upper and lower plate members 100 102 are preferably made of a material that is compatible with the bone and as noted previously will preferably facilitate or promote bone grafting the intermediate member 108 is preferably made of a material that is essentially non resilient or of low resiliency such as for example a metal a ceramic or a polymer having a low degree of resiliency the function or operation of the prosthesis 10 in approximating the function or operation of a natural disc comes essentially from the degrees of freedom of movement provided between the upper and lower plates and the intermediate member 108 disposed there between the illustrated embodiment can be constructed with dimensions that are small enough to enable use of the prosthesis as a cervical disc prosthesis where the intervertebral spacing is small e g on the order of 8 9 mm thus it is envisioned that the prosthesis 10 will be especially suitable for use in replacing damaged cervical discs however the prosthesis can be sized as required to serve as a lumbar disc prosthesis as well the present invention also comprises a locking feature by which the post 136 is inserted into the recess 140 in such a way as to lock into it without detracting from the partial rotation capabilities described above this may be accomplished with a variety of alternative and equally well suited configurations.