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

Abstract

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.