Locked facet joint

Locked facet joint is a type of facet joint dislocation that results from jumping of the inferior articular process over the superior articular process of the vertebra below and becomes locked in the position.

It can be unilateral or bilateral.

Radiographic features

Plain radiograph

The tip of the inferior articular process is seen anterior to the superior articular process of the vertebra below.

CT

Shows the radiographic findings in more details. The naked facet sign (a.k.a. reverse hamburger bun sign) sometimes can be seen on an axial scan.

MRI

Can show ligamentous injuries apart from the dislocation.