Cervical Facet Joint Dislocation

Cervical facet joint dislocation is a flexion distraction injury of the subaxial cervical spine in which the inferior articular process of the upper vertebra slips over the superior articular process of the vertebra beneath it. The facets are perched or locked. It may be unilateral or bilateral and is often associated with disc and ligament rupture and with spinal cord injury.

It accounts for 6 to 10% of cervical spine injuries and is most common at C5 to C6 and C6 to C7, in young adult men after road traffic collisions, diving and falls.

In unilateral dislocation the vertebra slips forward by less than 50% of the vertebral body width (about 25%), and nerve root injury is common (30 to 75%), while complete cord injury is uncommon (5 to 10%). In bilateral dislocation the slip is over 50%, and 60 to 85% have a cord injury, many of them complete.

Complications are cord injury and quadriplegia, root injury, vertebral artery injury (dissection or occlusion in up to 20 to 25%), neurological deterioration during reduction (disc herniation), persistent instability, chronic pain, and autonomic dysfunction (neurogenic shock, respiratory failure).

Pathophysiology.

Hyperflexion with rotation (unilateral) or hyperflexion with distraction (bilateral) ruptures the posterior ligamentous complex, the facet capsules and often the disc. The facets perch (tip on tip) and then lock, and the cord is compressed against the posterior edge of the lower vertebral body or by a herniated disc fragment. Rotation produces a unilateral locked facet with a "bow tie" appearance of the facets on the lateral view.

Neck pain and a fixed head posture (the head is tilted and rotated away from the locked side in unilateral injury), muscle spasm, a palpable step or gap between spinous processes, and neurological deficit that ranges from a single radiculopathy to complete tetraplegia. Neurogenic shock (hypotension with bradycardia) occurs with cervical and upper thoracic cord injury. Look for associated head, chest and other spinal injuries.

Examine under spinal precautions: airway and ventilation (diaphragm function depends on C3 to C5), blood pressure and heart rate, full neurological examination (motor and sensory levels, reflexes, perianal sensation, bulbocavernosus reflex), and vertebral artery signs (posterior circulation stroke). Grade the injury and record it before and after each intervention.

• CT of the cervical spine with sagittal and coronal reformats (the key test): facet position (perched, jumped, locked), degree of translation, fractures of the articular processes, laminae and vertebral body.
• CT angiography of the neck for vertebral artery injury.
• MRI of the cervical spine: disc herniation (before reduction in the obtunded patient or if reduction fails), cord injury, epidural haematoma, ligament disruption. Whether to obtain MRI before awake closed reduction is debated; it must not delay reduction in an alert patient who can be examined repeatedly.
• Radiographs of the rest of the spine; imaging of the chest and abdomen as needed.

Differential diagnosis.

• Facet fracture without dislocation and bilateral pedicle or pars fracture.
• Flexion teardrop fracture and burst fracture.
• Spinal cord injury without radiographic abnormality (children, older adults).
• Pre-existing ankylosing spondylitis or stenosis with minor trauma.

The aims are to protect the airway and the cord, reduce the dislocation quickly, stabilise the spine and prevent complications. Spinal cord injury care follows the same principles in all cervical injuries.

Initial care.

• Airway, breathing and circulation with in line stabilisation; early intubation if ventilation is failing (vital capacity under 15 mL/kg); avoid hypoxia and hypotension.
• Maintain mean arterial pressure at 85 to 90 mm Hg for the first 5 to 7 days after cord injury (noradrenaline 0.05 to 0.5 micrograms/kg/minute intravenously, titrated; atropine 0.5 mg intravenously for symptomatic bradycardia, repeated to 3 mg, or glycopyrronium 0.2 mg).
• Methylprednisolone is not used routinely because the risk of infection and haemorrhage outweighs unproven benefit.
• Gastric ulcer prophylaxis: omeprazole 40 mg orally or intravenously once daily.
• Analgesia: paracetamol 1 g every 6 hours; morphine intravenous 2 to 5 mg every 4 hours as needed (titrate; reduce in hypotension and renal impairment).
• Neuropathic pain: gabapentin 300 mg orally at night, increased to 300 to 600 mg three times daily (maximum 3600 mg daily; reduce at creatinine clearance under 60 mL/min).

