The role of torsion in cervical spine trauma.

A dynamic servocontrolled torsion machine has been used to characterize cervical injury due to pure rotation of the head. Resultant force moment, torque, and applied rotation have been measured. Torque applied to the base of the skull resulted in injury to the atlantoaxial joint. No evidence of lower cervical injury was observed by computed tomography, magnetic resonance imaging, in situ fluoroscopy, or visual inspection. Torque applied directly to the lower cervical spine induced ligamentous injury and unilateral facet dislocation; however, the torque to injure the lower cervical spine was significantly greater than the torque to injure the atlantoaxial joint. It was concluded that pure rotation of the head does not mediate lower cervical ligamentous injury because of the comparative weakness of the atlantoaxial joint.