Surgical Anatomy of the Spine, Revisited
For spine surgeons, an understanding of the ligaments of the cervical spine and their purpose is essential. Although delicate, the cervical spine is a well-crafted, remarkably strong, and flexible structure that houses the spinal cord and sends messages from the brain to control all aspects of the body and allow movement in all directions. The cervical spine is supported and stabilized by a complex system of ligaments, tendons, and muscles that serve as connective tissue for the spine. Ligaments of the spine are strong, fibrous bands that prevent suspicious activity but allow normal activity. At the craniocervical junction, the two main ligaments that hold the bones together are the alar—strongest ligament between skull and spine—and transverse—center of axial rotation—ligaments (Figure 1).
When trauma to the skull occurs, force is also transmitted to the alar and transverse ligaments of the cervical spine. Reported cases have involved motor vehicle accidents, a sudden jolt to the head, or something falling onto the head. Ligaments can stretch and become partially torn, or, as occurs more frequently with alar and transverse ligaments, they can break in half and snap back like a rubber band, leading to instability and excessive movement, irritation, further injury, and arthritis. Traumatic injuries may occur at multiple levels; thus, imaging of both the upper and lower cervical spine is required (Figure 2). Traumatic lesions are not usually apparent on radiographs, and computed tomography scanning and dynamic magnetic resonance imaging are most efficient for detection. Dr. Henry Bohlman extensively studied cervical spine injury and its treatment. In 1979, he reported on 300 cases of cervical spine injury and concluded that lack of immobilization led to spinal deterioration in some patients. Consequent to his work, spinal immobilization became the standard of care for patients with traumatic spinal cord injury, and physicians are cautioned against recommending physiotherapy for these patients. Dr. Bohlman went on to develop effective surgical techniques to decompress the spinal cord of patients with traumatic injury to achieve pain reduction and improved motor function.
Intervertebral discs account for one-fourth of the length of the spinal column. These discs are fibrocartilaginous cushions that protect the vertebrae, brain, and other structures. Intervertebral discs are complicated structures that consist of annulus fibrosus (including lamellae that buckle outward and fan in many directions), nucleus pulposus (structure that resists compression), and vertebral endplates (including apophyseal ring of specialized strong woven bone and an inner spongy, innervated, elastic portion). Subarticular collecting veins underlying the cancellous bony portion of the endplates branch and communicate and terminate in glomeruloid buds, which are highly vasoactive. Contrast magnetic resonance imaging shows transgression of nutrients and transport of metabolites and waste products through this system—not through the annulus.
Disc degeneration refers to normal changes in spinal discs that occur with aging. In some people (such as those who smoke or do heavy physical work), age-related changes such as loss of fluid in the discs (making them less flexible) and tiny cracks or tears in the outer layer (causing bulging, rupture, or breaking into fragments) lead to degenerative disc disease, which can take place throughout the spine but most often occurs in discs in lumbar and cervical regions (Figure 3). Initial treatment for degenerative disc disease ranges from ice or heat on the affected area to pain medication. For those who develop osteoarthritis, a herniated disc, or spinal stenosis, physical therapy and exercise may be recommended.