The Hip: Preservation, Replacement and Revision

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.

Original Text by Clifford R. Wheeless, III, MD.

Last updated by Data Trace Staff on Thursday, December 22, 2011 12:27 pm