US Patent 8092539 Intervertebral spacer device having a belleville washer with concentric grooves

An intervertebral spacer device may include first and second plates, each having inner and outer surfaces thereof, the plates may be disposed in a spaced apart relationship such that the inner surfaces face toward one another, and the outer surfaces face away from one another, the first plate including a retaining wall extending outwardly from the inner surface of the first plate; and a belleville washer, having narrow and wide ends thereof, may be 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 groove.