The discrepant clinical outcome predictions according to the differentiated centre of rotation shift after multilevel cervical total disc replacement.

PURPOSE: Cervical total disc replacement (TDR) aims to maintain normal cervical kinematics after surgery. This study investigates the relation between shifted location of centre of rotation (COR) and subsequent surgical outcomes after multilevel cervical TDR (MCTDR) and identifies radiological parameter that corresponded to this change of COR after MCTDR. METHODS: The study included a consecutive 24 patients treated with MCTDR following the diagnosis of multilevel cervical disc herniation or stenosis. Numeric Rating Scale (NRS), range of motion (ROM) at both C2-7 segment and TDR implanted levels, and location of COR at TDR level were evaluated at pre- and post-MCTDR. These parameters were compared between patients who experienced successful and unsuccessful pain relief. RESULTS: The inherent CORs relatively at ventro-cranial coordinates have demonstrated significant migrations to dorso-caudal location, more prominent shifts for the successful group, after MCTDR switch. The unsuccessful group showed markedly reduced C2-7 ROM and reduced angular improvement at C2-7 as well as MCTDR level in comparison with the successful group. Postoperative C2-7 ROM was related to postoperative COR along the X axis. CONCLUSION: The determinant for clinical success after MCTDR, other than mere preservation of the ROM both at C2-7 and TDR levels, was restoration of COR from ventro-cranial location close to normal coordinates by posterior and inferior shifts. The position of COR along the X axis after MCTDR was important factor to determine maintenance of C2-7 ROM.