A study of the nerve root damage in whiplash injury occurrence mechanisms using human head-neck finite element model

The number of whiplash injuries in rear-end collisions is still high worldwide. Since the 1990s, many researchers have studied the mechanisms of injury occurrence in which were focused in the early stage of the rear impact. However, the current situation is that it has not led to a significant reduction in the number of injuries. The authors created a head-neck FEM model with muscles and accurately reproduced the head-neck behaviors of male and female volunteers in the rear impact tests. Then, using the same model, it was clarified that the difference in muscle strength is a large factor in the gender difference in frequency of whiplash injuries. In this paper, we focused on nerve damage, which is the cause of chronic whiplash, and examined the possibility of nerve root damage in the early stage of rear impact. It is generally known that living soft tissues such as nerves have viscoelastic behavior. Using animal axons and nerve root characteristics, it was found that a hyperbolic relationship was established between the velocity and the deformation under compression load on nerve root. The higher the loading rate, the stronger the locality at the compression site, and the greater the possibility of damage even if the deformation is small. Next, we studied the possibility of nerve root damage during a rear impact using a C4-C5 spinal unit FEM model including nerve root model (nerve-spinal unit model). First, in the same model, it was confirmed that there is no nerve root damage during a daily head extension. Then, using male head-neck behavior data in rear impact, it was confirmed that there is a possibility of nerve root damage when the compression speed of the vertebral body increases. Finally, we also analyzed using female data and found that there was a higher possibility of nerve root damage than in male.