Cervical vertebra C1 (atlas)

Function

A ring-shaped vertebra with no body or spinous process. It cradles the skull's occipital condyles for nodding, while its lateral masses pivot on the axis to let the head rotate about 45° to each side.

Landmarks

• Anterior and posterior arches
• Lateral masses
• Transverse processes and foramina
• Groove for the vertebral artery

Articulations (joints)

• Occipital condyles (atlanto-occipital joints)
• Axis (atlantoaxial joints)

Clinical relevance

Jefferson burst fractures of the atlas ring occur from axial head-first loads; the vertebral artery groove places the artery at risk in rotatory subluxations.