The new injury severity score is a better predictor of extended hospitalization and intensive care unit admission than the injury severity score in patients with multiple orthopaedic injuries.

Objective: To compare the scoring efficacy of the injury severity score (ISS) and the new injury severity score (NISS) in predicting extended hospital length of stay (LOS) and intensive care unit (ICU) admission and to determine the effect of multiple orthopaedic injuries (MOI) on the discrepancies between the ISS and NISS and their impact on extended LOS and ICU admission.

Design: Prospective cohort study.

Setting: Level 1 university trauma center.

Patients: All consecutive trauma admissions during the 2-year period ending on December 31, 2000, with age older than 14 years and survival greater than 24 hours were entered into the study.

Main Outcomes: Extended (>or=10 days) hospital LOS and ICU admission.

Results: Of 3,100 patients, 7.5% had a higher NISS than ISS, spent more days in the hospital (22 versus 8; P < 0.001) and in the ICU (3.4 versus 0.1; P < 0.001), and had a higher mortality rate (8% versus 1.2%; P < 0.001) than patients with identical NISS and ISS. The NISS was found to be more predictive of longer (>or=10 days) LOS (receiver operating characteristic [ROC] NISS = 0.794, ISS = 0.782; P < 0.0001) and ICU admission (ROC NISS = 0.944, ISS = 0.918; P < 0.0001). The multivariate predictive model including NISS showed a better goodness of fit compared with the same model that included ISS. Patients with discrepant scores (NISS > ISS) spent a longer time in the hospital and in the ICU in addition to having an increased frequency of ICU admission. In 61% of the cases, MOI were responsible for the discrepant (NISS > ISS) scores.

Conclusions: MOI have a significant effect on trauma outcomes such as LOS and ICU admission. The recognition of this high-risk group is not possible using the traditional ISS alone from retrospective or prospective databases. Considering its easier calculation and better predictive power, it is suggested that the NISS should replace the traditional ISS in trauma outcome research.