The Impact of Global Imbalance on Pelvic Fixation Failure: A Single Institution Matched Case-Control Study

Study DesignRetrospective matched case-control study.ObjectivesPelvic fixation failure (PFF) is a rare, underrecognized mechanical complication from surgical management of adult spinal deformity (ASD). Studies show that residual postoperative malalignment may increase mechanical stress on pelvic instrumentation, but the role of global radiographic parameters in predicting PFF remains poorly defined. Our study aims to identify radiographic predictors of PFF and evaluate the time-dependent relationship between residual deformity and PFF rates.MethodsThis was a single-center, retrospective, matched case-control study of ASD patients who underwent pelvic fixation from 2016-2024 and had >1-year postoperative follow-up. PFF was defined as any reoperation for pelvic screw or rod failure, and patients were matched in a 1:4 ratio by age and sex. Global radiographic outcome measures were collected, and multivariable logistic regression and Cox proportional hazard models were used to assess PFF predictors and time-to-failure.Results31 (5.99%) of 517 eligible patients experienced PFF, and 94 patients were included in total after propensity matching with 63 eligible controls. Postoperative C2 Tilt (C2T) (OR: 1.15, P = 0.013) and ΔC7-Central Sacral Vertical Line (ΔC7-CSVL) (OR: 1.66, P = 0.007) were associated with increased PFF risk. T1-Pelvic Angle (T1PA) trended toward significance (P = 0.062). Time-to-event analysis confirmed these findings and identified a C2T cutoff for hazard ratio>1 of 6.9°.ConclusionsResidual postoperative global spinal imbalance, specifically C2T, is a significant predictor of PFF and accelerated time-to-failure. This highlights the importance of achieving global alignment intraoperatively to improve long-term construct durability and prevent PFF complications in ASD surgery.