• Skiing
• Helmet
• Head

We read with great interest the article of Sulheim et al.1 We agree with their conclusion that wearing a helmet while skiing or snowboarding is recommended strongly. We are troubled by the authors' conclusion in their abstract that there was an ‘unexpected reduction in protective effect of a skiing helmet’ when comparing the winter seasons 2002 and 2011. We feel that this wording is misleading, as there was no measure of the physical abilities of helmets in their study. Ski helmets typically meet or exceed the energy-attenuating abilities defined in the international standards (eg, ASTM F2040, EN1077 or EN1078) that have remained generally the same over this 10-year period. It is important to note that snow sport helmets offer limited protection, typically a significant reduction in head injury likelihood for a direct head impact at under 22 km/hour. The mean speed on ski slopes, however, can exceed 40 km/hour in some regions.2 ,3 The energy attenuation capabilities of a ski helmet may be better than those of helmets made 10 years prior, but still not be able to manage the energy of a high speed impact.

Sulheim et al1 also found that the proportion of all injuries that were head injuries decreased only 2.2% (from 17.6% to 15.4%) from 2002 to 2011, while the rate of helmet use increased from 23.8% to 77.1%. This comparison and the associated OR changes do not permit the direct examination of the protective abilities of ski helmets. Factors such as exposure (number of people skiing) and the rate of other injuries can influence significantly the proportions; for example, if the number of head injuries per skier day remained constant and the number of knee injuries per skier day decreased during the study period, then the proportion of head injuries would increase. In contrast to Sulheim et al,1 a longitudinal study by Shealy et al4 from 1995/1996 to 2011/2012 found a reduced incidence of any head injury and of potentially severe head injuries by 62% and 67%, respectively, while helmet usage increased over the same time from 8% to 84%. In our opinion, reporting head injury rates related to the total numbers of skier/snowboarder days for a given season (ie, the incidence that includes a measure of exposure) would represent a more appropriate measure of the preventive effect of ski helmet use.