Prosthetic disc for intervertebral insertion
A prosthetic disc for insertion between adjacent vertebrae includes a core having upper and lower curved surfaces, upper and lower plates, and peripheral restraining structure on at least one of the upper plate, the lower plate and the core. Each plate has an outer surface which engages a vertebra and an inner curved surface which slides over the curved surface of the core. The peripheral restraining structure serves to hold the core against a curved surface of at least one of the plates during sliding movement of the plates over the core.
1. A method of retaining a core in a prosthetic disc, the method comprising:
providing a first plate having a first surface which engages a vertebra and an opposite bearing surface;
providing a second plate having a first surface which engages a vertebra and an opposite bearing surface;
providing a rigid mobile core between the first and second plates, the core having first and second bearing surfaces configured to cooperate with the bearing surfaces of the first and second plates to allow the first and second plates to slide and translate over the core and a lateral edge between the first and second bearing surfaces;
providing a retaining formation including two or more recesses circumferentially spaced apart about the periphery of the core and two or more pegs on the first plate each peg opposing a circumferentially spaced recess, wherein the circumferentially spaced recesses extend in a direction radially inward from the lateral edge of the core toward a center portion of the core;
retaining the core between the first and second plates with the retaining formation.
2. A method as in claim 1 , wherein the pegs extend into the recesses during sliding motion of the plates over the core.
3. A method as in claim 1 , wherein at least one of the first and second bearing surfaces of the core is spherical.
4. A method as in claim 3 , wherein at least one of the bearing surfaces of the first and second plates is a concave spherical surface which matches a curvature of the spherical surface of the core.
5. A method as in claim 1 , wherein both of the first and second bearing surfaces of the core are spherical.
6. A method as in claim 1 , wherein the core has a substantially circular perimeter.
7. A method as in claim 1 , wherein the core is symmetrical about a central, equatorial plane which bisects the core laterally.
8. A method as in claim 1 , wherein the lateral edge is a continuous lateral edge.
9. A method as in claim 1 , further comprising a step of assembling the first and second plates and the core in an assembled configuration for implantation between adjacent spinal vertebrae.
10. A method as in claim 1 , wherein cooperation between the recess and the pegs of the retaining formation ensures that the core is held captive between the plates.
11. A method as in claim 1 , wherein the method allows anterior, posterior and lateral motion of the core with respect to the first plate.
12. A method as in claim 1 , wherein the method allows anterior, posterior and lateral motion of the core with respect to the second plate.