A decrease in both mild and severe bicycle-related head injuries in helmet wearing ages trend analyses in Sweden

Health Promotion International, Vol. 22 No. 3 doi:10.1093/heapro/dam020 # The Author (2007). Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org A decrease in both mild and severe bicycle-related head injuries in helmet wearing ages trend analyses in Sweden PETER BERG * and RAGNAR WESTERLING Department of Public Health and Caring Sciences and Social Medicine, Uppsala Science Park, SE-751 85 Uppsala, Sweden *Corresponding author. E-mail: peter.berg@pubcare.uu.se SUMMARY Several international studies point at the efficacy of bicycle helmets in reducing head injuries. In Sweden, observational studies show that from 1988 to 1996 helmet use increased in all categories of cyclists. The objectives of this study were to analyse the trends of bicycle-related head injuries based on their main diagnosis and external cause of injury by different age groups. Our study area was the whole population of Sweden from 1987 to 1996. Outcome evaluation was based on data from the Swedish National Hospital Discharge Register concerning all bicycle-related injuries from 1987 to 1996, which presented 49 758 reported in-patient care. The trends in incidence rates (IRs) were studied with regression analyses. The results show that children under 15 years had the highest IRs. For these children, the IR decreased by 46%. The head injuries in children decreased both in collisions with motor vehicles and in other accidents. Similarly, the IR of concussion and skull fracture decreased. For nonhead injuries, there were no significant changes for children. On the other hand, the incidence of both head and other injuries for adults aged 16 50 years increased. Ages above that showed no significant changes. Our conclusions are that the decrease in IR for bicycle-related head injuries refers to children in ages for whom bicycle helmet use during the period increased. This could not be explained by any general decrease in bicycle-related accidents or by any changes in the distribution of injuries after collision with motor vehicles. The increasing helmet use among younger schoolchildren probably contributed to the decrease in head injuries. Key words: bicycle helmet; head injuries; head protection; bicycle-related accidents INTRODUCTION A meta-analysis of 16 observational studies dated 1987 1998 by Attewell et al. (2001) concludes that bicycle helmets prevent serious injury and that there is mounting scientific evidence for this. Several international studies point at the efficacy of bicycle helmets in reducing head injuries. Cook and Sheikh (2000) state in their analysis of routinely collected data that the number of head injuries among cyclists in England fell markedly during a period of increasing helmet use. In Washington State, USA, at a level I trauma centre, head injuries decreased when the percentage of helmeted riders increased (Mock et al., 1995). In Canada, data from the British Columbia Children s Hospital were analysed and showed that 70% of injured cyclists reported no helmet use and that head injuries occurred more often among cyclists that did not use helmets (Linn et al., 1998). In Australia, an evaluation at Melbourne and Geelong hospitals showed that approved helmets reduced head injuries by 45% (McDermott et al., 1993). Moreover, a casecontrol study at two children s hospitals in 191

