Of 3,854 bicyclists who were injured or died during this time period, 3,390 (88 percent) were recruited for this study. This project was based on a case-control design in which individuals with head or brain injuries (cases) were identified and compared to those who were involved in crashes but did not suffer head or brain injuries (controls). Data were collected by self-report questionnaires, abstraction of medical records, and, in some cases, examination of bicycle helmets and measurements of cyclists' heads.
Questionnaires completed by subjects included demographic inquiries, as well as questions on cycling experience, circumstances of the crash, severity of damage to the bicycle, ownership and use of helmets, and self-reported helmet fit. Slightly more than half (50.6 percent) of subjects wore helmets at the time of their crashes.
The study found significant evidence that bicycle helmets prevent head and brain injury. Corollary research questions were also successfully answered.
Major findings include:
Bicycle helmets have been considered the single best means of protecting cyclists from the leading cause of injury and death: head injuries during crashes. Educational and legislative efforts have been successful in increasing the use of bicycle helmets.
Despite previous studies demonstrating that bicycle helmets are effective in preventing head and brain injuries, there remained significant questions about helmet efficacy. This study was designed to answer these questions by addressing the following aims:
Information was collected on possible differences between cases and controls (e.g., crash severity) that could obscure the central relationship between helmet use and head or brain injury, thus permitting needed adjustments between comparison groups through multivariate analysis. Analyses were also conducted on sub-groups (e.g., different age groups), different circumstances of the crash, and different helmet types.
Subjects were recruited from seven hospitals in Western Washington and from records of the King and Pierce County Medical Examiner's offices. The characteristics of the hospitals are as follows:
The questionnaire included inquiries regarding demographic characteristics of subjects, cycling experience, severity of damage to the bicycle, ownership and use of helmets, and self-reported helmet fit. Information on injuries was gathered from emergency room, hospital and medical examiner's records.
Injuries were assessed using the Abbreviated Injury Scale (AIS) for injuries in individual body regions, and the Injury Severity Score (ISS) for overall measure of severity. A commercial computer program, TRI-CODE, was used to ensure consistent and accurate coding and injury severity scoring for data gathered from seven hospitals.
For the purposes of this study, head injury, brain injury and severe brain injury are defined as follows:
The figures on these pages describe essential information on the subjects of this study. Subjects were most likely to be male, well educated, relatively affluent, and helmet owners.
More than two-thirds of the study population (72 percent) were male, and 43 percent were under 13 years of age (see Figure 1)). The subjects (or their parents, in the case of children) were an educated population, with nearly one-half (49 percent) having college degrees and nearly a quarter (24 percent) having post-graduate degrees (see Figure 2). Almost half (48 percent) had incomes of more than $35,000 annually (see Figure 3).
Nearly two-thirds (62 percent) of the cyclists reported that they bicycle daily. More than half of the adults (53 percent) rode more than five hours per week, and 37 percent rode more than 50 miles weekly.
Three-fourths of subjects (76 percent) reported they own bicycle helmets, with the rate of ownership lowest for teenagers (67 percent) and highest for cyclists older than 20 (79 percent) (see Figure 4). Slightly more than half (51 percent) were wearing helmets at the time time of the crash, with helmet use lowest (32 percent) among teens (see Figure 4).
Among helmeted cyclists, hard-shell helmets were most common (49 percent), followed by thin-shell helmets (29 percent) and helmets without shells (19 percent) (see Figure 5). When examined by testing standard, helmets were most commonly Snell-approved (54 percent) (see Figure 6).
The most common cause of crashes was loss of control by cyclists causing the cyclist to fall to the ground or hit an obstacle. Motor vehicles were involved in only 15 percent of crashes (see Figure 7). Crashes occurred most often (77 percent) while cyclists reported riding at speeds 15 mph or less (see Figure 8).
The majority of crashes occurred on paved streets (78 percent), followed by dirt, gravel and sand surfaces (see Figure 9). Almost half of the bicycles involved in crashes (43 percent) sustained some damage (see Figure 10).
