QUANTIFYING THE EFFECT OF USER SIZE ON INJURY TOLERANCE OF THE UPPER EXTREMITY SUBJECTED TO BEHIND-SHIELD BLUNT TRAUMA

Abstract

The deformation associated with a ballistic shield defeating a projectile can interact with the user’s upper extremity, resulting in the release of the shield, placing those behind the device at risk. This injury mechanism is known as behind-shield blunt trauma (BSBT). Previous studies investigating these interactions have used testing conditions not representative of those present during these behind-shield events and lacked sufficient testing to determine statistically relevant outcomes. In the present work, the loading present during ballistic shield deformation was characterized through testing using an Anthropomorphic Test Device (ATD) upper extremity placed behind a level III ballistic shield. Digital image correlation (DIC) and post-impacting X-ray imaging were used to assess the ballistic shield’s deformation. The data collected from ballistic testing informed the development of a projectile used with a pneumatic impactor for the application of BSBT in a lab-based setting. Using the projectile, ballistic impacts were replicated on the ATD upper extremity and translated to 5th and 95th percentile cadaveric arms. Load data were collected for the hand and forearm using piezoelectric force sensors embedded in the projectile. Similarly, PMHS were impacted in a stepwise fashion of increasing energy until fractures were identified using X-ray imaging. A novel scaling technique was developed where Partial Least Squares (PLS) was used to determine critical variables relating donor anthropometrics to peak impact force. The scaling equations generated using this technique offer future researchers the opportunity to employ a larger range of specimens when determining injury thresholds for the hand and forearm. Through the characterization of the conditions present during BSBT, the injury thresholds to these mechanisms were assessed for understudied populations. Additionally, this work presents scaling techniques that could reduce the number of specimens required to determine future upper extremity injury limits. The information presented within this work provides an important step in developing new standards for ballistic shields to better protect users from BSBT.