SUB-AXIAL CERVICAL DISSOCIATION - ANATOMIC AND BIOMECHANICAL PRINCIPLES OF STABILIZATION

Four fresh human cadaver spines were analyzed during and after disrupt ive hyperflexion and hyperextension to characterize the pathoanatomy o f three-column cervical dissociation. In both flexion and extension, t he posterior longitudinal ligament and facet capsules provided the gre atest resistance to disruption. At low loading rates, all structures f ailed through the soft tissues, Three-column disruption caused by eith er pure flexion or extension resulted in marked elongation of the neur al axis, inconsistent with cord survival. Biomechanical studies were c arried out in seven additional fresh frozen human cadaver specimens to determine the most rigid method of internally stabilizing three-colum n cervical dissociations. Specimens were tested in compressive flexion and distractive extension to evaluate stability of anterior, posterio r, and combined fixation constructs. Specimens were tested intact, aft er partial two-column disruption, and after complete three-column diss ociation. Posterior wiring provided significantly better flexural stab ility in two- rather than three-column disruptions. Posterior wiring r educed posterior displacement in two-column partial disruptions to 25% of control. In three-column dissociations, posterior wiring only redu ced posterior displacement to 50% of control. In extension, posterior wiring was ineffective in preventing displacement. Anterior plating, u sed alone, tolerated only 37% of the maximum flexion moment before ear ly failure. On the other hand, combined anterior plating and posterior Roger's wiring reduced posterior displacement in flexion to 20% of co ntrol, while reducing anterior displacement in extension to 50% of con trol. This improvement over the other constructs was statistically sig nificant. In highly unstable cervical injuries, Morscher anterior cerv ical plates and modified Roger's posterior wire fixation provide a saf e, rigid construct that protects neural function while allowing early and aggressive mobilization. The results of his study validate this ag gressive surgical approach in a carefully selected group of patients.