Physiology-Based Liver Injury Criteria for Behind Armor Blunt Trauma.

INTRODUCTION: For Warfighter protection and safety in the thoraco-abdominal region, body armors have been evaluated for behind armor blunt trauma (BABT) risk using the Roma Plastilina No. 1 clay. The BABT criterion of 44 mm was developed more than 50 years ago and applied to all regions of the thoraco-abdominal complex although injury responses and tolerances are region and organ dependent. The objectives of this study were to develop BABT liver injury risk curves using an experimental animal model. MATERIALS AND METHODS: Animal use approvals from the institution and U.S. Department of Defense were obtained to test live swine. An indenter simulating backface deformation profiles from a live fire round to human surrogates covered with body armor was designed. It was instrumented with an accelerometer and launched from a custom compressed gas-driven system. Impacts were focused on the liver region of the supine positioned animal. After sustaining the impact, animals were monitored for 6 hours, necropsies were performed, and injuries were scored. Using the viscous criterion metric and parametric survival analysis, liver injury risk curves were developed, and ±95% confidence intervals (CI) were used to determine their qualities. RESULTS: At 10 and 50% risks, the mean viscous criterion were 2.3 and 4.0 m/s for mild, and 4.0 and 7.1 m/s for moderate liver injuries. The qualities of the injury risk curves were in the good-to-fair category at these injury probability levels. The developed mean and CI injury risk curves and qualities are given in the body of the paper. CONCLUSIONS: This is the first study to develop BABT liver injury risk curves using survival analysis from live swine tests. They can be used as preliminary liver tolerance criteria for BABT applications. They may also be used to improve the assessment of current and future body armor and improve Warfighter safety and medical readiness for injuries to the liver region.