Types & Articular Surfaces
These joints comprise:
1. A pair of lateral atlanto-axial joints between the inferior facets of the atlas and the superior facets of the axis.
These are plane joints.
2. A median atlanto-axial joint between the dens (odontoid process) and the anterior arch and between dens and transverse ligament of the atlas.
It is a pivot joint.
The joint has two separate synovial cavities, anterior and posterior.
Ligaments
The lateral atlantoaxial joints are supported by:
a. A capsular ligament all around.
b. The lateral part of the anterior longitudinal ligament.
c. The ligamentum flavum.
The median atlantoaxial joint is strengthened by the following:
a. The anterior smaller part of the joint between the anterior arch of the atlas and the dens is surrounded by a loose capsular ligament.
b. The posterior larger part of the joint between the dens and transverse ligament (often called a bursa) is often continuous with one of the atlantooccipital joints.
Its main support is the transverse ligament which forms a part of the cruciform ligament of the atlas.
The transverse ligament is attached on each side to the medial surface of the lateral mass of the atlas.
In the median plane, its fibres are prolonged upwards to the basiocciput and downwards to the body of the axis, thus forming the crucifurm ligament of the atlas vertebra.
The transverse ligament embraces the narrow neck of the dens, and prevents its dislocation.
Movements
Movements at all three joints are rotatory and take place around a vertical axis.
The dens forms a pivot around which the atlas rotates (carrying the skull with it).
The movement is limited by the alar ligaments The rotatory movements are brought about by the obliqus capitis inferior, the rectus capitis posterior major and the splenius capitis of one side, acting with the sternocleidomastoid of the opposite side
Clinical Anatomy
Death in execution by hanging is due to dislocation of the dens following rupture of the
transverse ligament of the dens, which then crushes the spinal cord and medulla.
However, hanging can also cause fracture through the axis, or separation of the axis from the third cervical vertebra
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