Volume 194 - Issue 4
Trends in head injuries and helmet use in cyclists at an inner-city major trauma centre, 1991–2010
Authors: Chris E Rissel and Paul Martin
Med J Aust 2011; 194 (4): 215-216. || doi: 10.5694/j.1326-5377.2011.tb03795.x
Published online: 21 February 2011
Published online: 21 February 2011
To the Editor: Dinh and colleagues present data on head injuries among cyclists admitted to the emergency department of Sydney’s Royal Prince Alfred Hospital (RPAH) from 1991 to 2010,1 and conclude with their opinion that legislation mandating the wearing of bicycle helmets should be maintained. However, their data provide poor evidence of the efficacy of helmets and of the effectiveness of legislation requiring helmet use.
Almost all studies of helmet efficacy are case–control studies, which, to be of high quality, require a well defined and matched control group. In the study by Dinh et al, the control group was made up of patients who had been wearing a helmet. Many possible explanations for injury severity were not considered. For example, were the non-helmeted cyclists drinking alcohol or riding faster? Were they more likely to be risk-takers? Were the helmet wearers also wearing high-visibility vests or using lights at night? Case–control studies of this kind are a weak form of evidence (ranking just above anecdotal evidence and case studies) and cannot answer questions of causality.
The two graphs presented by Dinh et al show that head injury rates among cyclists were very low and fairly stable over most of the time period examined. RPAH treats thousands of trauma patients each year. The study reported on 287 cyclists admitted in a 2.5-year period — an average of 115 per year. Of these, only 14 (eight helmeted; six not wearing helmets) incurred major trauma — about six per year. Given that helmet legislation was in place for the entire study period, these data add no evidence for its effectiveness.
In public health terms, the risk of injury needs to be weighed against the benefits of increased physical activity, reduced chronic disease and reduced air pollution due to more people cycling. Because of the low absolute rate of cycling injuries, these benefits are nine to 20 times the size of the risk.2,3 Further, it is well documented that levels of cycling in Australia dropped by 30%–40% when helmet legislation was introduced. This had the unfortunate effect of making cycling less safe for the remaining cyclists because of the “safety in numbers” phenomenon.4 The poor uptake5 of the two public bicycle-hire schemes in Australia (in Melbourne and Brisbane) indicates that helmets are a significant barrier to short-trip and spontaneous cycling, with few potential or casual users carrying a bicycle helmet in case they decide to hire a bicycle.
Dinh and colleagues obviously believe in the efficacy of the bicycle helmet, but this does not mean that mandating their use is the best public health policy response. When helmet legislation was introduced, we did not have the epidemics of diabetes and obesity that now threaten to bankrupt state health budgets. Strategies to increase levels of physical activity among the whole population are desperately needed, even if there is a small risk involved.
References
- Dinh MM, Roncal S, Green TC, et al. Trends in head injuries and helmet use in cyclists at an inner-city major trauma centre, 1991–2010 [letter]. Med J Aust 2010; 193: 619-620. <eMJA full text>
- Johan de Hartog J, Boogaard H, Nijland H, Hoek G. Do the health benefits of cycling outweigh the risks? Environ Health Perspect 2010; 118: 1109-1116. doi: 10.1289/ehp.0901747. 0_CHDEBGJG
- De Jong P. The health impact of mandatory bicycle helmet laws. Feb 24, 2010. Social Science Research Network eLibrary. http://ssrn.com/abstract=1368064 (accessed April 2010).
- Jacobsen PL. Safety in numbers: more walkers and bicyclists, safer walking and bicycling. Inj Prev 2003; 9: 205-209. 0_CHDDGFAJ
- Lucas C. Bike share scheme saddles up slowly in bleak weather. The Age 2010; 12 Jun. http://www.theage.com.au/victoria/bike-share-scheme-saddles-up-slowly-in-bleak-weather-20100611-y3oe.html (accessed Jan 2011).