GB2365343A

GB2365343A - Joint socket

Info

Publication number: GB2365343A
Application number: GB0018847A
Authority: GB
Inventors: John Stephen Bradley
Original assignee: Individual
Current assignee: Individual
Priority date: 2000-08-02
Filing date: 2000-08-02
Publication date: 2002-02-20
Anticipated expiration: 2020-08-02
Also published as: GB2365343B; GB0018847D0

Abstract

An acetabular socket (7) comprising an outer shell (3) which is integral with an inner shell (4) by way of a bond, the socket being adapted to be inserted into the acetabulum with the outer shell in engagement with the hip bone, and the inner shell providing a bearing surface for the femoral stem. The socket is provided with keying means which comprises keying formations that inhibit withdrawal (7, 17) and tilting (12, 15) of the socket relative to the hip bone.

Description

<Desc/Clms Page number 1> JOINT SOCKET The present invention relates to joint sockets, and in particular to acetabular sockets for a femoral stem of an artificial hip joint.

According to the present invention there is provided an acetabular socket comprising an outer shell which is integral with an inner shell, the socket being adapted to be inserted into the acetabulum with the outer shell in engagement with the hip bone, and the inner shell providing a bearing surface for the femoral stem.

The outer shell is preferably bonded with the inner shell.

Preferably the outer shell and the inner shell are of generally hemispherical shape.

Preferably the outer shell comprises a plastics material.

Preferably the outer shell has a Young's Modulus of less that 40GPa. Preferably the inner shell comprises a ceramics material. The inner shell may alternatively comprise a metal.

The outer shell is preferably provided with keying means which, in use, engages with the acetabulum so as to restrict movement of the socket relative to the acetabulum.

The keying means preferably comprises first keying formations that inhibit withdrawal of the socket from the acetabulum.

The keying means preferably comprises second keying formations that inhibit tilting of the outer shell relative to the hip bone.

The keying means preferably comprises a relief configuration provided by the outer surface of the outer shell.

The invention will now be further described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a cross-sectional view on section 1-1 of a socket in accordance with the invention; Figure 2 shows a plan view of the socket shown in Figure 1; and Figure 3 shows an underside view of the socket shown in Figures 1 and 2.

Figure 1 shows an acetabular socket 1 comprising an outer shell 3 and an inner shell 4, the shells 3 and 4 being of generally hemispherical shape. The inner shell 4 is integral with the outer shell 3 by way of a physico- chemical bond between the two shells at the interface 18 therebetween which results from the moulding of the outer shell around the inner shell. The inner shell 4 is formed of ceramic material and comprises a smooth inner hemispherical surface 5. The surface 5 is dimensioned to accommodate the head (not shown) of a femoral stem (not shown) and the surface having suitably low friction and low wear characteristics.

The socket 1 is manufactured by placing the ceramic inner shell 4 into a moulding tool (not shown). The mould is then filled with carbon fibre filled polyetheretherketone so as to form the outer shell 3.

The outer margin of the inner shell 4 is provided with first keying means which comprises two vertically spaced coaxial annular grooves 20 and

21 which face horizontally outwards relative to the vertical central axis of the socket. The inner margin of the outer shell 3 comprises two associated inwardly extending circular projections 23 and 22 which fill the respective grooves 20 and 21.

The outer shell 3 further comprises an inwardly directed lip 25 which is located beneath the underside of the inner shell 4.

The outer shell 3 is formed from carbon fibre filled polyetheretherketone.

The outer margin of the outer shell is provided with two vertically spaced coaxial annular grooves 7 and 17, resulting in band portion 14 between the grooves 7 and 17 and lobe portion 13 which is located at the top of the outer shell 3. The grooves 7 and 17 face horizontally outwards relative to the vertical central axis of the socket.

The lobe portion 13 is provided with second keying means which comprises five equi-spaced circular recesses 12 and a circular recess 15 provided centrally thereof.

