IMPROVEMENTS IN ACETABULAR PROSTHESES

Abstract: In the surgical operation of total hip replacement an acetabular prosthesis is inserted into an acetabulum in the human pelvis and a mating femoral component is inserted in the femur. One of the major problems after such an operation is the danger of dislocation of the hip as a result of particular movements of the subject. This invention provides an acetabular prosthesis (1) including an outer surface (2), a femoral head receiving surface (3) and a face (4) which joins the edges of the two surfaces (2, 3), the femoral head receiving surface (3) being a blind bore extending from the face (4) towards the outer surface (2) along an axis (8) which is at an angle to the normal (9) to the plane defined by at least a major portion of the edge of the outer surface (2).

Description: IMPROVEMENTS IN ACETABULAR PROSTHESES This invention relates to improvements in acetabular prostheses used in artificial hip joints. In the surgical operation of total hip replacement, an acetabular prosthesis is inserted into an acetabulum in the human pelvis and a mating femoral component is inserted in the femur. After such a hip replacement operation one of the major problems is the danger of dislocation of the hip normally as a result of particular movements of the subject. This is particularly common after a revisionary operation. According to this invention there is provided an acetabular prosthesis including an outer surface, a femoral head receiving surface and a face which joins the edges of these two surfaces, the femoral head receiving surface being a blind bore extending from the face towards the outer surface along an axis which is at an angle to the normal to the plane defined by at least a major portion of the edge of the outer surface. Preferably the blind bore comprises a spherical part and a cylindrical part, the radius of the cylindrical part being the same as that of the spherical part, and the centre of the spherical part being on the axis of the cylindrical part. The axis of the cylindrical part lies at an angle to the normal to the plane defined by the major part of the edge of the outer surface. In many acetabular prostheses the face of the prosthesis lies on the plane defined by the edge of the outer surface, but in other prostheses the face is nonplanar and lies between the plane and the outer surface. Thus the acetabular prosthesis does not limit the range of movement of the femoral component but deters dislocation since the angled spherical surface together with the face form a lip which serves to increase the distance through which the femoral head has to rotate before coming out of the blind bore, Preferably the prosthesis is mounted in the pelvis such that the direction of the plane in which dislocation is more likely to occur is aligned with the axis of the blind bore forming the femoral head receiving surface. In this position the position where the lip is greatest is aligned with the plane in which dislocation is most likely to occur. The angle between the axis of the cylindrical part of the femoral head receiving surface and the normal to the plane is limited by the cylindrical surface fouling the outer surface of the prosthesis when the angle is too 0 large. Preferably the angle is in a range 43 - 53.ego The most preferable angle is 48.50. Preferably the face of the prosthesis is chamfered to increase the range of movement of the femoral component. The centre of the circle surface may lie on the central axis of the prosthesis but may be offset to give an increased thickness between the femoral head receiving surface and the outer surface of the prosthesis at the point where most stress is applied. The prosthesis may not include a flange, but preferably does include a flange. The socket may be made of any suitable material, for instance high density polyethylene. An example of an acetabular hip prosthesis will now be described with reference to the accompanying drawings, in which: Figure 1 is a plan view of an acetabular prosthesis; Figure 2 is a side projection of the prosthesis; Figure 3 is a view of the outer surface of the prosthesis; Figure 4 is a section along the line A-A of Figure 1; and, Figure 5 is a section along the line B-B of Figure 1. A hip prosthesis 1 includes an outer surface 2, an inner femoral head receiving surface 3, a planar face 4 and an annular flange 5. The prosthesis 1 is made of high density polyethylene. The femoral head receiving surface comprises a spherical part 6 and a cylindrical part 7. The cylindrical part 7 has the same radius as the spherical part. The centre of the spherical part 6 lies on the axis 8 of the cylindrical surface 7. The central axis 8 is at an angle to the normal 9 to the plane containing the face 4 of 48.50. A lip 10 is formed between the edge of the spherical part 6 and the face 4 which deters dislocation of the femoral head component. The centre 13 of the spherical part 6 of the bore lies on the central axis 9 of the prosthesis. Grooves 11 are formed in the outer surface 2 of the prosthesis which are used to help attach the hip prosthesis to the human pelvis. A chamfer 12 is included in the face 4 to increase the range of moYement of the femoral component, the chamfer 12 lying substantially parallel to the axis 8 of the cylindrical surface. The prosthesis shown is a left-handed prosthesis in which the chamfer is at the left hand side of the axis 8. A right handed prosthesis would be of similar construction with the chamfer situated at the right hand side of the axis of the cylindrical surface.

Claims: CLAIMS: 1. An acetabular prosthesis including an outer surface (2), a femoral head receiving surface (3) and a face (4) which joins the edges of these two surfaces (2, 3), characterised in that the femoral head receiving surface (3) is a blind bore extending from the face (4) towards the outer surface (2) along an axis (8) which is at an angle to the normal (9) to the plane defined by at least a major portion of the edge of the outer surface (2). 2. An acetabular prosthesis according to claim 1, further characterised in that the blind bore comprises a spherical part (6) and a cylindrical part (7), the radius of the cylindrical part (7) being the same as that of the spherical part (6), and the centre of the spherical part (6) being on the axis (8) of the cylindrical part (7). 3. An acetabular prosthesis according to claim 2, further characterised in that the angle between the axis (8) of the cylindrical part (7) of the femoral head receiving surface C3) and the normal (9) to the plane is in the range 43-53.5 . 4. An acetabular prosthesis according to claim 3, further characterised in that-the angle between the axis (8) of the cylindrical part (7) and the normal (9) to the plane is 48.50. 5. An acetabular prosthesis according to any ones owe claims 2 to 4, further characterised in that the centre (13) of the spherical part (6) is offset from the central axis of the prosthesis to give an increased thickness between the femoral head receiving surface t3) and the outer surface (2) of the prosthesis at the point where most stress is applied. 6. An acetabular prosthesis according to any one of the claims 2 to 4, further characterised in that the centre t13) of the spherical part (6) lies on the central axis of the prosthesis. 7. An acetabular prosthesis according to any one of the preceding claims, further characterised in that the the face (4) joining the two surfaces (2, 3) lies on the plane defined by the edge of the outer surface (2). 8. An acetabular prosthesis according to any one of claims 1 to 6, further characterised in that the face (4) joining the two surfaces (2, 3) is non-planar and lies between the outer . surface (2) and the plane defined by the edge of the outer surface (2). 9. An acetabular prosthesis according to any one of the preceding claims further characterised in that the prosthesis is mounted in the pelvis such that the direction of the plane in which dislocation is most likely to occur is aligned with the axis (8) of the blind bore. 10. An acetabular prosthesis according to any one of the preceding claims further characterised in that the face t4) is chamfered. 11. An acetabular prosthesis according to any one of the preceding claims further characterised in that it includes a flange (5). 12. An acetabular prosthesis according to any one of the preceding claims further characterised in that it is made of high density polyethylene.

Inventors: WROBLEWSKI, BOGUSLAW MICHAEL
Applicants: CHAS F THACKRAY LIMITED
Application year: 1984
Main classification: A61F2
IPC codes: A61F2, A61B17