Question #25

Considering the axis which of the following statements is most accurate about this atypical vertebra?

It has a prominent weight bearing odontoid process

It prevents rotation of the cervical vertebrae

It has a prominent peg extending from its posterior aspect

During development the centrum fuses with that of the adjacent vertebra

It has no body

The second cervical vertebra is also known as the axis. It is characterized by the odontoid peg, or dens, which extends superiorly from the body of the axis.

Embryolgically each vertebra is formed from a centrum which contributes to the body and the neural arch which contributes to the lateral components. The centrum of C1 (the atlas) fuses with the centrum of C2 to form the odontoid peg.

The atlanto-axial joint is supported by a number of different ligaments:

1. The transverse ligament running between the lateral masses of the atlas holding the odontoid peg against the anterior arch. This allows rotation but prevents posterior displacement. If this ligament is disrupted, usually following fracture of C2, the odontoid peg can displace posteriorly and compress the spinal cord. Since innervations for the diaphragm comes from the C3,4,5 nerve roots, compression above this level can prevent diaphragmatic movement which is essential for spontaneous respiration – the patient will be unable to breathe.
2. The alar ligaments run from the top of the odontiod peg and pass superiorly and laterally to the occipital condyles. They prevent excess rotation at the atlanto-axial joint.

Jefferson fracture is a fracture of C1

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