192 P. Berg and R. Westerling Brisbane, Australia showed that wearing a helmet reduces the risk of head injury (Thomas et al., 1994). Other studies show that helmets mitigate the risk of severe head injuries. Rivara et al. (2000) found that helmets reduced the risk by 63 88% of head, brain and severe brain injuries among cyclists of all ages. A retrospective study at the regional paediatric trauma centre in Buffalo, NY, USA, compared helmeted children with non-helmeted children and found that helmeted children were more likely to sustain concussion alone, but less likely to have other head injuries (Shafi et al., 1998). Another similar comparative study in Victoria, Australia showed that 80% of the head injuries of helmeted cyclists were mild (Grimard et al., 1995). However, in the examination of the meta-analysis performed by Attewell et al. (2001), Curnow (2003) disagrees and concludes instead that the meta-analysis does not provide scientific evidence that bicycle helmets, not being tested for capacity to mitigate the main factors that cause serious injury to the brain, do reduce it. As reported earlier in Health Promotion International (Nolén et al., 2005), since 1988, the Swedish National Road and Transport Research Institute have annually carried out observational studies of bicycle helmet usage in Sweden. These studies show that from 1988 to 1996 helmet use increased in all categories of cyclists. Helmet wearing increased from 20 to 35% among children (%10 years) riding bikes in their leisure time, 5 33% among school children and 2 14% in adults. In a previous study, we discovered that most pre-school children (80%) used a bicycle helmet, but a clear majority of the children stopped wearing them during their school years. Only 3% of the children aged 14 15 years used helmets and as few as 2% of the adults (Berg and Westerling, 2001). In Sweden, both Ekman et al. (2001) and Welander et al. (2001) studied the trend in bicycle-related injuries and made comparisons between geographic areas. They found that the incidence rates (IRs) for children aged 0 14 years decreased from 1987 to 1996, but they did not distinguish between different diagnoses of head injuries and the external cause of injury. On the other hand, Boström and Nilsson (2001) list the distribution of bicycle-related injuries from 1987 to 1994 based on whether a motor vehicle was involved and do not specifically study the trends of head injuries and external causes of injury in different age groups. During the last 20 years, several initiatives have been taken in Sweden to reduce bicyclerelated accidents. National bicycle helmet interventions were initiated by the Swedish National Road Administration in 1987 and by the Swedish Helmet Initiative Group in 1991. In 2000, the Swedish National Road Administration presented a national cycle strategy aimed to increase cycling by making cycling easier and safer. In this study, we analysed the trends of bicycle-related head injuries based on their main diagnosis and external cause of injury in different age groups. METHOD Study area and population Our study area was Sweden with a population of almost 9 million inhabitants, of which 19.6% are under 15 years of age, 48.3% are between 16 and 50 years of age and 32.1% are older. Sources of data Outcome evaluation was based on data from The Centre for Epidemiology at the Swedish National Board of Health and Welfare. We studied The Hospital Discharge Register (HDR) for a 10-year period, 1987 1996, concerning all bicycle-related injuries (n ¼ 49 758). Since 1987, the HDR has covered all public in-patient care in Sweden and reporting to HDR is compulsory. The register is nationwide and covers the whole Swedish population. Case definition A Swedish version of ICD-9 (WHO s International Classification of Diseases) was used to study the variables diagnosis and external cause of injury. We identified the diagnosis for head injuries as skull fracture (ICD-9 800-4), concussion (ICD-9 850) or head injury except concussion and skull fracture (ICD-9 851-4). The external cause of injury was identified as collision between bicycle and a motor vehicle (ICD-9 E819G) or other type of bicycle accidents (ICD-9 E 826X).

A decrease in both mild and severe bicycle-related head injuries in helmet wearing ages 193 Statistics Analyses were made using SAS version 6.12. The IR was defined as the number of hospital discharges in any 1 year divided by the mean population of that year multiplied by 100 000. To analyse the trends in IRs, linear regression was used with year as independent and type of injury as dependent variables. Both linear ( presented in the paper) and logarithmic models were used showing the same trends. Differences were considered significant with p-values,0.05. RESULTS Individuals under aged 15 had the highest IRs. The mean annual IR ranged between 65.2 for boys aged 0 15 years and 11.4 for elderly women over aged 66 years (Table 1). Head injuries were responsible for 50% of the studied injuries, and of these 75% were concussions. For children aged 0 15 years, the IR decreased by 46% ( p ¼ 0.0001) (Figure 1 and Table 1), which is equivalent to 550 fewer bicycle-related accidents resulting in head injuries each year. The IR decreased approximately twice as much for boys as for girls (Table 1). The IR decreased significantly for both concussion and skull fracture for children aged 0 15 years (Table 2). On the other hand, the IR of both head (p ¼ 0.0002) and non-head injuries (p ¼ 0.0022) for teenagers and adults aged 16 50 years increased (Figure 2 and Tables 1 and 2). For non-head injuries, there were no significant changes for children (Figure 2 and Table 2). For children aged 0 15 years, we also found a decrease in head injuries both in collision with motor-vehicles (p ¼ 0.0112) and in other accidents (p ¼ 0.0002) (Table 3). Ages.50 years showed no significant changes. DISCUSSION In our study, we found a decrease in bicycle-related head injuries for children aged 0 15 years from 1987 to 1996, but no significant changes in non-head injuries. In this age group, the head injuries also decreased significantly both in collisions with motor vehicles and in other accidents. For children, there was also a decrease in both concussion and in skull fracture. On the other hand, teenagers and adults aged 16 50 showed increased IRs for both head and non-head injuries, but no change in IR concerning head injuries when a motor vehicle was involved. The IR as a measure of changes in bicycle-related head injuries might be argued as it does not account for and is not independent of exposure (i.e. the amount of bicycling performed by each age group in terms of time or distance bicycled). The lack of exposure data is an endemic problem shared by all researchers in this subject matter when analysing injury data for an entire population. According to the Swedish Institute for Transport and Communications Table 1: The number and incidence of bicycle-related head injuries (ICD-9 800-4, 850-4) from 1987 to 1996 per 100 000 inhabitants by age and gender Gender Age group (year) Number of cases Mean annual incidence rate Yearly change in incidence rate 95% CI Level of significance Male 0 15 5664 65.21 24.11 (25.05 to 23.16) *** 16 50 5271 24.61 1.10 (0.75 1.46) *** 51 65 1449 21.94 0.49 (20.10 to 1.08) 66 1581 25.99 20.17 (21.09 to 0.74) Female 0 15 3562 43.20 22.82 (23.52 to 22.13) *** 16 50 3587 17.54 0.38 (0.16 0.60) ** 51 65 1220 18.02 0.04 (20.50 to 0.59) 66 947 11.36 20.15 (20.57 to 0.27) Total 0 15 9226 54.49 23.48 (24.23 to 22.73) *** 16 50 8858 21.17 0.75 (0.53 0.97) *** 51 65 2669 19.96 0.27 (20.26 to 0.80) 66 2528 17.53 20.17 (20.68 to 0.34) Level of significance: *p, 0.05, **p, 0.01, ***p, 0.001.

