Variation in the posterior vertebral contour line at the level of C-2 on lateral cervical roentgenograms: a method for odontoid fracture detection.

As an aid to the assessment of alignment and lordosis, four contour lines can be drawn on the lateral radiograph of the cervical spine. One of these contour lines is the posterior vertebral contour line, in which a smooth, gentle curve, convex anteriorly, is formed by a line drawn along the posterior margins of the cervical vertebral bodies. It is unknown whether discontinuity in the posterior contour line at this level represents a pathologic process of the odontoid. We analyzed the posterior cortex of C-2 and the odontoid in 500 lateral cervical spine radiographs to determine the amount of step-off (deviation from the posterior contour line) seen in normal lateral cervical roentgenograms. Only 15% (n = 75) showed any step-off; none exceeded 3 mm. We recommend that patients presenting with a history of cervical spine trauma who have a step-off at the posterior contour line at the odontoid/C-2 level of > or =3 mm should have fine-cut tomography or multiplanar computed tomography scanning to further assess the odontoid process and rule out fracture.