Patent ID: 8092539

Claim:
An intervertebral spacer device comprising: first and second plates, each having inner and outer surfaces thereof, said plates being disposed in a spaced apart relationship such that the inner surfaces face toward one another, and the outer surfaces face away from one another, said first plate including a retaining wall extending outwardly from said inner surface of said first plate; and a belleville washer, having narrow and wide ends thereof, disposed with said wide end contacting said inner surface of said first plate within said retaining wall, such that a compressive load applied to the outer surfaces of said plates is counteracted by said belleville washer, said belleville washer including a plurality of radially spaced concentric grooves; wherein each concentric groove of said plurality of radially spaced concentric grooves in said belleville washer has a respective length, a respective depth along said respective length, and a respective width along said respective length, at least one of said respective depth and said respective width being uniform along said respective length; wherein each of said plurality of radially spaced concentric grooves in said belleville washer is at a respective distance from an outer edge of said belleville washer, wherein said depths differ with respect to one another depending on said distances, and said widths differ with respect to one another depending on said distances.