Kinematic analysis of flailing injuries of lower extremities in side impacts

The objective of the study was to determine the biomechanics of post mortem human subjects (PMHS) in lateral impact with a focus on lower extremity trauma and aviation safety for side-facing seat applications. Four male three-point belted intact PMHS were seated upright with the Frankfurt plane horizontal on a custom seat, covered with aircraft cushion. The seat had an armrest. The change in velocity from the Federal Aviation FAR25.562 standards was input to two specimens, and a lower energy input was used in the other two specimens. Pre-test and posttest x-rays were obtained, and autopsies were conducted. Sled and pelvic acceleration signals were digitally gathered and processed according to the Society of Automotive Engineers specifications. A high-speed digital video camera was used to track the frontal plane kinematics with targets placed at appropriate lower extremity landmarks. Fractures of the left distal femur-knee complex in one and proximal sub-capital femur in the other specimen occurred in tests using the simulated FAR pulse. Tests at the lower energy input in the other specimens did not result in trauma. Coronal motions in PMHS occurred from initial flailing of the lower leg-knee-upper leg complex initiating after the onset of the side-impact pulse with the armrest acting as a limiting/boundary condition for the left femur-pelvis-region. These motions were attributed to be a causal agent for the observed lower extremity injuries. Although from a limited sample size, the present findings indicate that lower extremities may sustain trauma, and side-facing seats in aviation environments may need to be evaluated for occupant safety in the lateral mode.