Comparison of the Dynamic Response and Fracture Characteristics of Female and Male Lumbar Spine and Pelvis in Underbody Blast Loading

Abstract

Underbody blast (UBB) attacks on US Military vehicles in the recent conflicts resulted in debilitating injuries to mounted Warfighters. Biomechanical research studies in the last decade aimed to understand UBB related injuries to guide protective technology designs for military ground vehicles. The design of protective seats is driven by injuries to the pelvis and lumbar spine, which are aligned with the vertical direction of UBB loading. When the US Military began to open many combat roles to female soldiers in 2016, a need arose to understand the impact of survivability and protection for the female Warfighter population as well. Although several exist for males, there are no published studies that explore female pelvis and lumbar spine response and injury in UBB loading. It is unknown whether skeletal differences between females and males in the pelvis and lumbar regions would result in different fracture thresholds and damage patterns. Thus, critical information is missing to inform the design of injury mitigating technologies that protect the full Warfighter population.

As part of a female pilot study, this research compared the effect of UBB loading on the pelvis and lumbar spine of females and males. Whole-body and component post-mortem human surrogate (PMHS) tests were conducted to measure kinematic and injury response to UBB vertical loading. The study included small female, large female, and midsized male PMHS to evaluate the effect of both size and sex. Whole-body tests were conducted on a live blast driven rig to assess injury mechanisms under complex UBB conditions and the relationship between pelvis and lumbar responses. Isolated lumbar spine component tests were conducted using high-speed x-ray video to measure the fracture force and visualize the fracture propagation. Results suggest that there are differences between male and female UBB outcomes related to both sex and size. In whole-body tests, small females demonstrate a different injury pattern (pelvis fractures) than males (lumbar fractures), with large females exhibiting a mix of both. Mean fracture initiation forces in the lumbar component tests were different among the three PMHS groups, although the fracture propagation proved to be similar.