Atlanto-occipital joint
Articulatio atlantooccipitalis
Also known as: AO joint, yes joint, craniovertebral joint
A pair of condyloid synovial joints between the occipital condyles and the superior articular facets of the atlas, permitting nodding (flexion–extension) of the head.
Overview
Each joint is formed between the convex, kidney-shaped occipital condyle and the concave superior articular facet of the lateral mass of the atlas, enclosed in a loose capsule. The paired joints act together as a condyloid (ellipsoid) joint, allowing mainly flexion and extension (≈15–25° — the "yes" movement) and slight lateral flexion; there is little or no rotation.
The joints are supported by the anterior atlanto-occipital membrane (continuation of the anterior longitudinal ligament) and the posterior atlanto-occipital membrane, which is pierced on each side by the vertebral artery and the first cervical (suboccipital) nerve. Deeper craniovertebral ligaments — the tectorial membrane, alar and apical ligaments and the cruciform ligament — span both craniovertebral joints and are the main stabilisers of the head on the neck.
- Location
Junction of the skull base and the first cervical vertebra.
Anatomy
- Innervation
C1 spinal nerve (suboccipital nerve).
- Articulations
Occipital condyles ↔ superior articular facets of the atlas.
- Ligaments
Anterior and posterior atlanto-occipital membranes; tectorial membrane; alar and apical ligaments (shared with the atlanto-axial joints).
Function
- Nodding (flexion–extension) of the head
- Slight lateral flexion of the head
- Transmits the weight of the head to the vertebral column
Clinical significance
Atlanto-occipital dislocation
A usually fatal high-energy injury (more common in children because of horizontal condyles and lax ligaments); survivors have severe brainstem and cranial nerve injury.
Compiled from standard anatomy and physiology references — see the Skeletal System sources. For education only; not medical advice.