Whiplash Associated Disorders in Frontal and Rear-End Car Impacts - Biomechanical Guidelines and Evaluation Criteria based on Accident Data and Occupant Modelling

Doctoral thesis, 2004

Whiplash associated disorders, also called whiplash injuries or AIS1 neck injuries, represent one of the most significant types of injury in car crashes regarding both frequency and long-term consequences. The injury mechanisms are not fully understood, thus making it difficult to design and evaluate protection systems in cars. The highest risk is found in rear-end impacts, but the largest number of incidents is found in frontal impacts. This thesis focuses on occupants in frontal as well as rear-end impacts and presents an approach leading to development of AIS1 neck injury protection systems. Several parameters influencing risk of AIS1 neck injuries in frontal and rear-end impacts are identified by analysing accident data. Subsets of Volvo's accident database are used for the analyses. Additional information was collected for two of the studies regarding details in sitting posture and neck symptoms including duration, and in one study crash pulse information from on-board crash recorders is analysed. Field impact scenarios, with different AIS1 neck injury risk, are simulated using computer models and sled tests to get additional data on the loading conditions in the human body and to enable the identification of responses correlating to relative injury risk. Biomechanical guidelines have been derived, and evaluation criteria are suggested for rear-end impacts. A whiplash mitigation seat, WHIPS (WHIplash Prevention System), was developed for rear-end impacts, based on this study. The AIS1 neck injury reducing effect of WHIPS is evaluated, demonstrating not only the significant efficiency of the seat but also the feasibility of the approach chosen. For frontal as well as rear-end impacts, women are found to have a higher AIS1 neck injury risk. In rear-end impacts, increased occupant stature is related to increased injury risk, while in frontal impacts, decreased occupant weight is related to increased injury risk. Prior neck problems is found to be a risk factor irrespective of impact direction. Sitting posture, however, is influential with respect to different parameters in frontal and rear-end impacts. In frontal impacts, change of velocity and deceleration based measures are identified as possible impact severity measures using crash recorder data. In rear-end impacts, the biomechanical guidelines are to reduce occupant acceleration, reduce relative spine movements and reduce occupant rebound. In order to reflect the biomechanical guidelines in sled tests, evaluation criteria are suggested. Concerning frontal impacts, initial relative neck movements are suggested to be kept as small as possible in this first step. The significance of this thesis is twofold. Firstly, identification of various influential parameters and visualisation of possible injury causing kinematics, adding knowledge to the puzzle of understanding AIS1 neck injuries in frontal and rear-end impacts. Secondly, development and evaluation of a feasible and robust low-risk approach, implementing a safe direction in the development of protection systems for an injury type where the knowledge of injury mechanisms is limited.