Radiologic study of the influence of zygapophyseal joint orientation on spinal injuries at the thoracolumbar junction.

The change from coronal to sagittal plane orientation of the zygapophyseal (facet) joints at the thoracolumbar junction, coupled with differences in lumbar and thoracic spine mobility, may predispose the T10 to L2 segments to injury. To test for an association between the level of injury and variations in orientation of the zygapophyseal joints, CT investigations of 44 spinal injured patients were studied. Of these, 28 sustained burst/compression fractures and 16 demonstrated a rotation injury with disruption to one or both zygapophyseal joints. Injuries were examined to determine whether more congruent "mortice" joints localised the segmental level of trauma. The Chi-square statistic was used: to compare the transitional characteristics of 44 clinical cases with a "normal" patient database (n = 630); to examine differences in transition patterns between the "compression" and "rotation" injury groups; and to compare the incidence of mortice joints between the clinical and normal series. A significant difference between the transition patterns of the clinical and normal series (p less than 0.001) appeared to account for the higher frequency of abrupt transitions in the 44 injury cases. No significant differences distinguished the transition patterns of the two injury groups. A higher incidence of mortice joints was demonstrated in the injury group compared with the normal population (p less than 0.02). These findings suggest that individuals with an abrupt transition have a greater predisposition to injuries at the thoracolumbar junction.