BMJ  2005;330:281 (5 February), doi:10.1136/bmj.38314.480035.7C (published 4 January 2005)

Paper

Effectiveness of helmets in skiers and snowboarders: case-control and case crossover study

¹ Alberta Centre for Injury Control and Research, Department of Public Health Sciences, University of Alberta, Edmonton, AB, Canada T6G 2E1, ² Departments of Pediatrics and Epidemiology and Biostatistics, 1020 Pine Avenue West, McGill University, Montreal, QC, Canada H3A 1A2, ³ Direction de la promotion de la sécurité, Ministère des Affaires municipales, du Sport et du Loisir, 100 rue Laviolette, suite 306, Québec Gouvernement, Trois-Rivières, QC, Canada G9A 5S9, ⁴ Institut national de santé publique du Québec, 4835, Christophe-Colomb, Montreal, QC, Canada H2J 3G8

Abstract

Objective To determine the effect of helmets on the risk of head and neck injuries in skiers and snowboarders.

Design Matched case-control and case crossover study.

Setting 19 ski areas in Quebec, Canada, November 2001 to April 2002.

Participants 1082 skiers and snowboarders (cases) with head and neck injuries reported by the ski patrol and 3295 skiers and snowboarders (controls) with non-head or non-neck injuries matched to cases at each hill.

Main outcome measures Estimates of matched odds ratios for the effect of helmet use on the risk of any head or neck injury and for people requiring evacuation by ambulance.

Results The adjusted odds ratio for helmet use in participants with any head injury was 0.71 (95% confidence interval 0.55 to 0.92), indicating a 29% reduction in the risk of head injury. For participants who required evacuation by ambulance for head injuries, the adjusted odds ratio for helmet use was 0.44 (0.24 to 0.81). Similar results occurred with the case crossover design (odds ratio 0.43, 0.09 to 1.83). The adjusted odds ratio for helmet use for participants with any neck injury was 0.62 (0.33 to 1.19) and for participants who required evacuation by ambulance for neck injuries it was 1.29 (0.41 to 4.04).

Conclusions Helmets protect skiers and snowboarders against head injuries. We cannot rule out the possibility of an increased risk of neck injury with helmet use, but the estimates on which this assumption is based are imprecise.

Introduction

In 1983, Oh and Schmid argued that helmet use should be mandatory in skiers up to the age of 17 owing to the risk of severe head injuries.¹ Guided by compelling evidence that helmets are effective at preventing head, brain, and facial injuries in bicyclists, helmet use would seem to be reasonable.² Helmets are not yet widely recommended in skiers and snowboarders because of the paucity of information on their effectiveness. The best evidence suggests they are protective, but this was based on a study that was restricted to participants aged less than 13 years, had a small sample size, and lacked control for potential confounders.³ Helmets may increase the risk of spinal injury owing to the biomechanics of the association between the helmet and the head and neck^{4 5}—a particular concern for children, who have a greater head to body ratio. A helmet may exert large bending or twisting forces on the neck in the event of an otherwise "routine" fall. We determined the effect of helmet use on the risk of head and neck injuries in skiers and snowboarders.

Methods

We invited 20 of the largest ski areas in Quebec, Canada, to take part in our study over the 2001-2 ski season (November to April). We asked the ski patrols to send us their accident report forms every two or three weeks.

Cases and controls
Cases were those people with an accident report form completed by the ski patrol for a head (including face) or neck injury while skiing or snowboarding, as indicated by the body region recorded (head, face, neck or cervical spine). We defined potentially severe cases as people with isolated (one body region) head or neck injuries who needed to be evacuated by ambulance.

Controls were people with non-head or non-neck injuries who were reported by ski patrols at the same ski areas as for cases. We used a case crossover approach, with cases acting as their own controls by self reporting on their participation before the day of injury. We matched controls for ski area, activity (skiing or snowboarding), date of injury, age (< 15, 15-25, and 26), and sex.

Case crossover methods
For the case crossover approach we used information from cases with head injuries only. We chose the day the individual was injured as the case period of time, and we considered as the control period that same person's previous outing for skiing or snowboarding when they were not injured.

