Axis
The axis or second cervical vertebrae is the strongest of the cervical group. It shows similarity to typical cervical vertebrae with some obvious exceptions:
- odontoid peg or dens:
- sited anteriorly in the midline
- results from fusion with body of atlas
- facet on its anterosuperior surface projects superiorly onto facet of anterior arch of atlas
- pointed at apex where apical ligament attaches
- bevelled sides are origins of alar ligaments
- posteriorly flat surface lying anterior to transverse ligament
- vertebral canal: oval and broader in coronal plane
- body: connects to odontoid process medially and superiorly; superior articular processes and transverse processes laterally; and pedicles posterolaterally
- pedicles: relatively short and sited at junction of lamina, transverse process and body
- superior articular facet: the key weight-transmitting structure articulating with inferior facets of atlas
- slightly convex and face superolaterally
- permit rotation of atlas on axis
- inferior articular facet:
- at junction of pedicles and laminae
- slightly concave
- surface slopes anteriorly and inferiorly
- transverse processes:
- relatively small
- contain foramen transversarium
- no anterior tubercle
- bounded by costotransverse lamella
- laminae: broad and project posteriorly to spinous process in median plane
- spinous process:
- bifid
- relatively large allowing use as a palpation landmark
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