Postoperative Coronal Imbalance in Lenke 5C Adolescent Idiopathic Scoliosis: Evolution, Risk Factors, and Clinical Implications

Objective: To explore the changes in coronal imbalance (CIB) in Lenke 5C adolescent idiopathic scoliosis (AIS) after posterior selective fusion surgery and determine their implications for surgical decision-making. Methods: One hundred twenty patients were categorized according to the preoperative coronal pattern (type A, coronal balance distance [CBD] <20 mm; type B, CBD >= 20 mm and coronal C7 plumbline [C7PL] shifted to the concave side of the curve; type C, CBD >= 20 mm and C7PL shifted to the convex side of the curve). CIB group (CIB+) was defined as having a CBD >= 20 mm at the 2-year follow-up. Results: Compared to type A patients, the prevalence of postoperative CIB was higher in type C patients both immediately postoperative (22% vs. 38%, p <0.05) and at the final follow-up (5% vs. 29%, p < 0.05), whereas type A patients showed a greater improvement in CBD (9 of 12 vs. 6 of 24, p <0.05) at the final follow-up. The majority of patients in all groups had recovered to type A at the final follow-up (96 of 120). The proximal Cobb-1 strategy reduced the incidence of postoperative CIB (1 of 38) at the 2-year follow-up, especially in preoperative type C patients. Multivariate logistic regression analysis revealed that type C and overcorrection of the thoracolumbar curve were risk factors for CIB at the 2-year follow-up (p = 0.007 and p = 0.026, respectively). Conclusion: Patients with type C CIB in AIS exhibited unsatisfactory restoration, with 29% of them exhibiting CIB at the final follow-up. The selective fusion strategy of proximal Cobb-1 may reduce the risk of postoperative CIB especially when the preoperative coronal pattern is type C.