Abstract: BACKGROUND: Preliminary studies have shown that double-level cervical disc replacement can significantly improve the sagittal parameters of the cervical spine, and is superior to the double-level ROI-C fusion cage, but there are differences in the sagittal parameters of the cervical spine in different surgical segments.  
OBJECTIVE: To study the differences between single-level Mobi-C artificial cervical disc replacement and sagittal parameters of the cervical spine after ROI-C anterior cervical fusion.
METHODS: Sixty patients with radicular, spinal cord or mixed cervical spondylosis who were treated in Dongzhimen Hospital, Beijing University of Chinese Medicine from January 2018 to February 2020 were retrospectively analyzed and divided into Mobi-C cervical artificial disc replacement group (disc group) and ROI-C anterior cervical fusion group (fusion group) according to the surgical method. All patients completed effective follow-up for more than half a year, mean (12.1±5.0) months. Visual analogue scale scores, cervical spine JOA scores, and X-ray films were detected before and 1 week after surgery and during final follow-up. The following cervical sagittal parameters were measured: C2-7 Cobb angle, C0-2 Cobb angle, C2-7 sagittal vertical axis, neck tilt, T1 slope, C7 slope, thoracic inlet angle, and spinal function unit angle. Intra- and intergroup differences were analyzed between both groups. A Pearson correlation analysis was conducted.  
RESULTS AND CONCLUSION: (1) At the 1 week after surgery and the last follow-up, visual analogue scale scores were significantly lower than before surgery (P < 0.05). Cervical spine JOA score was significantly higher (P < 0.05). (2) Compared with the preoperative data, there were no significant differences in C2-7 Cobb angle, C2-7 sagittal vertical axis or T1 slope in intervertebral disc group (P > 0.05); C0-2 Cobb angle and high T1 slope decreased (P < 0.05), while spinal function unit angle increased (P < 0.05). There were no significant differences in C2-7 Cobb angle, C2-7 sagittal vertical axis or T1 slope in the fusion group (P > 0.05), but spinal function unit angle and C7 slope increased (P < 0.05). Spinal function unit angle of the disc group was higher than that of the fusion group (P < 0.05). (3) The postoperative sagittal parameters of the patients in the fusion group showed a significant positive correlation between C2-7 Cobb angle and C7 slope; neck tilt was significantly positively correlated with thoracic inlet angle; T1 slope was significantly positively correlated with C7 slope; C7 slope was significantly positively correlated with C0-2 Cobb angle. In replacement group, C2-7 Cobb angle was significantly positively correlated with C7 slope, spinal function unit angle and T1 slope, and significantly negatively correlated with C0-2 Cobb angle; neck tilt was significantly positively correlated with thoracic inlet angle, and negatively correlated with C2-7 sagittal vertical axis, T1 slope and spinal function unit angle; C2-7 sagittal vertical axis was significantly positively correlated with C7 slope, spinal function unit angle and T1 slope; T1 slope was significantly positively correlated with C7 slope and spinal function unit angle; C7 slope was significantly positively correlated with spinal function unit angle. (4) In the disc group, postoperative thoracic inlet angle, T1 slope and C0-2 Cobb angle of patients with high T1 slope were significantly lower than those before operation (P < 0.05), while the spinal function unit angle was significantly higher than that before operation (P < 0.05). However, no significant changes were found in the fusion group. (5) It is concluded that Mobi-C intervertebral disc and ROI-C fusion device have significant efficacy in the treatment of single-level cervical spondylosis. Compared with the ROI-C cage, the Mobi-C disc restores the physiological curvature mainly by reconstructing the local cervical lordosis and upper cervical lordosis, and still maintains this ability in the high T1 slope angle patient population.

Key words: single-level cervical spondylosis, Mobi-C cervical disc, ROI-C fusion, cervical sagittal parameter