The MSI-20 Score Provides Reproducible Mortality Risk Stratification in Spinal Infection: A Multicenter Registry Study and External Validation

Objective: Spinal infection (SI) is associated with substantial morbidity and mortality, and optimal treatment strategies remain debated, particularly in medically fragile patients. The Mortality in Spinal Infection (MSI-20) score was developed as the first dedicated prognostic tool for mortality risk estimation, but external validation in large cohorts has been lacking. This study aimed to externally validate the MSI-20 in a large multicenter registry cohort and assess its performance, clinical thresholds, and generalizability.Methods: This retrospective multi-institutional registry study included 1,122 adult patients with clinically, radiologically, and laboratory-confirmed SI treated at 6 tertiary referral centers between 2010 and 2023. The multicenter registry design enabled robust analysis of this relatively rare outcome. MSI-20 scores were calculated according to the original definition. Predictive performance was evaluated using receiver operating characteristic (ROC) analysis with 95% confidence intervals. Mortality across score strata and center-wise performance were analyzed, with exploratory assessment of additional baseline predictors.Results: Mean age was 66.4±13.1 years, and overall mortality was 18.3%. The MSI-20 demonstrated fair discriminative ability (area under the curve [AUC], 0.68; 95% confidence interval [CI], 64–72). The optimal ROC threshold was 3.5; a cutoff ≥4 yielded sensitivity 0.49 and specificity 0.74 (F1 score, 0.38). Mortality increased progressively, approaching 50% (47.4%) at scores ≥9. Performance was consistent across centers (AUC, 0.60–0.75). Exploratory univariable analyses did not identify additional baseline variables with consistent strong associations beyond the MSI-20 components.Conclusion: This large multicenter registry study provides the first external validation of the MSI-20, confirming reproducibility and generalizability. The score demonstrated fair discrimination and a clear risk gradient across increasing score categories. Given its simplicity and high negative predictive value, the MSI-20 may serve as an adjunctive tool to support risk communication, multidisciplinary discussion, patient counseling, and preoperative optimization in spinal infection.