Defining a Surgical Invasiveness Threshold for Increased Risk of a Major Complication Following Adult Spinal Deformity Surgery

Study Design. Retrospective review. Objectives. The aim of this study was to define a surgical invasiveness threshold that predicts major complications after adult spinal deformity (ASD) surgery; use this threshold to categorize patients into quartiles by invasiveness; and determine the odds of major complications by quartile. Summary of Background Data. Understanding the relationship between surgical invasiveness and major complications is important for estimating the likelihood of major complications after ASD surgery. Methods. Using a multicenter database, we identified 574 ASD patients (more than 5 levels fused; mean age, 60 +/- 15 years) with minimum 2-year follow-up. Invasiveness was calculated as the ASD Surgical and Radiographic (ASD-SR) score. Youden index was used to identify the invasiveness score cut-off associated with optimal sensitivity and specificity for predicting major complications. Resulting high- and low-invasiveness groups were divided in half to create quartiles. Odds of developing a major complication were analyzed for each quartile using logistic regression (alpha = 0.05). Results. The ASD-SR cutoff score that maximally predicted major complications was 90 points. ASD-SR quartiles were 0 to 65 (Q1), 66 to 89 (Q2), 90 to 119 (Q3), and >= 120 (Q4). Risk of a major complication was 17% in Q1, 21% in Q2, 35% in Q3, and 33% in Q4 (P<0.001). Comparisons of adjacent quartiles showed an increase in the odds of a major complication from Q2 to Q3 (odds ratio [OR] 1.8; 95% confidence interval [CI]: 1.0-3.0), but not from Q1 to Q2 or from Q3 to Q4. Patients with ASD-SR scores >= 90 were 1.9 times as likely to have a major complication than patients with scores <90 (OR 1.9, 95% CI 1.3-2.9). Mean ASD-SR scores above and below 90 points were 121 +/- 25 and 63 +/- 17, respectively. Conclusion. The odds of major complications after ASD surgery are significantly greater when the procedure has an ASD-SR score >= 90. ASD-SR score can be used to counsel patients regarding these increased odds.