Correlation between C₇ slope and cervical lordosis in patients after expansive open-door laminoplasty

Purpose of the article: To investigate the correlation between C₇ slope and cervical lordosis in patients after expansive open-door laminoplasty (EOLP).Material and methods: We retrospectively analyzed 57 patients who underwent EOLP between June 2013 and January 2017 in the Department of Spinal Surgery of our hospital. The operation time, intraoperative blood loss and follow-up time were recorded. The C₇ slope, C_2-7 sagittal vertical axis, and C_2-7 Cobb angle were measured anteroposterior radiograph of the cervical spine preoperatively and postoperatively. All patients were divided into two groups according to the preoperative C₇ slope (C₇ slope ≤20° group and C₇ slope >20° group).Results: The amount of intraoperative bleeding was 220.2 ± 180.9ml, and the operation time was 143.4 ± 51.2min. The average follow-up time was 24.9 ± 10.3months (range12-48 months). The C_2-7 Cobb angle was 13.49 ± 10.46°at the final follow-up, which was significantly lower than that preoperatively (p = .026). But, The C₇ slope and C_2-7 sagittal vertical axis showed no significant difference between preoperatively and postoperatively. Preoperative and postoperative C₇ slope and C_2-7 Cobb angle were positively correlated to age and significant difference was observed. In the group of C₇ slope >20°, significant difference was observed in term of the change of the C_2-7 Cobb angle and C_2-7SVA postoperatively (p = .009 and p= .020). However, there was no statistically significant difference detected in these two parameters in the group of C₇ slope ≤20°.Conclusion: This study indicated that C₇ slope could be used as an indicator of the change in the curvature of the cervical spine after EOLP. The loss of cervical curvature after surgery was prone to occur when C₇ slope was greater than 20°, which should be noted in clinical practice.