Traumatic brain injuries constitute a significant portion of injury resulting from automotive collisions, motorcycle crashes, and sports accidents. Despite its high prevalence and potentially serious long-term effects, a complete understanding of its causal mechanism, response and tolerance is still lacking.

Four inter-related studies were undertaken to investigate the biomechanical responses of the human head to traumatic impacts using finite elem ent (FE) modeling techniques. In the first study, the directional sensitivities of the human brain to varied impact directions were investigated using a 3-D FE model. Results show that a lateral impact produced a larger local skull deformation, a higher intracranial pressure, and a higher localized shear deformation compared to those due to a frontal impact of the same energy. These predictions provide quantitative measures consistent with previous qualitative findings using animal models.

In the second study, three forehead impacts, one concentrated impact and two uniformly distributed impacts, of the same force magnitude but covering different contact areas were simulated to investigate the effect of wearing a helmet on brain response. Results suggest that although there is a significant reduction in the levels of intracranial pressure and shear stress in the cerebral hemispheres, injury risk to the brainstem remains high even with the protection provided by a helmet.

Two 3-D FE models of modern football helmets and headform models were developed and validated against helmet drop tests in the third study. These helmet models were proven to be capable of capturing head acceleration response during impacts to several locations on the helmet. A reverse engineering method was employed to determine material properties of helmet components.

Finally, twenty-four actual field head-to-head collisions that occurred in professional football games were duplicated using an FE head model to study minor traum atic brain injury (MTBI). The model predicted that the upper brainstem was most susceptible to shear stress. Since the brainstem is considered as a probable anatomical substratum responsible for concussion, this localized high shear stress may be used as an injury predictor for MTBI. Statistical analyses further demonstrated that shear stress correlated with the occurrence of MTBI. Concussion threshold based on shear deformation and rotational acceleration were proposed.