Limited Predictive Performance of the Global Alignment and Proportion (GAP) Score for Mechanical Complications in Older Asian Patients With Adult Spinal Deformity: A Multicenter Validation Study

This retrospective multicenter Japanese study tested whether the Global Alignment and Proportion (GAP) score, designed to predict mechanical complications after adult spinal deformity surgery, works as well in older Asian patients as it does in the Western populations it was developed from. Among 274 patients followed at least 2 years, 34% developed a mechanical complication, and the GAP score failed to distinguish complication from non-complication patients overall; in patients 70 and older, those who developed complications actually had lower (more 'proportioned') GAP scores (6.6 vs 7.9, p=0.039) after matching, the opposite of what the score predicts, though the age-by-GAP interaction itself was not statistically significant. The ROC area under the curve for GAP score alone predicting complications was 0.466, essentially no better than chance.

AI summary · from the full text · reviewed by Pukhraj Gaheer, Medical Student, Queen's University before publishing

Why it mattersSpine surgeons using the GAP score to counsel older Asian patients about mechanical complication risk should know it performs poorly, essentially no better than a coin flip, in this population.

Presenting this at rounds? Start here

• ?If GAP score alignment targets don't predict mechanical complications in older Asian patients, should surgeons weight bone quality (e.g., Hounsfield units) or muscle mass more heavily than radiographic alignment when planning correction goals in this population?
• ?Given that well-aligned older patients still developed complications while some malaligned patients did not, should surgeons reconsider how aggressively they pursue GAP-defined 'proportioned' alignment in frail elderly patients if it doesn't reduce mechanical complication risk?