Twelve male volunteers participated in this study. They sat on a seat mounted on a newly developed sled that simulated actual car impact acceleration. Impact speeds (4, 6 and 8 km/h), seat stiffness, neck muscle tension, and cervical spine alignment were selected for the parameter study of the head-neck-torso kinematics and cervical spine responses. The motion patterns of cervical vertebrae in the crash motion and in the normal motion were compared. Subject's muscles in the relaxed state did not affect the head-neck-torso kinematics upon rear-end impact. The ramping-up motion of the subject's torso was observed due to the seatback inclination. An axial compression force occurred when this motion was applied to the cervical spine, which in turn developed the initial flexion, with the lower cervical vertebral segments extended and rotated prior to the motions of the upper segments. Those motions were beyond the normal physiological cervical motion, which should be attributed to the facet joint injury mechanism. The difference in alignment of the cervical spine affected the impact responses of head and neck markedly. Based on the differences in the alignment of the cervical spine between male and female occupants, it is pointed out that the neck injury incidence tends to become higher for women than for men.(A)
Abstract