Biomechanics of human head-neck in rear impacts

Rear end crashes account for a majority of whiplash trauma. Because of the complex neck anatomy, higher mass of the head compared to the neck, and inertial nature of the loading, various components of the head-neck contribute to the injury. This paper presents the role of spinal components in the injury and describes the mechanisms of injury. Although many mechanisms have been proposed and injury criteria were derived, because the actual injury was not identified, the validity of the mechanism and/or the applicability of the injury criteria are questionable. This inconclusive output is responsible for the confusion in the biomechanical assessment of rear impact. Dummies have been designed and validated based on other dummies without actually possessing injury information. The two important factors are the application of single event acceleration and injury documentation. Our studies using this methodology indicate that structures such as the facet joints are involved in chronic pain, and the kinematics are such that the joint undergoes characteristic motions during the early stages of impact acceleration. The transient non-physiologic S-curve (upper head-neck flexion) contributes to headaches, and the concomitant existence of lower cervical extension contributes to neck pain in rear impact.