Computational and experimental studies have been undertaken to investigate
injurious head-first impacts (HFI), which can occur during automotive rollovers.
Recent studies assume a torso surrogate mass (TSM) boundary condition, wherein
the first or first two thoracic vertebrae are potted and constrained to only
move in the vertical loading direction. The TSM boundary condition has not been
compared with a full body (FB) model computationally or experimentally for HFI.
In this study, the Global Human Body Models Consortium 50th percentile male
detailed human body model (M50-O, Version 6.0) was applied to compare the
kinematic, kinetic, and injury response of an HFI with a TSM boundary condition
(M50-TSM), and a full body boundary condition (M50-FB). Impacts (to M50-TSM and
M50-FB) were simulated between the head and a rigid plate using a commercial FE
code (LS-DYNA). The impact velocity of 3.1 m/s corresponded to the onset of
spinal injury in diving reconstructions, and the impact velocity reported in
experiments. The TSM boundary condition was simulated by applying a mass of 16
kg to the first thoracic vertebra (T1), and constraining motion to only the
vertical direction. A quantitative comparison of the head and spine impact
forces, spine kinematics, and prediction of hard tissue fracture was reported.
The M50-TSM model demonstrated a 53.4% lower (straighter) spinal curvature 10 ms
after impact, compared to the M50-FB. The lower curvature of the M50-TSM
resulted in higher neck loads during that timeframe (2.26 kN M50-TSM, 1.44 kN
M50-FB). The resulting hard tissue fracture in M50-TSM was attributed to direct
compression at an early time (<5 ms) in the impact, while M50-FB demonstrated
compression-extension fractures later (>16 ms) in the simulation. It was
concluded that kinematics, kinetics, and injury response differed for the TSM
and FB boundary conditions, and therefore these conditions are critical to
consider when investigating HFI.