Reduction.

• Awake closed reduction with skeletal traction (Gardner-Wells tongs) in an alert, cooperative patient who can be examined after each step, with continuous fluoroscopy.
• Traction: start at 4.5 kg (10 lb), add 2.3 to 4.5 kg (5 to 10 lb) every 10 to 15 minutes, with a neurological examination and a lateral radiograph after each increment.
• Most centres limit the weight to about 2.3 to 4.5 kg for each vertebral level (usual ceiling 30 to 35 kg in the lower cervical spine; higher weights only in specialist spinal units).
• Stop for neurological change, over distraction (disc space widening over 10 mm) or if reduction is achieved.
• Low dose sedation: lorazepam 0.5 to 1 mg or diazepam 2.5 to 5 mg intravenously, and morphine 2 to 5 mg intravenously, with monitoring; avoid deep sedation that blocks neurological examination.
• Failed closed reduction, or an obtunded patient, or a herniated disc on MRI: open reduction with anterior discectomy first (anterior cervical discectomy and fusion), or open posterior reduction.
• Closed reduction succeeds in 75 to 90% of bilateral injuries; neurological deterioration occurs in under 1% when the patient is awake and examined.

Stabilisation.

• Anterior cervical discectomy and fusion with plate (preferred when the disc is injured, particularly if there is a herniation).
• Posterior lateral mass fixation and fusion (when facet fractures prevent reduction or for gross posterior instability).
• Combined anterior and posterior fixation for severe injuries.
• Non-operative treatment in a halo vest or collar is rarely sufficient because recurrence of deformity is common.
• Early surgery (within 24 hours) may improve neurological recovery in incomplete cord injury.

Operative antibiotic prophylaxis. Cefazolin 2 g intravenously (3 g when weight is 120 kg or over) within 60 minutes before incision as a single dose. With severe penicillin allergy, vancomycin 15 mg/kg intravenously starting 90 to 120 minutes before incision as a single dose.

Perioperative adjuncts. Dexamethasone 8 mg intravenously once at induction for airway swelling and dysphagia (monitor glucose in diabetes); awake fibre optic intubation with minimal neck movement in the unreduced injury.

Thromboprophylaxis. High risk after spinal cord injury. Enoxaparin 40 mg subcutaneously once daily (or 30 mg twice daily) started within 24 to 72 hours once bleeding is controlled. Continue for 8 to 12 weeks in complete cord injury (20 mg once daily or 30 mg once daily at creatinine clearance under 30 mL/min; check the platelet count on days 5 to 14). Mechanical prophylaxis from admission.

Other complication prevention. Pressure care and turning every 2 hours; bowel programme; bladder catheterisation then intermittent catheterisation; respiratory physiotherapy and cough assistance; nutrition; early rehabilitation in a spinal injuries unit.

Monitoring. Neurological examination every hour at first, then every 4 hours; blood pressure and heart rate continuously for 5 to 7 days; respiratory function; review at 2 weeks, 6 weeks, 3 months, 6 months and 12 months with radiographs or CT to confirm fusion; MRI for neurological decline.

Referral and escalation. Every suspected cervical spine dislocation needs transfer to a specialist spinal injury centre. Emergency referral for any neurological deficit, signs of vertebral artery injury, respiratory compromise, or failed reduction.

Special groups.

• Unilateral dislocation without deficit: reduce and fuse; delayed presentation is common and carries a risk of late deficit.
• Obtunded or intubated patients: MRI before reduction or open anterior approach.
• Ankylosing spondylitis or DISH: regard the injury as an unstable long lever fracture and avoid forced traction; long segment fixation.
• Children: ligamentous injury and spinal cord injury without radiographic abnormality are more common; different dosing (paracetamol 15 mg/kg, morphine 0.05 to 0.1 mg/kg intravenously).