naked facet sign
Background The normal vertebral facet (apophyseal) joint space looks like a hamburger on axial CT: the superior articular process of the vertebra below forms a semicircular 'bun' atop the 'meat patty’; the inferior articular process of the vertebra above forms the bun beneath the patty. In facet joint dislocation, the articular facets are uncovered: the ‘hamburger bun’—the superior articular facet—lies posteriorly. The sign may be either unilateral if the facet dislocation is unilateral or bilateral if the dislocation is bilateral
Aetiology Flexion-distraction injury; a positive hamburger sign indicates severe ligamentous disruption and spinal instability