Spinal disc prosthetic devices are provided having up to six-degrees-of-freedom with three rotational and three translational degrees-of-freedom within the entire workspace of a Functional Spinal Unit (FSU). Certain embodiments of the prosthetic disc mechanisms attach to upper and lower plates anchored between vertebrae of an FSU allowing modularity of the devices. Scaling, conjoined mechanical programmability allow the devices to realize almost any nominal required spinal articulation, from the cervical to lumbar regions.