A spinal disc prosthetic for replacement of cervical and/or lumber discs, that in each case allows a limited degree of rotational articulation, as well as durability and resistance to fatigue. The prosthetic is formed with three primary layers, including a superior (upper) plate, inferior (lower) plate, and intermediate layer, in a sandwiched configuration. The superior plate member is adapted to be secured on one side to an upper vertebra in a spinal column, and has a formed concave side exposed downwardly. The inferior plate member is adapted to be secured on one side to a lower vertebra in the spinal column, and has a substantially flat side exposed upwardly. The intermediate member is sandwiched between the superior and inferior plate members with conforming sides, and a short cylindrical post protrudes downward from the intermediate member and is seated inside a circular recess in the inferior plate member to center it and to maintain a predetermined spacing there between. This allows a degree of rotational freedom. A variety of locking assemblies lock the post in the recess to prevent withdrawal, thereby increasing durability without obstructing the degree of freedom.