The vast majority of injuries sustained by cyclists (92 percent) were in the Injury Severity Score (ISS) range of 0-8. An ISS of 9 or greater indicates moderate to severe injury. Only 6 percent of the injured cyclists with scores of 8 or less were hospitalized compared to 73 percent with scores of 9 or greater.
Facial injuries were most common, found in 34.8 percent of subjects. Head injuries were suffered by 22.3 percent of cyclists, and 6.0 percent received brain injuries (see Figure 11). About a tenth (9.7 percent) required hospital admission, nine subjects died in hospitals, and five died before transport to a hospital.
In this study, analysis of the protective effect of helmet use for risk of head injury and brain injury show substantial efficacy in all age groups. Overall, helmets were found to prevent 69 percent of head injuries, 65 percent of brain injuries, and 74 percent of severe brain injuries (see Figure 12), with no significant difference in the protective effect for any age group (see Figure 13). While the protective effect appeared to be somewhat lower in teenagers, this was not significant. These results are the same as those obtained in that portion of our 1989 study with emergency room controls. As previously mentioned, had it been possible to employ population controls in the present work (e.g., crashing cyclists regardless of medical attention), comparably higher levels of protection would have been obtained.
Of 62 bicyclists with severe brain injuries, only 24 percent were helmeted (15 riders out of the 1,718 who were helmeted), compared to the 57 percent rate of helmet use by the control group (riders with injuries other than head trauma). No helmeted bicyclists who sustained crashes in the youngest group (under 6 years old) and the 13-19 group suffered a severe brain injury. This again demonstrates the excellent protective effect of bicycle helmets.
Of the helmet types used by cyclists in this study, 49 percent were hard-shell, 29 percent where thin-shell, and 19 percent were no-shell (see Figure 5). Over half the helmets (54 percent) were Snell- certified, 28 percent had ANSI certification and 0.4 percent had ASTM certification (see Figure 6). Since Snell certification is most stringent, helmets meeting this standard would also meet ANSI and ASTM standards.
The protective effect of different helmet types is shown in Figure 14. The protective effect of hard- shell helmets for brain injuries was 73 percent compared to the 58-59 percent for other types. The protective effect against severe brain injuries was 83 percent compared to 70 percent for thin-shell and
Snell and ANSI approved helmets provided similar protection against head and brain injuries. However, Snell helmets decreased the risk of severe brain injuries by 81 percent and ANSI helmets by 72 percent. In order for this difference to be statistically significant the number of people in the study would have had to be 53 times greater.
Of the 518 bicyclists who were involved in motor vehicles crashes, 42 percent were helmeted. A similar level of protection against head injury was found after comparing for the protective effects of helmets in crashes with and without motor vehicle involvement (see Figure 15).
Helmets are effective in preventing head and brain injuries in all types of crashes, including those involving motor vehicles. The three types of helmets (hard-, thin- and no-shell) offer approximately the same degree of protection. Hard-shell and Snell-certified helmets may provide more protection against severe head injuries. However, since only 15 helmeted riders had severe brain injuries, we were unable to show a statistical difference between the helmet types and certification standards in this study.
Facial injury was defined as any injury of the jaw, lips, cheeks, nose, ears, eyes, forehead and mouth. Only serious facial injuries--fractures and lacerations--were considered for this study. Minor facial injuries that were found when cyclists were treated for other injuries (e.g., head injuries or broken legs) were not counted. Facial injuries were categorized as occurring in three regions: the lower face (lips, mouth and lower jaw), the middle face (nose and cheeks) and upper face (forehead, orbit, eyes and ears).
Of the 3,388 injured bicyclists analyzed in this study, 34.8 percent had facial injuries, 700 (20.7 percent) of which had serious facial injuries. Lacerations were nine times more frequent than fractures, occurring most often to the chin, lip and forehead (see Figure 16). The most common fractures were to the nose and mandible, each occurring in about 4 percent of facial-injury patients. Children aged 5 to 12 were most likely to suffer facial injuries, as 51 percent of all facial injuries occurred to cyclists in this age group, compared to 38 percent of other injuries.
