Sub-axial cervical dissociation : anatomic and biomechanical principles of stabilization

Four fresh human cadaver spines were analyzed during and after disruptive hyperflexion and hyperextension to characterize the pathoanatomy of three-column cervical dissociation. In both flexion and extension, the posterior longitudinal ligament and facet capsules provided the greatest resistance to disruption. At low loading rates, all structures failed through the soft tissues. Three-column disruption caused by either pure flexion or extension resulted in marked elongation of the neural axis, inconsistent with cord survival. Biomechanical studies were carried out in seven additional fresh frozen human cadaver specimens to determine the most rigid method of internally stabilizing three-column cervical dissociations. Specimens were tested in compressive flexion and distractive extension to evaluate stability of anterior, posterior, and combined fixation constructs. Specimens were tested intact, after partial two-column disruption, and after complete three-column dissociation. Posterior wiring provided significantly better flexural stability in two- rather than three-column disruptions. Posterior wiring reduced posterior displacement in two-column partial disruptions to 25% of control. In three-column dissociations, posterior wiring only reduced posterior displacement to 50% of control. In extension, posterior wiring was ineffective in preventing displacement. Anterior plating, used alone, tolerated only 37% of the maximum flexion moment before early failure. On the other hand, combined anterior plating and posterior Roger's wiring reduced posterior displacement in flexion to 20% of control, while reducing anterior displacement in extension to 50% of control. This improvement over the other constructs was statistically significant. In highly unstable cervical injuries, Morscher anterior cervical plates and modified Roger's posterior wire fixation provide a safe, rigid construct that protects neural function while allowing early and aggressive mobilization.