HUMAN HEAD-NECK RESPONSE DURING LOW-SPEED REAR END IMPACTS

Neck injuries resulting from rear-end collisions rank among the top car safety problems and have serious implications for society. Many rear impact sled experiments with volunteers and PMHSs have been performed in the past. However, in most of these studies, T1 kinematics were not obtained so that the kinematic behavior of the neck could not be separated from the motion of the rest of the spine. Also, to the best knowledge of the authors, the effect of anthropometric parameters on the head-neck kinematics was not studied before. The objective of this study is to describe the kinematic response of the head-neck system during low severity rear end impacts. In addition, the effect of anthropometric parameters such as height, weight and neck circumference was investigated. For this purpose, a total of 43 tests with 19 subjects was performed. Values for (delta)V ranged between 6,5 and 9.5 km/h. Linear accelerations of the head-CG and the first thoracic vertebra (T1) and angular accelerations of the head were obtained. Head angle and head-CG trajectories were obtained from film targets. Finally, head restraint impact forces were measured using a strain gauge attached to the support rods of the head restraint. Trajectories of the occipital condyles (OC trajectories) as well as upper neck forces and moments were calculated. All measured and calculated kinematic data were presented in response corridors representing the mean +/- one standard deviation. Although only three females participated in this study, a marked increase in head x-acceleration was observed for the females compared to the males. Also, neck circumference correlated well with peak x-accelerations: a thinner neck resulted in higher values for the x-accelerations. The results of this study can be used for evaluation of biofidelity of crash dummy necks, and for validation of mathematical head-neck models. Also, our finding that thinner necks result in higher head peak accelerations may be a partial answer to the question why women are at higher risk for whiplash injuries compared to men.