Atlanto-occipital joint
This articulation (articulatio atlantooccipitalis) is responsible for attaching the skull to the spinal column.
Articular surfaces:
- Superiorly, the joint is formed by the occipital condyles (condyli occipitales).
- Inferiorly, they articulate with the superior articular surfaces of the first cervical vertebra, the atlas (facies articulares superiores atlantis).
A critical feature of this joint is that it is paired. Anatomically, these are two separate joints (right and left); however, biomechanically they represent a single whole and always function together.
In shape and biomechanics, this is a condylar (ellipsoid) joint. It possesses two axes of movement, allowing for the following actions:
- Flexion and extension of the head (nodding movements).
- Minor lateral tilting of the head (to the right and left).
- Circular motion, which is a combination of the movements described above.
Median atlanto-axial joint
This joint (articulatio atlantoaxialis mediana) forms the central pivot for head rotation. It is located between the first (atlas) and second (axis) cervical vertebrae.
Articular surfaces are represented by:
- The anterior articular surface of the dens of the axis (facies articularis anterior dentis).
- The articular facet for the dens located on the anterior arch of the atlas (fovea dentis atlantis).
Additionally, the posterior articular surface of the dens of the axis tightly contacts the transverse ligament of the atlas.
According to its classification, this is a cylindrical (pivot) joint. It is uniaxial: movement occurs exclusively around the vertical axis, which passes strictly through the dens of the axis. The primary function of this articulation is to provide rotation of the head to the right and left.
The stability of this crucial pivot is ensured by a robust ligamentous apparatus:
- Transverse ligament of the atlas (lig. transversum atlantis).
- Alar ligaments (ligg. alaria).
- Apical ligament of the dens (lig. apicis dentis).
Lateral atlanto-axial joints
The paired lateral joints (articulationes atlantoaxiales laterales) complement the function of the median joint.
They are formed by the following articular surfaces:
- Inferior articular surfaces of the atlas (facies articulares inferiores atlantis).
- Superior articular surfaces of the axis (facies articulares superiores axis).
Structurally, these are plane joints. They cannot function in isolation—they are always combined with the median atlanto-axial joint.
During head rotation, these joints undergo smooth sliding of the articular surfaces relative to each other, ensuring the unobstructed participation of the entire complex in rotating the head around the dens of the axis.
Briefly: answers to topical questions
Which ligaments fix the dens of the axis?
The ligamentous apparatus of the median atlanto-axial joint includes the transverse ligament of the atlas, alar ligaments, and apical ligament of the dens. The transverse ligament of the atlas runs behind the dens and holds it in place.
To easily remember their functions: in the atlanto-occipital joint we "nod" (flexion/extension), while in the atlanto-axial joints we "shake our head" (rotation around the dens).
Class and exam questions
What type of joint is the atlanto-occipital joint?
This is a biaxial condylar (ellipsoid) joint. Anatomically it is paired, but both parts always work together.
Which ligaments fix the dens of the axis in the median joint?
The dens is held in place by the transverse ligament of the atlas (its posterior surface contacts it), as well as the alar and apical ligaments.
What is the function of the lateral atlanto-axial joints?
These are plane joints combined with the median joint. Their main task is to provide surface sliding during left and right head rotation.
What else to study on this topic
- Topography of the articular surfaces of the occipital condyles and the atlas
- Mechanism of the combined function of the right and left atlanto-occipital joints
- Detailed structure of the transverse ligament of the atlas and its role
- Biomechanics of gliding in the lateral atlanto-axial joints during maximal rotation
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