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.