February 16, 2011 by dailybolusoflr
There are two types of facet dislocations: Unilateral facet dislocations and bilateral facet dislocations.
Unilateral facet dislocations:
· Mechanism is flexion and rotation
· One inferior facet of the vertebra on top is pushed anterior and over the superior facet of the vertebra below.
· The dislocation is always less than half of the diameter of the vertebral body
· This fracture is stable because the facets become locked.
· This is often missed on xray
o Lateral- anterior displacement of a vertebral body less than 50% the diameter
o AP- line formed by the spinous processes is disrupted
Bilateral facet dislocations:
Mechanism is flexion
· The upper vertebra is pushed superior and anterior so that both inferior facets are moved forward in relation to the lower vertebra.
· The dislocation is a displacement of more than half of the diameter of the vertebral body
· This fracture is unstable as it disrupts the annulus fibrosis, the anterior longitudinal ligament and the posterior ligamentous complex. It is associated with a high percentage of spinal cord injuries.
o Lateral: anterior displacement of a vertebral body more than 50% the diameter
Linda Regan, MD FACEP
Program Director, Emergency Medicine Residency
Johns Hopkins Medical Institutions