Perched facet joint is a vertebral facet joint whose inferior articular process appears to sit 'perched' on the ipsilateral superior articular process of the vertebra below.
Any further anterior subluxation will result in dislocation, with one facet "jumping" over the other and becoming locked in this position (see jumped facet joint).
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Pathology
Unilateral perched facet results from hyperflexion, lateral compression, and rotation of the cervical spine in motor vehicular accident 6. Perched bilateral facets are also possible.
Radiographic features
Plain radiograph
malalignment of the lateral masses
the tips of adjacent facets touch each other i.e. inferior articular process of a vertebra appears to sit 'perched' on the superior articular process of the vertebra below
CT
distracted facet with uncovering of the articular surface
Complications
spinal cord injury, especially with bilateral involvement, or in the setting of canal stenosis
vertebral artery injury, e.g. dissection, thrombosis
