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The abdomen includes the organs and viscera below the diaphragm and above the pelvic girdle. Although there is little bony structure to protect these organs from blunt impact, injuries to this region is relatively rare. Like the thorax, the abdomen can be the site of injuries sustained by inner parts of the car and restraint systems. As far as the crucial organs are concerned, the liver, spleen and kidneys are most frequently injured, and it seems to be the most serious and life-threatening. Injury mechanisms of the abdomen are thought to be primarily the result of deformation or penetration of the abdominal contents along with significant force or pressure generation in the deformed organs. In addition, solid organs, such as liver may undergo severe damage due to pressure generation alone at high impact velocities. There is evidence to show that these organs are viscoelastic, that the rate of loading is a crucial factor in injury causation, and that a compressive stress of 310kPa(45psi) will cause a superficial liver injury. Regarding dynamic response of the abdomen, the problem is complicated by the fact that there is a variety of surface geometries and component materials that can impact the abdominal area in a vehicle crash environment. In side impacts, however, the surface such as doors and armrests are somewhat well-defined, and dynamic load-deflection response curves do exist to a limited extent.
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