Statistical analyses
For baseline characteristics, we used descriptive statistics. For comparisons of LFT results 0-3 months before and 3-4 months after scoliosis surgery, a Wilcoxon-signed rank test was used. To investigate the trend of function decline, linear mixed effects models were fitted, which included a random intercept and random slope for time per individual. We introduced a linear spline for time (both fixed as random) with one knot at the time of surgery. Subsequently, we determined the rate of progression before and after surgery. Confidence intervals were estimated using bootstrapping (n =1000) and significance tests were based on the likelihood ratio test.
Results