By comparing the injuries suffered by helmeted cyclists with the injuries to those who were unprotected, it was found that helmets reduce the overall risk of serious facial injuries by 50 percent. Helmets were most effective in preventing injuries to the upper and middle facial regions, reducing(see Figure17).
This is the first study to demonstrate clearly that bicycle helmets provide protection to the midface region as well as the upper face.
Given the vulnerability of the lower face to serious injury in a bicycle crash, consideration should be given to adding a face bar or chin covering to the present design of bicycle helmets. Injuries in this area can be particularly disfiguring, lending an urgency to the need to develop such a protective modification.
Helmet fit was assessed by asking cyclists (or their parents for children younger than 14 years old) to report on helmet snugness, positioning on the head, custom fitting using adjustable foam pads, comfort, adjustability of straps, whether the helmet covered the forehead, and whether the helmet could be removed while the strap was fastened.
Factors in poor helmet fit included helmets worn too far to the back of the head instead of fitting on the center of the head. Cyclists whose helmets came off during a crash were three times more likely to have a head injury compared to those cyclists whose helmets were snugly fastened at the time of the crash.
Helmet fit proved to correlate closely with the degree of protection afforded by helmets during a crash. Overall, a clear dose-response relationship between self-reported fit and head injury emerged. Cyclists who reported that their helmets fit poorly were nearly twice as likely to suffer head injury than cyclists whose helmets fit the best. Cyclists reporting good and fair helmet fits received relatively less protection (see Figure 18).
Self-reported fit appears to be a valid measure of helmet fit and one that has easy applicability for assessing community programs to promote helmet use. There is a strong suggestion that fit, or lack thereof, may contribute to increased risk of head injury by a factor of two. However, since riders or parents were asked about fit after the injury that brought them to the emergency room, it is possible that those with head injuries may have had different recall of fit than those without such injuries. This phenomenon, known as recall bias, may partially explain these results.
In another portion of our study assessments of helmet fit were made by expert study personnel following a standard protocol. Their observations were compared to parent- and self-report of helmet fit. In general, the results indicated that many parents did not have an adequate understanding of "good fit." Based on this empiric experience, we have developed information describing how to test a helmet for proper fit.
In this study, helmets were purchased from cyclists who met any of the following criteria: helmeted cyclists who sustained head injury; helmeted cyclists who reported that they hit their head at the time of the crash; and cyclists who reported that their helmets were visibly damaged in the crash.
A total of 527 helmets were forwarded to the Snell Memorial Foundation for laboratory testing. Examiners were blinded to all information on circumstances of the crash and injuries to cyclists. Damage was scored according to the site (i.e., within an inch of the edge, middle or top of helmet) and severity.
The degree of damage was scored as follows:
Score = 0: No visible damage related to crash (40 percent of helmets);
Score = 1: Minimal damage, but none to liner (20 percent);
Score = 2: Moderate damage, with evidence of energy attenuation to liner (18 percent);
Score = 3: Major damage, with more than minimal compression of liner (14 percent);
Score = 4: Catastrophic damage, in which integrity of shell is lost (7 percent).
Damage occurred most frequently to the helmet front (47.1 percent of damaged helmets) and sides (30.4 percent). There was no difference between frequency of damage to the right and left sides of the helmets, and little damage occurred on the top or in the back of helmets. Damage to the edge of the liner accounted for nearly half of all impacts to the helmets (see Figure 19).
Damage score of helmets was found to be associated with the risk of head and brain injury to cyclists. Cyclists with catastrophic helmet damage were five times more likely to have suffered injury to the head (including the scalp, forehead, skull or brain) and nearly eleven more times as likely to have sustained a brain injury (i.e., concussion or worse) (see Figure 20 and Figure 21).
A relatively large proportion of helmets examined (39 percent) had damage to the liner. Damaged liners may not offer the same protection as new helmets, and many cyclists may be unaware that damage to the liner has occurred. For these reasons, the offer by many manufacturers of free replacement for helmets that have been involved in crashes appears to be appropriate.
