Intervertebral spacer device

1. An intervertebral spacer device comprising:

a first plate having an inner surface, an outer surface, a central region and a peripheral region surrounding the central region;

a second plate having an inner surface confronting the inner surface of said first plate, an outer surface facing away from said second plate, a central region and a peripheral region surrounding the central region;

a ball projecting from the inner surface of said second plate and extending toward the inner surface of said first plate;

a coupling element for coupling said first and second plates together, said coupling element having a central opening for receiving the ball projecting from said second plate, said coupling element having a convex surface facing the inner surface of said second plate and a concave surface facing the inner surface of said first plate, wherein the concave surface adjacent the central opening of said coupling element is spaced from the inner surface of said first plate; and

a retaining wall extending from the inner surface of said first plate, said retaining wall surrounding said coupling element, wherein a retaining ring overlying the central region of said first plate and spaced inwardly from the peripheral region of said first plate is engaged with and lies within said retaining wall and further lies circumferentially adjacent to the convex surface of the coupling element;

wherein said coupling element is maintained against said first plate by said retaining ring.

2. The device as claimed in claim 1 , wherein said coupling element and said ball cooperate for enabling first and second plates to pivot and rotate relative to one another.

3. The device as claimed in claim 1 , wherein said coupling element is a restoring force providing element that counteracts any compressive load applied to said first and second plates.

4. The device as claimed in claim 3 , wherein said restoring force providing element is a belleville washer.

5. The device as claimed in claim 1 , further comprising a post projecting from the inner surface of said second plate, said post being connected with said ball.

6. The device as claimed in claim 5 , wherein said ball and said post have a threaded bore that extends axially from said ball toward said second plate.

7. The device as claimed in claim 6 , further comprising a threaded set screw insertible into said threaded bore, wherein said ball is compressible before insertion of said set screw into said threaded bore and incompressible after insertion of said set screw into said threaded bore.

8. The device as claimed in claim 1 , wherein said retaining wall is spaced inwardly from the peripheral region of said first plate.

9. The device as claimed in claim 8 , wherein said retaining wall is in contact with the inner surface of said first plate.

10. The device as claimed in claim 1 , wherein said retaining wall and said retaining ring define a space over the inner surface of said first plate, and wherein said coupling element is movable relative to the inner surface of said first plate.

11. The device as claimed in claim 10 , wherein said retaining wall and said retaining ring cooperate together for limiting movement of said coupling element relative to said first plate.

12. The device as claimed in claim 1 , wherein said coupling element has an outer edge with a thickness greater than the thickness adjacent to the said central opening.

13. The device as claimed in claim 1 , wherein said coupling element has an outer edge and at least one slot extending radially from said outer edge towards said central opening.

14. An intervertebral spacer device comprising:

a first plate having an inner surface, an outer surface, a central region and a peripheral region surrounding the central region;

a second plate having an inner surface, an outer surface, a central region and a peripheral region surrounding the central region, wherein the inner surfaces of said first and second plates oppose one another;

a subassembly disposed between the inner surfaces of said first and second plates for coupling said first and second plates together and counteracting compressive load applied to said first and second plates, said subassembly comprising:

a convex element overlying the inner surface of said first plate, said convex element having a central opening,

a ball projecting from the inner surface of said second plate, said ball being captured in the central opening of said convex element,

a retaining wall extending from the inner surface of said first plate for maintaining the convex element against said first plate, said retaining wall surrounding said convex element and overlying the central region of said first plate,

wherein said subassembly further comprises a retaining ring engaged with said retaining wall and extending inwardly from said retaining wall toward the central region of said first plate.

15. The device as claimed in claim 14 , wherein said retaining wall and said retaining ring cooperate for holding said convex element against the inner surface of said first plate.

16. The device as claimed in claim 15 , wherein said restoring convex element is a belleville washer.

17. The device as claimed in claim 14 , wherein said subassembly establishes a center of rotation between said first and second plates.

18. The device as claimed in claim 14 , wherein said subassembly enables said first and second plates to pivot and rotate relative to one another.

19. The device as claimed in claim 14 , wherein said subassembly further includes a post structure extending from said second plate, and wherein said post structure includes said ball.

20. The device as claimed in claim 19 , wherein said post structure further includes a threaded bore that extends axially from said ball toward said second plate, and wherein said bore is adapted to receive therein a threaded set screw such that prior to insertion of said set screw therein, said bore permits said ball to compress radially inwardly, and such that after the insertion of said set screw said ball is not readily radially compressible.

21. The device as claimed in claim 14 , wherein said retaining wall is in contact with the inner surface of said first plate.

22. The device as claimed in claim 14 , wherein said retaining wall and said retaining ring define a space over the inner surface of said first plate, and wherein said convex element is movable relative to the inner surface of said first plate.

23. The device as claimed in claim 22 , wherein said retaining wall and said retaining ring cooperate together for limiting movement of said convex element relative to said first plate.

24. The device as claimed in claim 14 , wherein said convex element has an outer edge with a thickness greater than the thickness adjacent to the said central opening.

25. The device as claimed in claim 14 , wherein said convex element has an outer edge and at least one slot extending radially from said outer edge towards said central opening.