross-section through a prosthesis which comprises the primary component shown in Figure 1 and a secondary component which provides a flange for soft tissue attachment.

Referring to the drawings. Figures 1 and 2 show a primary component 2 of a femoral prosthesis for a hip joint, which

comprises a first portion 4 which is tapered for insertion into the medullary cavity of a femur. The component has a part- spherical head 6 at its proximal end for engaging the acetabulum of a patient.

The primary component has a curved portion 8 which provides a shoulder, on which there is provided a rib 10. The rib is straight by being cut into the primary component, and it is narrower at its base than at a point above its base when viewed in cross-section, having a generally dove-tailed cross-section. As can be seen from Figure 2, the rib is deeper at one end 12 than at its other end 14.

Figure 3 shows a secondary component 20 which has formed in it a groove 22, the cross-section of the groove being dove-tailed, to correspond approximately to that of the rib 10 on the primary component, but for the fact that the depth of the groove is substantially constant from one end thereof towards the other end. A cotter may be provided in the groove, as disclosed the application which claims priority from UK patent application no. 9122936.9, filed with the present application, bearing agents' reference P21249.

The secondary component has two laterally extending flanges 26, 28, one on each side of the groove 22,

Figures 4 and 5 shows the primary and secondary components of the prosthesis after they have been assembled, by sliding the groove 22 on the secondary component 20 onto the rib 10 on the primary component 2. The reduction in the depth of the rib along its length gives rise to a reduction in the space between the rib and the groove so that, as the rib is progressively received in the groove, a tapered cotter 30 in the space contacts the opposed surfaces of the rib and the groove to make the connection between the two components secure.

When the secondary component has been positioned on the primary

co ponent, the flanges 26, 28 extend laterally of the primary component, anteriorly and posteriorly respectively, so that they can control flow of cement located in the medullary cavity of a femur, when the tapered end of the primary component is inserted into the cavity. The flanges can also serve to transfer the weight of a patient onto cement in the upper half of the medullary cavity.

Figure 6 shows a prosthesis in which the secondary component is provided with flanges 32, 34 which are asymmetrical, in that the anteriorly extending flange is larger than the posteriorly extending flange. A prosthesis which has asymmetrical flanges of this type has the advantage that it is adapted to be received in a femur accommodating the differences between the left and right femurs.

Figures 7 (a) and (b) show a prosthesis in which the secondary component is provided with a flange 36, extending in the generally superior direction. The flange has apertures 38 extending through it for attachment to it of tissue, for example for attachment of the trochanter, by means of sutures.