Intervertebral rotations as a function of rear impact loading.

Rear impact loading of the cervical spine results in a complicated biomechanical problem due to the complex geometry and viscoclastic material properties of this anatomy. Although a number of investigations have been performed to understand the biomechanics of rear impact, the dependence of segmental kinematics on cervical level and input velocity has not been clearly outlined. An experimental investigation was performed for this purpose using 10 isolated head-neck specimens. Segmental motions of the cervical spine were obtained for levels C2-C3 to C6-C7 at rear impact velocities of 2.1, 4.6, 6.6, and 9.3 km/h. Increases in segmental motion from baseline kinematics were compared for the three higher velocity tests. Results indicated greater increase in magnitude of segmental motion for levels C5-C6 and C6-C7 at higher input velocities than all other investigated levels. This finding helps to define the kinematics of the cervical spine leading to whiplash injury.