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Anterior Subluxation (Hyperflexion Sprain) & Wedge Frx

- See: Hyperflexion Injuries

- Discussion:
    - partial or complete tear of posterior ligaments w/ varying degrees in widening of the interspinous and interlaminar spaces, as well as 
         subluxation, but not dislocation of Facet Joint;
    - hyperflexion sprain injury may include mild anterior subluxation of involved vertebral body;
    - this subluxation may be so subtle that it may only be appreciatted on lateral films obtained in flexion;
    - that stable injuries to Anterior column include compression frx of < 25% loss of vertebral body height & anteroinferior avulsion frxs 
         where the fragment width is < 20% of vertebral body width;
    - that unstable injuries to Anterior column include compression frxs w/ > 25% loss of ht indicating posterior ligament rupture, and 
         fractures thru vertebrae;
    - frx lines seen on lateral radiographs or CT scans, which extend thru vertebral body centrum in coronal plane represent 
         anterior column failure;
- Subluxation in RA:
    - anterior subluxation occurs as the result of Facet Joint disease and is most commonly seen at C5/6 level, which is level of greatest mobility;
    - any level may be affected, however, and it is common to see several levels showing anterior subluxation in a stepwise fashion;
    - subaxial involvement in R.A. in less common than atlantoaxial lesions;
- Powers Ratio:
    - identifies anterior subluxation and is described as ratio of BC/OA
    - BC is distance from basion to midvertical portion of posterior laminar line of the Atlas;
    - OA is distance from opisthion to midvertical portion of posterior surface of anterior ring of Atlas;
    - if this ratio is greater than 1, anterior subluxation exists

Upper cervical instability in rheumatoid arthritis.