Anatomy: Posterior Fossa, Hindbrain & Craniocervical Junction
Axis (C2 vertebra)
The axis is the second cervical vertebra, bearing the odontoid process, and is relevant to craniocervical alignment and stability in Chiari-related conditions.
In short: Axis (C2 vertebra)
- It is the second cervical vertebra.
- It bears the odontoid process (the dens), a peg the atlas rotates around.
- It is involved in head rotation.
- It is central to craniocervical alignment and stability assessments.
What it is
The axis is the second cervical vertebra (C2). It bears the odontoid process (the dens), a tooth-like bony projection extending upward, around which the atlas (C1) rotates to allow the head to turn. The axis is central to craniocervical alignment and stability, which are relevant in Chiari-related conditions.
Understanding Axis (C2 vertebra)
The axis's odontoid process forms a pivot around which the head rotates. The relationship between the axis, the atlas, and the skull is important for stability at the craniocervical junction. In Chiari-related conditions, abnormalities involving the axis and its odontoid are significant: a retroflexed (backward-tilted) odontoid can compress the brainstem from the front, and basilar invagination involves the odontoid pushing upward into the skull base. Craniometric measurements assessing alignment and instability often reference the axis and its odontoid. Understanding the axis clarifies a vertebra central to craniocervical alignment, stability, and the bony abnormalities that can accompany complex Chiari.
Why it matters
Understanding the axis helps families see how this vertebra and its odontoid are central to craniocervical alignment and stability, and how abnormalities involving it can accompany complex Chiari and affect treatment.
Common questions
What is the axis?
The second cervical vertebra, bearing the odontoid process.
What does it do?
It allows head rotation, with the atlas pivoting around its odontoid.
Why is it relevant to Chiari?
Its alignment and odontoid abnormalities matter in complex Chiari.
Bottom line
The axis is the second cervical vertebra bearing the odontoid, central to craniocervical alignment and stability in Chiari-related conditions.
Browse all 265 Chiari malformation definitions
Read the Chiari malformation patient guides
Not sure which page you need? Put words to it with the symptom navigator