WO2006030392A1

WO2006030392A1 - Joint prosthesis component

Info

Publication number: WO2006030392A1
Application number: PCT/IB2005/053026
Authority: WO
Inventors: Pieter Johannes Botha
Original assignee: Arthrosearch (Proprietary) Limited
Priority date: 2004-09-17
Filing date: 2005-09-15
Publication date: 2006-03-23

Abstract

This invention relates to a joint prosthesis component (10) having a body (12) defining an operatively outer bone contacting surface (20) and an operatively inner bearing surface (22), for articulating with either a natural or prosthetic counter-component of a joint, the operatively inner bearing surface (22) having a geometry which corresponds to the anatomy of a natural joint component for which the component (10) provides a prosthesis. The invention extends to an acetabulum hip prosthesis component and to a joint prosthesis assembly.

Description

JOINT PROSTHESIS COMPONENT

THIS INVENTION relates to the surgical repair of joints. More particularly, the invention relates to the implantation of a prosthesis in a joint.

The invention provides a joint prosthesis component, for use in at least partially replacing a natural joint. The invention extends to a joint prosthesis assembly.

Joint prosthesis assemblies typically include two separate components, at least one of which defines a bearing surface adapted to articulate with a counter-component of the joint (or a prosthesis thereof).

It is known to provide joint prosthesis components and prosthetic joint assemblies for hips, knees, ankles, shoulders, elbows, and wrists.

According to one aspect of the invention, there is provided a joint prosthesis component having a body defining an operatively outer (bone-contacting) surface and an operatively inner bearing surface, for articulating with either a natural or prosthetic counter-component of a joint, the operatively inner bearing surface having a geometry which corresponds to the anatomy of a natural joint component for which the component provides a prosthesis.

More particularly, the operatively inner surface may be contoured such that it corresponds to a profile of a bearing surface of a natural joint component for which the component provides a prosthesis. By "corresponds" is to be understood has a close similarity or agrees almost exactly to.

The component may include bone engaging means, defined on the operatively outer surface of the body, for engaging the joint component with a bone of the natural/biological joint.

In a preferred embodiment, the present invention provides a socket component of a joint replacement assembly, more particularly, an acetabular component of a hip replacement assembly. Naturally, however, the invention extends to the components of other articulating joints.

The hip joint in the human body includes a natural socket (the acetabulum) defined in the pelvis, which socket receives the head of the femur, or thigh bone, therein. A ball-and-socket joint is thus provided.

Due to various progressive deteriorative diseases or abnormal stresses applied to a joint, a joint may fail such that partial or total joint replacement is required and eroded or worn surfaces require replacement with artificial materials. In some cases, the acetabulum must be replaced.

The acetabulum is cotyloidal in shape, and is often referred to as a "cup". An implantable prosthetic hip joint includes an acetabular component for placement within the natural acetabulum socket of the pelvis and which defines an operatively inner bearing surface for articulating with the femoral head, which is received in the acetabular component for ball-and- socket movement therein.

The acetabular prosthetic component comprises a body having an operatively outer (bone-contacting) surface and an operatively inner bearing surface for articulating with the femoral head (or a prosthesis thereof). The acetabular component is typically of a metal or metal alloy, a polymeric substance (eg. ultra-high molecular weight polyethylene (UHMWPE)) or a ceramic material. Naturally, however, the prosthesis may be manufactured from other suitable materials.

According to another aspect of the invention, there is provided an acetabular hip prosthesis component, which acetabular component has a body defining an operatively outer (bone-contacting) surface and an operatively inner bearing surface, for articulating with either a natural or prosthetic femoral head, the operatively inner bearing surface being concave and generally hemispherical, having a radius of curvature of between about 21 mm and about 35 mm, and being delimited at an equatorial end thereof by a first plane inclined at an angle of between about 10 degrees and about 20 degrees relative to an equatorial plane and at a polar end by a second plane parallel to the equatorial plane and spaced between about 17 mm and about 29 mm from the equatorial plane, and a cut-out being defined in the body and extending between its equatorial and polar ends.

The body may have a side wall, defined between the outer surface and the inner surface, of a uniform thickness of between about 2 mm and about 6 mm. Preferably, the side wall is of a thickness of about 4 mm.

In a preferred embodiment, a centre point of the sphere lies in the first plane.

