Effects of Thoracic Ramping on Whiplash Kinematics

Whiplash injuries result from differential motion between the head and thorax. Experimental investigations using human volunteers and full body cadavers have described thoracic ramping due to interaction with the seatback and straightening of the thoracic spine. The effect of this motion on cervical kinematics has not been investigated. A head-neck computer model was used to determine the effects of thoracic ramping on whiplash kinematics. The model consisted of skull, cervical spine, first thoracic vertebra, intervertebral discs, spinal ligaments, facet joints, and passive musculature, and was subjected to 2.7 m/sec rear impact velocity. Vertical acceleration of T1 was prescribed according to literature. Segmental angulations and region dependent facet joint capsular ligament distractions were obtained from levels C2-C3 through C7-T1 during the time of cervical S-curvature. Maximum capsular ligament distractions during this time occurred in the dorsal region at the C2-C3 level and in the lateral region at the C3-C4 through C7-T1 levels. Increasing magnitudes of T1 ramping decreased segmental angulations and ligament distractions by less than 20% in most cases. Results of the present investigation demonstrated that thoracic ramping may play a secondary role in whiplash kinematics.