417 Optimizing Surgical Timing: Evaluating Disability, Frailty, and Deformity Severity Thresholds in Adult Spinal Deformity

INTRODUCTION: Adult spinal deformity is a complex condition with a challenging demographic that often has high frailty, disability, and deformity at the time of surgical correction. Thresholds at which there is a point of diminishing returns can help guide patients and surgical decision-making. METHODS: Patients were evaluated based on baseline deformity in pelvic tilt (PT), pelvic incidence to lumbar lordosis mismatch (PI-LL), and T1 pelvic angle (TPA). The modified adult spinal deformity frailty index (mASD-FI) was utilized to evaluate patients based on frailty score. Disability was assessed using the Oswestry disability index (ODI). The primary outcome was the difference in ODI from the baseline to the last follow-up. Multivariable logistic regression and conditional inference tree (CIT) machine learning were used to evaluate thresholds associated with the greatest increase in 2Y ODI from baseline. RESULTS: 289 patients met inclusion Baseline ODI was 42±17, which improved at 2Y to 24±19. Preoperative PT was 23°±10°, PI-LL was 13°±20°, and TPA was 20°±11.8°. CIT analysis determined independent thresholds for baseline disability of >35 for ODI as the threshold at which improvement of ODI at 2Y started diminishing. Similarly, baseline mASD-FI of >6.5, PT > 19°, PI-LL >20°, and TPA >16° were found as thresholds for maximal improvement of ODI at 2Y(all p<.01). In patients with BL ODI between 18-34, mASD-FI of <5 was found to be associated with greater disability improvement. Those with BL ODI >44 and <74 found mASD-FI of <8 to be predictive of greater return of baseline disability(all p<.05). CONCLUSIONS: We evaluated the intricate interplay between patient disability, frailty, and the severity of deformity to ascertain the critical thresholds at which surgical interventions start to yield diminishing returns.