Postoperative Coronal Imbalance Predicts Late Mechanical Failure and Revision Surgery After Adult Spinal Deformity Correction With Pelvic Fixation: A 5-Year Follow-Up Study in Elderly Patients

Purpose Postoperative coronal imbalance (CIB) is a persistent concern following adult spinal deformity (ASD) surgery. This study aimed to determine whether postoperative CIB independently increases the risk of mechanical complications and revision surgery, and to investigate whether the side of rod fracture correlates with the direction of coronal shift. Methods We retrospectively reviewed 241 patients aged ≥ 65 years who underwent long-segment ASD correction with pelvic fixation between 2010 and 2020. A total of 169 patients (70.1%) completed a minimum 5-year follow-up. Postoperative CIB was defined as C7CSVL > 3 cm. Mechanical complications included proximal junctional kyphosis (PJK), proximal junctional failure (PJF), and rod fracture. Revision surgery was recorded when reoperation was required for painful PJF or rod fracture. Survival analysis was performed using Kaplan–Meier and Cox proportional-hazard models. Results Thirty-four patients (20.1%) exhibited postoperative CIB. Compared with patients without CIB, these patients had greater preoperative coronal deviation (p < 0.001) and longer fusion constructs (9.9 ± 2.3 vs 9.2 ± 2.2 levels; p = 0.007), whereas sagittal vertical axis was comparable (p = 0.876). The incidence of rod fracture (35.3% vs 17.0%; p = 0.034) and revision surgery (35.3% vs 17.8%; p = 0.035) was significantly higher in the CIB group. Kaplan–Meier analysis showed reduced 5-year revision-free survival (HR = 2.0; 95% CI 1.0–4.0; log-rank p = 0.046), with divergence of survival curves evident after 2 years. Rod fractures occurred more frequently on the contralateral side to the direction of coronal shift (61.0%). Conclusions Postoperative coronal imbalance is an independent predictor of late mechanical failure and revision after ASD correction with pelvic fixation in elderly patients. The novel association between coronal shift direction and rod-fracture laterality provides clinical validation of asymmetric mechanical loading, underscoring the importance of precise coronal alignment and side-specific reinforcement to improve long-term construct durability. Level of Evidence: Ⅲ