According to the National Highway Traffic Safety Association, in 2008, 5,290 motorcyclists died and 96,000 were injured. Motorcycles make up ∼3% of all registered vehicles in the United States and account for only 0.4% of all vehicle miles traveled. However, motorcycle crashes accounted for ∼10% of all motor vehicle crash fatalities, and per mile traveled, motor cycle crashes are ∼37 times more lethal than automobile crashes.
Head injuries are one of the most common injuries after motorcycle crashes and were estimated to be the cause of death in >50% of these fatalities. In close to a third of these victims, the head injury is the sole organ system that is injured. However, in the majority of patients, estimated as high as 90% of some patient cohorts, a head injury is present along with other injuries. Despite these facts, it is estimated that only 50% of motorcyclists routinely wear helmets.
It was intuitive even to our earliest ancestors that a hard shell would protect the head from injury. However, establishing the effectiveness of the motorcycle helmet remains a challenging effort especially in light of the powerful opposition to universal helmet laws. Furthermore, quantifying the protective effect of helmets supports the promotion of helmet programs regardless of the controversial nature of legislative efforts.
In the United States, an increasing recognition that helmet use is associated with reductions in fatalities without apparent harm increased the implementation of universal helmet laws. In response to the 1966 Federal Highway Act, which withheld federal funds from states that did not enact a helmet law, Georgia became the first state to enact a mandatory universal motorcycle helmet law in 1967. By 1975, 47 of the 50 states had universal helmet laws. However, public and political concerns over individual rights versus public safety opened a new debate. In the following years, political changes reversed and/or limited previous sanctions and grants that encouraged states to enact universal helmet laws, which further eroded support for helmet laws. An increasing number of states either repealed their mandatory laws altogether or significantly reduced the laws to apply only to minors. At present, only 20 states have universal helmet laws, another 26 states require only partial coverage, and 4 states have no helmet laws (Colorado, Illinois, Iowa, and New Hampshire).
A large volume of literature has quantified the consequences of not wearing a helmet while riding a motorcycle. Although motorcycle riding and registration are increasing and more states with universal helmet laws are introducing bills to repeal their laws, the debate continues on the personal advantages of helmet usage. Therefore, we have reviewed the literature and summarize the evidence basis for the use of motorcycle helmets. In particular, we have sought to assess the impact of helmet use on overall mortality, head injury-related mortality, nonlethal head injury after a motorcycle crash, and the impact universal helmet laws on helmet use.
STATEMENT OF PROBLEM
Motorcycles are a significant cause of injury-related fatality and disability. In particular, head injury is a common associated cause of death and long-term disability after a motorcycle crash. Despite these facts, there remains an ongoing controversy as to the survival and disability advantages for riders who wear motorcycle helmets. In the public and legislative sectors, there remains a significant policy controversy resulting in a push to retain partial coverage helmet laws and to repeal universal helmet laws in many others.
QUESTIONS TO BE ADDRESSED
- Do nonhelmeted riders in comparison with helmeted riders have a higher or lower overall death rate after a motorcycle crash?
- Do nonhelmeted riders in comparison with helmeted riders incur higher or lower rates of lethal head injury after a motorcycle crash?
- Do nonhelmeted riders in comparison with helmeted riders incur higher or lower rates of nonlethal head injury or is the nonlethal head injury more or less severe after a motorcycle crash?
- Do geographical areas (i.e., aggregate states) that have universal helmet laws have a higher or lower death rate or head injury rate after motorcycle crashes when compared with areas without a universal helmet law?
METHODS AND PROCESS
A computerized search of the world's literature was undertaken using PubMed, of the US National Library of Medicine, extending back to 1990 to the present (2009) using the key words: helmet + (motorcycle OR crash). There were 507 citations identified. The abstract for each was reviewed, and 197 candidate articles having possible applicability to the guideline topic were retrieved and reviewed. General reviews, letters to the editor, single case reports, and retrospective reviews of poor quality were excluded. This left 45 articles that were felt to have sufficient merit to form the basis for the guidelines (Table 1). The articles were reviewed in detail by the authors J.M., G.H.T., and J.C.D.
Over the past decades, the volume of literature supporting helmet usage prevents, and ethically so, any randomized control trials or even controlled trials of helmet usage. Therefore, the most robust studies published in the past 20 years are predominantly prospective and retrospective epidemiologic studies. As there are no class I studies to review, the studies we did review do not vary across the classes of evidence in a useful manner. Therefore, we categorized the articles in this review by study design. There are prospective cohort and cross-sectional studies. However, the majority of the studies are retrospective, either before and after cross-sectional studies of helmet law changes or cross-sectional studies of helmeted in comparison with nonhelmeted riders. Finally, we also identified case-control studies.
All motorcyclists should wear motorcycle helmets when riding motorcycles to reduce the incidence of head injury and severe head injury after a crash.
NB: This statement was made a level recommendation despite a lack of class I data because of the volume of consistent class II data, including robust prospective data, to support this finding without any methodologically similar data to refute it.
