Background Previous case–control studies on bicycle helmet efficacy are mostly Anglo-Saxon, and based on data from the early 1990s when hard-shell helmets were common.

Methods In France, the Rhône county (1.6 million inhabitants) is covered by a road trauma registry that includes emergency department visits, hospital admissions, and fatalities. Over the 1998–2008 period, 13 797 cyclist casualties were identified. The injuries sustained were coded using the Abbreviated Injury Scale (AIS) for injuries to the head (AIS1+ and AIS3+), face (AIS1+), or neck (AIS1+). The study uses a case–control design where the control group includes cyclists injured below the neck—that is, not injured in the region associated with the helmet. We first adjusted for age, gender, and type of crash, as in a previously published Cochrane review. Then we adjusted for injury severity based on non-head, face, or neck injury, and when relevant, for crash location: type of road, urban/rural area.

Results The fully adjusted ORs of helmeted versus unhelmeted cyclists are: for AIS1+ head injuries, 0.69 (95% CI 0.59 to 0.81); for AIS3+ head injuries sustained in urban areas, 0.34 (95% CI 0.15 to 0.65), those sustained in rural areas, 0.07 (95% CI 0.02 to 0.23); for AIS1+ facial injuries, 0.72 (95% CI 0.62 to 0.83); and for AIS1+ neck injuries, 1.18 (95% CI 0.94 to 1.47).

Conclusion This study confirms the protective effect for head and facial injuries, even though soft-shell helmets have now become more common. The reduction of risk is greater for serious head injuries. The study is inconclusive about the risk for neck injuries.