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Atlantoaxial Subluxation in RA



- See:
      - Atlantoaxial Rotary Subluxation- Discussion:
      - Transverse Ligament Rupture:

- Discussion:
    - subluxation can occur in up to 70% of patients with rheumatoid arthritis, but frank dislocation occurs in about 25%;
          - approximately 11% of rheumatoid arthritis patients will develop cord compression from atlantoaxial subluxation;
          - among patients that develop myelopathy, 5 years survival rate is 80% but the 10 year survival rate is 28%, (as noted by Mori, et al 1998);
    - C1-C2 articulation is synovial which accounts for its frequent involvement in RA;
    - anterior instability is much more common than posterior instability and occurs more often in men;
    - etiology:
          - results from pannus formation at synovial joints between dens, C1, & transverse ligament, resulting in destruction of transverse 
                 ligament, dens or both;
          - transverse ligament elongation and rupture:
                 - stretching and destruction of these structures allows atlas vertebra to move forward relative to the axis;
                 - w/ C-spine flexion, atlas moves forward relative to axis;
                 - spinal cord being compressed between posterior arch of the atlas and the odontoid peg;
          - dens erosion:
                 - in some cases odontoid is totally eroded by inflammatory reaction;
    - risk factors:
          - corticosteroid use;
          - seropositivity;
          - RA nodules;
          - erosive and deforming disease;


- Exam:
    - limitation of motion, upper motor neuron signs, & detection of clunk w/ neck flexion (Sharp & Purser signs - not recommended);
    - rheumatoid compression of spinal cord or nerve roots results in long tract signs and root pain;
    - root pain is caused by anterior subluxation of Atlas on Axis leading to suboccipital (C2) root pain;
          - can be severe & is usually episodic & provoked by sudden movement;


- Radiographic Work Up;
    - cross table lateral:
    - dynamic flexion & extension view :
    - anterior atlantodens interval (ADI) is evaluated;
          - instability is present when a 3.5 mm ADI difference on flex/ext views,
          - 7 mm difference may imply disruption of the alar ligaments;
          - difference of > 9 mm is associated with an increase in neurologic injury & will require posterior fusion and wiring;

- Non Operative Treatment:
    - note that the most severe instability takes place in flexion, and therefore the main goal is to prevent flexion with an orthosis;
    - ref: Headmaster collar restricts rheumatoid atlantoaxial subluxation


- Surgical Treatment:
    - indications for surgery:
          - more than 9 mm of anterior atlantoaxial subluxation places pt at high risk for development of cord compression;
          - ADI of > 7 to 10 mm or posterior space (SAC) < 13 mm is contraindication surgery in other areas of body & C-spine should be stabilized first;
    - atlanto-axial fusion:
          - most indicated for patients w/ C1/C2 subluxation which is reducible;
          - results may be unacceptable if myelopathy is present;
          - sublaminar wiring may be contra-indicated in these patients when the SAC is less than 12 mm;
           - in RA, periodontoid pannus tissue is often present and can contribute to cord compression;
                  - after posterior cervical fusion, this pannus tissue will often resolve;
    - occipito-cervical fusion:
          - if myelopathy is present, this may be the procedure of choice;
          - if there is an associated irreducible atlanto-axial dislocation then consider additional decompressive laminectomy of the atlas;

- Complications:
    - surgery is less successful in patients w/ servere Ranawat IIIb lesions (non ambulatory with objective weakness);
    - complications include pseudoarthrosis & recurring myelopathy;
    - pseudoarthrosis rate can be decreased by extending fusion to occiput with wire fixation;


References

Cervical myelopathy and posterior atlanto-axial subluxation in patients with rheumatoid arthritis.

Atlantoaxial instability and neurologic indicators in rheumatoid arthritis.

Upper cervical instability in rheumatoid arthritis.

3- to 11-year followup of occipitocervical fusion for rheumatoid arthritis

Results after 24 years of prophylactic surgery for rheumatoid atlantoaxial subluxation.