Abstract
Protective helmets are believed to reduce the number of injuries from motorcyle accidents and lessen the severity of head injuries. This study was intended to investigate the mechanism of head injuries in helmeted motorcyclists. One hundred twenty helmets involved in motorcycle accidents were collected with information from the scene and examined. Helmets consist of two major components, the shell and the liner. Deformation of each component was inspected to grade the damage to the helmet. The severity of the head injury was evaluated according to the J-AIS code in each case. Head injuries were classified into three main groups, skull fracture, focal brain damage, and diffuse brain damage. The reports from the scene obtained from accident report forms enabled the cases to be divided into “wearing” cases, in which the helmet was secured to the motorcyclist's head throughout the accident, and “uncapping” cases, in which the helmet was knocked off by the initial impact. The severity of head injury was higher in “uncapping” cases. The “uncapping” cases showed a higher rate of skull fracture and focal brain damage. An analysis of the correlations between types of head injury and helmet damage disclosed the following results: motorcyclists wearing helmets were likely to sustain diffuse axonal injury when receiving an upper region impact. The assumption that diffuse axonal injury is produced by coronal plane angular acceleration is widely accepted. It seems reasonable to suppose that an impact to the upper region of the helmet would produce angular acceleration based on a consideration of the center of gravity of the head. The results of our study support this hypothesis. Motorcyclists who suffer brain damage, such as acute subdural hematoma, cerebral contusion or diffuse axonal injury, would die at the site if they had accidents without helmets. Again, we emphasize the beneficial effects of protective helmets.
