Kinematics of Cervical and Lumbar Total Disc Replacement

This article reviews the kinematics of disc arthroplasty and the different ways that current devices attempt to replicate normal segmental motion. All disc replacements are capable of rotation but not all are able to independently translate. It is “constraint” over the degree-of-freedom controlling independent translation of a prosthesis that dictates whether its center of rotation is fixed or can attempt to adjust to that of the implanted motion segment. Ball-and-socket-type articulations are constrained, while mobile core prostheses are unconstrained. The ideal kinematic type is yet to be determined and it may be that different circumstances will be best managed by different types of prostheses.