Cruciate Ligament of Atlas

Description

The cruciform ligament of atlas (cruciate may substitute for cruciform) is a cruciate ligament in the neck forming part of the atlanto-axial joint. The ligament is named as such because it is in the shape of a cross.

It consists of two bands:

• Longitudinal band.
• Transverse band.

Anatomy

Atlas osteology

• Atlas (C1) is a ring containing two articular lateral masses
• It lacks a vertebral body or a spinous process
• Embryology: Forms from 3 ossification centers
• Anatomic variation: Incomplete formation of the posterior arch is a relatively common anatomic variant and does not represent a traumatic injury

Function

It is an important ligament that holds the posterior dens of C2 in articulation at the atlanto-axial joint. It lies behind a large synovial bursa (surrounded by loose fibrous capsule) and consists of two bands:

• Longitudinal band: joins the body of the C2 (axis) to the foramen magnum
• Transverse band: attaches to the inner margin of the C1 (atlas) lateral masses on both sides.

Clinial relevance

Atlas Fracture

Epidemiology

• Makes upto ~7% of cervical spine fractures
• Risk of neurologic injury is low
• Commonly missed due to inadequate imaging of occipitocervical junction

Pathophysiology

• Mechanism: includes hyperextension, lateral compression, and axial compression

• Associated conditions:

1. spine fracture
2. 50% have an associated spine injury
3. 40% associated with axis fx

Prognosis:

stability dependent on degree of injury and healing potential of transverse ligament.

Assessment:

Landells Atlas Fractures Classification
Type I	Isolated anterior or posterior arch fracture. A "plough fracture is an isolated anterior arch fracture caused by a force driving the odontoid through the anterior arch. Stable. Treat with hard collar.
Type II	Jefferson burst fracture with bilateral fractures of anterior and posterior arch resulting from axial load. Stability determined by integrity of transverse ligament. If intact, hard collar. If disrupted, halo vest (for bony avulsion) or C1-2 fusion (for intrasubstance tear)..
Type III	Unilateral lateral mass fx. Stability determined by integrity of transverse ligament. If stable, treat with hard collar. If unstable, halo vest.

Treatment:

• Nonoperative
  • hard collar vs. halo immobilization for 6-12 weeks 
    • indications
      • stable Type I fx (intact transverse ligament)
      • stable Jefferson fx (Type II) (intact transverse ligament)
      • stable Type III (intact transverse ligament)
    • technique
      • controversy exists around optimal form of immobilization
• Operative
  • posterior C1-C2 fusion vs. occipitocervical fusion
    • indications
      • unstable Type II (controversial)  
      • unstable Type III  (controversial)
    • technique
      • may consider preoperative traction to reduce displaced lateral masses

References

This article incorporates text in the public domain from the 20th edition of Gray's Anatomy (1918)

Anatomy of Spinal Vertebrae Tutorial Archived 2007-10-10 at the Wayback Machine.

Federative Committee on Anatomical Terminology (1998). Terminologia anatomica: international anatomical terminology. Thieme. pp. 27–. ISBN 978-3-13-114361-7. Retrieved 17 June 2010.

http://www.orthobullets.com/spine/2015/atlas-fracture-and-transverse-ligament-injuries

Original Editor - Sally FahmyTop Contributors - Kim Jackson, George Prudden and Sally Fahmy