Radiologic diagnosis of traumatic occipitovertebral dissociation: 1. Normal occipitovertebral relationships on lateral radiographs of supine subjects.

In adults, the occipitovertebral junction can be considered normal when both the basion-axial interval and basion-dental interval are 12 mm or less. In children less than 13 years old, the basion-dental interval is not reliable because of the variable age at which complete ossification and fusion of the dens occur. The normal basion-axial interval in children did not exceed 12 mm. This simple, anatomically based method of recognizing normal occipitovertebral relationships facilitates identification of occipitovertebral dissociation.