Protective effect of helmet use on mortality in bicycle crashes in South Korea: a matched case-control study

Cycling-related injuries are a growing public health concern. Although bicycle helmets are intended to reduce head injury severity, evidence regarding traumatic brain injury and mortality remains limited in large emergency department (ED)-based datasets.

This matched case-control study used South Korean ED-based Injury In-depth Surveillance data from 2011 to 2021. Cases were injured cyclists who died in the ED; controls were injured cyclists whose ED disposition was not coded as death. Controls were matched to cases at a 1:4 ratio by age, sex and year of visit. Conditional logistic regression assessed associations of recorded helmet use with traumatic brain injury, the primary outcome and ED mortality, the secondary outcome.

Among 1394 injured cyclists, 282 were cases and 1112 were controls; 155 patients (11.1%) were recorded as wearing helmets. Recorded helmet use was associated with lower odds of traumatic brain injury, but the association was not statistically significant after adjustment (adjusted OR: 0.76, 95% CI 0.40 to 1.44). It was also associated with lower odds of ED mortality (adjusted OR: 0.30, 95% CI 0.14 to 0.65); however, only 11 helmeted patients died in the Evening crashes:ED arrival during evening hours (18:00-24:00) was associated with higher odds of ED mortality compared with daytime hours (06:00-18:00), and motor vehicle collisions were associated with higher odds of ED mortality.

Recorded helmet use was not significantly associated with traumatic brain injury after adjustment. Its association with lower ED mortality was based on only 11 helmeted deaths and may reflect limited precision, residual confounding and unmeasured crash severity. This finding should be interpreted cautiously and confirmed in larger studies with detailed crash data.