Statistical analysis
neurological impairments, NDI
REGRESSION
Descriptive statistics are presented with mean value (mean) and standard deviation (SD), or number (n) with percentage (%). Between-group difference in postoperative neurological outcomes including persistent neurological impairments and recovery at one- and two-year follow-up was analysed with the Chi-square test. Change over time in the presence of neurological impairments was analysed in both groups with the Cochrane Q test, and post-hoc tests with the McNemar test. Univariate associations between one-year persistent neurological impairments in sensibility, motor function, arm reflexes and a positive Spurling test were reported. Further, the contribution of the preoperative factors sex, age, surgical procedure, randomization group and preoperative neurological impairments to one-year persistent neurological impairments were investigated with multiple forward logistic regression analysis. The results are presented with odds ratio (OR) and 95% confidence interval (CI). Finally, stepwise linear regression analysis was used to investigate association between persistent neurological impairments and the primary outcome NDI at one- and two-year follow-up. Sex, age, surgery and randomization were also entered into the model, and significant associations were reported with B coefficient, 95% CI and the adjusted coefficient of determination (adj. R2). The required sample size for the study was determined based on the primary outcome of the RCT; NDI with an expected 10% between-group difference, assuming 80% power, and a level of significance of 5%, with allowance for drop-outs (n = 82). A total of 202 patients were recruited. Statistical Package for the Social Sciences (SPSS) Statistics 26 was used for statistical analyses. All analyses were performed by a university statistician and according to intention-to-treat principles, keeping the initial randomization. A p < 0.05 was regarded as significant.