Practice Essentials
Atlantoaxial instability (AAI), also known as atlantoaxial subluxation, is radiologically identified increased mobility or laxity between the body of the first cervical vertebra (atlas) and the odontoid process of the second cervical vertebra (axis) (see the image below).
The subluxation can be anterior, posterior, or lateral, and symptoms occur as a result of cervical cord impingement.
Medial-sagittal cross-sectional view of the atlas (C1) and the odontoid process of the axis (C2).