Shear Stress Distribution in the Porcine Brain due to Rotational Impact

Two-dimensional finite element models for three coronal sections of the porcine brain have been developed and the results were compared with injury data from animal experiments performed at the University of Pennsylvania (Ross et al, 1994). The models consisted of a three-layered skull, dura, CSF, white matter, gray matter and ventricles. Model I, a section at the septal nuclei and anterior commissure level, contains 490 solid elements and 108 membrane elements. Model II, a section at the rostral-thalamic level, contains 644 solid elements and 130 membrane elements. Model III, a section at the caudal hippocampal level, contains 548 solid elements and 104 membrane elements. Plane strain conditions were assumed for all models. Material properties of the brain were taken from previous human brain models, but the white matter was assumed to be about 60% stronger than the gray matter with the same Poisson's ratio. A prescribed angular velocity was applied to the outer table and impact responses were computed by finite element analysis. The maximum shear stress distribution produced from the models was found to be in good agreement with experimental findings. Diffuse axonal injury as indicated by the experiments was found in areas of high shear stress which persisted for relatively longer periods during the impact. The simulation results suggest that shear stress or strain could be the cause of diffuse axonal injury.