Axis

The second cervical vertebra (C2) of the spine is named the axis (from Latin axis, “axle”) or epistropheus.

Anatomy of axis (C2).

The pars interarticularis is located between the inferior and superior articular facets (shown in solid blue). The pedicle (green cross-hatching) connects to the vertebral body.

It forms the pivot upon which the first cervical vertebra (the atlas), which carries the head, rotates.

The most distinctive characteristic of this bone is the strong odontoid process known as the dens.

Apical, alar ligament, and transverse ligaments provide further stabilization by allowing spinal column rotation; this prevents posterior displacement of the dens in relation to the atlas.

Odontoid fractures:

The most common fracture of the axis and the most common cervical spine fracture in patients over 65.

see Axis fracture.