194 P. Berg and R. Westerling Fig. 1: The incident of bicycle-related head injuries (ICD-9 800-4, 850-4) and non-head injuries from 1987 to 1996 per 100 000 inhabitants for children aged 0 15 years. Analysis [data from annual national Travel Habit Statistical Survey (RVU) for the years of 1978, 1984 1985, 1994 1998] and The Swedish National Road and Transport Research Institute (data from RVU 92), children,15 years were not a part of the survey until 1994. Therefore, we can only see that their bicycle usage did not change from 1994 to 1996. Because we found no significant changes in non-head injuries for children aged 0 15 years from 1987 to 1996, we assume that there were no changes from 1987 to 1993 in their bicycle usage that might have influenced the result. On the other hand, adult bicycle usage decreased by one-third from 1992 to 1996. Another way to avoid the potential problem of not having exposure data could be to use the proportion of each injury type to the total number of injuries per period as the measure. This measure was used by Lee et al. (2005) in their analysis of bicycle-related injuries in Table 2: The number and incidence of bicycle-related head injuries (ICD-9 800-4, 850-4) and non-head injuries from 1987 to 1996 per 100 000 inhabitants by age and diagnosis Diagnosis Age group (year) Number of cases Mean annual incidence rate Yearly change in incidence rate 95% CI Level of significance Concussion (ICD-9, 850) 0 15 8390 49.55 23.27 (24.03 to 22.51) *** 16 50 6297 15.05 0.69 (0.50 0.88) *** 51 65 1645 12.30 0.23 (20.12 to 0.59) 66 1417 9.83 20.12 (20.35 to 0.10) Skull fracture (ICD-9, 800-4) Head injury except concussion and fracture (ICD-9, 851-4) 0 15 478 2.82 20.19 (20.28 to 20.10) ** 16 50 1587 3.79 20.07 (20.15 to 0.01) 51 65 505 3.78 20.07 (20.18 to 0.04) 66 347 2.41 20.12 (20.27 to 0.04) 0 15 358 2.11 20.02 (20.12 to 0.08) 16 50 974 2.33 0.13 (0.05 0.20) * 51 65 520 3.89 0.11 (20.06 to 0.27) 66 764 5.30 0.08 (20.19 to 0.34) Non-head injuries 0 15 6505 38.42 20.26 (20.58 to 0.07) 16 50 7477 17.87 0.70 (0.39 1.02) ** 51 65 4060 30.36 20.22 (20.77 to 0.33) 66 6430 44.59 0.25 (20.49 to 1.00) Level of significance: *p, 0.05, **p, 0.01, ***p, 0.001.

A decrease in both mild and severe bicycle-related head injuries in helmet wearing ages 195 Fig. 2: The incident of bicycle-related head injuries (ICD-9 800-4, 850-4) and non-head injuries from 1987 to 1996 per 100 000 inhabitants aged 16 50 years. California. They found the bicycle safety helmet legislation in California to be associated with a reduction of 18.2% in the proportion of traumatic brain injuries among injured youth cyclists aged 17 years, who were subjected to the law. In this age group, the reduction was the same for accidents both involving and not involving a motor vehicle. On the other hand, for adult cyclists, not subjected to a helmet law, the proportion did not significantly change. In our study, we found a reduction of 11.5% in the proportion of head injuries among children aged 0 15 years, but no change in the proportion among teenagers and adults aged 16 50 years. Another interesting question is whether bicycle helmets have the capacity to protect against severe injury or not. In the examination of the meta-analysis performed by Attewell et al. (2001), Curnow (2003) especially points to the importance of diffuse axonal injury and the angular acceleration of the head. The importance of well-fitting helmets was shown in a study in Washington State, USA. Individuals whose helmets were reported to fit poorly had a 1.96-fold increased risk of head injury when compared with those whose helmets fitted well (Rivara et al., 1999). In our study, we have no knowledge of the capacity of the helmets used, but we can presume that the helmet-wearers used helmets approved by the authorities according to the standards given during the study period. We found that for children aged 0 15 years, the head injuries decreased significantly both in collisions with motor vehicles and in other Table 3: The number and incidence of bicycle-related head injuries (ICD-9 800-4, 850-4) from 1987 to 1996 per 100 000 inhabitants by age and type of accident Type of accident Age group (year) Number of cases Mean annual incidence Yearly change in incidence rate 95% CI Level of significance Without motor vehicle involved With motor vehicle involved 0 15 7138 42.16 22.82 (23.68 to 21.96) *** 16 50 6057 14.48 0.68 (0.53 0.84) *** 51 65 1699 12.70 0.34 (20.02 to 0.70) 66 1386 9.61 0.02 (20.22 to 0.27) 0 15 2088 12.33 20.66 (21.05 to 20.27) ** 16 50 2801 6.69 0.06 (20.10 to 0.22) 51 65 970 7.25 20.07 (20.37 to 0.23) 66 1142 7.92 20.19 (20.55 to 0.17) Level of significance: *p, 0.05, **p, 0.01, ***p, 0.001.