Results

Of the 20 ski areas invited to participate in our study, one failed to return its accident report forms in time and was excluded from analysis. The overall response rate was 70.1% (68.7% (1082 participants) for cases with head, face, and neck injuries and 70.6% (3295 participants) for controls), similar to snowboarders (71.9% (2041)) and skiers (68.7% (2335)) and age group (67.0% (1582) to 73.0% (1726 participants)). Response rates varied between ski areas (55.1% (27) to 84.7% (133)).

Overall, 693 people had head injuries, with 69.7% (483) assessed as concussion. Of the 469 participants with isolated head injuries, 32.4% (152) were evacuated by ambulance; this proportion increased to 43.2% (107) when we considered only isolated head injuries assessed as concussion. In total, 44.3% (58) of the neck injuries were assessed as sprains, 16.0% (21) were assessed as fractures, and 6.9% (9) were assessed as muscle or nerve strains. Of the participants with isolated neck injuries, 56.1% (23) were evacuated by ambulance.

Cases with head injuries reported a collision or jump related injury more often than controls (table 1). Compared with controls, cases with neck injuries were more likely to be younger, to be female, to have participated for 11 or more days and for fewer hours before the injury, and to have had a previous head or neck injury.

View this table: [in this window] [in a new window]   Table 1 Characteristics of cases and controls and event around injury. Values are numbers (percentages)

 

The proportion of participants with head injuries (25.3%, 175 participants) or potentially severe head injuries (24.3%, 37) who wore a helmet was similar to that of controls (28.2%, 929) but was higher among those with neck injuries (39.1%, 9) (see also bmj.com). The prevalence of helmet use decreased with increasing age for all groups. Cases aged less than 15 years with head injuries had a higher prevalence of helmet use than controls whereas cases aged less than 15 years with potentially severe head injuries had a lower prevalence of helmet use than controls. The proportion of helmet users among cases aged 15 to 25 with potentially severe neck injuries (37.5%, 3) was greater than among controls (17.0%, 202), although this result is based on only eight cases.

Less than 50% of our case-control sets were well matched for date of injury, age, and sex. Therefore, we considered age, sex, and environmental conditions for our conditional logistic regression model. We found no evidence of effect modification by age. The ideal model with the 27 covariates produced a helmet effect estimate of 0.73 (95% confidence interval 0.49 to 1.08) for any head injury (table 2). A backward deletion strategy produced a final adjusted helmet effect estimate of 0.71 (0.55 to 0.92). A forward selection strategy produced an adjusted helmet effect estimate for potentially severe head injuries of 0.44 (0.24 to 0.81).

View this table: [in this window] [in a new window]   Table 2 Effect of helmet use

 

For those aged less than 15 years the estimate of the helmet effect for neck injuries was 0.92. After removal of the product terms from the model and using a forward selection strategy starting with helmet use, age and sex, our final model for any neck injury included age, sex, and days of participation that season. This gave a helmet effect of 0.62 (0.33 to 1.19).

We carried out no adjustments beyond matching owing to the limited number (n = 13) of discordant sets for those sustaining neck injuries who were evacuated by ambulance. The conditional logistic regression estimate was 1.29 (0.41 to 4.04).

For the case crossover analysis we focused on 35 participants with head injuries who had discordant helmet use on the day of injury compared with their previous outing (estimated odds ratio for helmet use 0.6, 0.28 to 1.22). The odds ratio decreased to 0.43 (0.09 to 1.83) when we restricted the analysis to those injured during recreational participation.

Discussion

Wearing a helmet while skiing or snowboarding may reduce the risk of head injury by 29% to 56%—that is, for every 10 people who wear helmets, three to six may avoid head injuries. This may even be an underestimate if, as in cycling, the helmets were worn incorrectly or were in poor condition,⁶ or were not designed for skiing or snowboarding.⁶ The effect of helmet use on neck injuries is less clear. Although we found no statistically significant estimates for neck injury and no evidence of effect modification by age, our sensitivity analysis suggests an increased risk of neck injuries with helmet use.

Limitations
When we included non-responders in the analyses, we found few differences for all outcomes except potentially severe neck injuries, where the estimate increased (see sensitivity analysis on bmj.com). This suggests possible under-response in helmet users. Few of these injuries, however, produced considerable random error and precluded the addition of potential confounders.

