Influence of Crash Severity on Various Whiplash Injury Symptoms: a Study Based on Real-life Rear-end Crashes with Recorded Crash Pulses

Whiplash injuries resulting from rear impacts are one of the most important injury categories with regard to long-term consequences. Most rear impacts lead to no injury or to symptoms that are temporary. Impacts where the duration of symptoms differs need to be separated in analyses in order to isolate representative rear impact conditions in which more long-lasting whiplash injuries occur. The aim of this study was to evaluate the influence of crash severity on symptoms duration of Whiplash Associated Disorders, WAD, separated for males and females, and for different grades of WAD (1-3) according to Quebec Task Force. Since 1995, approximately 60 000 vehicles on the Swedish market have been equipped with crash pulse recorders measuring the acceleration time history in rear impacts. With the inclusion criteria of single rear-end crashes with a recorded crash pulse, and front seat occupants with no previous long-term AIS1 neck injury, 207 front-seat occupants in 150 crashes remained to be analyzed in this study, where the change of velocity and the crash pulse were measured. A correlation was found between duration of symptoms and crash severity measured as mean acceleration and change of velocity. The risk of WAD symptoms for more than one month was found to be 20% at a change of velocity of approximately 8 km/h and at a mean acceleration approximately 5 g. A correlation was also found between grades of WAD and crash severity measured as mean acceleration and change of velocity. Out of all crashes with a recorded crash pulse only one out of 207 occupants sustained WAD symptoms for more than one month at mean acceleration below 3.0 g. Given the same crash severity, females had a higher risk of initial WAD symptoms than males. INTRODUCTION In the last decade some studies have been presented showing influence of duration of symptoms on crash severity in rear impacts. Regarding initial neck symptoms, the following studies describe the impact severity when no injury or short-term consequences occur. Hell and Langwieder (1998) found that most occupants sustained symptoms in impacts where the change of velocity was 10-15 km/h. Mc Connell et al (1995) performed low-speed rear impacts with seven male volunteers, with velocity changes of up to 10.9 km/h. None of the volunteers reported whiplash symptoms after a few days. Ono and Kaneoka (1997) and Siegmund et al (1997) found similar results from volunteer tests. In another study with volunteers (Eichberger et al 1996), where the sled impact velocities were 8-11 km/h and the mean deceleration 2.5g, the volunteers suffered whiplash symptoms for approximately 24 hours. The influence of crash severity on more longlasting symptoms is rarely studied. Based on a follow-up questionnaire with 65% answering frequency, Jakobsson (2004) found that 21% sustained long-term consequences in rear impacts with Volvo cars where the impact severity was defined as moderate. The impact severity “moderate” represented impacts in which the WHIPS recliner would have been activated. When the Volvo data was grouped according to whether the impact area involved rear members (reflecting a probable increase in the crash pulse amplitude) there was a tendency of higher initial AIS 1 neck injury risk for those with engaged rear members as compared to those with impact area outside rear members. Another study that tried to reflect the influence of the crash pulse on the injury outcome was Krafft (1998). It was found a relationship between the crash pulse on the neck injury risk in rear impacts, by showing that a longitudinally mounted engine (compared with a transversal one) in the striking car also increased the risk of longterm consequences in the struck car.