Subluxations and dislocations of facet joints are part of facet joint injury spectrum that ranges from facet capsule disruption to complete, bilateral locked facets.
Anterior subluxation is also known as hyperflexion sprain. The posterior ligamentous structures fail because of the hyperflexion of the cervical spine.
A pure subluxation injury has no associated fractures. A subluxation would be like following diagram.
Radiographic findings can include a fanning or widening of the spinous processes at the level of injury. The disc space may be widened posteriorly and narrowed anteriorly.
Cervical spine radiographs may be normal if the hyperflexion sprain has not caused a fracture and the subluxation has been reduced.
Flexion and extension views should be obtained in awake and cooperative patients to further evaluate for injury.
Anterior subluxation is a stable injury but patient should be examined to ensure absence of any associated spinal injuries, and prevent the development of delayed instability and pain syndromes.
Dislocations
Unilateral Facet Dislocation
Simple unilateral facet dislocation involves disruption of the posterior ligament complex ( capsule, posterior longitudinal ligament, and annulus). The injury occurs when one side of vertebra rotates forward on contra-lateral facet joint. It is a type of flexion-rotation injury in which the superior facet on contralateral side rides upward, forward,& over tip of inferior facet of involved joint, coming to rest in intervertebral foramen anterior to inferior facet of joint.
This also results in subluxation of vertebral body [About 25%]. There is also disruption of capsule of non dislocated joint and partial tearing of posterior longitudinal ligament on affected side. The anterior longitudinal ligament remains intact
Bilateral Interfacet Dislocation
Integrity of all ligaments, including posterior ligaments, anterior & posterior longitudinal ligaments, disc, and the articular facet joints is lost.
This injury is considered unstable.
The injury may cause inferior articular facets to lie anterior to superior articular facet of body below. This causes locking of the facets. [see image below]
In such cases there is a 50% anterior spondylolisthesis occurs at involved level. There could be associated disc herniation and epidural hematoma.
Facet dislocation is a kind of hyperflexion injury.
Diagosis
There would be history of neck trauma and patient presents with severe neck pain and in a number of cases with neurological deficit. Patient also might have torticollis.
Plain radiographs play a very important role in diagnosis. Anteroposterior, lateral and oblique views should be taken. Vertebral body displacement should be looked for and any dislocation of the facet joints should be noted. It is suggested by widening of interspinous distance on AP film and on oblique films, articular mass lies in intervertebral foramen.
MRI can tell about disc herniation and status of cord.
Treatment
The nature of injury warrants a closed reduction failing which open reduction should be done. If open reduction is done an internal stabilization should be done.
Minimal subluxation can be treated with cervical collar for 6 wks. However, frequent monitoring should be done to ensure progressive subluxation does not occur. The closed reduction is attempted if translation is <3.5 mm and is done by means of skeletal traction. It should be done under flouroscopy. Successful closed reduction is followed either by halovest for 3 month or by posterior wiring & bone grafting.
Following patients would need surgery
- Failed closed reduction-
- There is middle column injury as this injury frequently leads to late instability. This injury is suggested by
- Unilateral facet dislocation with > 25% subluxation
- >1.7 mm of disc widening
- Initial displacement is > 3.5 mm
- Angulation > 11 degree more than adjacent levels
Overall, the role of nonoperative treatment for facet dislocations is minimal. If it is elected, it should be reserved for unilateral facet dislocations in patients without any signs of neurologic injury or for those who are too sick to undergo surgery.
Images Credit : http://faculty.washington.edu/alexbert/MEDEX/Winter/EM1DisordersSpine.htm
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