Modified Injury Severity Score

Used to stratify anatomic trauma severity and predict mortality by summing the squares of the three highest AIS injuries regardless of body region. Indicated for moderate–severe trauma, registry reporting, benchmarking, and as a predictor of survival (higher scores correlate with mortality; ISS independently associated with in‑hospital death, OR 1.02 per point 1 [Level II evidence]). Useful when multiple severe injuries occur in the same region, where traditional ISS underestimates risk.

Identifies overall anatomic burden more intuitively than ISS, but shares key limitations: relies on AIS coding, which is subjective and inconsistently applied, leading to unreliable stratification similar to ISS issues noted in ECMO‑trauma evidence 1. Overestimates severity when multiple moderate injuries cluster in one region; may misclassify complex polytrauma. Not validated for triage or outcome prediction, and calibration is untested. Use only as a rough comparative index, not for clinical decision‑making.