Cervical Facet Dislocations

A facet dislocation is a spectrum rather than a single lesion, running from a unilateral perched facet to bilateral locked facets with a complete cord injury. All of it is high-energy: road traffic collisions, diving and falls.

Mechanism. Flexion-distraction is the primary mechanism. Add a rotational component and one facet fails, which gives a unilateral dislocation; pure flexion-distraction fails both and gives a bilateral one.

The facet joints. The subaxial facets sit at roughly 45 degrees to the horizontal, the superior articular process facing posterolaterally and the inferior process facing anteromedially. The capsule is the primary restraint to flexion, and it is the structure a flexion force overpowers.

How a facet locks. With the capsule torn, the superior facets slide superiorly and anteriorly; carried past the inferior facet they come to rest in front of it and are locked. The same capsular rupture is what allows the abnormal translation seen on the lateral film.

Stability. These are three-column injuries. The posterior tension band is destroyed and the disco-ligamentous complex is always disrupted, so they are unstable and require surgical stabilisation.

What the cord and roots do. A unilateral dislocation compresses the root at the level of the injury, so a C6-7 dislocation compresses the C7 root, and those root injuries generally recover well. A bilateral dislocation compresses the cord, with a complete injury in up to 50%; an incomplete injury carries a better prognosis than a complete one.

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Perched or locked. Perched facets sit tip-to-tip, balanced on one another. A locked facet has jumped past its partner completely and lies in front of it. Perched facets may reduce more easily; locked facets often require open reduction.

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History. The mechanism (collision, dive, fall), any transient neurological symptoms at the scene, where the neck hurts, and what the patient can feel and move now.

Inspection. Swelling, bruising and deformity of the neck, and torticollis, which is classic for a unilateral dislocation: the chin is rotated away from the side of the dislocated facet. Log-roll and examine the whole spine.

Neurological examination. Motor testing myotome by myotome, dermatomal sensation including the perianal area, deep tendon reflexes and Babinski. Look specifically for sacral sparing, because it separates ASIA A from ASIA B and so decides the prognosis.

What each pattern looks like. A unilateral dislocation gives torticollis, cervical tenderness and possibly a radiculopathy. A bilateral dislocation gives severe pain, the patient frequently holding the head with both hands, with quadriparesis or quadriplegia if the cord is injured.

Differential Diagnosis

The painful, deformed, post-traumatic cervical spine has several mimics. Distinguishing them changes urgency and approach.

Imaging answers three questions: what the bones are doing, what the disc and cord are doing, and whether the vertebral artery survived.

What to record from the CT. The report that is useful to the surgeon who has to reduce the injury says five things:

• Facet relationship - normal, perched or locked
• Translation, as a percentage of vertebral body width
• Rotation, seen as asymmetry of the spinous processes and facets
• Associated fractures of the facet, vertebral body or lamina
• Canal compromise, as percentage occlusion

The clock. An incomplete cord injury is the emergency: reduce urgently, with decompression inside 24 hours. A complete injury is less urgent, but it is still reduced. A root injury is painful and distressing and allows time for a full workup.

Neurological worsening is the complication that is feared above the others. It follows a disc herniation that was not addressed, a forced reduction or over-distraction, which is why pre-reduction MRI, neuromonitoring and gentle technique are the prevention.

Failed closed reduction occurs in 10-30% of closed attempts, usually because the facets are severely locked or because disc or bone is interposed. The answer is open reduction, not more weight.

The collar. A hard collar - Miami J or similar - for 6-12 weeks after surgery. Wean earlier if the fusion is evidently solid and the construct stable, and keep it on longer in osteoporosis or where there is concern about the fixation.

Neurological recovery follows the presenting grade. A complete injury (ASIA A) has a poor neurological prognosis and the effort turns to stability and rehabilitation. An incomplete injury has significant potential to improve, particularly with early decompression. A root injury generally recovers well over 6-12 months.

What else predicts the result. The ASIA grade at presentation, the time to reduction and decompression, the quality of the reduction, associated head and chest injuries, and patient factors such as age and comorbidities.

Global epidemiology. Cervical facet dislocations are high-energy injuries of the subaxial spine, most often at C5-6 and C6-7, typically from road traffic collisions, falls and diving. They sit within the broader burden of traumatic spinal cord injury: in the STASCIS cohort the majority of subaxial dislocation/translation injuries presented with complete or incomplete cord injury, and early decompression (less than 24h) more than doubled the odds of a ≥2-grade AIS improvement at 6 months (Fehlings 2012, PMID 22384132). Bilateral locked facets carry the highest cord-injury risk; unilateral injuries more often produce a same-level radiculopathy.

Practice variation. The pre-reduction MRI question is the main genuine divergence. North American practice (AANS/CNS, supported by Grant 1999) favours immediate awake closed reduction in alert, examinable patients with significant deficit, accepting that reduction can displace disc material but rarely worsens neurology. Many UK/European units prefer MRI before reduction in the neurologically intact, citing the rise in disc herniation after reduction (Vaccaro 1999, PMID 10382247). The shared ground: in incomplete SCI, do not let MRI delay decompression beyond the ≤24h window (Badhiwala 2021, PMID 33357514). In limited-resource settings without rapid MRI or neuromonitoring, awake closed traction reduction with serial neurological checks remains the pragmatic standard.

Registry note. There is no implant joint registry for cervical trauma equivalent to the arthroplasty registries (NJR, AJRR, AOANJRR); evidence is driven by prospective cohorts and pooled analyses such as STASCIS and the Badhiwala 2021 individual-patient pooled analysis rather than registry data.