Atlanto-axial joints

Study entry

Classification

Three joints: two lateral (plane synovial, gliding) and one median (pivot), between the dens of the axis and the anterior arch of the atlas.

Surfaces

Inferior surfaces of the lateral masses of C1 with the superior ones of C2 (the lateral joints); dens of C2 with the anterior arch of the atlas (the median joint).

Capsule

The dens is the pivot, held in a collar formed in front by the anterior arch of the atlas and behind by the transverse ligament of the atlas, a strong band between tubercles on the medial surfaces of the lateral masses of C1. Superior and inferior longitudinal fascicles (to the occipital bone and the body of C2) arise from it; the whole forms the cruciate ligament of the atlas. The alar ligaments (short, round cords about 0.5 cm thick) run from the sides of the dens to the lateral borders of the foramen magnum and restrict excessive rotation. The tectorial membrane is the upper continuation of the posterior longitudinal ligament: it leaves the body of C2, crosses the foramen magnum and attaches to the central part of the floor of the posterior cranial fossa.

Movements

Rotation of the head from side to side (as in shaking "no"): the skull and C1 turn together on C2.

Blood supply

[CHECK: Moore does not describe it in the passages consulted (look in another source).]

Innervation

[CHECK: Moore does not describe it in the passages consulted (look in another source).]

Source: cap. 2, «Articulaciones craneovertebrales»

Other structures in this region

• Ligamenta flava
• Cruciate ligament of the atlas (transverse ligament and longitudinal bands)
• Alar ligaments
• Tectorial membrane
• Anterior and posterior atlanto-occipital membranes
• Lumbosacral joints
• Joints of the vertebral bodies (intervertebral discs)
• Zygapophysial (facet) joints