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Head Injury Control: Past, Present and Future
Published January 27, 1991 by International Association for Accident and Traffic Medicine in Sweden
The emphasis of this first international conference on traffic safety on the "vulnerable road user" is particularly appropriate to head injuries. When one examines the epidemiologic data on head injury incidence according to causative factors, motor vehicle injuries are the major cause of such injuries and if we define the vulnerable road user as the young, the old and the unduly exposed (whether it be the pedestrian or the rider of bicycles and motorcycles) damage to the head is the major target for harm. In my presentation today I will not be able to address the issue of head injury control from all its aspects e.g. epidemiology, prevention and clinical management. My central theme will be the evolution of our understanding of the biomechanics of head injuries and physiopathologic mechanisms of the primary injuries to the brain caused by mechanical loading as it applies to the development of rational criteria for head injuries. At the outset however, I would like to mention four recent clinical studies on traffic related injuries to illustrate the importance of correlating the biomechanical and physiopathologic data in the development of preventive strategies in head injury control.
The first is a study on helmet use, injury patterns and outcome in the state of Maryland. Of 1900 motorcycle drivers, helmet usage was only 35% overall, 30% in fatal cases, and only 16% in drivers with prior drug/alcohol convictions. Head injuries were almost twice as likely to occur in the unhelmeted (40% compared to 21% in the helmeted drivers) with acute care costs rising to thrice the amount in the unhelmeted as compared to helmeted drivers. Because of a lack of adequate data on the injury mechanisms in this study it was not possible to ascertain the types of head injuries sustained and how they differ in the presence and absence of helmets. Additionally there is a great paucity of data in this and similar studies on the types of helmet damage correlated with the brain injury patterns on lethal and sub-lethal cases. Field data of this type would be of great value.
The second study is one by Agran and her colleagues on one of the most vulnerable groups of road users: children on bicycles. Head injuries, as expected, were the most common of all injuries in this series of bicycle with motor vehicle collisions examined (N - 247_. Analysis of the data by location of the crash indicated that while there were major differences between the age and behavioral characteristics of the children either crossing at intersections, or at mid-block, or riding on the street there were no significant differences for head injury incidence by location of the event. Children crossing at mid-block were younger and sustained a greater number of injuries overall suggesting the need to evaluate the age at which children develop the cognitive/motor skills to use bicycles in traffic. This study also indicates the uniformity of head injury risk when helmets are not worn (75).
The third report concerns injuries in the elderly sustained in a traffic environment in a small town in Sweden. While the majority of injuries were associated with fall, vehicle associated injuries became more common with advancing age resulting in the most severe and critical injuries, fatalities and total costs. Head injuries were not as prevalent as fractures, but excluding bruises, fractures and strains, intracranial injuries, head injuries were the most common, particularly in pedestrians, but with equal incidence for cyclists and car occupants.
The fourth study by Dinesh Mohan and two neurosurgical colleagues is an excellent analysis of head injury patterns of 2-wheeler riders hospitalized in Delhi. This is the first study to compare collision patterns, age distribution, injury severity and driving experience in a developing nation to similar data from industrialized countries. Thus impacts to the rear of two wheelers were almost 40% as compared to less than 10% in industrialized nations. The intracranial injury patterns were of particular interest in that extradural hematomas and contusions were twice that found in helmeted drivers. These data clearly support the general conclusion that available motorcycle helmets provide significant protection to the head and most effectively against the contact phenomena of impacts (e.g. absence of extradural hematomas in helmeted drivers) and reducing by 50% but not eliminating the intracerebral damage (caused by inertial loading mechanisms). This study also emphasizes an important fact in that it was not based on police-reported accident data, but on tracking the accident data on 87 crash victims admitted to one trauma center. We have previously recommended that this technique is more effective in obtaining higher quality matching of the biomedical and engineering data sets in retrospective crash analysis as compared to the usual analyses of data bases based on police reported crashes.
We will now consider the biomechanics of head injuries with particular reference to the evolution of rational criteria for this type of injury. It is only by the application of such criteria in the development of better helmets and improved occupant protection systems that the severity of head injuries can be controlled in the vulnerable road user when more general pre-impact traffic safety control strategies fail or are not available.