Cervical Facet Dislocations & Fractures - Spine

Introduction

Represent spectrum of osteoligamentous pathology that includes
- unilateral facet dislocation
  - most frequently missed cervical spine injury on plain xrays
  - leads to ~25% subluxation on xray
  - associated with monoradiculopathy that improves with traction
- bilateral facet dislocation
  - leads to ~50% subluxation on xray
  - often associated with significant spinal cord injury
- facet fractures
  - more frequently involves superior facet
  - may be unilateral or bilateral
Epidemiology
- location
  - ~75% of all facet dislocations occur within the subaxial spine (C3 to C7)
  - 17% of all injuries are fractures of C7 or dislocation at the C7-T1 junction
    - this reinforces the need to obtain radiographic visualization of the cervicothoracic junction
Pathophysiology
- mechanism
  - flexion and distraction forces +/- an element of rotation

Classification

Descriptive classification (subaxial cervical spine injuries)
- includes
  - compression fracture
  - burst fraction
  - flexion-distraction injury
  - facet dislocation (unilateral or bilateral)
  - facet fracture
- more commonly used in clinical setting
Allen and Ferguson classification (of subaxial cervical spine injuries)
- typically used for research and not in clinical setting
- based solely on static radiographs and mechanisms of injury

Allen and Ferguson Classification (of subaxial spine injuries)
1. Flexion-compression
2. Vertical compression
3. Flexion-distraction	Stage 1: Facet subluxation
	Stage 2: Unilateral facet dislocation
	Stage 3: Bilateral facet dislocation with 50% displacement
	Stage 4: Complete dislocation (100% displacement)
4. Extension-compression
5. Extension-distraction
6. Lateral flexion

Presentation

Physical exam
- monoradiculopathy
  - seen in patients with unilateral dislocations
    - C5/6 unilateral dislocation
      - usually presents with a C6 radiculopathy
        
        weakness to wrist extension
        
        numbness and tingling in the thumb
    - C6/7 unilateral dislocation
      - usually presents with a C7 radiculopathy
        
        weakness to triceps and wrist flexion
        
        numbness in index and middle finger
- spinal cord injury symptoms
  - seen with bilateral dislocations
  - symptoms worsen with increasing subluxation

Imaging

Radiographs
- lateral shows subluxation of vertebral bodies
- unilateral dislocations lead to ~ 25% subluxation
- bilateral facet dislocation leads to ~ 50% subluxation on xray
- loss of disc height might indicated retropulsed disc in canal
CT scan
- essential to demonstrate
  - bony anatomy of the injury
  - malalignment or subtle subluxation of facet
  - facet fracture
  - associated fractures of the pedicle or lamina
MRI
- indications are controversial but include
  - acute facet dislocation in patient with altered mental status
  - failed closed reduction and before open reduction to look for disc herniation
  - any neurologic deterioration is seen during closed reduction
- timing
  - timing of MRI depends on severity and progression of neurologic injury
  - an MRI should always be performed prior to open reduction or surgical stabilization
    - if a disc herniation is present with compression on the spinal cord, then you must go anterior to perform a anterior cervical diskectomy
- valuable in demonstrating
  - disc herniations
  - extent of posterior ligamentous injury
  - spinal cord compression or myelomalacia

Treatment

Nonoperative
- cervical orthosis or external immobilization (6-12 weeks)
  - indications
    - facet fractures without significant subluxation, dislocation, or kyphosis
Operative
- immediate closed reduction, then MRI, then surgical stabilization
  - indications
    - bilateral facet dislocation with deficits in awake and cooperative patient
    - unilateral facet dislocation with deficits in awake and cooperative patient
  - technique
    - never perform closed reduction in patient with mental status changes
    - surgical stabilization following successful closed reduction
      - unilateral dislocations are more difficult to reduce but more stable after reduction
      - bilateral dislocation are easier to reduce (PLL torn) but less stable following reduction
      - always obtain MRI prior to surgical stabilization
        
        PSF or ACDF can be performed in the absence of significant disc herniation
        
        ACDF performed if significant disc herniation present
  - outcomes
    - 26% of patients will fail closed reduction and require open reduction
- immediate MRI then open reduction surgical stabilization
  - indications
    - facet dislocations (unilateral or bilateral) in patient with mental status changes
    - patients who fail closed reduction
  - technique
    - always obtain MRI prior to open reduction and stabilization
      - if disc herniation with presence of spinal cord compression then you must use an anterior approach and do a discectomy

Techniques

Closed reduction
- requirements
  - adequate anesthesia
  - sedation
  - supervision of respiratory function
  - serial cross table laterals
- technique
  - gradually increase axial traction with the addition of weights
  - a component of cervical flexion can facilitate reduction
  - perform serial neurologic exams and plain radiographs after addition of each weight
  - abort if neurologic exam worsens and obtain immediate MRI
Anterior open reduction & ACDF
- indications
  - facet dislocations reduced through closed methods with a MRI showing cervical disc herniation with significant compression on the spinal cord
  - unilateral facet dislocations that fail closed reduction with a disc herniation with significant compression on the spinal cord
- anterior open reduction techniques
  - can be used to reduce a unilateral facet dislocation
  - reduction technique involves distracting vertebral bodies with caspar pins and then rotating the proximal pin towards the side of the dislocation
  - not effective for reducing bilateral facet dislocations
Posterior reduction & instrumented stabilization
- indications
  - when unable to reduce by closed or anterior approach
  - no anterior compression of spinal cord(no disc herniation)
- technique
  - performed with lateral mass screws
  - usually have to fuse two levels due to inadequate lateral mass purchase at level of dislocation
Combined anterior decompression and posterior reduction / stabilization
- indications
  - when disc herniation present that requires decompression in patient that can not be reduced through closed or open anterior technique
- technique
  - go anterior first, perform discectomy, position plate but only fix plate to superior vertebral body
  - this way the plate will prevent graft kick-out but still allows rotation during the posterior reduction
  - this technique eliminates the need for a second anterior procedure