Cervical Spine

The cervical spine is an integral structural unit of the spinal column, responsible for numerous biomechanical functions and the protection of the spinal cord and the exiting neural elements. However, the cervical spine is susceptible to degeneration, injury, infection, deformity, and tumors as well as being prone to developmental anomalies. Comprehension of the anatomy and function of the cervical spine is imperative for understanding its role and relation to the head and spinal column.

The cervical spine is composed of seven vertebral segments that together provide support for the head and protection for the spinal cord, and facilitate various dynamic movements of the neck. The cervical spine is composed of two basic regions: upper (C1C2) and lower cervical spine (C3-C7). All of the cervical vertebrae have numerous ligamentous structures that serve as bands connecting the various bony elements together. In addition, the cervical spine is unique in comparison to the rest of the spine in that it accommodates passage of the vertebral artery, which is a branch of the subclavian artery that proceeds toward the head to join the basilar artery, thereby supplying a portion of the blood supply to the brain. In addition, the cervical spine from C1 to C4 accommodates the passage of nerve roots that give rise to the cervical plexus, whereas the cervical spine from C5 to C7 gives rise to the brachial plexus. These bundles of nerve branches are responsible for innervating various regions of the body.

The atlas (C1) is the first cervical vertebra, which articulates with the base of the skull and forms the occipitoatlantal joint. The axis (C2) is the second cervical segment, which articulates directly with the atlas above and the third cervical segment below. The atlas and axis are the only two cervical vertebrae that are not associated with an intervertebral disc. Anatomically and biomechanically, these two cervical segments differ from the rest of the cervical spine. The atlantoaxial joint accounts for approximately 50 percent of rotation (turning of the head left and right) of the cervical spine, whereas the occipitoatlantal joint accommodates the greatest amount of flexion and extension of the head (nodding). However, excessive movements by the occipitoatlantal and atlantoaxial joints are prevented due to their distinct ligamentous structures and unique bony morphology.

The lower cervical spine differs considerably from the upper cervical region. More notably, the lower cervical spine has uncovertebral joints and facets [Page 370]joints that prevent excessive rotation. The intervertebral disc is an important structure that acts as a shock absorber and is located between each vertebral segment of the lower cervical spine as well as throughout the thoracic and lumbar spine. The intervertebral disc is composed mainly of an inner and outer region, and contributes approximately 20 to 30 percent of the height of the spinal column.

The normal spinal canal of the cervical spine exhibits a triangular configuration; however, the sagittal diameter of the spinal canal decreases from the level of the head on downward. As such, the spinal cord occupies less space in the upper cervical spine region, but more space in the lower cervical spine region.

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