Atlas fractures can be stable or unstable injuries. This fracture has very high association with injuries to other areas of the spine.
A fracture of atlas vertebra should cause enough alert to search for injuries in other region of the spine.
Almost 43% of all C-1 fractures are found to be associated with a C-2 fracture.
Atlas fractures have been divided into following 5 types.
- Transverse process fracture
- Postreior arch fracture
- Anterior arch fracture
- Comminuted or lateral mass fracture
- Burst fracture
Transverse Process Fracture
An extraarticular fractures of the transverse process. While these fractures are usually mechanically stable, involvement of the vertebral foramen may imply vertebral artery injury.
Posterior Arch Fracture
Posterior arch fractures are caused by a hyperextension mechanism. They are stable fractures.
Anterior Arch Fracture
Isolated anterior arch fractures are subdivided into minimally displaced, comminuted, and unstable. They are caused by a hyperextension mechanism in which the odontoid is thrust against the anterior arch of the atlas.
A blowout fracture of the anterior arch leads to displacement of the odontoid anterior to the lateral masses and is inherently unstable.
Lateral Mass Fracture
Lateral mass fractures are either unilateral intraarticular split type or occur as comminuted fractures. These fractures are caused by lateral flexion or rotational forces. These are unstable fractures.
Burst Fracture
Bursting-type fractures result from an axial load and split the ring of the atlas into several fragments.
Complete transverse ligament insufficiency is said to occur if the combined overhang of the C-1 lateral masses relative to the lateral mass walls of C-2 is 7 mm or more. Transverse ligament insufficiency signifies instability.
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