The Effect of Unfused Segments in Coronal Balance Reconstitution After Posterior Selective Thoracolumbar/Lumbar Fusion in Adolescent Idiopathic Scoliosis

STUDY DESIGN A retrospective radiographical analysis. OBJECTIVE To assess the effect of unfused segments in the reconstitution of coronal balance after posterior selective thoracolumbar/lumbar (TL/L) curve fusion for adolescent idiopathic scoliosis. SUMMARY OF BACKGROUND DATA Current literature suggests that compensatory changes occur after selective TL/L curve fusion surgery. Hitherto, the roles of the unfused levels in coronal balance reconstitution have not been fully understood. METHODS Radiographical data of patients with idiopathic scoliosis who underwent selective posterior TL/L curve fusion Peking Union Medical College Hospital before October 2011 with a minimum of 2 years of follow-up period were retrospectively analyzed. Changes of coronal trunk shift during the follow-up period were studied and multiple linear regression analysis was performed to determine its correlation with changes of upper and lower curve of unfused thoracic segments, instrumented segments angle, distal unfused segments angle, and coronal sacral inclination. RESULTS A total of 43 patients were included in this study. Preoperative and first erect radiographs demonstrated trunk shifts of 21.1 mm and 18.7 mm respectively, showing no significant differences (P = 0.205). At the last follow-up, it compensated to 9 mm, which showed significant differences (P < 0.01). Regression analysis of all patients showed that coronal trunk shift changes only correlated with distal unfused segment angle changes. Subgroup analysis based on the magnitude of preoperative thoracic curve found that only distal unfused segments had an impact on coronal balance reconstitution. However, subgroup analysis based on the flexibility of preoperative thoracic curve showed that both proximal unfused thoracic segments and distal unfused lumbar segments contributed to coronal balance compensation in patients with a thoracic curve flexibility rate of more than 70%. CONCLUSION The reconstitution of coronal balance was mainly compensated by distal unfused segments after selective posterior fusion of TL/L idiopathic scoliosis. The effect of unfused thoracic segments in coronal balance reconstitution mainly depended on its flexibility.