Blast events are widely associated with serious injuries that can have lifelong effects on Service members. Soldiers seated in military vehicles are particularly susceptible to underbody blast injuries, which can occur in contemporary combat environments as a result of vertical acceleration caused by contact with improvised explosive devices (IEDs) or anti-tank landmines; this seated posture makes the pelvis and spinal column more vulnerable to the effects of these blasts, as they absorb the brunt of the impact. It is difficult to directly apply safety standards for civilian vehicles to military vehicles, as the unique injury mechanisms for humans in combat (vertical loading due to explosives) differ greatly from those of civilian automobile accidents, which are almost exclusively in the lateral plane. Injury risk curves (IRCs) can be developed to create projections of injury burdens that help to define thresholds of force that the body can withstand before being damaged by vertical impact loading from vehicle underbody blasts.
A recent publication1 from a collaborative effort led by Prof. Narayan Yoganandan at the Medical College of Wisconsin examined the effects of underbody blast on the lumbar portion of the human spinal column. Spinal specimens were obtained from 43 male post-mortem human subjects and were fixed in place to a vertical acceleration device designed to mimic Soldier seating positions in armored vehicles; the bone mineral density of each specimen was also calculated to assess pre- and post-impact structural integrity. The specimens were divided into two groups that were subjected to a weight-drop model to deliver either single or multi-level spinal fractures that increased in severity until damage was observed in the specimens through post-test imaging and dissection. IRCs demonstrating a range of pathologies were determined through statistical analysis of the changes in either bone mineral density or body area as a result of the impacts of the different forces applied to the underbody.
Comparison of the IRCs between the two groups of specimens demonstrated that the best descriptors of injury were: 1) the combination of the entire system of forces applied to the base of the lumbar spine and bone mineral density and 2) the combination of the axial force applied to the top portion of the lumbar spine and body area. This publication draws attention to the variable physical forces that act on the human body during blast events, which are reflected in the cumulative injuries sustained by each specimen. Simulation of underbody blasts is crucial to our understanding of the interactions between biomechanics, combat training and operational environments, and injury prevention. IRCs, such as those presented by Yoganandan et al.1, can be used to inform the development of computational models and crash-test dummies to improve combat vehicle design to enhance Service member safety.
1 Yoganandan N, Moore J, DeVogel N, et al.
"Human lumbar spinal column injury criteria from vertical loading at the base: Applications to military environments."
J Mech Behav Biomed Mater 2020;105:103690.
This research was supported in part by Cooperative Agreement W81XWH-16-01-0010, Department of Veterans Affairs, United States Army Medical Research and Development Command, and the Department of Neurosurgery at the Medical College of Wisconsin, United States. This work was performed as part of the Biomechanics Product Team led by the Johns Hopkins Applied Physics Laboratory, United States (JHU/APL) and supported under contract #N00024-13-D- 6400, sponsored by the U.S. Army Research Lab in support of the WIAMan Program.
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