Female and Male Whole Spinal Alignment and Cervical Kinematic Responses in Rear Impacts

Licentiate thesis, 2017

The susceptibility of women to Whiplash Associated Disorders (WADs) has been the focus of numerous epidemiologic studies. Summarising the epidemiologic WAD studies, women were found to be at three times higher risk of sustaining WADs than men. Analysis of insurance claims records indicate that certain whiplash protection seats have reduced the risk of sustaining WADs more effectively for men than for women. However, many aspects of WADs are still unknown, including what role gender differences play in the risk of sustaining WADs. In order to obtain fundamental knowledge to understand the gender difference involved in the risk of sustaining WADs, this thesis reanalysed previous rear impact sled test series comprising female and male volunteers to clarify the dynamic characteristics of inertia-induced cervical vertebral kinematics during rear impacts for women and men. Furthermore, cervical spinal alignment has been suggested as one of several possible causes of the gender differences seen in the risk of sustaining WADs. In addition, it has been reported that the initial position of the thoracolumbar spine against a seatback affects vertebral kinematics as well as the cervical spine. Therefore, this study also investigated whole spinal alignments in one automotive seated posture using an upright open MRI system for both genders, and estimated average gender specific spinal alignment patterns. During rear impacts, the female subjects presented with a more pronounced S-shape in the cervical spine than the male subjects, beyond the voluntary muscle-induced cervical kinematics range for female subjects. In contrast, for the male subjects, the peak S-shape appeared within the voluntary muscle-induced cervical kinematics range. The estimated average spinal alignment pattern in the automotive seated posture was slight kyphotic, or almost straight cervical spine with less-kyphotic thoracic spine for the female subjects, and lordotic cervical spine with more pronounced kyphotic thoracic spine for the male subjects. The findings support previous studies which have indicated influences of cervical spinal alignment on cervical vertebral kinematics. Potential impacts of any gender differences in whole spinal alignment on cervical vertebral kinematics can be investigated with a whole-body human finite element model in future work based on this thesis.