Analysis of the risk factors for increasing cervical sagittal vertical axis after cervical laminoplasty for cervical spondylotic myelopathy.

Abstract

The cervical sagittal vertical axis (cSVA) as another aspect of cervical alignment been recognized as one of the important factors affecting the pain and disability outcomes of cervical spine surgery. The purpose of the present study was to analyze the risk factors for increasing cSVA after cervical laminoplasty for cervical spondylotic myelopathy (CSM). This retrospective study included 110 consecutive patients (68 males and 42 females, average age 72.6years) who underwent laminoplasty for CSM between January 2007 and June 2018. We recorded the operative time, blood loss, Japanese Orthopaedic Association (JOA) score and the recovery rate. Radiological measurements were performed to analyze the following parameters: pre- and 1-year postoperative McGregor's slope (McGS), occiput to C2 Cobb angle (O-C2 angle), C2-C7 Cobb angle (C2-7 angle), T1-slope (T1S), C2-7 SVA (cSVA) and calculated the change (Δ). Patients were divided into two groups according to whether ΔcSVA was positive or negative. We also used Spearman's correlation coefficient and multiple regression analysis. ΔC2-7 angle, ΔT1S-preoperative C2-7 angle, ΔO-C2 angle were different between the two groups significantly. Correlation analysis between the ΔcSVA and the various sagittal parameters showed some independent explanatory factors including the ΔC2-7 angle (r = -0.25, p = 0.010), T1S-preoperative C2-7 angle (r = -0.28, p = 0.004), postoperative O-C2 angle (r = 0.26, p = 0.007), ΔO-C2 angle (r = 0.37, p = 0.001). Multiple regression analysis revealed that ΔcSVA was associated with the T1S-preoperative C2-7 angle (β = -0.25, p = 0.034) and ΔO-C2 angle (β = 0.32, p = 0.001). The imbalance between T1S and preoperative C2-7 angle influences the change of cSVA after cervical laminoplasty. If cSVA increases postoperatively, the O-C2 angle increases to compensate and maintain the horizontal gaze.