Helmet protection against basilar skull fracture
In Australia, it is compulsory for all motorcyclists, pillion passengers and side-car passengers to wear helmets certified to AS/NZS 1698. Most riders prefer to wear full-face helmets, which appear to offer better facial protection during a crash. Some researchers have noted a greater prevalence of fractures to the base of the skull in full-face helmeted riders. The aim of this study was to improve the understanding of basilar skull fracture (BSF) causation in motorcycle crashes, to assess the capability of current helmets in reducing the risk of this injury and to assist in future standards setting.
A review of available field data on the incidence and causation of BSF to motorcyclists was completed and the findings compared with crashes collected in the CASR Head Injury Database. This database contains in-depth investigations of 174 mainly fatal motorcycle accident cases collected in South Australia between 1983 and 1994. It includes autopsy data, including an investigation of neck injury, the helmet and a detailed crash report. The CASR data was found to be representative of fatal crash studies in the literature and to consist of high severity crashes. In 70% of the cases full face helmets were worn. BSF was seen in 59% of these cases. Almost 50% of the severe impacts to the head were in the facial region and 42% of these impacts were to the chin bar. The prevalence of BSF was found to be mainly due to the migration of the skull fracture to the base of the skull due to the severity of the impact to the face (and other regions of the head).
Only two motorcycle helmet standards currently include chin bar tests: Snell M2005 and UN ECE 22.05. The tests have significant differences in their requirements and do not specifically address the issue of basilar skull fracture. The test requirements were assessed using a typical current Australian full face helmet. The results are discussed in terms of the protective requirements demonstrated in the field accident data and an understanding of current biomechanical injury tolerance. The study shows that the protection offered by the Australian motorcycle helmet needs to be extended to cover the facial area, with the aim of reducing facial fractures. The conflicting criteria required of a test method, to protect from facial fracture and brain injury, whilst not causing neck injury are also discussed, and the needs for further work are outlined.