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http://upload.orthobullets.com/topic/2064/images/Lat Xray - Unilateral facet dislocation_moved.jpg
http://upload.orthobullets.com/topic/2064/images/CT bilateral facet dislocation combined_moved.jpg
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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
 

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