Patent ID: 7771477

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 increase incrementally with decreasing said distances, and said widths increase incrementally with decreasing said distances.