Axis (C2)

Axis

The axis is characterized by the dens (odontoid process), a tooth-like projection that extends superiorly from the body to articulate with the anterior arch of the atlas. This unique arrangement allows approximately 50% of cervical rotation.

Type Bone
Body System Skeletal
Body Region Spine
Latin Name Axis
FMA ID 12520

Function

The second cervical vertebra that provides a pivot point for rotation of the head. The dens (odontoid process) projects superiorly and acts as the axis around which the atlas rotates.

Clinical Significance

Odontoid fractures are common cervical spine injuries, especially in elderly patients. Hangman's fracture involves bilateral pars interarticularis fractures of C2. Atlantoaxial instability occurs in rheumatoid arthritis and Down syndrome.

Frequently Asked Questions

What is special about the axis vertebra?
The axis (C2) is the second cervical vertebra and is unique for its prominent superior projection called the dens (odontoid process). The dens projects upward through the ring of the atlas (C1) and acts as a pivot around which the atlas and skull can rotate. This arrangement allows approximately 50% of total cervical rotation, enabling the head to turn left and right.
How does the axis connect to the atlas?
The axis articulates with the atlas (C1) primarily through the atlantoaxial joint complex. The dens of the axis fits into the anterior arch of the atlas, held in place by the transverse ligament of the atlas. This forms a pivot joint. Additional articulations occur at two lateral facet joints between C1 and C2. The transverse ligament is critical; its rupture can cause life-threatening cord compression.
What injuries affect the axis vertebra?
Axis fractures include odontoid (dens) fractures, which are classified into three types by the Anderson-D'Alonzo system. Type II fractures at the base of the dens are most common and often require surgical stabilization. Traumatic spondylolisthesis of the axis (Hangman's fracture) involves bilateral pedicle fractures of C2, typically from hyperextension injuries such as motor vehicle accidents.

Related Structures

articular surface articular system joint system articulation joint Atlas (C1) Atlas attachment site axial skeleton plus cranial skeleton skeleton axiale bone collagen fibril bone condensation

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Educational Disclaimer

This content is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider for medical decisions.

Data sources: Terminologia Anatomica, Foundational Model of Anatomy, Wikidata.