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.



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

Last updated by Data Trace Staff on Wednesday, April 11, 2012 4:36 pm