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Atlas (C1)

Atlas

Ring-shaped and unusual in lacking both a vertebral body and a spinous process, the atlas is the first cervical vertebra and supports the skull. Its structure consists of anterior and posterior arches joined by two lateral masses. The concave superior articular facets of these masses cradle the occipital condyles at the atlanto-occipital joint, an arrangement that permits nodding movements, the flexion and extension of the head. Axial loading of the vertebra can produce a Jefferson fracture, a burst fracture of the ring, while atlanto-occipital dislocation is usually fatal. Among congenital anomalies, assimilation of the atlas describes its fusion with the occipital bone, a condition known as occipitalization.

The atlas is a ring-shaped vertebra unique in lacking a vertebral body and spinous process. It consists of anterior and posterior arches connected by lateral masses. The superior articular facets are concave and cradle the occipital condyles of the skull.

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Typ Bone
Körpersystem Skeletal
Körperregion Spine
Lateinischer Name Atlas
FMA ID 12519

Funktion

The first cervical vertebra that supports the skull. Allows nodding movements (flexion and extension) of the head at the atlanto-occipital joint.

Klinische Bedeutung

Jefferson fractures (burst fractures of the atlas) result from axial loading. Atlanto-occipital dislocation is usually fatal. Congenital anomalies include atlas assimilation (occipitalization).

Frequently Asked Questions

What makes the atlas vertebra unique?

The atlas (C1) is unique among vertebrae because it has no vertebral body and no spinous process. Instead, it consists of an anterior arch, a posterior arch, and two lateral masses. The superior surfaces of the lateral masses bear concave facets that articulate with the occipital condyles of the skull, forming the atlanto-occipital joint responsible for nodding movements of the head.

What movements does the atlas allow?

The atlas facilitates two key movements. The atlanto-occipital joint (between C1 and the skull base) primarily allows flexion and extension — the 'yes' nodding movement. The atlantoaxial joint (between C1 and C2) is a pivot joint that allows approximately 50% of total cervical rotation — the 'no' shaking movement. Together, these joints provide most of the neck's range of motion.

How can the atlas be fractured?

The most common atlas fracture is a Jefferson fracture, a burst fracture caused by axial loading (vertical compression), typically from a diving accident or a blow to the top of the head. The force causes the occipital condyles to drive down onto the lateral masses of C1, splitting the ring at its weakest points. Jefferson fractures may be stable or unstable depending on whether the transverse ligament is intact.

References

  1. Foundational Model of Anatomy — FMA:12519 Reference anatomy ontology (University of Washington)

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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.