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Three Part Question

In [adult pedal cyclists] does [the use of a crash helmet] affect [severity of and outcome following head injury]

Clinical Scenario

A 32 year old un-helmeted cycle courier is brought to the ED after a collision with a car. He has an isolated severe head injury (GCS=7) and is intubated before transfer to the CT scanner. You wonder if the severity of his injury, or his outcome, would be improved had he been wearing a helmet.

Search Strategy

Medline 1966- May 2011 using the OVID interface.
(("Bicycling" [Mesh] OR bicycle)) AND (("Head Protective Devices" [Mesh] OR helmet)) AND (("Craniocerebral Trauma" [Mesh] OR head injury))
LIMITS: Human AND English language.

Search Outcome

472 papers of which 10 were relevant to the clinical question.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Amoros E, Chiron M, Martin JL, Laumon B. 2011 France	8373 cyclists with and without helmets with bicycle related trauma	Case-control. Trauma registry, 3b	Head Injury ISS 1+	Adjusted estimate odds ratio for head injury (ISS 1+) helmet wearers vs non-helmet wearers 0.78 (95% CI 0.67 to 0.90).	No separation of adult and child data. Heterogeneity of demographics between cases and controls. Helmet status missing for 39% of cases - results unchanged by this. Trauma Registry data, therefor no record of cyclists uninjured in crashes/not seeking medical aid.
			Severe Head Inury ISS 3+	Adjusted estimate odds ratio for severe head injury (ISS 3+) 0.41 (95% CI 0.23 to 0.68).
Heng KW, Lee AH, Zhu S, Tham KY, Seow E. 2006 Singapore	160 cyclists with and without helmets with bicycle related trauma	Cross Sectional. 3b	Head Injury	Significant (p = 0.01) reduction in incidence of head injury in helmeted group. Odds Ratio for head injury helmet vs non-helmet was 0.14 - not statistically significant.	No separation of adult and child data. Proportion of helmeted cyclists 10.6% and small sample size. ISS Significantly higher in unhelmeted casualties. No record of length of hospital stay.
			Discharge from Hospital	No statistically significant difference in discharge status.
Ji M, Gilchick RA, Bender SJ. 2006 USA	1116 cyclists with and without helmets with bicycle related trauma	Cross Sectional. Trauma Registry. 3b	Serious Head Injury (AIS 3+)	Odds ratio for serious head injury, helmet wearers vs non-helmet wearers, 0.43 (0.28-0.66)	Trauma registry data. No consideration of minor (ISS <3) head injury.
Attewell RG, Glase K, McFadden M, 2001 Australia	7302 adult cyclists with and without helmets	Meta Analysis. 1a	Fatal Injury	Combined estimate odds ratio, helmet wearers vs non-helmet wearers, 0.27 (0.1-0.71 95%CI)	No adjustnment for potential confounders. Unable to consider effect of helmet on rider behaviour
Thompson DC, Rivara F, Thompson R. 1999 USA	4394 cyclists who had crashed while riding a bicycle	Meta analysis. 1a	Head Injury	The summary odds ratio, helmet wearers vs non-helmet wearers, for head injury 0.31 (95% CI 0.26 to 0.37); ;	No separation of adult and child data.
			Brain Injury	The summary odds ratio, helmet wearers vs non-helmet wearers, for brain injury 0.31 (95% CI 0.23 to 0.42)
			Severe Brain Injury (AIS 3+)	The summary odds ratio, helmet wearers vs non-helmet wearers, for severe brain injury was: adjusted 0.26 (95% CI 0.14 to 0.48)
Thompson DC, Rivara FP, Thompson RS. 1996 USA	3390 cyclists with and without helmets and bicycle related trauma	Case control. Prospective. 3b	Head Injury	Summary odds ratio, helmet wearers vs non-helmet wearers, for any head injury OR 0.31 (95% CI 0.26-0.37);	Heterogeneity of type of helmet used and lack of statistical power to diffentiate between groups. Heterogeneity of cases and controls. Unclear whether helmet wearing is self-report or medical notes.
			Brain Injury	Summary odds ratio, helmet wearers vs non-helmet wearers, for brain injury OR 0.35 (95% CI 0.25-0.48)
			Severe Brain Injury (AIS 3+)	Summary odds ratio, helmet wearers vs non-helmet wearers, for severe brain injury OR 0.26 (95% CI, 0.14-0,48).
C Maimaris, C L Summers, C Browning, C R. Palmer. 1994 UK	1040 cyclists with and without helmets and bicycle related trauma	Case control. Prospective. 3b	Head Injury	Adjusted odds ratio for head injury, unhelmeted vs helmeted, 3.25 (95% CI 1.17 - 9.06)	No separation of adults and children
McDermott FT, Lane JC, Brazenor GA, Debney EA. 1993 Australia	1710 cyclists with and without helmets and cycling trauma	Case control. Prospective. 3b	Head Injury Severity	Relative proportion for head injury, helmet wearers vs. non-helmet wearers, 0.71 (95% CI 0.58-0.86). Significant increase in the duration of period of loss of consciousness in unhelmeted vs. helmeted cyclists (p=0.05). Significant reduction in head AIS in unhelmeted vs. helmeted	No raw data presented for period of LOC or head AIS. Excludes both minor injuries not presenting to ED and cyclists who died at scen or during transport to ED. No separation of child and adult data.
Thompson RS, Rivara FP, Thompson DC. 1989 USA	776 cyclists with and without helmets and cyclign related injuries	Case control prospective. 3b	Head Injury Severity	Odds ratio for: head injury, helmet wearers vs. non-helmet wearers, 0.26 (95% CI 0.14-0.42); brain injury, helmet wearers vs. non-helmet wearers, 0.19 (0.06-0.57)	Only included patients presenting to ED within one health insurance provider. No separation of adult and child data. Confounding due to variable rates of helmet wearing within different age groups.
Dorsch MM, Woodward AJ, Somers RL. 1987 Australia	197 cyclists with and without helmets and a cycling related incident where the head had been struck in past 5 years	Cross sectional. Survey. 4	Head Injury Severity,	Statistically significant reduction in head injury severity in helmet wearers (Chi squared = 25.0 p < 0.005).	Sampling bias: those killed/disabled by injury will not return questionnaire; only surveyed club cyclists. Recall bias. Variable types of helmet used.

