Spine · Interactive 3D

Atlas & axis (C1–C2)

The atlas (C1) sitting on the axis (C2) from above and behind, with the dens of C2 projecting up into the ring of the atlas.

Interactive — drag to rotate

AI-assisted model. Labels checked against standard anatomy references; specialist review pending.

What to look at

1The atlas is a ring with no body and no spinous process; its lateral masses carry the occipital condyles on kidney-shaped superior facets.
2The dens of C2 sits against the back of the anterior arch of C1, held there by the transverse ligament; about half of neck rotation happens at C1–C2.
3A Jefferson fracture is a burst of the C1 ring from axial load; displacement of the lateral masses suggests a torn transverse ligament.
4Odontoid fractures are classified by level (Anderson and D'Alonzo); a hangman's fracture is through the pars of C2.

Hotspots

1Dens of C2 — Represents the body of C1, fused to C2; type II odontoid fractures at its base have the highest non-union rate.
2Anterior arch of C1 — The dens articulates with its posterior surface.
3Superior articular facet of C1 — Kidney-shaped; receives the occipital condyle (flexion and extension — the 'yes' joint).
4Transverse foramen of C1 — Transmits the vertebral artery, which then grooves the posterior arch.
5Posterior arch of C1 — The vertebral artery runs in a groove on its upper surface.
6Bifid spinous process of C2 — Large and bifid — the first palpable spinous process below the occiput.

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