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Ligamentous Instability

- See:
   - Flexion and Extension Views
   - SCIWORA Syndrome:

- Anterior Ligamentous Disruption:
    - detected by presence of small anteroinferior avulsions and segmental disc widening;
    - ligaments include: anterior longitudinal ligament & Annulus fibrosus;
    - w/ complete cervical dislocation from anterior ligament failure, more stable internal fixation (posterior plate stabilization) should be
          considered to permit early patient mobilization;
    - note: failure of the anterior vertebral body should always suggest posterior ligament failure;
    - if posterior ligament failure is ruled out, then treat patient w/ hard collar;
    - w/ post. lig. disruption (or with middle column collapse)
         - treat w/ gradual traction, reduction, & posterior stabilization and then fusion;
- Middle Column Ligamentous Disruption:
    - note: that the Middle column ligaments are also critical for stability against distractive forces; (post. long. lig. & annulus fibrosis)
        - sectioning of middle ligamentous complex (posterior longitudinal ligament and annulus) creates segment angulation of 11 deg and
             translation of 3.5 mm;
        - hence, evidence of middle ligamentous complex disrupton
             - interspinous or intervertebral angulation 11 deg greater than the adjacent spinal segment (normally 2-4 deg)
             - horizontal translation greater than 3.5 mm;
             - intervetebral disk space separation > 1.7 mm;
- Posterior Ligamentous Disruption:
    - failure of posterior ligamentous complex may occur in conjunction w/middle complex disruption or with other instability patterns;
    - radiographic signs of posterior ligamentous disruption include dislocation or subluxation of facets, Facet Joint widening, &
         malalignment of the spinous processes on the AP view;
    - if vertebral body translation of > 3.5 mm occurs in conjuction w/facet dislocation, then middle ligament complex is disrupted as well;
         - this is a highly unstable injury w/ neurologic deficits
         - decompression of vertebral fragments may be necessary
         - reconstruction of the spinal segment with neural decompression then requires strut graft placement & either prolonged halo
              immobilization or internal fixation thru a posterior approach;
         - anterior plating alone may not be rigid enough to restore stability to the spine;
    - disruption of posterior ligamentous complex in face of anaterior frx or dislocation is a strong indication of instability and of
         potential necessity for surgical stabilization;
    - exceptions may include the upper thoracic spine, which is inherently more stable, and with bony Chance Fracture;
    - compression frx of 3 sequential vertebrae leads to increase in risk of posttraumatic kyphosis;
- Flexion Instability:
    - there are two types of flexion instability patterns in which posterior and middle ligamentous complexes are ruptured but the anterior
         complex is intact;
         - in one of these patterns there may be posterior element widening w/subtle compression frx of vertebral body;
         - other pattern is bilateral facet dislocation

Hyperextension-dislocation of the cervical spine. Ligament injuries demonstrated by magnetic resonance imaging.

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