The purposes of this study were to measure the relative linear and angular displacements of each pair of adjacent cervical vertebrae, and to compute changes in distance between two adjacent facet joint landmarks during low posterior-anterior (+Gx) acceleration without significant hyperextension of the head. Six unembalmed human cadavers were instrumented and exposed to a total of twenty-six low speed rear-end impacts using a high-speed x-ray system and the HYGE mini-sled. Two seatback orientations were studied. It was concluded that upper cervical vertebrae went into relative flexion with respect to their adjacent lower cervical vertebra, while in the global coordinate system the entire cervical spine was in extension after the onset of rear-end impact. However, the lower cervical spine quickly changed into relative extension while the upper cervical spine, expecially C1-C2, experienced a much longer period of relative flexion. Maximum facet capsule strains between the inferior facet landmark of the upper vertebra and the superior facet landmark of the lower vertebra occurred prior to the head reaching its maximum rotation and before the head contacted the head restraint. The 20-degree seatback tests resulted in less cervical lordotic curvature, more upward ramping motion of the thoracic spine, and more relative rotation of each cervical motion segment (C1/C2 to C5/C6) in comparison with the 0-degree seatback tests.
Samenvatting