This study first examined the correlation between types of acute phase head injuries to cyclists and consciousness disturbance by using data from patients at the emergency room of Dokkyo Medical University Koshigaya Hospital in Japan. The injuries were compared for cases where the cyclists experienced consciousness disturbance and otherwise. The results showed that skull fractures and brain contusions were the most frequent consequences of head injuries to cyclists in general. However, the average number of head injuries by types for cyclists suffering consciousness disturbance was higher than that for cyclists who had not experienced it, for both head fractures (0.9 versus 0.7) and brain injuries (1.9 versus 0.5). This implies that head fractures and brain injuries may increase the probability of consciousness disturbance. Next, considering a cyclist who had sustained a head injury and suffered acute consciousness disturbance in an accident while not wearing a helmet, a case study was conducted to quantify the effectiveness of a bicycle helmet in reducing the intensity of traumatic head injuries by using a whole-body model, a finite element model of the human head, and a model of the bicycle helmet on a mathematical dynamic modeling software. A comparison of the peak values computed for cases of cyclists with and without a helmet showed that in the former, strain on the skull was reduced by 95.9% in cases of skull fractures, and the von Mises stress on the brain was reduced by 23.3% for cases of brain contusions. The results suggest that helmet use reduces the risk of skull fracture and brain contusions in cyclists because it considerably reduces the impact. Moreover, the use of helmets can reduce the probability of consciousness disturbance.

Keywords

Cyclist, Traffic accident, Head injury, Consciousness disturbance, Finite element simulation

Paper information

[Advance Publication] (Proper information for citation will be announced after formal publication)

Severe head injuries can occur in cyclists involved in traffic accidents. In Japan, head injuries accounted for 62% of cyclist fatalities in 2015 (ITARDA, 2016). The purpose of this study is to estimate head injuries for cyclists and quantify the effectiveness of a bicycle helmet by performing finite element (FE) simulations of head impacts against roads. Impacts with and without a helmet over a range of relative head velocities and head impact angles were simulated. A number of possible head injuries were assessed; skull fracture by skull strain, traumatic intracerebral hematoma (ICH) by brain pressure, brain contusion by brain negative-pressure and von Mises stress, and moderate and severe diffuse axonal injuries (DAIs) by von Mises stress. Results showed that without a helmet, the peak values of all metrics exceeded the 50% probability point for head injury in all impacts. The 50% probability points of moderate and severe DAIs were exceeded under impacts of 8.22 m/s at 26.5 degrees and 10.33 m/s at 15.0 degrees for moderate DAI, and 10.33 m/s at 15.0 degrees for severe DAI, without a helmet. All the peak values were reduced when a bicycle helmet was worn, and the largest reduction was found in the skull strain. These results predict that the risks of head injuries due to road impacts may be considerably decreased by helmet use.

Keywords

Bicycle helmet, Cyclist, Head injuries, Impact against road, Finite element simulation

Paper information

Shoko OIKAWA, Hiromichi NAKADATE, Yuelin ZHANG, Takahiro UENO, Shigeru AOMURA, Yasuhiro MATSUI, “Finite element analysis of the effectiveness of bicycle helmets in head impacts against roads”, Journal of Biomechanical Science and Engineering, Vol.12, No.4 (2017), p.17-00175. doi:10.1299/jbse.17-00175. Final Version Released on September 15, 2017, Advance Publication Released on July 18, 2017.