Atlantoaxial Instability

Atlantoaxial instability (AAI) is the loss of stability at the junction between the first cervical vertebra (C1, atlas) and the second cervical vertebra (C2, axis). This is usually due to a problem with the ligament that helps stabilize the two bones, but it may also arise from bony defects. The main concern is that excessive movement at the C1-C2 joint may damage the spinal cord.

The diagnosis cannot be made clinically but must be made by radiographs. Once the diagnosis is made, however, the clinical symptoms and signs are more important. ...