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Unilateral Facet Dislocation

- See:
       - Facet Joint Injuries
       - Hyperflexion Injuries
       - Oblique projections;
       - Pillar View

- Discussion:
    - simple unilateral facet dislocation is often a stable injury, eventhough there is disruption of the posterior ligament complex (involved 
           joint capsule, posterior longitudinal ligament, and annulus);
    - mechanism & anatomy of injury:
           - injury involves forward rotation of one side of vertebra about contra-lateral facet joint;
           - simultaneous flexion-rotation injury produces unilateral interfacetal dislocation;
           - interfacetal joint on side of direction of rotation is pivot:
           - superior facet on contralateral side rides upward, forward,& over tip of inferior facet of involved joint, coming to rest in intervertebral 
                  foramen anterior to inferior facet of joint;
           - in this position, the intervertebral forament is "locked;"
           - central portion of vertebral body subluxates about 25% of AP body diameter;
    - associated injuries:
           - inferior facet of dislocated joint is frequently treated;
           - capsule of non dislocated joint is frequently disrupted;
           - facet dislocations can also occur w/ concomitant frx of either facet or the entire lateral mass;
           - partial tearing of posterior longitudinal ligament on affected side(s);
           - anterior longitudinal ligament remains intact;

- Clinical Manifestation:
      - physical exam of the cervical spine:
      - delays in diagnosis are not rare (40% of patients in one study).
      - pts may have torticollis:
      - axial rotation to contralat side & lateral bend to injured side.

- Radiographs:
      - AP View:
              - involved spinous process points to involved side;
      - lateral view:
              - mild anterior subluxation of vertebral body above &soft-tissue swelling anteriorly;
              - vertebral body is anteriorly displaced ( < 50% AP diameter)
              - decrease overlap of articular processes relative to facet joint above;
              - two lateral masses of dislocated vertebra will overlap only partially on lateral view producing"bow tie" sign;
      - oblique view:
              - anteriorly dislocated inferior articular process is forced down into lower 1/2 of neuroforamen, causing nerve root compression;
              - may readily be seen on the trauma oblique radiograph.
      - dynamic lateral radiographs:
              - (physician supervised) may determine if there is hypermobility;
      - tomography:
              - is useful to determine presence of a frx & extent of displacement;
- MRI:
      - disk herniation can be identified either by MRI or by myelography;
      - anterior diskectomy and interbody fusion may be necessary if significant disk extrusion is present;
      - failure to recognize a significant disk extrusion, which more commonly occurs with bilateral facet dislocation, can result in a catastrophic 
              neurologic deficit;

- Reduction:

- Non Operative Treatment:
       - management of the spine injured patient:
       - minimal subluxation is treated w/ Philadelphia-type collar for 6 wks;
       - need careful f/u to ensure progressive subluxation does not occur;
       - w/o disk widening or subluxation, unilateral facet dislocation is stable injury;
       - if there is < 3.5 mm of translation assoc w/ this frx-dislocation, spine can undergo attempted reduction & halo immobilization;
       - first try skeletal traction, followed by open reduction if unsuccessful.
       - use of closed reduction by manipulation under GEA should be used only w/ flouroscopy:
       - successful closed reduction is followed either by halovest (for 3 month), or by posterior wiring & bone grafting.
       - closed reduction w/ halo traction is successful in 50 % of pts;
       - these may be treated with halo vest immobilization;

- Indications for Surgery:
    - failed closed reduction:
    - if flexion extension views demonstrate persistent instability after 12 weeks, posterior stabilization is indicated;
    - middle column injury
          - this injury frequently leads to late instability;
          - early single level posterior fusion is therefore recommended;
          - signs of middle column disruption
          - unilateral facet dislocation accompanied by > 25% subluxation;
          - greater than 1.7 mm of disk widening;
          - if initial displacement is > 3.5 mm;
          - angulation > 11 deg (more than adjacent segments)

- Posterior Approach:
    - open reduction is generally performed posteriorly, which allows direct visualization of the articular processes;
    - posterior wiring w/ ICBG is performed for progressive subluxation;
    - internal fixation must neutralize rotational forces;
    - facet wiring & lateral mass plating may be used;
    - w/ articular process frx or floating lateral mass bony block then resisting anterior shift on affected side may be lost, & additional 
           fixation is needed;

- Anterior Approach:
    - provides a limited view & further disrupts disk;
    - allows complete removal of disk, which eliminates risk of inducing paralysis from disk extrusion during reduction

- Case Example:

Closed reduction of cervical spine dislocations.

Unilateral facet dislocations and fracture-dislocations of the cervical spine.

Neurological deterioration after reduction of cervical subluxation. Mechanical compression by disc tissue.

Anterior decompression and arthrodesis of the cervical spine: long-term motor improvement. Part I--Improvement in incomplete traumatic quadriparesis.

Anterior decompression and arthrodesis of the cervical spine: long-term motor improvement. Part II--Improvement in complete traumatic quadriplegia.

Unilateral facet dislocation of the cervical spine. An analysis of the results of treatment in 26 patients.