With reference in particular to Figures 2 and 3 there are provided nine equi-spaced circular bores 9 which extend through the outer margin of the outer shell 3. The socket 2 further comprises three circular bores 11 which extend through the outer shell 3 and the inner shell 4. The circular bores 11 are located at a radius which is between that of the apertures 9 and the recesses 12.

In use the socket 1 is inserted into the acetabulum of the patient. The tissues of the acetabulum engage with the relief provided by the grooves 7 and 17 of the outer shell 3 so as to provide frictional grip to secure the

socket in the acetabulum by restricting movement of the socket therefrom. In the medium term the grooves 7 and 17 allow for in situ bone ingrowth for increase stability.

Since in the inventive socket 1 the inner shell 4 is integral with the outer shell 3 the problem of the production of debris is eliminated. Production of debris is a problem which occurs with known socket assemblies comprising two shell components which are attached together at operation and which in situ allow interfacial motion of the inner shell and the outer shell (i.e. so-called 'micromotion') which generates wear debris at the interface therebetween which may be released into surrounding tissues. The outer shell of known sockets is conventionally made of metal which has a relatively high stiffness. The outer shell of the inventive socket, however, being formed of a plastics material has a relatively lower stiffness which results in a more favourable stress distribution to the hip bone.

The bores 9 allow a surgeon to incorporate fixation screws should a simple 'press fit' of the socket into the acetabulum provide insufficient stability.

The circular recesses 12 and 15 provide in the medium term a degree of anti-tilting stability by accommodating some bone ingrowth therein but also add a little elasticity to the structure of the socket 1.

The three bores 11 provide fixation points for an introducer tool for insertion of the socket into the acetabulum and similarly accommodate some bone ingrowth for improved in situ stability and also increase the elasticity of the socket.

It should be appreciated that the outer shell 3 may be coated with a biocompatible substance such as hydroxyapatite substance to promote bonding of the supporting tissue of the acetabulum with the socket 1. Furthermore, although the inventive socket is designed principally for fixation without the use of bone cement, bone cement may be used provided that the coating of hydroxyapatite is not used.

It should also be appreciated that the outer shell 3 may be formed of any suitable carbon fibre filled polymer or, as an alternative to the specific example described above, unfilled polyetheretherketone or a close chemical relative thereof may be used.

It should further be appreciated that the inner shell 4 may alternatively be formed from a suitable metal.

Claims

CLAIMS 1. An acetabular socket comprising an outer shell which is integral with an inner shell, the socket being adapted to be inserted into the acetabulum with the outer shell in engagement with the hip bone, and the inner shell providing a bearing surface for the femoral stem.
2. An acetabular socket as claimed in claim 1 in which the outer shell is bonded with the inner shell.
3. An acetabular socket as claimed in claim 1 or claim 2 in which the outer shell and the inner shell are of generally hemispherical shape.
4. An acetabular socket as claimed in any preceding claim in which the outer shell comprises a plastics material.
5. An acetabular socket as claimed in any preceding claim in which the outer shell has a Young's Modulus of less that 40GPa.
6. An acetabular socket as claimed in any preceding claim in which the inner shell comprises a ceramics material.
7. An acetabular socket as claimed in any of claims 1 to 6 in which the inner shell comprises a metal.
8. An acetabular socket as claimed in any preceding claim in which the outer shell is provided with keying means which, in use, engages with the acetabulum so as to restrict movement of the socket relative to the acetabulum.

<Desc/Clms Page number 7>
9. An acetabular socket as claimed in claim 8 in which the keying means comprises first keying formations that inhibit withdrawal of the socket from the acetabulum.
10. An acetabular socket as claimed in claim 9 in which the keying means comprises second keying formations that inhibit tilting of the outer shell relative to the hip bone.
11. An acetabular socket as claimed in any of claims 8 to 10 in which the keying means comprises a relief configuration provided by the outer surface of the outer shell.
12. An acetabular socket substantially as hereinbefore described with reference to the accompanying Figures.