Epidemiology and Outcomes of Battlefield-Related Penetrating and Closed Traumatic Brain Injuries Compared to Non-Head Injuries: A Retrospective Cohort Study

Introduction: Traumatic brain injuries (TBIs) are associated with substantial morbidity and mortality. We examined characteristics and outcomes among military personnel with battlefield-related penetrating TBI (pTBI) compared to closed TBI (cTBI) and non-head injuries (without cranial injuries). Materials and Methods: Military personnel admitted to participating U.S. military hospitals (2009-2014) were classified based on injury patterns: pTBI, cTBI (head Abbreviated Injury Scale [AIS] ≥3), and non-head (≥1 non-head injury AIS ≥3). Propensity score and inverse probability of treatment weighting (IPTW) were used to assess associations with mortality, hospital stay, and infection burden. Results: The study population included 106 pTBI patients, 259 cTBI patients, and 715 patients with non-head injuries. Patients with pTBIs were more severely injured with differing injury mechanisms compared to the other 2 groups. Patients with pTBIs had more critical care requirements versus both cTBI and non-head injury patients (P < .05) and longer hospitalization (median 27 days vs. 22; P = .041) compared to cTBI patients. More central nervous system (CNS) infections were diagnosed among patients with pTBIs (11.3%) versus cTBIs (1.2%) and non-head injuries (0.7%; P < .001). Although the overall proportion of patients who developed non-CNS infections was not significantly different between the TBI groups, there was a higher proportion among pTBI versus non-head injury patients (53.8% vs. 40.8%; P = .012). Patients with pTBIs also had less skin and soft-tissue infections and more pneumonia compared to non-head injury patients (P < .05). There was no significant difference in the proportion of mortality between the pTBI and cTBI patients (7.6% vs. 3.1%); however, it was higher compared to patients with non-head injuries (1.0%; P < .001). Sustaining any TBI (penetrating or closed) was associated with greater risk of mortality compared to non-head injuries (risk ratio: 3.71; 95% CI, 1.83-7.55). Conclusions: Patients with pTBIs are critically injured with substantial critical care requirements and morbidity. Between patients with pTBIs and cTBIs, there was not a significant difference in non-CNS infection burden or mortality, but pTBI patients did have longer hospitalization. When compared to severely injured military personnel with non-head injuries using propensity scores and IPTW analysis, sustaining a TBI (penetrating or closed) was not associated with having more non-CNS infections or a longer hospital stay. This may be a result of the high injury severity (median of 26) and relative occurrence of polytrauma in the total population. Patients with TBIs (penetrating or closed) did have a greater risk of mortality compared to patients with non-head injuries.