The Atlas or C1 is the first bone in the neck, is simply a ring, with facets above and below to articulate with occiput above, and the Axis (C2) below.
The Axis (C2) too is quite unique. There is a pivot articulation between the odontoid process of the axis and the ring formed by the anterior arch and the transverse ligament of the atlas.
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There are two atlanto-axial joints: median and lateral.
The median joint has one joint between the posterior surface of the anterior arch of atlas and the front of the odontoid process and other between the anterior surface of the ligament and the back of the odontoid process
The lateral atlantoaxial joint involves articular process of the lateral mass of atlas and axis forming an arthrodial or gliding joint.
Anterior atlantoaxial ligament, Posterior atlantoaxial ligament and Transverse ligament of the atlas are important ligaments between these two vertebrae.
Thus the atlantoaxial joint in common terminology is actually a composition of three - two lateral and one median atlantoaxial joints.
This atlanto axial joint is responsible for most of the rotatory movements of the neck.
Because of its proximity to the brain stem and importance in stabilization, fracture or injury at this level can be dangerous.
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