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. A method of inserting an intervertebral prosthesis in an intervertebral space, the method comprising:
providing an articulating intervertebral prosthesis including:
a first prosthesis plate having a major surface to engage a first vertebra and a cooperating surface disposed opposite the major surface;
a second prosthesis plate comprising a major surface to engage a second vertebra and a cooperating surface disposed opposite the major surface;
a core located between the first and second plates, wherein the cooperating surfaces of the first and second plates are arranged to cooperate with the core to form an articulate joint;
a peg projecting centrally from the cooperating surface of the first plate;
a central opening in the core;
wherein the peg locates loosely in the opening of the core, whereby the plates can slide over the core while the peg holds the core captive and wherein the second plate does not include a central projecting peg;
a first annular rim disposed around the cooperating surface of the first plate, the first rim having an empty groove formed adjacent to the rim;
a second annular rim disposed around the cooperating surface of the second plate, the second rim having an empty groove formed adjacent to the rim;
each groove configured and arranged to facilitate handling of the plates by an instrument used to place the prosthesis in use; and
manipulating the prosthesis with an instrument to place the prosthesis entirely within the intervertebral space;
wherein each groove facilitates manipulation and holding of the prosthesis while the prosthesis is placed in the intervertebral space.
2. The method according to claim 1 , wherein the first and second prosthesis plates are secured to the first and second vertebrae adjacent the intervertebral space by upstanding elongated projections on the major surfaces of the first and second plates.
3. The method according to claim 1 , wherein the core has a height extending between the plates which is smaller than a width of the core in a direction perpendicular to the height.
4. The method according to claim 1 , wherein the cooperating surface of the first plate is complementary in shape to a curved surface of the core of the prosthesis.
5. The method according to claim 1 , wherein the core is a doughnut-shaped body and the central opening therein is provided by a central passage extending axially through the body.
6. The method according to claim 1 , wherein the central opening of the core is a blind recess extending partway through the core.
7. The method according to claim 1 , wherein the peg is arranged to abut the side of the opening at the predetermined limit of sliding movement of the plate over the core.
8. The method according to claim 1 , wherein the peg and opening are complementary in shape.
9. The method according to claim 1 , wherein the first plate comprising the central projecting peg is a lower plate.
10. The method according to claim 1 , wherein the major surfaces of the first and second plates comprise coarse machined serrated finishes.
11. The method according to claim 1 , wherein the plates are formed of titanium.
12. The method according to claim 1 , wherein the core is formed of high molecular weight polyethylene.
13. The method 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.
14. The method according to claim 1 , wherein each prosthesis plate is formed in one piece of titanium and configured to be received entirely within the disc space.