Coronal and Sagittal Balance Following Posterior Spinal Fusion for Adolescent Idiopathic Scoliosis

Background:Achieving and maintaining global spinal balance is a crucial goal in posterior spinal fusion for adolescent idiopathic scoliosis (AIS). Despite its substantial impact on operative success, there is a noticeable gap in the literature regarding a systematic evaluation of the trajectory and durability of this critical parameter. With this study, we aimed to characterize the evolution of global balance after posterior spinal fusion for AIS.Methods:A prospective, multicenter spinal deformity database was retrospectively queried for patients with AIS undergoing posterior spinal fusion. Standing, 2-view radiographs (anteroposterior and lateral) were obtained at the first-erect visit, 6 months, 1 year, 2 years, and 5 years, with a subset of patients having radiographs at the 10-year mark. Coronal balance was defined as the difference, in centimeters, between the C7 plumb line and the central sacral vertical line (CSVL). The sagittal vertical axis (SVA) measured sagittal balance, calculated as the difference, in centimeters, between the C7 plumb line and the posterosuperior corner of the superior end plate of S1.Results:The study included 477 patients with 5 years of follow-up and 84 patients with a decade of follow-up. The mean patient age was 14.1 years, 67.9% of the patients were White, and 81.6% of the patients were female. Preoperative assessment revealed that 50.7% of the patients demonstrated optimal global balance. The initial postoperative evaluation showed essentially no improvement, with only 55.6% achieving optimal balance (Coronal and Sagittal Harmony [CASH] A0) at the first-erect visit. Subsequent follow-up demonstrated steady improvement, with 81.8% reaching optimal balance at 5 years and 87.7% at the 10-year mark.Conclusions:This study offers a comprehensive analysis of global spinal alignment and traces the balance trajectory (in both the coronal and sagittal planes) after posterior spinal fusion in AIS. To our knowledge, it is the largest and longest follow-up study of its kind. The findings highlight a profound and steady postoperative improvement in global balance over time, advancing our understanding of postoperative spinal balance in AIS. The novel CASH classification introduced here serves as a possible tool for evaluating overall alignment and balance in patients with AIS.