Episode 2

Atypical Cervical Vertebrae

.

.

Three of the cervical vertebrae are classified as atypical. These are the first cervical vertebra called the atlas, the second cervical vertebra called the axis, and the seventh cervical vertebra called the vertebra prominens

.

The Atlas

.

The first cervical vertebra is called the atlas because it articulates superiorly with the base of the skull, and bares its weigh. The atlas is atypical because it lacks pedicles, laminae, and spinous process. Instead it has an anterior and a posterior arch. Two large lateral masses lie between the arches having on their superior and inferior surfaces the four articular processes and their facets. The picture below demonstrates the two large superior articular processes, one on each lateral mass, which through their facets articulate with the occipital condyles on the skull base

The large lateral masses and their superior articular processes are seen. They are connected by an anterior and a posterior arch. The atlas does not have a vertebral body, pedicles, laminae, or a spinous process, which makes it atypical

The superior articular processes and occipital condyles form two joints called the atlantooccipital joints. These joints provide flexion and extension movements between the neck and skull such as in motioning “yes” by nodding of one's head

the upper cervical spine demonstrates the atlantooccipital joints formed by the condyles of the occipital bone and the superior articular processes of the atlas. The arrows point to the atlantooccipital joints which are superimposed on the lateral view

The Axis C2

.

The second cervical vertebra is also atypical in that the body of the vertebra is expanded bearing a tooth like process called the odontoid process (dens). It is the strongest of the cervical vertebrae. It possesses large superior articular processes for articulation with the atlas that rests upon them. Its parts are a bifid spinous process, inferior articular processes, superior articular processes, transverse processes and transverse foramina, pedicles, and a vertebral body that bares an expanded tooth-like process called the odontoid process

.
.
The superior articular processes of the axis, along with the two inferior articular processes of the atlas, form two atlantoaxial joints. A transverse ligament holds the odontoid peg of C2 in place against a facet on the posterior wall of the anterior arch of C1. These joints are functionally important because this is where the atlas and skull and rotate as a unit upon the axis. It is a side-to-side rotation as in disapproval nodding, which is contraindicated in acute head and neck trauma because such movement can cause spinal cord injury if certain types of traumatic fracture(s) involving the cervical vertebrae are present

.

.

The drawing (right) and lateral radiograph (left) demonstrates the odontoid process of C2 which articulates with the anterior tubercle and transverse ligament of the atlas

.

The atlantoaxial joints are also radiographically important, therefore, the radiographer should understand their relationship to normal anatomical function. These joints are aligned like all vertebrae along the lateral margins. Because these joints are diarthrodial joints, they are spaced between the articular processes by a synovial membrane and synovial fluid. Therefore, they should have a spacing that reflects this anatomy

.

Vertebra prominens C7

.

The seventh cervical vertebra is considered an atypical cervical vertebra because of its long spinous process that can be seen and felt in the back of the neck. Also, it has long transverse processes resembling a thoracic vertebra, but is distinguished by the absence of rib attachment. The vertebral arteries do not pass through the transverse foramen of the seventh cervical vertebra. Therefore the atypical vertebrae are C1, C2, and C7

.

.

wait for next episode on true scene by dr bassem el baz