In 1946 Pudenz and Shelden (1946) reported superficial brain deformation and shift occurred following a head impact to apes. Over thirty years later, Gennarelli et al. (1982) studied the mechanical and pathophysiological aspects of primate head injury. They reported that lateral rotational impacts to the head (coronal acceleration) were the most significant in the production of diffuse brain injury. Little academic research has been done on primates since Gennarelli’s report, although primate species present an obvious homology with humans.

As primate based experiments have declined, computer-based physical simulation studies have simultaneously been increasing, both in frequency and in sophistication. The author and co-workers developed a 2D simulation study in which it was possible to demonstrate diffuse brain injury lesions similar to those seen in clinico-pathological settings. An impactor was applied to the right temporal side of the model at the level of the third ventricle, at a point which was at the same level as the center of gravity at a speed of 2 m/s. The model moved freely after the impact without any fixation. Major mechanical stresses on the brain parenchyma were observed in the midbrain, basal ganglia and corpus callosum underneath the falx cerebri (Fig. 7.2). Recent developments of the 3D voxel method enable it to provide a more precise representation of shear stress in the brain parenchyma after various impacts to the head in coronal and/or sagittal planes under different strain conditions (Fig. 7.3).

Further development of the methods involved in simulation studies are expected to further elucidate the mechanical aspects of concussions.

Pathophysiological reactions and consequences of mechanical stress in brain parenchyma have been proposed as follows:

These pathological reactions may provoke various lesions and their associated loss of fiber connections in neuronal structures, and may result in transient brain dysfunction similar to that seen under various clinical syndromes. These pathological reactions are considered to be transient and reversible.

Recent advances in sports medicine have reached the conclusion that concussions should be minimized. The main reason for prophylaxis of concussions is to avoid the following associated conditions: