Eur J Trauma Emerg Surg DOI 10.1007/s00068-014-0471-y
Helmet use in bicycle trauma patients: a population‑based study E. Zibung · L. Riddez · C. Nordenvall
Received: 10 April 2014 / Accepted: 3 November 2014 © Springer-Verlag Berlin Heidelberg 2014
Abstract Introduction In recent years, the increasing number of bicyclists has evoked the debate on use of bicycle helmet. The aim of this study was to investigate the association between helmet use and injury pattern in bicycle trauma patients. Patients and methods We performed a retrospective population-based study of 186 patients treated for bicyclerelated injuries at a Level 1 Trauma Centre in Sweden during a 3-year period. Data were collected from case records. Unconditional logistic regression was used to calculate odds ratios (ORs), and 95 % confidence intervals (CIs). Results 43.5 % of the 186 patients used a bicycle helmet at the time of the crash. Helmet users were less likely to get head and facial injuries in collisions than non-helmet users (OR, 0.3; 95 % CI, 0.07–0.8, and OR, 0.07; 95 % CI, 0.02–0.3), whereas no difference was seen in single-vehicle accidents. The risk of limb injuries was higher among helmet users. Conclusions Non-helmet use is associated with an increased risk of injury to head and face in collisions, whereas helmet use is associated with an increased risk of limb injuries in all types of crashes. E. Zibung · L. Riddez · C. Nordenvall Department of Molecular Medicine and Surgery, Karolinska Institute, Stockholm, Sweden L. Riddez e-mail: [email protected]
C. Nordenvall e-mail: [email protected]
E. Zibung (*) Gastrocentrum, P9:03, Karolinska University Hospital, 17176 Stockholm, Sweden e-mail: evelyne.zibung‑[email protected]
Keywords Bicycle trauma · Bicycle helmet · Head injury · Facial injury
Introduction Due to the steadily rising health and environmental awareness over the past years, the number of bicyclists is increasing. Large investments in bicycle infrastructure are made and mandatory bicycle helmet legislation has been implemented in several states in Australia, New Zealand, Canada and the USA. In 2005, a bicycle helmet law was enacted in Sweden, but this regulation only applies to children under 15 years of age. Data from case–control studies and two cohort studies have shown that helmet use can prevent head and face injuries as well as fatalities [1–9]. However, the prevalence of helmet users in the cohort studies was low, and mandatory helmet legislation is still controversial. Critical voices claim that the protecting effect of bicycle helmets is overestimated  and that helmet laws and helmet campaigns could be counterproductive by discouraging cycling and thereby causing harm to the environment as well as the public health [11, 12]. In New South Wales, Australia, the enactment of a helmet law for cyclists 20 years ago led to a steady decrease of head injury rates over a long period and despite mandatory helmet legislation the number of bicyclists increased . The aim of our retrospective population-based study was to investigate the association between bicycle helmet use and injury pattern in adult patients presenting at a Level 1 Trauma Centre in a population with a high prevalence of voluntary helmet use.
E. Zibung et al.
Patients and methods
hospital stay, admittance to the intensive care unit (ICU) and discharge to a rehabilitation unit.
