A modular spinal disc prosthesis, with up to three independent rotational and up to three independent translational degrees-of-freedom. The prosthesis can maintain non-separable, and non-restrictive, mechanical linkage by establishing a linked series of kinematic pairs between components. Embodiments can include a superior plate, fixedly attached to a superior vertebra in an FSU that links to a planar pair, which links to an orthogonal prismatic pair, which links to a spherical pair, which links to an inferior plate that is fixedly attached to an inferior vertebra of an FSU, completing the jointed kinematic chain. The subject invention can enforce the kinematic constraints to realize the kinematic pairs and can also limit the range of operation of the degrees of freedom for each pair. A surrounding, protective boot can be used to isolate the elements of the invention.
