ZA200603171B

ZA200603171B - An intervertebral prosthesis

Info

Publication number: ZA200603171B
Application number: ZA200603171A
Authority: ZA
Inventors: Walker Richard Mervyn
Original assignee: Walker Richard Mervyn
Priority date: 2003-11-28
Filing date: 2006-04-20
Publication date: 2007-09-26
Also published as: WO2005053580A1

Description

AN INTERVERTEBRAL PROSTHESIS

FIELD OF THE INVENTI ON

THIS INVENT ION relates to an intervertebral prosthesis.

BACKROUND OF THE INVEENTION

Spinal discs rmay be removed for a number of remasons. When removed, the opposed vertecbrae can be fused or the spinal disc may be replaced by an intervertebral prosthesis. The intervertebral preosthesis should provide the necessary articulation between the opposed vert=ebrae.

SUMMARY OF INVENTION

According to the invention there is provided an interve-riebral 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 3 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 rmeniscus 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 cn which the end formations can articzulate.

The radius of curvatu re 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 nay have a greater radius of curvature than trme complementary concave articulation surfaces of the meniscus.

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

Each end formation may Wbe in the form of an end plate Faving an inner side defining the convex art iculation surface and an outer side defining a projecting keel formation #or fixing the end plate to a verteabra.

The outer sides of the ened plates from which the kee! formations project may be generally convex to conform to the natural conca~ve curvature of the vertebrae.

The outer sides of the en~d plates may define a beaded o uter surface.

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

BRIEF DESCRIP TION 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 1I - II of Figure 1;

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

Figure 4 shows a schematic bottom plan view of the end plate of Figumre 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, sectieoned along line VI - VI of Figure 5;

Figure 7 shows 2 schematic anterior viewwy of an intervertebral proosthesis located between vertebrae in accordance vavith the invention; and

Figure 8 shows a schematic side view eof the intervertebral prosthesis of

Figure 8 located between the vertebrae.

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

The intervertebral prosthesis 10 includes end formations in the forum of end plates 12.1 and 12.2 that can be attached to opposing ends of adjacent vertebrae 16.1 and 16.2, respectively, an-d a meniscus 14 locatable between the en«d plates 12.1 and 12.2 on which th e end plates 12 can articulate. The intervesrtebral prosthesis 10 is located, ir use, between the vertebmral bones 16.1 amd 16.2 to replace a damaged natu ral intervertebral disc.

The emd plate 12.1 is attached to the ssuperior vertebra 16.1 and the end plate “12.2 is attached to the inferior vertesbra 16.2. The end plates. 12.1 and 12.2 a_re identical in shape and configuration.

The emnd plates are of cast cobalt chrome=. Each end plate 12 define san inner side 2=1 and an outer side 22. The inner side 21 defines a convex articulation surfacce 18. The outer side 22 define s 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 locatirag the keel formation 20 of the end plate 12 therein. The end plates 12 d efine an operative anterior side 32 ard an operative posterior side 34. The end plates 12 are kidney-shaped &n plan view and define an indentations 30 at the posterior side 34 to accosmmodate 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 sumrface 18 and thus the loading point, is disposed relatively closer to the posterior side 34 of the end plate 12, thereby po sitioning the loading point closer to th. e 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 th e keel formation is disposed opposite the apex 24 of the convex articulation ssurface 18. The surface 38 of the outer side 22, is convex to fit the natural concave curvature of the vertebra 1 6. The surface 38 is coated with a titanium and hydroxyapatite (HA) coati ng to improve bone growth. The b-eading 40 on the surface 38 enhances fixation of the end plate 12 to the veertebra 16 by improving bone growth onto the end plate.

The meniscus 14 is of casst cobalt chrome, is disc-shap=ed and is concavo- concave to define two comncave articulation surfaces 26 and 28 which are identical in shape and co nfiguration. In use, the mermiscus 14 is located between the two endplate=s 12.1 and 12.2 so that the concave articulation surfaces 26 and 28 are in contact with the convex articu Yation surfaces 18 of the two end plates 12.1 amnd 12.2, respectively. The raadius of curvature of the concave articulation =surfaces 26 and 28 is different to the radius of curvature of the convex awticulation surfaces 18 of the rneniscus 14 thereby to reduce the amount of metal-on-metal contact betwween 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 meriscus.

In use, in order to impla nt the intervertebral prosthesiss 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 uppmer 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 chisel Jed notches. The ends 36 of the keel formations 20 serve as indicators to asssist a surgeon to gauge the possition of the apices 24

W/O 2005/053580 8 PCT/IB2004 J002827 (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 verteabrae 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 articulatior surfaces 26 and 28. The meniscus 14 is thus a separate component of the inte=rvertebral prosthesis 10 that is located in a Floating arrangement between the end plates 12 of the intervertebral prosthesis 1 0.

Claims

WO» 2005/053580 = PCT/TB2004/0028327 CLAIMS

1. An intervertebral prosthesis which is locatable between two adj acent vertebral bones, includes first and second end formations that can each be attached to a differert 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 th e end formations defines a convex articulaation surface and the meniscus defines a complementary concave articulation surface.

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

3. An intervertebral prosthesis as clairmed 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 complem entary concave articulation surfaces of thee meniscus to thereby reduce the aarea of contact between the articulation surfraces, in use.

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

5. An intervertebral prosthesis as claimed in any the preceding claimss, characterised in that the apex of the convex articulating surface of each ermd formation is disposed relatively closer to an operative posterior side of thme 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 fom of an end plate havirg an inner side clefining the convex articulation swurface and an outer sicie defining a projecting keel formation for fixing the ermd plate to a vertebra.

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

8. An intervertebral prosthesis as claimed in Claim & 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 desecribed in the specification.

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