Responses of the human cervical spine to torsion.

The passive torsional responses of the human cervical spine were investigated using unembalmed cervical spines in a dynamic test environment. Kinematic constraints were designed to simulate in vivo conditions. A physiologic axis of twist was determined based on a minimum energy hypothesis. Six- axis load cells completely described the resultant forces. Results include viscoelastic responses, moment- angle curves, and piece- wise linear stiffness.