An artificial intervertebral disc assembly including upper and lower end
plates, an expandable bladder carried by the end plates and
circumscribing a containment area therebetween. A biocompatible fluid is
disposed within the containment area. A cylinder having a plurality of
apertures therein projects from the lower plate into the containment
area. A piston having a curvilinear upper surface is reciprocally
moveable within the cylinder and projects from the open end thereof. A
cylindrical projection depending from the upper plate bears against and
mates with the upper surface of the piston so as to allow relative
rotational movement of the end plates into and out of parallel alignment.
By varying the size of the apertures in the cylinder and the elasticity
of the bladder, the amount of axial load necessary to effect inward
movement of the end plates can be varied.