Non-fatal injuries to car occupants : injury assessment and analysis of impacts causing short- and long-term consequences with special reference to neck injuries

Abstract

This thesis addresses non-fatal injuries leading to disability following motor vehicle collisions. The main focus is on minor (AIS 1) neck injuries, also called whiplash injuries. The purpose is to describe the distribution of disabilities among car occupants over time and to study the importance of different injury severity assessment levels on the priority ranking of the disability pattern. Another purpose is to study the characteristics and associated risk factors of rear impacts causing short- and long-term consequences to the neck (AIS 1) regarding crash severity and risk of injury in the struck car, in different car models. The materials used in the studies were data from insurance files, police reports and crash recordings of real-life rear impacts where the change of velocity and the crash pulse were measured.

It was found that during the last two decades there has been a change in the distribution of disabilities. Two body regions dominated the change. Injuries to the lower extremities decreased since the 1970s and AIS 1 neck injuries increased. Furthermore, depending on level of disability, different types of injuries were predominant. For example, head injuries dominated higher disability levels were while for lower disability levels, neck injuries (AIS 1) followed by injuries to the extremities dominated.

Concerning risk factors for AIS 1 neck injuries in rear impacts there were differences regarding crash severity parameters for long- and short-term consequences. Earlier studies have shown that the risk of initial symptoms to the neck are strongly related to the change of velocity. In this study it was found that, given initial symptoms, disability seemed to be more related to the acceleration of the struck car. It was also found that the relative disability risk was higher in cars manufactured at the end of 80s and beginning of the 90s than at the beginning of the 80s. Results from 22 Crash- Pulse-Recorders indicated that the shape of the pulse as well as the peak acceleration vary widely in real-life rear impacts. However, disability can occur when the change of velocity is at least 23 km/h and the peak acceleration 15 g.

The principal conclusion is that AIS 1 neck injuries have increased both in proportion and in number and are the dominating injury among non-fatal injuries leading to disability. Better knowledge of risk factors causing disability is needed, especially the influence of crash severity measured as change of velocity and acceleration. This should preferably be evaluated with on-board measurement techniques in real-life collisions. In addition, it is recommended that the prevention of neck injuries in rear impacts should be directed toward the seat characteristics of the car. Also, priorities for intervention should be based on fatalities and injuries causing long-term consequences.