Combined Bending and Axial Loading Responses of the Human Cervical Spine

The lateral, anterior and posterior passive bending responses of the human cervical spine were investigated using unembalmed cervical spinal elements obtained from cadavers. Bending stiffness was measured in six modes ranging from tension-extension through compression-flexion. Viscoelastic responses studied included relaxation, cyclic conditioning and constant velocity deformation. A five-axis load cell was used to measure the applied forces. Results include moment-angle curves, relaxation moduli and the effect of cyclic conditioning on bending stiffness. The Hybrid III ATD neckform was also tested and its responses are compared with the human. It was observed that the Hybrid III neckform was more rate sensitive than the human, that mechanical conditioning changed the stiffness of the human specimens significantly, and that changing the end condition from pinned-pinned to fixed-pinned increased the stiffness by a large factor.