Mechanisms and Tolerance Curves of Traumatic Diffuse Axonal Injury (DAI)

Abstract

Diffuse Axonal Injury (DAI) is a common brain lesion in all kinds of fatal traffic accidents, such as car occupants, pedestrians, motorcycle and bicycle riders. The objective of this real accident study is to complete knowledge of significant injury mechanisms causing DAI, and, in particular, to identify tolerance limits. 16 fatalities were examined, all selected from autopsy cases of Munich University Institute for Legal Medicine. Based on extensive microscopic neuropathological examination, "brain maps" were developed to illustrate DAI location and frequency and to identify significant injury mechanisms related to causative head loading parameters determined by accident reconstruction. Findings suggest that DAI in brain stem and medulla oblongata occurs in cases exposed to axial linear acceleration of the head (±gz). DAI in the corpus callosum region is caused when rotational head acceleration around vertical z-axis is predominant. Shear forces due to extensive skull deformation and tensile forces, in particular parietal, are causing DAI in the hemispheres. DAI tolerance limits are identified as follows: (1) Mean linear acceleration 130 g for short duration (10 ms) and 110 g for longer duration (20 ms); (2) Rotational velocity 38 rad/s at 7.500 rad/s², and (3) Rotational acceleration 5,500 rad/s² for short duration (10 ms) and 3,500 rad/s² for longer duration (20 ms).