A modular hydraulic spinal intervertebral prosthetic device offering individualized optimization of an implantable disc prosthesis by having selectable crown plates modules with differing lordosis angles and differing cross-sectional profiles, and selectable bellows cartridges having differing load-bearing capabilities. The device offers substantially full physiological degrees of motion, and by the incorporation of both a dashpot mechanism and a biasing element within reversibly displaceable and tiltable bellows provides hydraulic load bearing capability. The bellows assembly is advantageously pre-loaded to sub-atmospheric pressure. The dashpot assembly further increases resistance to lateral shear loading beyond the bellows convolutions acting alone. Rotational coupling of the upper crown plate and center bearings plate permits normal twisting movements, and spinal flexural freedom is provided by the bellows interposed between the center bearings plate and the lower end plate. The bellows also provides a hermetic seal which prevents any wear debris from migrating to the surrounding body tissue.