Comment(s)

There is a large body of evidence, including a Cochrane review, that demonstrates bicycle helmets reduce the incidence of head injury. A reduction in the severity of head injury of helmet wearers has also been demonstrated using head AIS and duration of loss of consciousness, although this is not seen with GCS. The reduction in the odds ratio for head injury with increasing injury severity suggests that helmets may protect against severe injuries to a greater extent than minor injuries. Evidence for outcomes is conflicting: Attewell demonstrated a reduced odds ratio for fatalities amongst helmeted cyclists, however Heng found no statistical difference in discharge status between helmeted and unhelmeted cyclists.

Clinical Bottom Line

Helmets reduce the incidence of head injuries in cyclists. There is also compelling evidence that also reduce the severity of head injuries. It is reasonable to infer from this that clinical outcome is improved and their use should be encouraged in all cyclists.

References

1. Amoros E, Chiron M, Martin JL, Laumon B. Bicycle helmet wearing and the risk of head, face, and neck injury: a French case-control study based on a road trauma reg Injury Prevention 2011
2. Heng KW, Lee AH, Zhu S, Tham KY, Seow E. Helmet use and bicycle-related trauma in patients presenting to an acute hospital in Singapore. Singapore Medical Journal 2006
3. Ji M, Gilchick RA, Bender SJ. Trends in helmet use and head injuries in San Diego County: the effect of bicycle helmet legislation. Accident Analysis and Prevention 2006
4. Attewell RG, Glase K, McFadden M, Bicycle helmet efficacy: a meta-analysis. Accident Analysis and Prevention 2001
5. Thompson DC, Rivara F, Thompson R. Helmets for preventing head and facial injuries in bicyclists Cochrane Collabaration 1999
6. Thompson DC, Rivara FP, Thompson RS. Effectiveness of bicycle safety helmets in preventing head injuries. A case-control study. Journal of the American Medical Association 1996
7. C Maimaris, C L Summers, C Browning, C R. Palmer. Injury patterns in cyclists attending an accident and emergency department: a comparison of helmet wearers and non-wearers British Medical Journal 1994
8. McDermott FT, Lane JC, Brazenor GA, Debney EA. The effectiveness of bicyclist helmets: a study of 1710 casualties. Journal of Trauma 1993
9. Thompson RS, Rivara FP, Thompson DC. A case-control study of the effectiveness of bicycle safety helmets. New England Journal of Medicine 1989
10. Dorsch MM, Woodward AJ, Somers RL. Do bicycle safety helmets reduce severity of head injury in real crashes? Accident Analysis and Prevention 1987