An intervertebral spacer device includes a first plate having a bone
engaging face and an inner face, and a second plate having a second bone
engaging face and a second inner face, the first and second plates being
juxtaposed with one another so that the first inner face of the first
plate opposes the second inner face of the second plate. The spacer
device also includes a belleville washer disposed between the first inner
face of the first plate and the second inner face of the second plate for
counteracting compressive loads applied to the first and second plates.
The belleville washer has at least one concentric groove and at least one
spiral slot, whereby the at least one concentric groove has a depth and a
width, with at least one of the widths and the depths varying along the
length of the at least one concentric groove.
