Patent ID: 8048159

Claim:
An intervertebral spacer device comprising: first and second plates disposed in a spaced apart relationship, each said plate having an inner surface and an outer surface, the inner surfaces of said opposing plates facing one another; at least one restoring force providing element disposed between the inner surfaces of said first and second plates, wherein a compressive load applied to the outer surfaces of said first and second plates is counteracted by said at least one restoring force providing element; said at least one restoring force providing element including at least one slotted belleville washer having a convex shape when unloaded and a flatter shape when loaded, wherein one or more slots of said belleville washer widen when compressively loaded, wherein said at least one slotted belleville washer is unloaded when no load is applied to said outer surfaces of said first and second plates, and is loaded when said compressive load is applied to said outer surfaces of said first and second plates; a retaining wall extending outwardly from the inner surface of the second plate, said retaining wall having an annular recess formed in an inner surface thereof; and a retaining ring held in the annular recess of the retaining wall, wherein a wide end of said at least one belleville washer is captured by said retaining wall and said retaining ring for maintaining the wide end adjacent the inner surface of said second plate.