Effectiveness of Different Types of Motorcycle Helmets and Effects of their Improper Use on Head Injuries

Wen-Yu Yu; Chih-Yi Chen; Wen-Ta Chiu; Mau-Roung Lin

Disclosures

Int J Epidemiol. 2011;40(3):794-803. 

In This Article

Discussion

The results of this case–control study indicate that of the three commonly used helmet types, half-coverage helmets provide the least protection against head injuries for motorcycle riders when a crash occurs, and no significant difference in the protection was detected between full- and open-face helmets. Moreover, improper helmet use may affect helmet fixation in a motorcycle crash and thus reduce the helmet's effectiveness for preventing head injuries.

The better performance of full-face helmets in preventing head injuries over other helmet types may result from coverage of the entire head and the presence of a chin bar. Usually, a motorcycle helmet consists of a hard shell of fibreglass or thermoplastic to reduce the force of a direct blow to the skull, an energy-absorbing foam liner to dissipate deceleration forces and a retention system consisting of a chin strap.[35] Most half-coverage helmets do not have a visor, whereas full-face and open-face helmets do have a visor or faceguard to cover the face. Full-face helmets also incorporate a chin bar that extends upwards to a height just below the lips. Half-coverage helmets are cheaper than other helmet types; however, they are less likely to meet national safety standards.[36] There is still much that can be done to reduce head injuries and deaths among helmeted riders, particularly in countries where half-coverage helmets are commonly used (e.g. >60% of Taiwanese in this study).

Our results also reflect the importance of correct helmet use for maximal protection against head injuries. Given the same crash severity, the fixation of a helmet during a crash was most closely related to the retention system. The result of a further subgroup analysis showed that helmet detachment was correlated with the helmet being loosely fastened [point biserial correlation coefficient (rpb ) = 0.64]. Nevertheless, helmet retention systems are rarely tested in the laboratory or regulated by safety standards, and very few empirical data are available. In many Asian countries, more than one-third of motorcycle riders were found to wear a helmet improperly, such as wearing it unfastened or loosely fastened in order to exhibit 'token' compliance with helmet-use laws, and some even put on a helmet only when the police are nearby.[25] Furthermore, the police seldom enforce proper helmet use.[26] In sum, this study demonstrates for riders, policemen and policymakers that wearing a helmet improperly might not be sufficient to prevent head injuries.

Crash severity is seldom controlled for in studies of helmet use and head injuries. Without controlling for it, such studies implicitly assume similar distributions of crash severities between helmeted and non-helmeted riders, and this assumption is often violated.[37,38] There are no standardized measures of severity for motorcycle crashes. In this study, crash severity was indicated by the cost of repairs to the damaged motorcycle, the type of collision and the object with which the motorcyclist had collided. Motorcycle repair costs might be affected by social and economic factors, and collision type and collision object might not be able to discriminate severity levels among various collision objects or among single-vehicle crashes. A commonly used alternative is a modification of the ISS that calculates injuries to body regions other than the head.[30] However, the non-head ISS index could no better explain the risk of head injury in the regression model, and more importantly, it had to assume that the occurrence of injuries to body regions other than the head was independent of the incidence of head injuries or the use of helmets. In reality, this assumption might not be valid.[39]

There are several limitations to the present study. First, a referral pattern might exist if case and control motorcyclists were not selected from the same population base. Motorcyclists who had serious injuries were probably more likely to have been referred to the study hospital than those with minor or no injuries. For instance, the emergency room controls had a different distribution of helmet-fastening status compared with motorcyclists at petrol stations. Nevertheless, the biased direction of the referral pattern may have tended to underestimate the effect of improper helmet use. Second, riders who wore full-face helmets may have been more aware of traffic safety than those wearing half-coverage or open-face helmets. Personality characteristics such as risk-taking were not directly measured and controlled for in the study, although they may have differed among riders who wore different helmet types and with different fastening statuses. Third, information bias might exist because eligible subjects who had serious head injuries were less likely to respond to our interviews, and case motorcyclists were more likely than control motorcyclists to have proxy information and missing values. Accordingly, differential ascertainments of exposure information such as the helmet type and fastening status between the case and control groups might have occurred, and a prospective cohort study to validate these results is warranted. Fourth, to estimate the population-based prevalences of helmet types and fastening statuses, data from petrol station motorcyclists at the time of crash would be more valid than at the study time. However, direct observations at petrol stations may help avoid recall errors, memory lapses and defensive responses. Fifth, missing data on some helmet-related characteristics such as fixation status during the crash were unbalanced between case and control motorcyclists; in addition, only 36.7% of motorcyclists (39.3% of cases and 32.3% of controls) carried their helmets into the emergency room. Further analyses showed that motorcyclists who had missing values for the fixation status during the crash or those who did not carry their helmets tended to have higher non-head ISS scores or higher repair costs for motorcycle damage (i.e. higher levels of crash severity). Since the repair cost for motorcycle damage was controlled for in the statistical analysis, a potential bias in the result due to this selecting factor should have been avoided. Finally, there was a possibility of misdiagnosing motorcyclists who consumed alcohol as having head injuries. Nevertheless, the proportion of motorcyclists who consumed alcohol at the time of the crash was very low in the study.

This study demonstrates that the type and fastening status of a helmet can affect the helmet's effectiveness in preventing head injuries. For a long time, injury prevention workers have focused on whether or not motorcycle riders wear a helmet, rather than on which helmet type should be worn or how the helmet is worn. Now it is high time to promote legislation that requires motorcycle riders to wear safer helmets (e.g. full-face helmets) as well as to fasten the helmets properly.

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