Segmental contribution toward total cervical range of motion: a comparison of cervical disc arthroplasty and fusion

Prospective radiographic evaluation of patients that underwent cervical total disc replacement (TDR-C) or anterior cervical discectomy and fusion (ACDF) for one-level cervical disc disease. To evaluate the following: (1) total cervical range of motion (ROM) from C2 to C7, and (2) the relative contribution to total cervical ROM from the operative level and each adjacent level after one-level TDR-C or ACDF. The development of symptomatic adjacent segment disease after ACDF has served as the impetus for the development of motion-preserving alternatives, most notably cervical disc arthroplasty. While previous reports have evaluated device-level and total cervical motion, no study has comprehensively quantified the relative contribution made from each of the adjacent levels to total cervical ROM in TDR-C and ACDF. Radiographic review of 187 randomized patients from a multicenter, prospective, randomized trial comparing TDR-C with ACDF for one-level cervical disc disease. There were 93 TDR-C and 94 ACDF patients included. ROM measurements were performed independently using quantitative motion analysis, a custom digitized image stabilization software program, to evaluate total cervical ROM and relative contribution to total ROM from each level from C2 to C7 preoperatively and at 24 months. The most common operative level was C5/C6 (57%) followed by C6/C7 (34%). At 2 years, the TDR-C group underwent a statistically greater improvement in total cervical ROM (+5.9°) compared with ACDF (-0.8°, P = 0.001). In TDR-C, the relative contributions to total cervical ROM from the operative level and each caudal and cranial adjacent level were statistically equivalent from baseline to 24 months. In contrast, ACDF patients had significantly reduced contribution to total cervical ROM from the operative level (by 15%, P < 0.001), and significantly elevated contribution from the caudal adjacent level (by 5.9%, P < 0.001), first cranial adjacent level (by 3.3%, P < 0.001), second cranial adjacent level (by 5.3%, P < 0.001), and third cranial adjacent level (by 3.0%, P < 0.001). Compensation for the loss of motion at the operative level in ACDF is seen throughout the unfused cervical spine. Cervical disc arthroplasty, however, increases total cervical ROM compared with ACDF and maintains a physiologic distribution of ROM throughout the cervical spine at 2 years, potentially lowering the risk for adjacent segment breakdown.