The cut-out may have circumferentially spaced edges and extend between about 8 mm and about 14 mm to either side of a plane which intersects the surface perpendicularly where a length of the surface measured between its equatorial and polar ends is a minimum. Preferably the edges of the cut-out are spaced 8 mm to either side of the plane.

The spaced edges of the cut-out may be parallel.

The words "generally hemispherical" are intended to cover a spherical range which includes deviations from hemispherical, including less than hemispherical and slightly more than hemispherical.

Preferably the inner bearing surface has a radius of curvature of

21 mm. Preferably the first plane is inclined at an angle of 15 degrees relative to the equatorial plane. Preferably the second plane is spaced 17,4 mm from the equatorial plane.

According to still another aspect of the invention, there is provided a joint prosthesis assembly which includes at least one joint prosthesis component as hereinbefore described.

The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings.

In the drawings,

Figure 1 shows a side view of a joint prosthesis component in accordance with the invention; Figure 2 shows a top perspective view of the component of Figure 1 ; and

Figure 3 shows a top plan view of the component of Figure 1.

In the drawings, reference numeral 10 refers generally to a joint prosthesis component. The component 10 has a roughly cup-shaped body 12 which is configured to receive a generally ball-shaped natural or prosthetic femoral head (not shown) therein, such that it is freely articulated in the body 12. The body 12 defines an operatively outer bone-contacting surface 20 and an operatively inner bearing surface 22, for articulating with the natural or prosthetic femoral head which provides the counter-component of the hip joint.

The operatively inner bearing surface 22 has a geometry which corresponds to the anatomy of the natural joint component for which the component 10 provides a prosthesis and is contoured such that it has a close similarity to the profile of a bearing surface of the acetabulum socket for which it provides a prosthesis, as described in more detail below. More particularly, in cross section the geometry of the inner bearing surface corresponds to/represents the best fit of normal/natural acetabular geometry.

The body 12 is truncated and generally hemispherical and is delimited at an equatorial end 16 thereof by a plane P, inclined at an angle α of 5 degrees relative to an equatorial plane E and in which a centre point I of the body 12 lies (ie. the plane P passes through the centre point I and is inclined at 15 degrees to the equatorial plane E). The body 12 is delimited at a polar end 18 thereof by a plane Q which is parallel to the equatorial plane E. The plane Q is spaced a distance y of 17.4 mm from the equatorial plane E.

The body 12 defines a convex operatively outer surface 20, having a radius of curvature of 23 mm, and a concave operatively inner surface 22, having a radius of curvature of 21 mm. The body 12 has a side wall 26, defined between the two surfaces 20, 22, of a uniform thickness of 4 mm. A cut-out 24 is defined in the body 12 to extend between its ends 16, 18. The cut-out 24 has parallel circumferentially spaced edges 28 and extends 8 mm to either side of a plane R which intersects the side wall 26 at that portion where a length I of the side wall 26 (and of each of the external surface 20 and internal surface 22 therefore), measured between the ends 16, 18 of the body 12, is a minimum.

It is to be appreciated that the side wall 26 will typically be of greater thickness (up to about 6 mm) where the radius of curvature of the inner surface 22 is greater than 21 mm, as in the present example, eg. to accommodate a larger femoral head.

Surgical implantation of the component 10 requires only a limited amount of bone removal viz. at the articulating surface of the host acetabulum. The operatively outer bone contacting surface 20 defines bone engaging means by which the component 10 is engaged with the reduced articulating surface of the host acetabulum (ie. the bone of the natural/ biological joint).

The Applicant believes that the component 10 of a prosthesis assembly in accordance with the invention will provide a prosthesis component of minimized thickness. It is believed that, in the hip joint, this will permit of a greater amount of movement of the femoral head within the acetabular component 10 (ie. normal physiological freedom of movement), minimising contact of the neck of the femur with the edge of the acetabular component 10 (i.e. impingement), so that a patient's movements do not tend to dislocate the ball/femoral head from the joint. This is attributable to the fact that the component 10 provides a real sectorial-type prosthetic implant. Moreover, the component 10 lends itself to favourable stress distribution on both periprosthetic bone and the articulating surface. It is believed that wear- attendant debris production will be minimised. Further, the applicant believes that a larger femoral head will be capable of being accommodated within the acetabular component 10. This in turn it is believed will allow for a greater sinovial fluid film between the joint components thereby to enhance and improve lubrication of articulation.

