Assessment of the interaction effect between injury regions in multiple injuries: A nationwide cohort study in Japan

BACKGROUND: There have been no clinical studies to sufficiently reveal the interaction effect generated by combinations of injury regions of multiple injuries. We hypothesized that certain combinations of trauma regions might lead to increased risk of traumatic death and aimed to verify this hypothesis using a nationwide trauma registry in Japan. MATERIALS AND METHODS: This was a retrospective study of trauma patients registered in the Japan Trauma Data Bank between 2004 and 2017. We included patients who suffered blunt trauma with an Injury Severity Score of 16 or more. The trauma was classified into four regions (head, chest, abdomen, and extremities), and a multivariable logistic regression analysis was performed that included interaction terms derived from the combination of two regions as covariates. RESULTS: We included 78,280 trauma patients in this study. Among them, 16,100 (20.6%) patients were discharged to death. Multivariable logistic regression showed the odds ratio (OR) of in-hospital death compared with patients without injury of an Abbreviated Injury Scale score of 3 or more in each injured region as follows: head score, 2.31 (95% confidence interval [CI], 2.13–2.51); chest score, 2.28 (95% CI, 2.17–2.39); abdomen score, 1.68 (95% CI, 1.56–1.82); and extremities score, 1.84 (95% CI, 1.76–1.93), respectively. In addition, the ORs of the statistically significant interaction terms were as follows: head-chest 1.29 (95% CI, 1.13–1.48), chest-abdomen 0.77 (95% CI, 0.67–0.88), chest-extremities 1.95 (95% CI, 1.77–2.14), and abdomen-extremities 0.70 (95% CI, 0.62–0.79), respectively. CONCLUSION: In this population, among patients with multiple injuries, a combination of head-chest trauma and chest-extremities trauma was shown to increase the risk of traumatic death. LEVEL OF EVIDENCE: Prognostic, Level III.