Relationship between preoperative supine radiographs and intraoperative coronal spinal alignment in thoracic adolescent idiopathic scoliosis

Significant variability exists among surgeons regarding planning methods for adolescent idiopathic scoliosis (AIS) surgery. Lenke et al. advocated the use of preoperative supine full-spine radiographs, but their accuracy in predicting intraoperative alignment remains debated. This study aimed to compare preoperative supine radiographs with intraoperative prone radiographs during AIS posterior fusion. A total of 139 patients undergoing AIS posterior fusion at a single center were prospectively studied. Frontal radiographic parameters from preoperative supine full-spine films were compared with those from prone radiographs at the beginning of surgery to verify the lower instrumented vertebra (LIV). Pearson correlation coefficients assessed the relationship between preoperative supine and intraoperative non-instrumented (NI) radiographs. Strong correlations were found for thoracic and lumbar Cobb angles (r > 0.8). The main thoracic angle decreased from 46° to 44° (mean difference 2°, p = 0.004), and the lumbar angle from 27° to 25° (mean difference 2°, p < 0.0001). The C7-Central Sacral Vertical Line (CSVL) correlation was weaker (r = 0.3). All curves showed significant reduction intraoperatively compared with preoperative supine films (p = 0.045 for thoracic and p = 0.03 for lumbar). The apical vertebral translation ratio (AVTMT/AVTL) showed no significant difference (p = 0.2). Preoperative supine radiographs reliably predict intraoperative alignment and are valuable for AIS surgical planning. However, parameters related to CSVL, LIV tilt, and Disc Wedging Angle (DWA) may be more influenced by positioning and soft-tissue release.