Setting Statistical analysis Karolinska Trauma Centre at the Karolinska University Hospital in Stockholm, Sweden, is a Level 1 Trauma Centre and the largest Trauma Centre in Sweden treating about 1,500 trauma patients per year. All major trauma activity in Stockholm is centralised, i.e. all trauma patients with deviant vital signs or severe injuries (e.g. flail chest, pelvic fracture or paralysis) are referred to the Karolinska Trauma Centre. Study population Between January 2010 and December 2012, all adult patients (≥15 years old) who were admitted to the Karolinska Trauma Centre after a bicycle trauma and treated in hospital were identified. Of 212 patients registered with an ICD-10 code V10–19 (“Pedal cyclist injured in transport accident”), 19 were excluded due to false coding (offroad mountain bikers, BMX riders or pedestrians carrying a bicycle or riding a scooter). If data on helmet use were missing (n = 23), this information was retrieved by mail. Seven patients were excluded due to missing data on helmet use [no response to our letters (n = 4), living abroad (n = 2), missing address (n = 1)], leaving 186 bicycle trauma patients in the final cohort. Data sources All medical data were collected by reviewing the case records. We recorded if the patient used a helmet (helmet user), or not (non-helmet user) at the time of the crash. We specified the type of crash as either a single-vehicle crash or a collision (involvement of a motor vehicle, another bicycle, a pedestrian or a stationary object). We recorded Glasgow Coma Scale (GCS), vital signs and blood alcohol level at time of admission and collected data on injuries to head, face, neck, thorax, abdomen, spine and limbs. Head injury was defined as the presence of cranial fractures, subdural haemorrhage, traumatic subarachnoid haemorrhage or other intracranial bleeding on Computer Tomography scan. Soft tissue damage only was not included. Facial injury was defined as fractures of the upper, middle and lower face, including dental damage. For limb injuries we included fractures, dislocations, contusions and sprains, but no lacerations or abrasions. Injury Severity Score (ISS)  was extracted from the trauma register database “Kvittra” (a quality register used in Swedish trauma care until 30 June, 2011) , and SweTrau (the national trauma register used after 30 June, 2011) . We registered the length of the patient’s
The data collection was converted into STATA software datasets and analyses were done using Stata, version 12.1 (StataCorp, TX, USA). The statistical software was used to evaluate descriptive information and to calculate p values using the Wilcoxon–Mann–Whitney test. All tests were two tailed and considered significant at a p value less than 0.05. Unconditional logistic regression was used to calculate odds ratios (ORs) and corresponding 95 % confidence intervals (CIs) on the risk of head injury, facial injury and limb injury. The multivariate analyses were adjusted for age (1 days 87 (46.8 %) ICU stay 26 (14 %) Death
3 (1.6 %)
respectively). The median hospital stay was 1 day (range 0–69 days). There was no difference in length of hospital stay or in discharge to a rehabilitation unit. Three deaths occurred within 2–72 h of hospital attendance (one caused by a single-vehicle crash, one caused by a collision with another bicycle, and one caused by collision with a car). None of these three patients was wearing a bicycle helmet and all three died due to extensive traumatic brain injury. At the time of admission, 38 patients were affected by alcohol and the mean serum ethanol level among those patients was 16 mmol/l (range 4–98 mmol/l). Only 7 % of the helmet users had consumed alcohol compared to 30.5 % of the non-helmet users. However, there was no significant difference in ISS ≥16 among alcohol consumers compared to those who had not consumed alcohol (p value 0.7). In collisions, helmet use was associated with a lower risk of head and facial injuries compared to non-helmet
Helmet users (n = 81)
Non-helmet users (n = 105)
1 (1.2 %) 10 (12.3 %)
8 (7.6 %) 18 (17.1 %)
16 (19.8 %) 14 (17.3 %) 11 (13.6 %) 3 (3.7 %) 23 (28.4 %) 7 (8.6 %) 40 (49.4 %)
33 (31.4 %) 33 (31.4 %) 9 (8.6 %) 6 (5.7 %) 24 (22.9 %) 11 (10.5 %) 33 (31.4 %)
0.08 0.03 0.3 0.5 0.4 0.3 0.01
39 (48.2 %) 7 (8.6 %)
48 (45.7 %) 19 (18.1 %)
3 (2.9 %)
use, whereas no difference was observed in single-vehicle crashes (Table 3). The risk of limb injury was higher among helmet users. Excluding patients with missing data on alcohol (10 patients) did not change the results.
