WO2005053580A1

WO2005053580A1 - An intervertebral prosthesis

Info

Publication number: WO2005053580A1
Application number: PCT/IB2004/002827
Authority: WO
Inventors: Richard Mervyn Walker
Original assignee: Richard Mervyn Walker
Priority date: 2003-11-28
Filing date: 2004-09-01
Publication date: 2005-06-16
Also published as: ZA200603171B

Abstract

The intervertebral prosthesis (10) is used to replace a damaged natural intervertebral disc. The intervertebral prosthesis includes end plates (12.1 and 12.2) that are attached to opposing ends of adjacent vertebrae (16.1 and 16.2), respectively, and a floating meniscus (14) locatable between the end plates on which the end plates (12) articulate. Each end plate defines an inner side defining a convex articulation surface and an outer side defining a projecting keel formation and a beaded outer surface. The meniscus is concavo-concave defining complementary concave articulation surfaces on which the end plates articulate.

Description

AN INTERVERTEBRAL PROSTHESIS

FIELD OF THE INVENTION

THIS INVENTION relates to an intervertebral prosthesis.

BACKROUND OF THE INVENTION

Spinal discs may be removed for a number of reasons. When removed, the opposed vertebrae can be fused or the spinal disc may be replaced by an intervertebral prosthesis. The intervertebral prosthesis should provide the necessary articulation between the opposed vertebrae. SUMMARY OF INVENTION

According to the invention there is provided an intervertebral prosthesis which is locatable between two adjacent vertebral bones, the intervertebral prosthesis may include

first and second end formations that can each be attached to a different one of the vertebral bones; and

a meniscus which is locatable between the end formations and on which the end formations can articulate, characterised in that at least one of the end formations defines a convex articulation surface and the meniscus defines a complementary concave articulation surface.

Each of the end formations may define a convex articulation surface and the meniscus may be concavo-concave defining complementary concave articulation surfaces on which the end formations can articulate.

The radius of curvature of each of the convex articulation surfaces of the end formations may be different to the radius of curvature of the complementary concave articulation surfaces of the meniscus to thereby reduce the area of contact between the articulation surfaces, in use. The convex articulation surfaces of the end formations may have a greater radius of curvature than the complementary concave articulation surfaces of the meniscus.

The apex of the convex articulating surface of each end formation may be disposed relatively closer to an operative posterior side of the end formation.

Each end formation may be in the form of an end plate having an inner side defining the convex articulation surface and an outer side defining a projecting keel formation for fixing the end plate to a vertebra.

The outer sides of the end plates from which the keel formations project may be generally convex to conform to the natural concave curvature of the vertebrae.

The outer sides of the end plates may define a beaded outer surface.

The convex and concave articulation surfaces may be of cast cobalt chrome.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features of the invention are described hereinafter by way of a non- limiting example of the invention, with reference to and as illustrated in the accompanying diagrammatic drawings. In the drawings:

Figure 1 shows a schematic top plan view of an end plate of an intervertebral prosthesis in accordance with the invention;

Figure 2 shows a sectional side view of the end plate of Figure 1 , sectioned along line II - II of Figure 1 ;

Figure 3 shows a sectional posterior end view the end plate of Figure 1 , sectioned along line III - III of Figure 1 ;

Figure 4 shows a schematic bottom plan view of the end plate of Figure 1 ;

Figure 5 shows a schematic top plan view of a meniscus of an intervertebral prosthesis in accordance with the invention;

Figure 6 shows a sectional end view the meniscus of Figure 5, sectioned along line VI - VI of Figure 5; Figure 7 shows a schematic anterior view of an intervertebral prosthesis located between vertebrae in accordance with the invention; and

Figure 8 shows a schematic side view of the intervertebral prosthesis of Figure 8 located between the vertebrae.

With reference to the drawings, an intervertebral prosthesis in accordance with the invention is designated generally by reference numeral 10.

The intervertebral prosthesis 10 includes end formations in the form of end plates 12.1 and 12.2 that can be attached to opposing ends of adjacent vertebrae 16.1 and 16.2, respectively, and a meniscus 14 locatable between the end plates 12.1 and 12.2 on which the end plates 12 can articulate. The intervertebral prosthesis 10 is located, in use, between the vertebral bones 16.1 and 16.2 to replace a damaged natural intervertebral disc.

The end plate 12.1 is attached to the superior vertebra 16.1 and the end plate 12.2 is attached to the inferior vertebra 16.2. The end plates 12.1 and 12.2 are identical in shape and configuration.

The end plates are of cast cobalt chrome. Each end plate 12 defines an inner side 21 and an outer side 22. The inner side 21 defines a convex articulation surface 18. The outer side 22 defines a convex outer surface 38 and a projecting keel formation 20. The outer surface 38 is beaded and as such, defines a number of spaced "as cast" beads 40 which are formed in the casting process of the end plate.

