A 50-year-old woman with rheumatoid arthritis on long-term methotrexate develops cervical spine instability. The atlantoaxial instability in RA is due to:
- A Synovial pannus eroding the transverse ligament of the atlas and the odontoid process, allowing anterior subluxation of C1 on C2 ✓
- B Fracture of the odontoid process (dens) from direct trauma
- C Vertebral artery compression causing posterior circulation ischaemia
- D Disc prolapse at C1–C2 compressing the cord
Explanation
Rheumatoid synovitis at the atlantoaxial joint destroys the transverse ligament (the primary stabiliser limiting anterior translation of the atlas on the axis) and erodes the odontoid process through synovial pannus invasion. This allows anterior atlantoaxial subluxation, diagnosed when the atlantodental interval (ADI) exceeds 3.5 mm (adults) or 4 mm (children) on flexion radiograph. The 'space available for the cord' (SAC = distance from posterior dens to posterior arch of C1) must be ≥13 mm to avoid myelopathy. Occipitocervical or C1–C2 fusion is indicated for neurological compromise or ADI >8 mm.
Reference: Maheshwari Essential Orthopaedics, 6th ed.
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Written and medically reviewed by the StethoPrep medical team.