Relationship between the course of postoperative pelvic axis rotation and shoulder balance in patients with Lenke types 1 and 2 adolescent idiopathic scoliosis

Background: Posteroanterior radiographs of patients with adolescent idiopathic scoliosis (AIS) show bilateral differences in the iliac wings. This is due to pelvic axis rotation (PAR) associated with scoliosis. We often encounter cases wherein the PAR changes with surgery and postoperatively. We investigated the course of preoperative PAR and the relationship between PAR and shoulder balance in patients with Lenke 1,2 AIS. Methods: In total, 28 patients with Lenke 1,2 AIS undergoing scoliosis correction were included. The PAR and shoulder parameters were measured on posteroanterior radiographs. The correlation between the measured parameters and the extent of changes in each parameter was also examined. Results: Eleven patients (39.3 %) underwent preoperative PAR. Six patients (21.4 %) showed a greater change in PAR from 1 week to 2 years postoperatively. The rotation did not change significantly from preoperatively to immediately postoperatively but changed during the first three months postoperatively. The rotation group had significantly more balanced shoulders at 2 years (P = 0.025). The rotation group had a greater change in shoulder balance in the postoperative course significantly (P < 0.05). The extent of change in pelvic rotation from 1 week to 2 years postoperatively correlated with the extent of change in shoulder balance. Conclusion: The PAR in patients with Lenke 1,2 AIS significantly changed during 3 months postoperatively. Patients with Lenke 1,2 AIS with preoperative PAR can be expected to have postoperative shoulder rebalancing.