Discussion The popularity of commuting with a bicycle has increased in the last few years. However, bicycle trauma is common and can lead to serious morbidity and mortality resulting in individual suffering as well as high costs for the society [17–19]. In this population-based retrospective study of 186 adult bicycle trauma patients we found that bicycle helmet users were less likely to suffer from head and facial injuries, which is in line with previous studies [3, 6]. The risk of limb injury was higher among helmet users, indicating that helmet users were involved in more serious crashes than
E. Zibung et al. Table 3 The risk of head, facial, or limb injury among helmet users and non-helmet users in 186 adult bicycle trauma patients, stratified by type of crash
Collision with another vehicle, a stationary object or a pedestrian b
Adjusted for sex, age, and alcohol use OR odds ratio, CI confidence interval
Head injury Non-helmet user Helmet user Facial injury Non-helmet user Helmet user Limb injury Non-helmet user Helmet user
95 % CI
95 % CI
95 % CI
95 % CI
non-helmet users. No fatal injury occurred among helmet users compared with three deaths among non-helmet users. The effectiveness of helmet use for cyclists has been questioned, and critics have been concerned about risk compensation, i.e. that cycling with a helmet leads to a riskier behaviour in road traffic . However, in our study only 43.5 % of the patients were using a helmet at the time of the crash. At the same time, an observational study found that more than 75 % of the bicyclists in Stockholm, Sweden, used a helmet . These numbers indicate that helmet-using bicyclists are underrepresented in our trauma population. An explanation to the underrepresentation of helmet users in our study could be that helmet users behaved more cautiously in road traffic than non-helmet users. Another possible explanation is that helmet users were equally involved in crashes but did not need advanced medical treatment to the same extent, in particular after a single-vehicle crash. If non-helmet users with minor injuries were more likely to be sent to hospital than helmet users, there is a risk of detection bias. In Sweden, 80 % of the bicycle crashes are single-vehicle crashes, often caused by loose grit, poor surface maintenance or insufficient winter service, and about 90 % of all crashes with seriously injured cyclists occur in urban areas . In our opinion, further investments in bicycle infrastructure have to be done by segregating cyclists from motorised traffic and maintaining cycle lanes. Furthermore, mandatory bicycle helmet legislation could reduce morbidity and mortality in bicycle trauma. Strengths with our study include its population-based nature in a population where the prevalence of helmet use is higher than in previous cohort studies (43.5 % compared to 11.0 and 25.8 %) [3, 8]. Our interest was the effect of helmet use in bicycle trauma that requires specialised care, and we were not able to identify uninjured or only slightly injured patients. Patients who died at the site of the accident
were not included which could bias the results. However, during the studied period only four cyclists died in the prehospital phase in Stockholm . In addition, only 3.6 % of the patients were excluded due to missing data, and since all trauma patients are centralised to the Karolinska Trauma Centre we believe that the risk of selection bias is small and that the results are generalizable. Our study is limited by its small size. Another limitation is its retrospective character and the possibility of inconsistent documentation in the case records. We believe that the risk of recall bias and misclassification is small. All trauma patients were treated according to a local trauma protocol. We chose to study hard facts such as GCS, vital signs, blood alcohol level, X-ray findings and length of hospital stay, which are more or less independent of the examiner. All case records were reviewed and categorised by a physician with trauma expertise. The study was limited by its lack of data on potential confounders such as rider behaviour and weather conditions, and the possibility of unmeasured or residual confounding factors cannot be excluded.
Conclusion Non-helmet use is associated with an increased risk of injury to head and face in collisions, whereas helmet use is associated with an increased risk of limb injuries in all types of crashes. Conflict of interest Louis Riddez and Caroline Nordenvall declare that they have no conflict of interest. Evelyne Zibung received the Swedish Trauma Associations scholarship 2013, sponsored by Takeda Nycomed, as well as the Swedish Traffic Medical Research Funds scholarship 2014. Ethical standards Ethical approval was acquired from the Regional Ethical Board at Karolinska Institute (KI; Stockholm, Sweden).
Helmet use in bicycle trauma patients According to KI’s policy informed consent for each patient is not needed in this cohort study. Ethical guidelines All authors comply with the Ethical guidelines for authorship and publishing in the European Journal of Trauma and Emergency Surgery.
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