196 P. Berg and R. Westerling accidents, but that for teenagers and adults aged 16 50 years no change occurred when a motor vehicle was involved. During the study period, a general improvement in road safety might have affected the result by reducing the rate of injuries to cyclists involved in accidents with motor vehicles. For instance, from 1998 to 2002 Sweden had a safer traffic environment for bicyclists because both the number of roads with a speed limit of 30 km/h and bike paths increased (Nilsson and Thulin, 2003). Because reporting to HDR is compulsory, the drop-out rates are low, usually,4 5%. In 1996, the main diagnosis was missing in 1.46% of the hospital stays reported (Homepage of the Swedish National Board of Health and Welfare, www.sos.epc.par). CONCLUSION The decreased IR for bicycle-related head injuries from 1987 to 1996 in Sweden refers to children in ages for whom bicycle helmet use during the same period increased (Nolén et al., 2005). This could not be explained by any general decrease in bicycle-related accidents or by any changes in the distribution of injuries after collision with motor vehicles and there was no evident change in bicycle use for children, but a decrease among adults during the study period. Most bicycle-related accidents with head injuries (70%) happen without the involvement of motor vehicles (single accidents), but this study shows a decrease in head injuries also in collisions with motor vehicles. It also shows a decrease in both concussion and skull fracture. It seems likely that the increasing helmet use among younger schoolchildren contributed to the decrease in head injuries and the use of bicycle helmets may even reduce severe head injuries. It is therefore necessary to reduce the consequences from these accidents by promoting an increased use of bicycle helmets. Implications for prevention In pursuing the aims of Agenda-21 (The Rio Declaration on Environment and Development: June 1992), Sweden has, together with many other countries, realized that increased emphasis on walking, cycling and public transport is essential for the requirements of the future concerning a transport system designed to minimize environmental impacts. A mandatory law may obstruct this aim due to the fear that the compulsory use of bicycle helmets may reduce bicycle use and therefore negatively affect public health. Nevertheless, a mandatory law for children up to 15 years of age was initiated in Sweden from the first of January 2005. This is in line with that we, in our previous study (Berg and Westerling, 2001), found that bicycle helmet use decreased as the children grew older. However, international studies in countries where mandatory laws earlier have been introduced show that bicycle helmet use not becomes 100% (www. liikenneturva.fi; Robinson, 1996; Leblanc et al., 2002). Other international studies reveal a better effect if laws are combined with information and campaigns (Dannenberg et al., 1993; Macknin and Medendrop, 1994). Parental involvement seems also to be of great importance for the use of bicycle helmets among schoolchildren that our previous study also relieved with the help from a LisRel analysis. Our findings may be used in the debate about whether it is important to increase the use of bicycle helmets. Further interventions and studies are needed to follow-up the effect of the recently initiated mandatory law in Sweden concerning bicycle helmet use for children and to see if bicycle head-injury rates are affected. ACKNOWLEDGEMENTS Peter Berg was, in this study, funded by Stiftelsen Länsförsäkringsbolagens Forskningsfond (a Swedish insurance company research foundation), Ragnar Westerling was supported by the Department of Public Health and Caring Sciences, Uppsala University, Sweden. REFERENCES Attewell, R., Glase, K. and McFadden, M. (2001) Bicycle helmet efficacy: a meta-analysis. Accident Analysis and Prevention, 33, 345 352. Berg, P. and Westerling, R. (2001) Bicycle helmet use among schoolchildren the influence of parental involvement and children s attitudes. Injury Prevention, 7, 218 222. Boström, L. and Nilsson, B. (2001) A review of serious injuries and deaths from bicycle accidents in Sweden from 1987 to 1994. Journal of Trauma, 50, 900 907.

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