- See
-
Normal Variants
-
Development of Atlas:
-
Atlantooccipital disassociation
-
Jefferson frx
- Discussion:
- C1 has no central body
- C1 vertebra is ring of bone w/ large lateral masses that provide only two wt bearing articulations between skull & vertebral column;
- superior articulation of C1 is concave anteroposteriorly to provide flexion and extension of the convex occipital condyle;
- flexion arc is approximately 20 to 30 deg;
- inferior articulations are concave mediolaterally to provide rotation on the convex
C2 superior articular facet;
- anterior tubercle of C1 vertebra is quite thin & is held adjacent to odontoid by
transverse ligament posterior to odontoid;
- this limits amount of rotation & anteroposterior excursion of C1 on
C2;
- posterior element of C1 is thin, bony ring, which completes neural arch;
- ring of C1 is quite thin just posterior to
facet joint;
- this is because of depression in superior aspect of ring, which allows vertebral artery to pass between ring of C1 & occiput after it
emerges from foramen transversarium of C1 w/o danger of compression;
- approx 50% of cervical rotation occurs between atlas &
axis, around laterally central but anteriorly eccentric odontoid process;
- lateral wall of
Atlas rotates to a considerable extent across canal of axis, physiologically decreasing opening between these two segments;
- canal of atlas is about 3 cm in its AP diameter, & is occupied equally by spinal cord, the odontoid process, & free space, each of which measures approximately one centimeter;
- anterior displacement of atlas that exceeds one centimeter may jeopardize the adjacent segment of the spinal cord;
- Surgical approach:
- posterior element of C1 is thin & is hidden deeply between prominences of occiput and the large
C2 spinous process;
- careful dissection from below exposes posterior membrane between C1 and the
C2;
Effect of C1-C2 rotation on canal size.
Computed axial tomography in C1-C2 trauma.
Fractures of the atlas
