Risk factors and clinical impact of persistent coronal imbalance after posterior spinal fusion in thoracolumbar/lumbar idiopathic scoliosis

Abstract

OBJECTIVE Persistent coronal imbalance (PCI) can develop postoperatively. In this study, the authors aimed to clarify the risk factors and clinical impact of PCI after posterior spinal fusion (PSF) in idiopathic scoliosis (IS) patients with a major thoracolumbar/lumbar (TL/L) curve. METHODS Data on 108 patients with Lenke type 5C or 6C IS who underwent PSF with a minimum of 2 years of follow-up were retrospectively analyzed. PCI was defined as coronal imbalance persisting 2 years after surgery. Radiographic parameters and clinical outcomes were compared between the PCI (+) and PCI (−) groups. Multivariate regression analyses of associated factors were performed to determine the risk factors for PCI. RESULTS Of the 108 patients, 48 (44%) had immediate postoperative coronal imbalance, and 10 of these patients (9%) had coronal imbalance persisting 2 years after surgery. The PCI (+) group had significantly worse postoperative subtotal and satisfaction scores than the PCI (−) group. Preoperative apical vertebral translation (AVT) of the TL/L curve (AVT-TL/L) and postoperative coronal balance (CB) were identified as independent risk factors for PCI. The cutoff values of preoperative AVT-TL/L at 49.5 mm (area under the curve [AUC] 0.835, p = 0.001, 95% CI 0.728–0.941, sensitivity 70.0%, specificity 72.4%) and those of postoperative CB at −27.5 mm (AUC 0.837, p < 0.001, 95% CI 0.729–0.945, sensitivity 78.6%, specificity 70.0%) were used to predict PCI. In selective fusion cases, older age (OR 2.110, 95% CI 1.159–3.842, p = 0.015), greater preoperative AVT-TL/L (OR 1.199, 95% CI 1.029–1.398, p = 0.020), and less postoperative CB (OR 0.855, 95% CI 0.743–0.983, p = 0.027) were independent risk factors for PCI. CONCLUSIONS Preoperative AVT-TL/L and postoperative CB are important parameters for predicting PCI. PCI adversely affects postoperative clinical outcomes. In selective fusion surgery, PCI tends to occur in older patients due to reduced flexibility and compensatory abilities.