Reaction of a human head/neck/torso system to shock

The purpose of this study is to predict human response to, and potential damage from, impact loading by using numerical and physical models to monitor the head and thoracic reactions, intervertebral disk pressures, muscle elongations, and some internal organ pressures. The numerical model consists of a three-dimensional lumped-parameter system of ten rigid bodies connected by nine intervertebral joints and 28 muscle pairs. The masses represent the head; cervical vertebrae C1-C2, C3-C4, C5-C6, C7-T1 (the first thoracic vertebra); the entire thorax; lumbar vertebrae L1-L2, L3, L4-L5; and the pelvis. The physical model consists of: a water-filled cadaver skull, held in position by attached ligaments; plastic skeletal components involving vertebrae, sternum, ribs and pelvis; silicon rubber intervertebral disks; fabric muscles and ligaments; and water-filled containers replicating the liver, spleen and kidneys. The pelvis of the model is affixed to a plate mounted on a sled that runs on a track. Loading is applied by deceleration from a given velocity that occurs due to the impact of the sled with a fixed aluminum block. Results from the numerical model are compared with corresponding experimental information from the physical structure. Good correlation was obtained in these comparisons up to about 200-250 ms after impact. The results indicate that the head, cervical muscles and disks in the lumbar region are subjected to the greatest force changes and thus are most likely to be injured.