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.

種類 Bone
器官系 Skeletal
身体部位 Spine
ラテン語名 Axis
FMA ID 12520

機能

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.

臨床的意義

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.

よくある質問

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.

関連構造

articulation joint nutrient foramen conduit outer fibrous layer of periosteum capsular layer of periosteum periosteum pre-cartilage condensation pre-chondrogenic condensation postcranial axial skeleton axial skeleton radial element actinost cavity of bone organ bone organ cavity

医療免責事項

このコンテンツは教育および情報提供のみを目的としています。専門的な医療アドバイス、診断、または治療の代替として意図されていません。医学的状態に関する質問がある場合は、必ず医師またはその他の資格のある医療提供者に相談してください。このウェブサイトで読んだことを理由に、専門的な医療アドバイスを無視したり、相談を遅らせたりしないでください。

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.