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Middle Column: the posterior half of the vertebral body

- See: Ligamentous Instability:

- Discussion:
    - compressive forces are transmitted thru the posterior vertebral body wall onto the two Uncovertebral joints;
         - there is no significant disk material in this middle column;
    - tensile forces are w/ stood by posterior longitudinal ligament and the posterior Annulus fibrosus;
    - middle column is critical to maintaining stability;
    - comprimise of the middle column is indicated by widening of the pedicles, loss of more than 25% of the posterior vertebral ht.,
         and the presence of fracture lines thru the posterior vertebral body cortex (usually seen on CT);
    - that middle column ligaments are also critical for stability against distractive forces; (post. long. lig. & annulus fibrosis);
         - sectioning of the middle ligamentous complex (the posterior longitudinal ligament and annulus) creates segment angulation
              of 11 deg & 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;
    - isolated failure of the posterior wall (middle colum) w/o posterior ligament failure is an unusual lesion;
    - 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 greater than 3.5 mm occurs in conjuction with a facet dislocation, then the middle ligamentous
         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 the middle column (seen as widening of interpedicular distances on AP view or change in ht of posterior cortex of the 
         body) results in an unstable injury that may require operative fixation

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