Anatomical variations in the articular masses of the seventh cervical vertebra simulating fracture.

The articular masses of the seventh cervical vertebra are variable in that about 87% of patients the superior and inferior facets are not parallel. IN ADDITION, THE INFERIOR FACETS ARE OFTEN POSTERIORLY PLACED IN RELATION TO THE SUPERIOR FACETS. These factors contribute to a notched undulating articular mass seen bilaterally on the lateral and oblique projections simulating fracture. The difference in inclination of the superior and inferior facets may cause either the superior or inferior facets to be obscured on the AP VIEW ANGLED CAUDAD--THE POSTERIOR ARCH VIEW. Since these anomalies are bilateral and fractures are almost always unilateral, the differentiation is most easily made on this posterior arch view.