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The craniocervical junction

Where the skull meets the spine. The atlas carries the skull, the axis lets the head turn, and a small set of ligaments, above all the transverse ligament, holds the joints together.

Updated 2026-10-023 sources

Depth:

Why it matters

The top of the spine carries the skull and lets the head nod and turn, yet it has to keep the cord safe while doing so. Ligaments bind the skull, atlas and axis together and provide the stability of the junction [1].

What it is

The craniocervical junction is made of two major joints: the atlanto-occipital joint, between the skull and C1, and the atlanto-axial joint, between C1 and C2 [1].

  • The first cervical vertebra, the atlas, supports the skull on top of the column; it articulates with the occipital condyles of the skull [2].
  • The atlas has no body and no spinous process [2].
  • The second cervical vertebra, the axis, is the axis of rotation when the head turns right or left; it is recognised by the dens, a bony projection that extends upward from its body [2].

How it works

The two joints move differently [1]:

  • At the atlanto-occipital joint, flexion and extension predominate, and the angle of the occipital condyles limits rotation [1].
  • The atlanto-axial joints allow flexion, extension, axial rotation and, to a lesser degree, lateral flexion; because the joint is inherently unstable, its ligaments stabilise it [1].

The mechanical properties of the atlanto-occipital joint are mainly set by bone, and those of the atlanto-axial joint mainly by ligaments [1].

Why it is built this way

The dens joins the inner side of the anterior arch of the atlas, where the transverse ligament holds it in place [2]. The transverse ligament fixes the dens firmly against the anterior arch and is the major stabiliser of the atlanto-axial articulation: it permits rotation, while the alar ligaments prevent excessive rotation [1].

  • The paired alar ligaments attach the axis to the base of the skull, running from the upper part of the dens; they limit axial rotation and lateral flexion to the opposite side [1].
  • With the transverse ligament, the alar ligaments are the primary stabilisers of the craniocervical junction [1].
  • The tectorial membrane is a thin upward extension of the posterior longitudinal ligament, running behind the cruciform ligament [1, 3].
  • The cruciform ligament has transverse and vertical parts forming a cross behind the dens; its vertical part is relatively weak [1].

When it does not behave

If the transverse and alar ligaments are torn by trauma, the atlanto-axial joints are poorly equipped to tolerate axial rotation, whereas the atlanto-occipital joints are less affected by ligament injury [1].

Common misconceptions

Misconception: The atlas is a vertebra like the others.

It has no body and no spinous process; it is a ring that carries the skull and turns around the dens of the axis [2].

Check yourself

Which joint does most of the turning when you shake your head?

The atlanto-axial joint between C1 and C2; the axis is named for being the axis of that rotation [2, 1].

What holds the dens against the atlas?

The transverse ligament [2, 1].

Read next

References

  1. Offiah CE, Day E. The craniocervical junction: embryology, anatomy, biomechanics and imaging in blunt trauma. Insights into Imaging. 2016;8(1):29-47. doi:10.1007/s13244-016-0530-5
  2. Betts JG, Young KA, Wise JA, Johnson E, Poe B, Kruse DH, et al.. 7.3 The Vertebral Column. Anatomy and Physiology 2e. OpenStax. 2022. https://openstax.org/books/anatomy-and-physiology-2e/pages/7-3-the-vertebral-column
  3. Lee SH, Cho TH, Kwon HJ, Hong JE, Lee YH, Yang HM. An anatomical and radiological study of the tectorial membrane and its clinical implications. Scientific Reports. 2022;12(1). doi:10.1038/s41598-022-25213-2

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