Atlantooccipital

Atlantooccipital refers to the paired atlantooccipital joints, the articulation between the atlas (the first cervical vertebra, C1) and the occipital bone of the skull. There are two symmetric joints located at the sides of the foramen magnum. Each is a synovial ellipsoidal (condyloid) joint formed by the superior articular facets of the atlas and the occipital condyles. The joints are enclosed by a capsule and strengthened anteriorly by the anterior atlantooccipital membrane and posteriorly by the posterior atlantooccipital membrane.

Ligaments in the region include the alar ligaments, which extend from the dens of the axis (C2) to the occipital bone and help limit rotation at the craniocervical junction, and the tectorial membrane, a continuation of the posterior longitudinal ligament that provides additional support from the body of the axis to the skull. The atlantooccipital membranes (anterior and posterior) contribute to the stability of the joints by connecting the atlas with the occipital bone.

Function and movement: The primary movement at the atlantooccipital joints is flexion and extension of the head, enabling nodding. There is limited lateral flexion, and these joints work together with surrounding ligaments and muscles to balance mobility with stability for the head on the neck.

Clinical relevance: Injury to the craniocervical junction, including atlantooccipital dislocation, can occur in high-energy trauma and is a potentially life-threatening condition requiring prompt assessment. Anatomical variations such as atlas assimilation to the occipital bone can alter joint mechanics.