Despite the association between the degree of helmet damage and the risk of head and brain injury, it should not be assumed that a causal relationship exists. Cyclists who have been in high- energy crashes generally have both head injuries and helmet damage. It's quite possible that injury to the head or brain would have been far worse for unhelmeted cyclists involved in the identical crashes. The association does suggest, however, that for certain types of crashes the helmet's energy-absorbing threshold has been exceeded.
Location of helmet damage (primarily to the front and at the edge) suggests that manufacturers should consider building an extra energy-absorbing capacity in the front, designing the helmet to fit as close as possible to the top of the eyes, and improve the retention system to prevent the helmet from rotating back.
The large number of injuries to the forehead suggest that either helmet design provides inadequate coverage or that the helmet is being worn improperly (see "Helmet Fit and the Risk of Head Injury"). The frequency of these injuries indicates the need for further investigation of these issues.
Injured cyclists most commonly had abrasions, lacerations and contusions, while one-fourth of the study group suffered fractures. Brain injuries (defined as concussion or more severe brain injury) occurred to 6.0 percent of riders. Injuries to internal organs and to blood vessels and nerves were un-common.
Researchers correlated circumstances of crashes with injury severity (ISS) to determine the importance of various risk factors. Collisions with motor vehicles increased the risk of severe injury (ISS>8) by 360 percent and markedly increased the risk of fatal injury. Riding at speeds greater than 15 mph increased the risk of severe injury by 40 percent. Children under the age of 10 were most likely to sustain injuries to the head and face, while teenagers and young adults were more apt to suffer injuries to the extremities.
Cyclists who sustained neck injuries (2.7 percent of the study group) tended to be more severely injured, with 22.3 percent having ISS>8, compared to 6.4 percent of cyclists without neck injuries. Neck injuries included sprains, cervical spine fractures, and nerve-cord injuries. There was no correlation between neck injury and helmet use or helmet type.
Of 14 fatal injuries, 10 were suffered by cyclists hit by motor vehicles, and only one, a 6-year-old child crushed by a truck, was helmeted.
Injuries occurring to cyclists riding at greater speeds may argue for separate facilities for these riders or for a version of the leather clothing worn by motorcyclists or the neoprene suits worn by ski racers. The number of facial injuries suffered by such high-risk groups as children and young adults suggests the need for additional facial protection on helmets for these cyclists. Fractures and dislocations to the extremities dictates study of the effectiveness of elbow and knee pads and wrist guards.
The number and severity of injuries to the face and body indicate that bicycle helmets alone are not sufficient to prevent injury to cyclists. Multiple approaches to intervention, including educational programs, product modification and regulation, are clearly warranted as strategies in the overall cycling-safety effort.
Educational programs can increase the rate of helmet use dramatically, yet there is national and international evidence that the rate of compliance plateaus when helmet use remains voluntary. A legislative approach, similar to the mandate that motor vehicle drivers wear seat belts, would appear to be the most promising next step.
Bicycle helmets cannot protect riders against all trauma, as the findings on neck injuries and extremity fractures, abrasions and contusions indicate. Environmental changes, such as safer roads and separate bike lanes, should be explored as an additional means of reducing injuries to cyclists.
This study of 3,390 injured cyclists, the largest undertaken to date, produced a wealth of data and the inevitable conclusion that bicycle helmets are the single most important protection against head injury and brain injury. Other issues that arose during the course of the study may inspire others to proceed with further investigations. The design of this study can be readily adapted to the evaluation of other questions regarding bicycle injuries.
Co-Principal Investigator: Robert S. Thompson, MD; Research Staff: Esther Normand, Mary Sunderland, Kathryn Reiss, Tom Thompson, Bob Hartl, Gracie Melton-Holman
Funding for this study was provided by a grant from the Snell Memorial Foundation.
For additional copies, contact:
Snell Memorial Foundation
Editor: Larry Zalin
Designer: Gina Davidson
© 1996 Snell Memorial Foundation. This report may not be reproduced without permission from the Snell Memorial Foundation.