Interplay of Dynamic Extension Reserve and T1 Slope in Determining the Loss of Cervical Lordosis Following Laminoplasty: A Novel Classification System

Abstract

Background Laminoplasty causes destruction of the posterior musculoligamentous complex, which may result in cervical kyphosis, or more commonly loss of cervical lordosis (LOCL). In this study, we evaluated the role of various preoperative radiologic parameters in predicting not only the LOCL/kyphosis but also the functional outcomes in the form of change in Oswestry Disability Index (ODI) score following laminoplasty. Methods Patients were evaluated both clinically and radiologically with dynamic cervical spine radiograph, noncontrast-enhanced computed tomography, and magnetic resonance imaging of the cervical spine preoperatively as well as at 1 year follow-up. Results One hundred twenty-one patients who underwent laminoplasty for cervical spondylotic myelopathy/ossified posterior longitudinal ligament from 2011 to 2018 at our center were included in final analysis. In multivariate analysis, preoperative Cobb angle (P = 0.001), T1 slope (TIS; P = 0.001), and dynamic extension reserve (P < 0.001) were found to have an independent effect on LOCL. The receiver operating characteristic curve using the regression model significantly predicted LOCL >10° with an area under the curve of 88.3% (P < 0.001). Similarly, preoperative T1S (P = 0.036) and SVA (P < 0.001) were found to be independent predictors of significant improvement in ODI after laminoplasty. The receiver operating characteristic curve using the regression model significantly predicted change in ODI with an area under the curve of 83.7% (P < 0.001). Based on these findings, classification and scoring systems with good accuracy have been proposed for prediction of LOCL and improvement in ODI. Conclusions We have found that the chances of significant LOCL is determined by an interplay of preoperative Cobb angle, T1S, and dynamic extension reserve.