Computed tomography diagnosis of facet dislocations: the "hamburger bun" and "reverse hamburger bun" signs.

Unilateral or bilateral facet dislocations are difficult to diagnose. Computed tomography (CT) is being used more extensively to screen patients with suspected cervical vertebral injury. We describe two new signs, the "hamburger bun" sign of normal facet joints and the "reverse hamburger bun" sign that should be useful in establishing a diagnosis of facet dislocation. Normal facet joints are oriented on a CT examination so that they resemble the sides of a hamburger bun. Facet dislocations upset this relationship and reverse the orientation of the "bun" halves to each other.