The vertebral column is connected to the skull by three joints: the atlanto-occipital, the median atlanto-axial and the lateral atlanto-axial joint.
Let’s learn about the structure of the median atlanto-axial joint (articulatio atlantoaxialis mediana).
The first one is formed between the anterior articular surface of the dens of the axis (facies articularis anterior dentis) and the facet for the dens of the atlas (fovea dentis)
The second joint is formed between the posterior articular surface of the dens of the axis (facies articularis posterior dentis) and the transverse ligament of the atlas (ligamentum transversum atlantis).
The articular capsule (capsula articularis) is attached along the edge of the facet for the dens and partially covers the dens of the axis.
According to the classification, this joint is cylindrical, uniaxial, simple and combined (with lateral atlanto-axial joints).
The following range of motions is possible in the joint:
Around the vertical axis: rotation of the head to the right and left
The ligamentous apparatus includes several ligaments:
Cruciate ligament of the atlas (ligamentum cruciforme atlantis). It consists of three bundles:
The superior longitudinal fasciculus (fasciculus longitudinalis superior)
The inferior longitudinal fasciculus (fasciculus longitudinalis inferior)
The transverse ligament of the atlas (ligamentum transversum atlantis)
The joint is also strengthened by the alar ligaments (ligamenta alaria), which restrict excessive rotation of the head to the right and left. Each such ligament arises from the lateral surface of the dens and passes externally, obliquely and upward, where it inserts into the internal surface of the corresponding condyle of the occipital bone.
Another ligament is the apical ligament of the dens (ligamentum apicis dentis), it is unpaired, thin, and stretched between the edge of the foramen magnum and the apex of the dens.
And the last ligament that strengthens the joint is the tectorial membrane (membrana tectoria).
The following vessels and nerves take part in the blood supply and innervation of the joint.
Arteries: branches of the deep cervical, occipital and vertebral arteries
Nerves: anterior branch of the second spinal nerve
Median atlanto-axial joint
- Median atlanto-axial joint
- articulatio atlantoaxialis mediana
- Anterior articular surface of the dens
- facies articularis anterior dentis
- Facet for the dens
- fovea dentis
- Posterior articular surface of the dens
- facies articularis posterior dentis
- Transverse ligament of the atlas
- ligamentum transversum atlantis
- Articular capsule
- capsula articularis
- Cruciate ligament of the atlas
- ligamentum cruciforme atlantis
- Superior longitudinal fasciculus
- fasciculus longitudinalis superior
- Inferior longitudinal fasciculus
- fasciculus longitudinalis inferior
- Alar ligaments
- ligamenta alaria
- Apical ligament of the dens
- ligamentum apicis dentis
- Tectorial membrane
- membrana tectoria