Human Head Tolerance to Sagittal Impact Reliable Estimation Deduced from Experimental Head Injury Using Subhuman Primates and Human Cadaver Skulls

In experiments to investigate the relationship between head impacts and changes in vital functions, translational and rotational acceleration impacts were performed on live monkeys using a head restraint mask with broad contact area, as well as impacts of the unrestrained head against a padded flat surface. The results indicate that the occurrence and severity of concussion, cerebral contusion, and skull fracture in the monkeys depended on translational vs. rotational impact, contact area size, amplitude and direction of the resultant head acceleration, and frontal vs. occipital impact direction. The occurrence of concussion indicated the tolerance threshold, representing a transitory and reversible disturbance of vital functions. A threshold of concussion occurrence (TCO) curve was derived. The occurrence of skull fracture indicated the danger threshold (severe or fatal brain injury likely). Free-drop impact experiments were conducted on human cadaver skulls to obtain a fracture threshold curve. The dimensional analysis method of Stalnaker et al. was applied to the monkey TCO to estimate the human TCO. Combining this with the human cadaver skull fracture threshold, a human head impact tolerance threshold was derived.