Patent ID: 6887274

Claim:
An intervertebral spacer device comprising: first and second plate members, each having first and second plate surfaces thereof, said plates being disposed in a spaced apart relationship such that first ones of said plate surfaces oppose one another, and second ones of said plate surfaces face in opposite directions; and at least one restoring force providing element disposed between said first surfaces of said first and second plate members, and disposed such that a compressive load applied to said second surfaces of said first and second plate members is counteracted by said at least one restoring force providing element, said at least one restoring force providing element including at least one belleville washer having at least one radially spaced concentric groove; wherein said at least one radially spaced concentric groove in said at least one belleville washer comprises a plurality of radially spaced concentric grooves, and wherein at least one of said plurality of radially spaced concentric grooves in said at least one belleville washer has a length; wherein said at least one of said plurality of radially spaced concentric grooves in said at least one belleville washer has a depth and a width, and at least one of said width and said depth varies along said length.