All motorcyclists should wear motorcycle helmets when riding motorcycles to improve overall survival and reduce head injury-related mortality after a crash.
Mandatory universal motorcycle helmet laws should be introduced or reenacted to reduce mortality and head injury after a crash.
The evidence reviewed here that assesses the effectiveness of helmets for motorcyclists comes from the following 45 study designs:
- Prospective cohort study of motorcycle riders.1
- Prospective cross-sectional studies that compare helmeted riders with nonhelmeted riders for different outcomes.2–5
- Retrospective before and after cross-sectional studies in which outcomes of motorcycle crashes are compared before and after either the repeal of or the enactment of a mandatory universal helmet law.6–24
- Case-control studies of motorcycle riders.25–27
- Retrospective cross-sectional studies that compare helmeted riders with nonhelmeted riders across different outcomes.28–43
- Comparison of mortality between states with helmet laws and states without helmet laws.44,45
The outcomes reported included any one or more of the following: mortality, head injury-related mortality, prevalence of head injury, and prevalence of severe head injury.
Do Nonhelmeted Riders in Comparison With Helmeted Riders Have a Higher or Lower Overall Death Rate After a Motorcycle Crash?
Two prospective cross-sectional studies showed a reduction in mortality for helmeted riders in comparison with nonhelmeted riders, with an odds ratio (OR) of 0.40 and 0.22, respectively.2,5 However, Kelley's sample size was not adequate to reach statistical significance, and therefore, no death reduction can be concluded from this study. Nine retrospective cross-sectional studies reported mortality as an outcome, but two showed no reduction35,42 while seven showed reductions that varied from a maximal OR estimate of 0.2933 to a minimal OR estimate of 0.84.28 Of the studies that showed a mortality reduction, only three were adjusted for rider and/or environmental factors.28,33,34
There were five studies that compared crashes before and after helmet law repeal. Two of the studies showed an increase in fatality after repeal of the helmet law, 26% and 30% increases, respectively.8,10 However, two further studies had nonsignificant increases in the ORs of death: OR of 1.087 (per 10,000 motorcycle registrations) and OR of 1.019 (per 1,000 crashes). Interestingly, although the study of Bledsoe and Li did not show an overall reduction in mortality, there was a significant increase in riders who were blood alcohol positive at the time of the crash and who were also not wearing a helmet after the repeal when compared with before (14.2% vs. 33.6%, OR: 2.37, p < 0.05).
There were 12 studies that compared crashes before and after helmet law establishment or reenactment. Auman et al. showed close to a halving of the relative risk (RR) of fatality after the law was reenacted (RR: 0.51, 9.3 fatalities per 10,000 motorcycle registrations to 4.7 fatalities per 10,000 registrations). Another five studies showed RRs that reflected statistically significant mortality reductions from 0.57 to 0.81.15,21–24 One study, by Chiu et al., showed no change in mortality during the study period (4.0%).
Do Nonhelmeted Riders in Comparison With Helmeted Riders Incur Higher or Lower Rates of Lethal Head Injury After a Motorcycle Crash?
The RR of head injury-related mortality was reduced by more than half after the enactment of a helmet law in Texas from 6.8 fatalities to 3.1 fatalities per 10,000 motorcycle registrations23 (RR: 2.19, p < 0.05). In Pennsylvania, after the repeal of the helmet law, the head injury-related death rate per 10,000 motorcycle registrations increased by 36.9%6 (1.6 to 2.2 fatalities per 10,000 registrations, p < 0.05).
Do Nonhelmeted Riders in Comparison With Helmeted Riders Incur Higher or Lower Rates of Nonlethal Head Injury or Severity of Nonlethal Head Injury After a Motorcycle Crash?
All 25 of the studies that had prevalence of a nonfatal head injury as an outcome had a significantly lower incidence for helmeted riders, after reenactment or before repeal of a helmet law. One of the prospective studies that observed motorcycle riders to determine the incidence of head injury-associated crashes showed that nonhelmeted riders sustained a head injury more than twice the rate of helmeted riders1 (4.7% vs. 1.9%). Three studies showed an ORs of a head injury after a crash to vary from 2.3 times to 4.4 times higher for nonhelmeted riders when compared with helmeted riders3,4 (p < 0.05). Ouellet and Kasantikul showed an ORs of sustaining a serious injury to be 3.5 times higher (p < 0.05) for nonhelmeted riders.
Retrospective studies confirm the consistent findings of the prospective studies that head injury is uniformly more frequent and more severe when sustaining a crash without a helmet. The magnitude of the increased prevalence of a head injury after a nonhelmeted crash is as high as 4.3 times to a low of 1.7 times higher than after a helmeted crash in nine retrospective cross-sectional studies. However, for severe head injuries, most commonly defined as an Abbreviated Injury Scale score ≥2, the magnitude of the estimate is uniformly larger. For three retrospective studies, the ORs of a severe head injury were 18.1 (12.5–25.3), 4.4 (2.58–7.37), and 3.7 (1.9–7.3), respectively.13,32,38 Lin et al. showed a 41% increase in trauma-induced brain hemorrhage, including subarachnoid, subdural, and epidural hematomas when a rider was nonhelmeted during a crash.
