The segmental distribution of cervical range of motion: A comparison of ACDF versus TDR-C.

This study was a retrospective radiographic evaluation of patients after cervical total disc replacement (TDR-C) or anterior cervical discectomy and fusion (ACDF) for one-level cervical disc disease. Our objective was to evaluate (1) total cervical (C1-C7) range of motion (ROM) during dynamic imaging, and (2) relative contribution to total cervical ROM from operative and adjacent levels. Radiographic review of 64 patients who underwent TDR-C (n = 30) or ACDF (n = 34) for one-level cervical disc disease. ROM measurements were performed independently using a vertebral motion analysis system to evaluate total cervical ROM and relative contribution to total ROM from each level (C1-C7) preoperatively and at 12-month follow-up. At follow-up, TDR-C patients had significantly greater improvement in total cervical ROM (+5.67°, 1.15 mm) than ACDF patients (-0.96°, 0.12 mm) (P = 0.001). In TDR-C patients, relative contributions to total cervical ROM from operative and adjacent caudal and cranial levels were statistically equivalent to baseline values. ACDF patients had a significantly reduced contribution to total cervical ROM from the operative level (-22.5%, P < 0.001) and significantly elevated contributions from the adjacent caudal level (+16.5%-21.3%, P < 0.001) and from the adjacent first (20.6% vs. 34.6%, P < 0.001), second (22.9% vs. 30.4%, P < 0.001), and third cranial levels (17.5% vs. 25.6%, P < 0.001). The cervical spine compensates for loss of ROM at the operative level in ACDF patients. However, total cervical ROM increases with TDR-C and maintains physiologic distribution of ROM throughout the cervical spine at 12-month follow-up, potentially reducing the risk for adjacent segment breakdown.