Cervical Facet Dislocations & Fractures - Spine

Summary

Cervical facet dislocations and fractures represent a spectrum of tramatic injury with a varying degree of cervical instability and risk of spinal cord injury.
Diagnosis can confirmed with radiographs or CT scan. An MRI should be performed before surgery to identify an associated disk herniation.
Definitive treatment usually involves closed or open reduction followed by surgical stabilization.

Science

Epidemiology
- demographics
  - high energy trauma in young
    - motor vehicle accidents and motor cycle accidents
      - high speed deceleration injury
    - contact sports injuries
  - low energy trauma in elderly
- location
  - 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
Pathoanatomy
- represent spectrum of osteoligamentous pathology that includes
  - facet fractures
    - more frequently involves superior facet
    - may be unilateral or bilateral
    - decreases the threshold for facet dislocation
      - loss of tethering effect of interlocked facets
  - 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
      - inferior facet of the cephalad vertebrae encrouches the neuroforamina
  - bilateral facet dislocation
    - leads to ~50% subluxation on xray
    - often associated with significant spinal cord injury (~80% of cases)
- mechanism
  - flexion and distraction forces +/- an element of rotation
    - rotational moment associated with unilateral facet dislocation
Associated injuries
- head injuries
- noncontiguous spinal injuries
  - often occurs in the thoracolumbar, cervicothoracic, and occipitocervical junction
- appendicular injuries
Prognosis
- neurologic recovery
  - lower probability of motor improvement with increasingly severe neurologic injury
  - increased age associated with decreased neurologic recovery
  - poor motor recovery potential with spinal cord hematoma

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 sprain with slight subluxation, focal kyphosis <10°
	Stage 2: Unilateral facet dislocation
	Stage 3: Bilateral facet dislocation with 50% displacement (perched facets)
	Stage 4: Complete dislocation (100% displacement)
4. Extension-compression
5. Extension-distraction
6. Lateral flexion

Presentation

History
- history of trauma involving flexion-distration mechanism
- obtain relevant past history
  - ankylosing spondylitis / DISH
  - previous cervical spine fusion
Symptoms
- pain
  - neck pain in setting of flexion-distraction mechanism
- unilateral dislocation
  - numbness and tingling radiating down a single arm
    - C5/6 presents with numbness in thumb
    - C6/7 presents with numbness in index and middle finger
- bilateral dislocation
  - subjective weakness in b/l upper and lower extremeties
  - paresthesias and sensory changes in b/l lower extremities
Physical exam
- inspection
  - gross spinal alignment
    - angular deformity may suggest a unilateral facet dislocation
  - scalp and head lacerations or contusions
    - suggest a overlying head injury
- monoradiculopathy
  - seen in patients with unilateral dislocations
    - C5/6 unilateral dislocation
      - presents with a C6 radiculopathy
        
        weakness to wrist extension
        
        numbness and tingling in the thumb
    - C6/7 unilateral dislocation
      - 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
  - perform thorough neruologic examination
    - assess motor and sensory status
    - neurologic reflexes
    - document findings via ASIA scoring

Imaging

Radiographs
- views
  - ap, lateral, oblique, open-mouth odontoid
- findings
  - 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
  - widening of the interspinous distance
  - hypolordosis, especially at the injury level
  - soft tissue swelling
- additional views
  - flexion-extension lateral radiographs
    - indications
      - required whenever facet fracture seen due to possibility of spontaneous reduction and occult instability
CT scan
- indications
  - most cases require a CT scan
- findings
  - bony anatomy of the injury
  - malalignment or subtle subluxation of facet
  - facet fracture
  - associated fractures of the pedicle or lamina
MRI
- indications
  - acute facet dislocation in patient with altered mental status
    - must be performed emergently followed by open reduction and stabilization
  - failed closed reduction and before open reduction to look for disc herniation
  - any neurologic deterioration is seen during closed reduction
  - any patient going to OR for surgical stabilization needs an MRI in advance
- timing (controversial)
  - 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
- findings
  - disc herniations
    - need to know if large anterior disc is present prior to surgery
  - extent of posterior ligamentous injury
    - disruption of the supraspinous and interspinous ligaments
    - posterior longitudinal ligament and posterior annulus disruption
      - 40% of cases in unilateral dislocation
      - 80% of cases in bilateral dislocation
    - sprain or disruption of the posterior facet capsules
  - spinal cord compression or myelomalacia
  - spinal cord hematoma
    - poor prognostic sign for motor recovery

Differential

Cervical Lateral Mass Fracture Separation
- important to identify as cervical lateral mass fracture separations require fusing two levels while a facet dislocation only requires fusing a single level

Treatment

Nonoperative
- external immobilization x 6-12 weeks
  - indications
    - stable facet fracture
      - unilateral reduced facet fractures without radiographic instability and involving <40% of the lateral mass or an absolute height <1 cm
        
        must first rule out instability with flexion-extension radiographs
  - technique
    - halo vs. hard orthosis depending on degree of instability and age of patient
  - outcomes
    - >30% rate of subluxation or redislocation
      - increased pain associated with late redislocations
    - high incidence of persistent pain and instability
Operative
- single level instrumented stabililzation
  - indications
    - unstable facet fracture
      - bilateral facet fracture
      - unilateral fracture involving >40% of the lateral mass or an absolute height >1 cm
  - technique
    - go anterior if anterior disc with resulting spinal cord or nerve root compression
    - if no anterior disc herniation can be performed from anterior or posterior approach
- emergent closed reduction, emergent MRI, then urgent surgical stabilization
  - indications
    - bilateral facet dislocation with deficits in awake and cooperative patient
    - unilateral facet dislocation with deficits in awake and cooperative patient
  - timing
    - emergent to obtain reduction especially when you have bilateral dislocation
    - once reduction is obtain, and patient in a collar, then obtain MRI emergently. If MRI shows reduction and no significant compression on spinal cord, then can perform stabilization on urgent (within 24 hours basis)
  - technique
    - closed reduction
      - usually precedes surgical intervention
        