We did not include in our injured control series those who fell and hit their heads but did not sustain an injury because they were wearing a helmet. Including these individuals would have increased the protective effect of helmets.

Where appropriate we adjusted for personal characteristics and events at the time of injury. The small number of neck injuries, however, precluded control for more than a few covariates. As 13 of the participants with neck injuries who required evacuation by ambulance were in discordant matched sets, we did not consider further adjustment beyond that provided by the matching.

Recall on the day of injury of a participant with head injuries was confined to a specific event for the case crossover analysis,⁷ whereas recall on the previous outing may have been less accurate. If cases had over-reported previous helmet use then the protective effect of helmets would have been overestimated, but we found a consistent helmet effect between the matched case-control and case crossover analyses.

Comparison with previous research
To our knowledge only one other case-control study has been carried out to determine whether helmets protect skiers and snowboarders against head injuries.³ Those investigators evaluated combined head, face, and neck injuries in participants aged less than 13 years. After adjustment for activity, helmets were associated with a 43% reduction in the risk of head, face, and neck injuries, and no serious neck injury occurred in those using helmets. Our estimates for all age groups confirm the protective effect of helmets on head injuries found by this previous study.³ Although other investigators have examined the relation between helmet use and risk of neck injury in skiers and snowboarders, unlike us they did not examine this in isolation or did not report an effect estimate.^{3 8}

What is already known on this topic Helmets protect bicyclists against head injuries Evidence is limited on the effectiveness of helmets against head and neck injuries in skiers and snowboarders What this study adds Helmets may reduce the risk of head injuries in skiers and snowboarders by 29% to 56% Evidence is limited on the relation between helmet use and the risk of neck injury

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This is the abridged version of an article that was posted on bmj.com on 4 January 2005: http://bmj.com/cgi/doi/10.1136/bmj.38314.480035.7C

We thank Genevieve Gore, Liam Gore, Helen Magdalinos, Gail Martin, and Anna Sampogna for their invaluable assistance; Nicole Marchand (Quebec Secretariat au loisir et au sport) for her help in copying and sending on the accident report forms; and the Quebec Ski Areas Association and participating ski areas for their cooperation with data collection.

Contributors: See bmj.com

Funding: Canadian Institutes of Health Research and the Quebec Secretariat au loisir et au sport. BEH was funded by the Alberta Heritage Foundation for Medical Research.

Competing interests: None declared.

Ethical approval: This study was approved by the ethics committee of McGill University-Montreal Children's Hospital Research Institute. The Commission d'accès à l'information du Québec gave permission for information to be used from the accident report forms.

References

1. Oh S, Schmid UD. Head injuries in childhood caused by skiing accidents and optimal prevention. Z Kinderchir 1983;38: 66-72.[ISI][Medline]
2. Thompson DC, Rivara FP, Thompson R. Helmets for preventing head and facial injuries in bicyclists. Cochrane Injuries Group. Cochrane Data-base Syst Rev 2000;2:CD001855.
3. Macnab AJ, Smith T, Gagnon FA, Macnab M. Effect of helmet wear on the incidence of head/face and cervical spine injuries in young skiers and snowboarders. Inj Prev 2002;8: 324-7.[Abstract/Free Full Text]
4. Deibert M, Aronsson D, Johnson R, Ettlinger C, Shealy J. Skiing injuries in children, adolescents, and adults. J Bone Joint Surg 1998;80-A: 25-32.[Abstract/Free Full Text]
5. Katagi K. A heady debate. Ski Magazine 2000;Oct: 219-23.
6. Parkinson GW, Hike KE. Bicycle helmet assessment during well visits reveals severe shortcomings in condition and fit. Pediatrics 2003;112: 320-3[Abstract/Free Full Text]
7. Harlow SD, Linet MS. Agreement between questionnaire data and medical records: the evidence for accuracy of recall. Am J Epidemiol 1989;129: 233-48.[Free Full Text]
8. Bridges EJ, Rouah F, Johnston KM. Snowblading injuries in eastern Canada. Br J Sports Med 2003;37: 511-5.[Abstract/Free Full Text]

(Accepted 3 November 2004)

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Absolute risk reduction is the figure that counts

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