The laterally tilted dens: a sign of subtle odontoid fracture on plain radiography.

Type III (low) odontoid fractures may be subtle on initial plain film radiographic examination. We describe a sign on the routine open-mouth view, the laterally tilted dens, which has not been previously stressed in the radiologic literature, and is an important diagnostic sign of type III fractures of the odontoid process of the axis. In a series of 82 nontraumatized patients, no odontoid angle of less than 87 degrees (3 degrees from perpendicular) was observed. In a series of type III odontoid fractures, tilting of the dens in excess of 5 degrees was present in eight (67%) of 12 cases. This may be the only readily apparent finding on the initial cervical spine series. Of eight type III odontoid fractures in which an abnormal odontoid angle was identified, it was the only definite abnormality that could be recognized prospectively in two cases (25%) and that supported very subtle findings in two other cases (25%).