The subject invention provides a modular six-degrees-of-freedom spatial mechanism for 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, or chain, of kinematic pairs (joints) between components. In embodiment, a superior plate links to a planar pair (two independent degrees of translational freedom), which links to spherical pair (three independent degrees of rotational freedom), which links to a prismatic pair (one independent degree of translational freedom), which links to an inferior plate, completing the jointed kinematic chain. The kinematic pairs can be lower (surface contact) or higher (point, line, and/or curve contact) order pairs, or combinations. 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.