The objective was to examine significant differences in the bony structure of cervical spine vertebrae based on gender and spinal level that may influence injury risk in women following automotive rear impact. Male and female subjects were recruited for a separate study and data from two subsets were selected for inclusion in this study. Subjects were size-matched based on sitting height (17 males, 11 females) and head circumference (9 males, 18 females). Axial CT scans were obtained of the cervical spine from the C1 through C6. Bony boundaries of cervical vertebrae were defined using image-analysis software and biomechanically-relevant dimensions were derived at spinal levels C2 through C6. Six of seven vertebral dimensions were significantly dependent upon gender and spinal level in both subgroups. Male vertebrae had larger dimensions for each metric. Depth dimensions were greatest at caudal and cranial extents, whereas width dimensions were smallest at C2 and increased caudally. Greater linear and areal dimensions in size-matched male subjects indicates a more stable cervical spinal column that may be more capable of resisting inertial loading of the head-neck complex during automotive rear impacts. Although the explanation for greater injury susceptibility in females is likely multi-factorial, including differences in spinal material properties, soft tissue tolerance thresholds, occupant-seatback orientation, and neck muscle size/orientations, the present study has identified significant differences in cervical spine anatomical dimensions that may contribute to greater rates of whiplash injury in that population.
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