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

Purpose of the article: To investigate the correlation between C-7 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 C-7 slope, C2-7 sagittal vertical axis, and C2-7 Cobb angle were measured anteroposterior radiograph of the cervical spine preoperatively and postoperatively. All patients were divided into two groups according to the preoperative C-7 slope (C-7 slope <= 20 degrees group and C-7 slope >20 degrees 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 C2-7 Cobb angle was 13.49 +/- 10.46 degrees at the final follow-up, which was significantly lower than that preoperatively (p = .026). But, The C-7 slope and C2-7 sagittal vertical axis showed no significant difference between preoperatively and postoperatively. Preoperative and postoperative C-7 slope and C2-7 Cobb angle were positively correlated to age and significant difference was observed. In the group of C-7 slope >20 degrees, significant difference was observed in term of the change of the C2-7 Cobb angle and C(2-7)SVA postoperatively (p = .009 and p= .020). However, there was no statistically significant difference detected in these two parameters in the group of C-7 slope <= 20 degrees. Conclusion: This study indicated that C-7 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 C-7 slope was greater than 20 degrees, which should be noted in clinical practice.