Intervertebral prosthesis
An intervertebral prosthesis for insertion between adjacent vertebrae includes upper and lower prosthesis plates locatable against respective vertebrae and having opposing, concavely curved recesses therein, and a core located between the plates. The core has opposed, convexly curved surfaces received in the recesses of the plates to allow the plates to slide in articulated manner over the core. The opposed surfaces of the core and the recesses of the plates have cooperating spherical curvatures. The recess of each plate surrounds a locating peg projecting centrally from the base of the recess and is bounded by an annular rim, such that the annular rims of the plates are arranged to contact one another at a predetermined limit of sliding movement of the plates over the core. The peg locates loosely in an opening located centrally in a curved surface of the core, whereby the plates can slide over the core in all directions while the peg holds the core captive.
1. An intervertebral prosthesis for insertion between adjacent vertebrae, the prosthesis comprising:
first and second prosthesis plates locatable against respective vertebrae, each of the first and second prosthesis plates having an outer surface locatable against a vertebra and an oppositely facing inner bearing surface;
at least one upstanding elongated protrusion on the outer surface of each of the first and second prosthesis plates;
a core located between the first and second prosthesis plates, the core having a height extending between the first and second prosthesis plates which is smaller than a width of the core in a direction perpendicular to the height, the core having opposed, first and second bearing surfaces configured to allow the first and second prosthesis plates to slide in an articulated manner over the core;
a peg projecting centrally from the inner bearing surface of the first prosthesis plate;
wherein the peg locates loosely in an opening located centrally in the first bearing surface of the core, whereby the first prosthesis plate can slide over the core while the peg holds the core captive;
wherein the opening is a blind opening; and
wherein a recess of each of the first and second prosthesis plates is bounded by an annular rim having a first diameter, and wherein each of the first and second prosthesis plates includes a groove having a second diameter, each groove of the first and second prosthesis plates being adjacent to the respective rim of the first and second prosthesis plates, wherein the first diameter is larger than the second diameter such that each groove of the first and second prosthesis plates is configured and arranged to facilitate handling of a respective prosthesis plate by instruments used to place the prosthesis in use.
2. The prosthesis according to claim 1 , wherein the peg and the opening in which it locates are conically shaped.
3. The prosthesis according to claim 1 , wherein the inner bearing surface of the second prosthesis plate is concave and complementary in shape to a convexly curved second bearing surface of the core.
4. The prosthesis according to claim 1 , wherein the inner bearing surface of the second prosthesis plate includes a continuously, spherically curved surface.
5. The prosthesis according to claim 1 , wherein the opening located centrally in the first bearing surface of the core is a blind recess extending partway through the core.
6. The prosthesis according to claim 1 , wherein the peg is arranged to abut a side wall of the opening at a predetermined limit of sliding movement of the plates over the core.
7. The prosthesis according to claim 1 , wherein the peg and the opening are complementary in shape.
8. The prosthesis according to claim 1 , wherein the outer surfaces of the first and second prosthesis plates comprise coarse finishes.
9. The prosthesis according to claim 1 , wherein the first and second prosthesis plates are formed of titanium.
10. The prosthesis according to claim 9 , wherein the core is formed of high molecular weight polyethylene.
11. The prosthesis according to claim 1 , wherein during articulation, the peg remains in the opening and the articulation of the prosthesis is limited to a maximum of 12° of articulation.
12. The prosthesis according to claim 1 , wherein the first and second prosthesis plates are each formed in one piece of titanium and configured to be received entirely within the disc space.
13. The prosthesis according to claim 1 , wherein the rim of the first prosthesis plate contacts the rim of the second prosthesis plate to prevent further articulation.
14. The prosthesis according to claim 1 , wherein the peg of the first prosthesis plate contacts the core to prevent further articulation of the first and second prosthesis plates over the core.
15. The prosthesis according to claim 14 , further wherein the rim of the first prosthesis plate contacts the rim of the second prosthesis plate to additionally prevent further articulation of the first and second prosthesis plates over the core.
16. The prosthesis according to claim 14 , wherein the opening of the core includes sides, and the peg of the first prosthesis plate contacts the sides of the opening to prevent further articulation of the first and second prosthesis plates over the core.
17. The prosthesis according to claim 5 , wherein the blind recess extends partway through the core.