Anterior subluxation of C4 on C5, with other imaging demonstrating unilateral locked left facet and perched right facet at C4-C5.

Findings

Figure 1: Lateral Cervical spine plain film demonstrates anterior subluxation of C4 on C5 and widening of spinous processes.
Figure 2: Sagittal MRI image shows anterolisthesis of C4 on C5 with central disc herniation. The spinal cord demonstrates normal signal intensity. Increased T2 signal intensity is present posteriorly, consistent with ligamentous disruption with edema and hematoma of posterior soft tissues.


Diagnosis: Anterior subluxation of C4 on C5, with other imaging demonstrating unilateral locked left facet and perched right facet at C4-C5.


Hyperflexion injuries can occur during trauma and are described as a combination of distraction and flexion that disrupts the ligamentous structures between two adjacent vertebrae, but the anterior longitudinal ligament remains intact. The height of the anterior interspace is narrowed and the posterior height is widened. There is also a possibility of disruption of the facet joints. Hyperflexion can result in injury to the posterior and middle columns whereas hyperextension may lead to injury to the anterior and/or middle columns.

A unilateral locked facet is secondary to excessive flexion and rotation and is considered a stable injury. The inferior facet of the superior vertebra moves up and anterior to the inferior vertebra thereby causing them to sit in a “locked” position. In unilateral locked facets there is typically anterolisthesis of the superior vertebral body of <50% of the width of the vertebral body. If there is translation of more than 50%, then there is most likely bilateral locked facets, which is an unstable injury.

Cervical spine CT with sagittal reconstructions or lateral cervical plain films can be used for measuring cervical translation. Lines are drawn along the involved posterior vertebral bodies and the transverse distance is measured between the lines at the level of the inferior endplate of the upper vertebra.

MRI may be used in patients with acute cervical spine trauma to evaluate neurologic or ligamentous integrity. It is indicated in patients with negative radiographs and negative CT who have neurologic symptoms, and also in patients with fracture or unstable injury. It has recently been noted that MR imaging has high sensitivity for most ligamentous injuries, in particular posterior longitudinal ligament, interspinous ligaments, disc annulus and facet capsular ligaments. Sensitivity is somewhat lower for anterior longitudinal ligament and ligamentum flavum injury after comparing with intraoperative findings. It should also be noted that, while sensitive, MR findings were generally not found to be highly specific with respect to intraoperative findings and can result in overestimation of ligamentous injury.