Effect of preoperative dynamic cervical sagittal alignment on the loss of cervical lordosis after laminoplasty

Purpose: Cervical laminoplasty (CLP) is a developed surgical procedure for the treatment of cervical spondylotic myelopathy (CSM), but only a few of those studies focus on preoperative dynamic cervical sagittal alignment and the study of different degrees of loss of cervical lordosis (LCL) is lacking. This study aimed to analyze patients who underwent CLP to investigate the effect of cervical extension and flexion function on different degrees of LCL. Methods: This was a retrospective study of the patients who underwent CLP between January 2019 and December 2020. The cervical lordosis (CL), T1 slope (T1S), cervical sagittal vertical axis (cSVA), CL in flexion (Flex CL), CL in extension (Ext CL), cervical spine range of motion (ROM), cervical spine range of flexion (Flex ROM) and extension (Ext ROM) were measured. The extension ratio (EXR) was defined as 100 × Ext ROM/ROM. LCL was defined as preoperative CL - postoperative CL. Patients were classified into the following three groups according to the LCL: stability group: (LCL ≤ 5°); mild loss group (5° 10°). The Japanese Orthopedic Association (JOA) score was used. Results: Seventy-nine patients were enrolled (mean age 62.92 years; 51 men, 28 women) in the study. Among the three groups, cervical extension Ext ROM was the best in the stability group. Compared with the stability group, Flex ROM was significantly higher and the extension ratio (EXR) was significantly lower in the severe loss group. Compared with the severe loss group, JOA recovery rates were better in the stability group. Receiver-operating characteristic curve (ROC) analysis to predict LCL > 10° (area under the curve = 0.808, p < 0.001). The cutoff value for EXR was 16.80%, with sensitivity and specificity of 72.5% and 82.4%, respectively. Conclusion: CLP should be carefully considered for patients with a preoperative low Ext ROM and high Flex ROM, as a significant kyphotic change is likely to develop after surgery. EXR is a useful and simple index to predict significant kyphotic changes.