It is further believed that, by virtue of the geometry of the operatively inner surface 22 of the component 10 for a prosthesis assembly in accordance with the invention, a frictional torque between the operatively outer surface 20 and the bone which it contacts/engages will be reduced such that a propensity for the component 10 to loosen or be displaced from the bone is reduced.

The Applicant believes that the geometry of the operatively inner surface 22 of the component 10 will make it possible to preserve the normal anatomical structures, such as, for example, the Haversian fat pad (Fovea centralis) in the hip and similar structures in the knee and other joints (eg. Hoffa's fat pad), as well as the acetabular blood supply through the obturator artery on surgical implantation of the component 10. These features are important to the normal anatomical and physiological functioning of joints insofar as lubrication and immunological factors are concerned.

It is believed that the surgical procedure to reconstruct or replace a joint (arthroplasty) employing the joint prosthesis component of the invention will involve minimal invasive surgery due to the geometrical profile of the component 10 closely resembling the natural/anatomical acetabular profile. Further, it is believed that blood supply to natural/biological joint components (ie. bony elements), as well as normal physiological defence mechanisms to remove wear particles will be preserved and that minimal removal of natural bony tissue will be required.

Claims

CLAIMS:

1. A joint prosthesis component having a body defining an operatively outer bone-contacting surface and an operatively inner bearing surface, for articulating with either a natural or prosthetic counter-component of a joint, the operatively inner bearing surface having a geometry which corresponds to the anatomy of a natural joint component for which the component provides a prosthesis.

2. A joint prosthesis component as claimed in Claim 1 , in which the operatively inner surface is contoured such that it corresponds to a profile of a bearing surface of a natural joint component for which the component provides a prosthesis.

3. A joint prosthesis component as claimed in Claim 1 or Claim 2, which includes bone engaging means, defined on the operatively outer surface of the body, for engaging the joint component with a bone of the natural/biological joint.

4. A joint prosthesis component as claimed in any one of Claims 1 to 3, inclusive, which provides a socket component of a joint replacement assembly.

5. A joint prosthesis component as claimed in Claim 4, which provides an acetabular component of a hip replacement assembly.

6. An acetabular hip prosthesis component, which acetabular component has a body defining an operatively outer bone-contacting surface and an operatively inner bearing surface, for articulating with either a natural or prosthetic femoral head, the operatively inner bearing surface being concave and generally hemispherical, having a radius of curvature of between 21 mm and 35 mm, and being delimited at an equatorial end thereof by a first plane inclined at an angle of between 10 degrees and 20 degrees relative to an equatorial plane and at a polar end by a second plane parallel to the equatorial plane and spaced between 17 mm and 29 mm from the equatorial plane, and a cut-out being defined in the body and extending between its equatorial and polar ends.

7. An acetabular hip prosthesis component as claimed in Claim 6, in which a centre point of the sphere lies in the first plane.

8. An acetabular hip prosthesis component as claimed in Claim 6 or Claim 7, in which the cut-out has circumferentially spaced edges and extends between 8 mm and 14 mm to either side of a plane which intersects the surface perpendicularly where a length of the surface measured between its equatorial and polar ends is a minimum.

9. An acetabular hip prosthesis component as claimed in Claim 8, in which the edges of the cut-out are spaced 8 mm to either side of the plane which intersects the surface perpendicularly where a length of the surface measured between its equatorial and polar ends is a minimum.

10. An acetabular hip prosthesis component as claimed in Claim 8 or 9, in which the spaced edges of the cut-out are parallel.

11. An acetabular hip prosthesis component as claimed in any one of Claims 6 to 10, inclusive, in which the inner bearing surface has a radius of curvature of 21 mm.

12. An acetabular hip prosthesis component as claimed in any one of Claims 6 to 11 , in which the first plane is inclined at an angle of 15 degrees relative to the equatorial plane.

13. An acetabular hip prosthesis component as claimed in any one of Claims 6 to 12, inclusive, in which the second plane is spaced 17,4 mm from the equatorial plane.

14. An acetabular hip prosthesis component as claimed in any one of Claims 6 to 13, inclusive, which includes bone engagement means defined on the operatively outer surface of the body, for engaging the acetabular component with a bone of the natural/biological joint.

15. An acetabular hip prosthesis component as claimed in any one of Claims 6 to 14, inclusive, in which the body has a side wall defined between the outer bone-contacting surface and the inner bearing surface of thickness between 2 mm and 6 mm.

16. A joint prosthesis assembly which includes at least one prosthesis component as claimed in any one of Claims 1 to 15, inclusive.