What are the radiological findings and clinical implications of atlantoaxial instability in patients with rheumatoid arthritis?

In rheumatoid arthritis, inflammatory changes (pannus) can erode the transverse ligament of C1, leading to atlantoaxial instability. Radiologically, this may present as increased atlantodental interval on lateral cervical spine radiographs. Clinically, the dens may slide posteriorly, intermittently compressing the spinal cord and causing myelomalacia. Approximately 5% of RA patients develop frank atlantoaxial instability. Key diagnostic features include MRI showing pannus formation and CT for bony erosions. Be cautious of mimickers such as congenital anomalies or trauma-related instability.