New Mechanics of Spinal Injury

The prediction and prevention of spinal injury is an important aspect of preventive health science. The spine, or vertebral column, represents a chain of 26 movable vertebral bodies, joint together by transversal viscoelastic intervertebral discs and longitudinal elastic tendons. This paper proposes a new locally–coupled loading–rate hypothesis, which states that the main cause of both soft– and hard–tissue spinal injury is a localized Euclidean jolt, or SE(3)−jolt, an impulsive loading that strikes a localized spine in several coupled degrees-of-freedom simultaneously. To show this, based on the previously defined covariant force law, we formulate the coupled Newton–Euler dynamics of the local spinal motions and derive from it the corresponding coupled SE(3)−jolt dynamics. The SE(3)−jolt is the main cause of two basic forms of spinal injury: (i) hard–tissue injury of local translational dislocations; and (ii) soft–tissue injury of local rotational disclinations. Both the spinal dislocations and disclinations, as caused by the SE(3)−jolt, are described using the Cosserat multipolar viscoelastic continuum model.