Head injuries sustained by helmeted and unhelmeted bicyclists in US passenger vehicle-to-bicyclist crashes

Background Head injuries are a leading cause of life-threatening injury and death in bicyclist crashes. This study explored real-world crash reconstructions of US bicyclists struck by passenger vehicles to identify if wearing a helmet influenced the occurrence of different types of head injuries. Methods Real-world crash reconstructions of 91 helmeted and 204 unhelmeted bicyclists struck by passenger vehicles were examined. Data included medical codes of head injuries, injury attribution, medical imaging, bicyclist demographics and descriptions of crash configuration. Head and facial injuries were categorised based on severity and type of injury. A logistic regression controlling for crash factors was performed to compare the odds of head injuries by helmet status. Results Fewer cranial fractures (OR: 0.039; p=0.03) and intracranial haemorrhages (OR: 0.0696; p=0.04) were observed for helmeted bicyclists. All severe head injuries for helmeted and unhelmeted bicyclists were attributed to primary impact with the vehicle, and for 9 out of 13 cases the location was where vehicle countermeasures such as an external airbag could be effective. For concussion-level injuries, 50% of helmeted and 43% of unhelmeted injuries were judged to be from secondary contact with the ground. Discussion Preventing life-threatening bicyclist injuries will require more than helmet redesigns. Vehicle countermeasures, such as windshield airbags or bicyclist autobrake systems, can supplement helmets for protecting bicyclists. Conclusion Helmeted bicyclists struck by passenger vehicles in the USA had fewer severe head injuries compared with unhelmeted bicyclists. However, no protective effect of helmets was observed for concussion-type injuries.