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 prosthetic disc for insertion between adjacent vertebrae, the prosthetic disc comprising:
a first plate having a first surface configured to engage a vertebra and an opposite inwardly directed bearing surface;
a second plate having a second surface configured to engage a vertebra and an opposite inwardly directed bearing surface;
a rigid mobile 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; and
a retaining formation which holds the core captive between the first and second plates;
wherein the retaining formation includes two or more recesses circumferentially spaced apart about the periphery of the core and two or more inwardly directed 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.
2. A prosthetic disc as in claim 1 , wherein at least one of the first and second bearing surfaces of the core is spherical.
3. A prosthetic disc as in claim 2 , 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.
4. A prosthetic disc as in claim 2 , wherein both of the first and second bearing surfaces of the core are spherical.
5. A prosthetic disc as in claim 1 , wherein the retaining formation defines a stop structure to limit relative inclination of the plates during sliding movement of the plates over the core.
6. A prosthetic disc as in claim 1 , wherein the retaining formation allows anterior, posterior and lateral motion of the core with respect to the first and second plates.
7. A prosthetic disc as in claim 1 , wherein the core has a substantially circular perimeter.
8. A prosthetic disc as in claim 1 , wherein each peg extends into a recesses.
9. A prosthetic disc as in claim 1 , wherein the core is symmetrical about a central, equatorial plane which bisects the core laterally.
10. A prosthetic disc as in claim 1 , wherein the lateral edge is a continuous annular lateral edge.