Each end plate 12 is fixed to a vertebra 16 by cutting a notch in the vertebra and locating the keel formation 20 of the end plate 12 therein. The end plates 12 define an operative anterior side 32 and an operative posterior side 34. The end plates 12 are kidney-shaped in plan view and define an indentation 30 at the posterior side 34 to accommodate the spinal cord, in use. The apex 24 of the convex articulation surface 18 defines a loading point. The apex 24 of the convex articulation surface 18 and thus the loading point, is disposed relatively closer to the posterior side 34 of the end plate 12, thereby positioning the loading point closer to the posterior side.

The keel formation 20 projects from the outer surface 38 of each end plate 12 and is configured so that an end 36 of the keel formation is disposed opposite the apex 24 of the convex articulation surface 18. The surface 38 of the outer side 22, is convex to fit the natural concave curvature of the vertebra 16. The surface 38 is coated with a titanium and hydroxyapatite (HA) coating to improve bone growth. The beading 40 on the surface 38 enhances fixation of the end plate 12 to the vertebra 16 by improving bone growth onto the end plate. The meniscus 14 is of cast cobalt chrome, is disc-shaped and is concavo- concave to define two concave articulation surfaces 26 and 28 which are identical in shape and configuration. In use, the meniscus 14 is located between the two endplates 12.1 and 12.2 so that the concave articulation surfaces 26 and 28 are in contact with the convex articulation surfaces 18 of the two end plates 12.1 and 12.2, respectively. The radius of curvature of the concave articulation surfaces 26 and 28 is different to the radius of curvature of the convex articulation surfaces 18 of the meniscus 14 thereby to reduce the amount of metal-on-metal contact between the articulation surfaces, in use. As such, body fluids are allowed to enter the gaps between adjacent articulation surfaces. This feature makes the articulation surfaces less prone to cold welding. In particular, the convex articulation surfaces 18 of the end plates 12 have a greater radius of curvature than the complementary concave articulation surfaces of the meniscus.

In use, in order to implant the intervertebral prosthesis a damaged natural intervertebral disc is surgically removed from its location between two adjacent vertebrae. Notches are then chiselled into the lower end of the superior vertebra 16.1 and the upper end of the inferior vertebra 16.2 from the anterior sides 32 of the vertebrae. The end plates 12.1 and 12.2 are fixed to the vertebrae 16.1 and 16.2, respectively, by locating the keel formations 20 of each end plate 12 in the chiselled notches. The ends 36 of the keel formations 20 serve as indicators to assist a surgeon to gauge the position of the apices 24 (and therefore the loading points) of the convex articulation surfaces 18. The position and depth of the ends 36 of the keel formations 20 in the vertebrae can be gauged by observing X-rays of the area. The meniscus 14 is positioned between the end plates 12 so that the convex articulation surfaces 18 of end plates 12.1 and 12.2 respectively, articulate on the concave articulation surfaces 26 and 28. The meniscus 14 is thus a separate component of the intervertebral prosthesis 10 that is located in a floating arrangement between the end plates 12 of the intervertebral prosthesis 10.

Claims

1. An intervertebral prosthesis which is locatable between two adjacent vertebral bones, includes

2. An intervertebral prosthesis as claimed in Claim 1 , characterised in that each end formation defines a convex articulation surface and the meniscus is concavo-concave defining complementary concave articulation surfaces on which the end formations can articulate.

3. An intervertebral prosthesis as claimed in Claim 2, characterised in that the radius of curvature of each of the convex articulation surfaces of the end formations is different to the radius of curvature of the complementary concave articulation surfaces of the meniscus to thereby reduce the area of contact between the articulation surfaces, in use.

4. An intervertebral prosthesis as claimed in Claim 3, characterised in that the convex articulation surfaces of the end formations have a greater radius of curvature than the complementary concave articulation surfaces of the meniscus.

5. An intervertebral prosthesis as claimed in any one of the preceding claims, characterised in that the apex of the convex articulating surface of each end formation is disposed relatively closer to an operative posterior side of the end formation.

6. An intervertebral prosthesis as claimed in any one of Claims 2 to 5, characterised in that each end formation is in the form of an end plate having an inner side defining the convex articulation surface and an outer side defining a projecting keel formation for fixing the end plate to a vertebra.

7. An intervertebral prosthesis as claimed in Claim 6, characterised in that the outer sides of the end plates from which the keel formations project are generally convex to conform to the natural concave curvature of the vertebrae.

8. An intervertebral prosthesis as claimed in Claim 6 or Claim 7, characterised in that the outer sides of the end plates define a beaded outer surface.

9. An intervertebral prosthesis as claimed in any one of the preceding claims, characterised in that the convex and concave articulation surfaces are of cast cobalt chrome.

10. A new intervertebral prosthesis substantially as described in the specification.

11. An intervertebral prosthesis substantially as described in the specification, with reference to and as illustrated in the accompanying diagrammatic drawings.