The case-control studies showed an adjusted OR of 0.26 (0.14–0.48) and 0.41 (0.21–0.81), which represents a significant protective effect of wearing a helmet in reducing the incidence of a head injury after a motorcycle crash.26,27 In four retrospective studies in which universal motorcycle helmet laws were enacted, the incidence of nonlethal head injury decreased from 29% to reductions of 63%.
In one study in which the motorcycle law was repealed, the incidence of hospitalizations for head injury increased by 42%, from 15.4 to 21.9 per 10,000 motorcycle registrations (p < 0.05).6
Do Geographical Areas (i.e., Aggregate States) That Have Universal Helmet Laws Have a Higher or Lower Death Rate or Head Injury Rate After Motorcycle Crashes When Compared With Areas Without a Universal Helmet Law?
Two studies compared regions with and without helmet laws. Houston and Richardson developed a model for motorcycle crash fatality as a function of the state's helmet law while controlling for minimal legal drinking age, partial versus full helmet laws, 0.08 blood alcohol concentration law, roads with maximum speed limit of 65, daily temperature, daily percent precipitation, gender, age, per capita income, per capita alcohol consumption, and population density. Their results showed 1.3 fewer fatalities per 10,000 motorcycle registrations in helmet law states that can be attributed in their model to the presence of the helmet law. Furthermore, using hospital discharge data from 33 states, Coben et al. calculated a RR of 0.65 (p < 0.05) and 0.72 (p < 0.05), respectively, for severe head injury and fatalities in states with universal helmet laws when compared with states without universal helmet laws.
The main limitation of these uncontrolled and observational studies involves the collection and incorporation in the analysis of potential confounders for the outcomes studied. The wearing of helmets is associated with multiple factors, many of which have also been shown to be associated with the incidence and severity of crashes. Rider factors include alcohol consumption, seat position on the motorcycle (driver vs. passenger), age, and gender. There are also environmental factors such as weather, time of day; other policy factors such as speed limits and DUI laws; and other intrinsic motorcycle factors such as the size and type of motorcycle itself (the potential kinetic energy of the crash) also contribute to motorcycle crash occurrence and severity and ultimately crash consequences for the rider. Unfortunately, many of these factors are not easy to reliably measure on a crash-to-crash basis, and therefore, only nine studies, in part, adjusted for at least a portion of these factors. There were other studies that stratified the study group by various factors but did not control for them in their analysis. The majority of the studies did not control for any potential confounders. A second methodological concern is selection bias. The subjects in these studies were not selected randomly, except for the one cohort study that chose the students randomly. There were missing data, and no studies had information on those “not chosen” to confirm that they were the same as those included in the study.
A large number of the studies reported fatalities and prevalence of head injuries as a rate, a function of either the number of motorcycle registrations or the number of crashes. This eliminates the misinterpretation of changes in absolute fatalities that reflect changes in the number of riders or the number of riders who crash. However, changes in registrations may not be an accurate denominator to reflect the active riders who are engaging in motorcycle usage and, therefore, may obscure difference. Perhaps, vehicle miles driven are a better denominator for this purpose for the same reason it is used in motor vehicle collision fatality rates. A good example is in the study by Bledsoe and Li, in which registrations decreased and thereby crashes decreased, but the fatality rate increased. However, perhaps because of the decreases, the absolute increase seems minimal and statistically not significant.
The variation in helmet usage in these studies was substantial. Internationally, Conrad et al. reported that the helmet usage was as high as 89% in Indonesia, whereas LaTorre et al. reported only a 12% rate of helmet usage in Italy. Nationally, in America, Brandt et al. reported in their study from Michigan a prevalence of 80.5% of riders wearing a helmet during a crash, whereas a study conducted in Illinois by Kelly et al. reported a 14.6% prevalence of helmets in riders involved in crashes. Without nonrandom selection of these studies, the variation in helmet usage can also impact the results obtained.
The studies reviewed here discuss only the use of helmets. However, the issue of misuse as noted by Peek-Asa et al. in his 1999 study in Thailand can also be a major factor in postcrash injury. Further study is required to better understand and to quantify this problem. Furthermore, in these studies, we did not explore in depth the impact of partial helmet laws, although the studies by Houston and Richardson and Tsai SY attempted to address this issue. Interestingly, Houston and Richardson found that partial helmet laws showed no improvement in outcomes over states with no helmet laws.
- The use of motorcycle helmets decreases the overall death rate of motorcycle crashes when compared with nonhelmeted riders.
- The use of motorcycle helmets decreases the incidence of lethal head injury in motorcycle crashes when compared with nonhelmeted riders.
- The use of motorcycle helmets decreases the severity of nonlethal head injury in motorcycle crashes when compared with nonhelmeted riders.
- Mandatory universal helmet laws reduce mortality and head injury in geographical areas with the law when compared with areas without it.
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