Bicycle-related head injury: a study of 86 cases

Abstract

Within the framework of a bicycle helmet research program, we have set up a database of bicycle accident victims, containing both accident and clinical data. The database consists of a consecutive series of 86 victims of bicycle accidents who underwent a neurosurgical intervention in our hospital between 1990 and 2000. Data were obtained from police files, medical records, computed tomography head scans and a patient questionnaire. In only three victims, the wearing of a helmet was documented. In this study, the head injuries are analysed and the relation between the different types of head injuries and outcome is assessed.

Forty-four accidents were collisions with a motor vehicle and 42 accidents were falls. Most impacts occurred at the side (57%) or at the front (27%) of the head. The most frequent injuries were skull fractures (86%) and cerebral contusions (73%). Age was negatively correlated with outcome (P=0.0002) and positively correlated with the number (P=0.00002) and volume (P=0.00005) of contusions and the presence of subdural haematomas (P=0.0004). The injuries with the strongest negative effect on outcome were: subarachnoid haemorrhage (P=0.000001), multiple (P=0.000005) or large (P=0.0007) contusions, subdural haematoma (P=0.001) and brain swelling (P=0.002). A significant coexistence of these four injuries was found. We hypothesise that in many patients the contusions may have been the primary injuries of this complex and should therefore be considered as a main injury determining outcome in this study. We believe that such findings may support a rational approach to optimising pedal cyclist head protection.

Introduction

Victims of bicycle accidents are prone to head injury. Twenty-one to 61% of the victims of bicycle accidents seeking medical care have a head injury (Collins et al., 1993, Eilert-Petersson and Schelp, 1997, Elsen et al., 1997, Fife et al., 1983, Wood and Milne, 1988). Moreover, head injury is the cause of death in 69–93% of fatal bicycle accidents (Elsen et al., 1997, Fife et al., 1983, Guichon and Myles, 1975, Ostrom et al., 1993, Wood and Milne, 1988).

Bicycle accidents are not uncommon in Belgium, where pedal cycling always has been popular. On a random day in 1999 9.6% of the questioned Belgians made a ride on their bikes and the bicycle comprised 7.3% of the transport means to work and 19.2% of the transport means to school (NIS, 2000). Moreover, pedal cycling as a recreational sport has been gaining more and more popularity. This results in a relatively high number of bicycle accidents: in 2000, 6655 injured cyclists and 134 cycling fatalities were counted on public roads for a population of 10 million Belgians. As such, pedal cyclists comprised 9.8% of all road traffic accident victims and 9.1% of road traffic deaths (NIS, 2002). This is a high number compared with ‘only’ 728 pedal cyclist deaths in the United States in 2001, representing 1.7% of road traffic fatalities (National Highway Traffic Safety Administration, 2002). The wearing of a bicycle safety helmet is not mandatory in Belgium, except in cycling competition, and only rarely helmeted cyclists are seen in the streets. However, the authorities recently launched a promotion campaign and helmet use has also been promoted in media and sports events.

The protective effect of bicycle helmets has been demonstrated in numerous epidemiological studies (Dorsch et al., 1987, Maimaris et al., 1994, McDermott et al., 1993, Thomas et al., 1994, Thompson et al., 1989). Other authors, however, have outlined that the currently used helmets are still susceptible to improvement (Ching et al., 1997, Gilchrist and Mills, 1996, McIntosh et al., 1995, Williams, 1991). An important shortcoming in the current helmet standards is that linear head acceleration is the only injury mechanism being considered, while it has been demonstrated by several investigators in the field that the occurrence of certain head injuries is correlated with other mechanical parameters rather than linear acceleration. Consequently, tolerance criteria which relate the occurrence of all brain injuries exclusively to translational head motions have been criticised for a long time (Hirsch and Ommaya, 1970). Unfortunately, precise lesion-specific tolerance criteria for head injury in humans do not exist. Such criteria, in combination with the knowledge of the relative frequencies of the different types of traumatic brain lesions for each situation where head protection is desirable and information on the importance of the different brain lesions towards outcome, would allow for a systematic approach to improving protective headgear.

In the context of a multidisciplinary bicycle helmet research program, we have set up a database of bicycle accidents drawn from our patient population. We have collected data on the accident circumstances, the sustained injuries and outcome. The goal of this study was to gain more information on the mechanical input on the head in bicycle accidents and to perform a profound analysis of the resultant skull and brain injuries. For this purpose, accident reconstruction techniques have been developed and selected cases have been simulated (described in detail in a separate manuscript, in preparation). In the present report, we describe the head injuries sustained by these 86 pedal cyclists with serious head injury. Moreover, we have investigated the relation between the different types of head injuries and outcome, in order to assess which would be the most important lesions to protect against if lesion-specific protection were possible.