The radiologic assessment of post-traumatic vertebral stability.

The stability of the vertebral column depends upon the integrity of the bones, ligaments, and joints. The vertebral column can be divided into three distinct anatomic zones: anterior, middle, and posterior. Disruption of any single zone does not produce instability. Disruption of two contiguous zones will, however, significantly decrease the load-carrying capability of the spine and result in instability. Five radiographic signs indicative of vertebral instability have been identified: (1) displacement implies injury to major ligamentous and articular structures; (2) a wide interlaminar space implies injury to the posterior ligamentous structures and the facet joints; (3) wide facet joints imply injury to the posterior ligamentous structures; (4) a disrupted posterior vertebral body line implies burst injury with disruption of anterior bony and posterior ligamentous structures; (5) a wide vertebral canal implies injury to the entire vertebra in the sagittal plane. Each of these signs indicates disruption of a major skeletal, ligamentous, or articular structure and the presence of only one is sufficient to establish a diagnosis of instability. These conclusions are based upon a study of 138 injuries observed in 125 patients.