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Axis (C2)

Axis

The second cervical vertebra, the axis provides the pivot around which the head rotates. Its defining feature is the dens, or odontoid process, a tooth-like projection that extends superiorly from the body to articulate with the anterior arch of the atlas above it. This arrangement accounts for roughly half of the rotation available in the cervical spine. Odontoid fractures are common cervical injuries, particularly in elderly patients, and a hangman's fracture involves bilateral fractures of the pars interarticularis of C2. Atlantoaxial instability, in which the joint between the atlas and axis becomes abnormally mobile, is associated with rheumatoid arthritis and Down syndrome.

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.

On this page
유형 Bone
신체 계통 Skeletal
신체 부위 Spine
라틴어 명칭 Axis
FMA ID 12520

기능

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.

임상적 의의

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.

References

  1. Foundational Model of Anatomy — FMA:12520 Reference anatomy ontology (University of Washington)

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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.