Atlanto-axial articulation

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The atlanto-axial articulation is a complex of three synovial joints, which join the atlas (C1) to the axis (C2).

Gross anatomy

Articulations
  • paired lateral atlanto-axial joints: classified as planar-type synovial joint between the lateral masses of C1 and C2, though somewhat more complex in shape with concavity of the superior axial facets
  • median atlanto-axial (atlanto-dental or atlanto-odontoid) joint: pivot- type synovial joint with anterior and posterior articulations of odontoid process/dens of C2 and anterior arch and transverse ligament of C1
  • fibrous capsules of the lateral and medial joints are thin and provide only minimal support, therefore ligamentous attachments provide the majority of support
Attachments
  • anterior longitudinal ligament: thick fibrous band attaches from inferior border of anterior arch of C1 to the anterior axial body
  • posterior atlanto-occipital membrane (continuation of ligamenta flava): attaches from lower border of atlantal arch (and more superiorly to the occipital bone) and upper borders of lamina of C2
  • cruciform ligaments: superior, transverse and inferior bands posterior to dens; transverse is strongest portion which stabilizes odontoid to the lateral mass of C1 limiting lateral motion of C1 over C2 and limiting subluxation of the joint
  • accessory atlanto-axial ligament: from posterior body of C2 to lateral mass of C1
  • there are a number of ligaments which attach the axis to the occipital bone including the tectorial membrane, the paired alar ligaments, median apical ligament and the longitudinal parts of the cruciform ligaments
Function

The atlanto-axial joint allows 10-15 of flexion/extension, 30of axial rotation and only minimal lateral flexion.

Variant anatomy

There are a number of congenital anomalies which can affect the atlas, axis and the joint between the two:

  • aplasias, hypoplasias, and clefts of the atlas anterior and posterior arches 
  • split atlas (fusion defects in both the anterior and posterior arches)

Abnormalities of the axis tend to affect the odontoid process and include :

Related pathology