        rarely closed reduction followed by immobilization performed
        
        medically frail patients
        
        facet dislocations associated with high degree of instability and ligamentous injuries
      - technique
        
        never perform closed reduction in patient with mental status changes
        
        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
      - outcomes
        
        26% of patients will fail closed reduction and require open reduction
        
        unilateral facet dislocations effectively closed reduced in 25% of cases
    - anterior cervical discectomy and fusion (single level)
      - indications
        
        large disc herniation present following reduction with compression on the spinal cord or nerve roots
        
        if closed reduction is failed, may attempt open reduction from anterior approach by distracting across casper pins with simulatenous rotation
        
        1-level interbody arthrodesis with anterior plating
    - posterior reduction & instrumented stabilization
      - indications
        
        when no anteior disc present
        
        bilateral or unilateral facet dislocations that are not reducible from the front or through closed reduction
    - 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
- emergent MRI then emergent 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

Halo external immobilization
- technique
  - halo is suboptimal in lower cervical spine and therefore hard orthosis may be satifactory without complications associated with a halo
  - requires close radiographic follow-up
    - risk of redislocation or subluxation
  - morbidly obese patients may not fit or be adequately stabilized in a halo brace
Closed reduction
- requirements
  - adequate anesthesia
  - sedation
  - supervision of respiratory function
  - serial cross table laterals
  - ability to perform serial neurologic examinations
- technique
  - application of Gardner-Wells tongs
    - 1 cm above the pinna and in line with the external auditory meatus
    - below the equator of the skull
      - avoids pin migration and slippage
  - gradually increase axial traction with the addition of weights
    - usually in 5 to 10 lbs increments
    - can add up to 140 lbs of weight or 70% body weight
    - average weigh required for reduction ~9.4 to 9.8 lbs per segment above the injury level
  - a component of cervical flexion can facilitate reduction
    - flexion moment can be created with pulley system or posterior placement of the Gardner-Wells tongs pins
  - once reduced, decrease traction weight be 10-15 lbs and apply an extension moment to the cervical spine
    - adjusting pulley system
    - placing pad underneath thorax
  - perform serial neurologic exams and plain radiographs after addition of each weight addition
    - abort if there is over distraction of the spinal segment
      - >1.5 times that if the adjacent uninjured disc space
  - can switch to carbonfiber Gardner-Wells tongs if need to obtain MRI in traction
    - traction limit ~80 lbs
  - abort if neurologic exam worsens and obtain immediate MRI
Anterior cervical diskectomy and fusion +/- open reduction
- 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
  - standard Smith-Robinson approach
    - generous removal of the anterior-inferior aspect of the cephalad vertebra
      - allows disc space visualization
  - unilateral dislocations can be reduced by distracting vertebral bodies with caspar pins and then rotating the proximal pin towards the side of the dislocation
  - bilateral dislocations are reduced by placing converging Caspar pins (10-20° angle) and then compressing the ends together to unlock the facets
    - posterior directed force applied to rostral vertebral body with currette
  - alternatively, lamina spreaders applied to the endplates
  - not effective for reducing bilateral facet dislocations
- pros and cons
  - overdistraction of the disc space
    - often the PLL and posterior ligaments are disrupted
    - excessively large graft may be used to obtain a press-fit interbody graft
    - will demonstrate the facet joints being gapped posteriorly
    - places hardware at risk for failure
    - over distraction also has risk of added spinal cord injury
Posterior instrumented stabilization +/- open reduction
- indications
  - when unable to reduce by closed or anterior approach
  - no anterior compression of spinal cord(no disc herniation)
- technique
  - instrumentation performed with lateral mass screws
  - reduction
    - Penfield 4 inserted between facets and used to lever back into position
      - can remove the superior aspect of the superior facet of the caudad vertebrae to facilitate difficult reductions
    - distraction of the affected level between the affected spinous processes or lamina with use of lamina spreaders
  - usually have to fuse two levels due to inadequate lateral mass purchase at level of dislocation
Combined anterior decompression and posterior reduction / stabilization
- 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

Complications

Surgical site infections
- increased risk with posterior surgery
- tissue trauma from injury increases risk of infection
Recurrent dislocation
- unilateral dislocations treated with immobilization
- treated with anterior diskectomy, reduction, and interbody fusion
Respiratory complications
- ARDS
  - higher risk in the multitraumatized patient
- pneumonia
  - due to prolonged recumbency and need to tracheostomy
Vertebral artery injury
- occurs in up to 11% of patients with cervical spine injuries
  - increased risk when injury involves lateral mass and transverse process
- often go unrecognized and untreated
Esophageal injury
- related to anterior reduction and fixation
- primary repair with throacic surgeon upon identification
Pin tract infections
- associated with Halo vest immobilization
- can result in decreased pin purchase
- rarely result in meningitis if ther inner table of the skull is violated
- treat with local care and antibiotics