Mechanical complications and reoperations after adult spinal deformity surgery: a clinical analysis with the GAP score

Purpose: Adult spinal deformity (ASD) surgery is prone to postoperative complications, leading to high reoperation rates. The global alignment and proportion (GAP) score is a novel method to predict mechanical complications (MC) based on the optimal parameters related to individual pelvic incidence. The aim of this study was to determine the cut-off point and the predictive value of the GAP score for those MCs that require reoperation. A secondary aim was to investigate the cumulative incidence of MCs requiring reoperation during a long follow-up period. Methods: In total, 144 ASD patients were operated at our institution due to marked symptomatic spinal deformity between 2008 and 2020. The cut-off point and the predictive value of the GAP score for the MCs that required reoperation and the cumulative incidence of reoperated MCs after index surgery were determined. Results: A total of 142 patients were included in the analysis. The risk for having an MC that required reoperation was significantly lower when the postoperative GAP score was < 5 (HR = 3.55, 95% CI: 1.40–9.02). The discriminative power of the GAP score to predict MCs that require reoperation was good with an AUC of 0.70 (95% CI: 0.58–0.81). The cumulative incidence of reoperated MCs was 18%. Conclusion: The GAP score was associated with the risk for MCs that require reoperation. The best predictive value for surgically treated MC was with the GAP score ≥ 5. The cumulative incidence of the reoperated MCs was 18%.