The cervical spine is one of the most important structures in the human body. Its unique anatomy is responsible for providing a highly mobile, functional support for the skull, while protecting the spinal cord from injury. It is only when the cervical spine becomes dysfunctional that we begin to appreciate the importance of its role in the performance of daily activities.
The cervical spine is capable of extremely complex patterns of motion. We can enhance our ability to understand these patterns by subdividing it into an upper complex consisting of C0, C1, and C2 (the occipital-atlanto-axial joint), and a lower complex consisting of C3-C7 (the typical cervical vertebrae). We will further divide the upper complex into two motion segments, (C0/C1 and C1/C2), where each motion segment consists of two adjacent bony structures and their associated soft tissues. We always need to keep in mind that the occiput, atlas, and axis function as a unit whose individual movements are closely coupled one to another. By summing the contributions of each section, we will be able to account for the total range of motion of the cervical spine.
The vertebral motion segment consists of the superior and inferior adjacent vertebra and the intervening disc and ligamentous structures. Vertebral motion, typically capable of up to six degrees of freedom, is normally described in terms relative to the subadjacent vertebra. The posterior and transverse processes provide a convenient reference system for us to quantify motion. In describing rotation, the anterior surface of the vertebra is used rather than the posterior process.
Posterior StructuresThe trapezious muscles are the most superficial layer of muscles on the posterior cervical spine. Under the trapezius we have a multitude of primary extensors that can be generalized as to falling into one of two groups:
The suboccipital muscles (back view --- oblique view), linking C0, C1, and C2, are sometimes overlooked because of their small size compared to the principle movers.
The nuchal ligament attaches to the inion and extends to the C7 spinous process. It overlays and is intimately attached to each spinous process of the cervical vertebrae.
On the anterior cervical spine, we have the sternocleidomastoids as the primary rotators and the primary flexors. The scalene muscles provides a major contribution to lateral sidebending of the cervical spine.
The anterior longitudinal ligament is a broad and strong band of fibers that extends along the anterior surfaces of the vertebral bodies from the axis to the sacrum.
While flexion and extension, lateral flexion (sidebending), and axial rotation all occur in the cervical spine, the difficulty in accurately measuring the magnitude of these movements is emphasized by the wide range of values that have been reported in many studies. For our discussion we will be using data summarized from the published research of A. A. White and M. M. Panjabi (Clinical Biomechanics of the Spine, J.B. Lippincott Company, 1978).