Hip prosthesis with a modular acetabular cup assembly

1. A hip prosthesis comprising:

an acetabular liner including a hemispherical convex back and a face opposite the hemispherical convex back, the hemispherical convex back defining a polar region, a concave bearing surface extending into the liner through the face toward the polar region, a screw thread spiraling around a portion of the hemispherical convex back, the screw thread having a thread crest and a thread root, the thread crest following a spherical profile as it spirals around the hemispherical convex back toward the polar region; and

an acetabular shell including a hemispherical cavity for receiving the convex back the hemispherical cavity having a polar region, a screw thread spiraling around a portion of the cavity, the screw thread having a thread root following a spherical profile as it spirals around the cavity toward the polar region, the thread root being engageable with the thread crest of the liner screw thread.

2. The hip prosthesis of claim 1 wherein the liner thread root is coincident with the hemispherical convex back and the liner thread crest projects beyond the hemispherical convex back and follows a spherical profile spaced from the spherical convex back.

3. The hip prosthesis of claim 1 wherein the liner thread comprises a conical profile thread root and the acetabular shell cavity thread comprises a corresponding conical profile thread crest.

4. The hip prosthesis of claim 1 wherein the liner thread comprises a cylindrical profile thread root and the acetabular shell cavity thread comprises a corresponding cylindrical profile thread crest.

5. The hip prosthesis of claim 1 wherein the liner thread crest spirals-over most of the hemispherical convex back between the face and the polar region.

6. The hip prosthesis of claim 5 wherein the liner thread and shell thread comprise a self-locking arrangement in which a portion of the shell thread profile differs in a dimension from a corresponding portion of the liner thread profile, the shell thread and liner thread defining a self-locking thread interference.

7. The hip prosthesis of claim 1 further comprising a femoral prosthesis including a stem portion and a head portion, the head portion being matingly engageable with the concave bearing surface of the acetabular liner.

8. The hip prosthesis of claim 1 further comprising bone cement positionable between the shell and acetabulum to fix the shell in the acetabulum.

9. The hip prosthesis of claim 1 wherein, the liner thread crest is coincident with the spherical convex back and the liner thread root extends into the spherical convex back and follows a spherical profile spaced from the spherical convex back.

10. A hip prosthesis comprising:

an acetabular liner including a hemispherical convex back and a face opposite the hemispherical convex back, the hemispherical convex back defining a polar region, a concave bearing surface extending into the liner through the face toward the polar region, a screw thread spiraling around a portion of the convex back, the screw thread having a thread crest and a thread root, the thread root following a spherical profile as it spirals around the hemispherical convex back toward the polar region; and

an acetabular shell including a hemispherical cavity for receiving the hemispherical convex back, a screw thread spiraling around a portion of the cavity, the hemispherical cavity having a polar region, the screw thread having a thread crest following a spherical profile as it spirals around the cavity toward the polar region, the thread crest being engageable with the thread root of the liner screw thread.

11. The hip prosthesis of claim 10 wherein the liner thread comprises a conical profile thread crest.

12. The hip prosthesis of claim 10 wherein the liner thread comprises a cylindrical profile thread crest.