Some clinical studies have suggested that intervertebral discs may be a cause of low back pain. Another possible cause of low back pain, which is often associated with herniated discs, is a torn annulus fibrosus, which can be induced by injection of saline or contrast material into the disc in patients with herniated discs such as these. The main components of the intervertebral disc are collagen, proteoglycans, and water, which make up 90 to 95 percent of the disc volume. The composition of these components changes with degeneration or aging and is primarily characterized by a decrease in proteoglycans and water. In addition, the proportions of chondroitin sulfate and keratan sulfate increase while the proportion of polymers decreases. During the course of disc injury, peripheral tearing of the annulus fibrosus can be caused by overloaded torsion. An internal tear can occur on top of this tear and eventually form a complete radial tear. The sinus vertebral nerve (SVN) innervates intravertebral structures and is distributed ventrally to the posterior longitudinal ligament, dural sac, and posteriorly to the vessels and annulus fibrosus. The ventral and lateral aspects of the annulus fibrosus are innervated by branches originating from the ventral primary and sympathetic nerves. The anterior longitudinal ligament is innervated by branches of the sympathetic trunk of the gray traffic branch. These nerves contain nociceptive fibers that are thought to sense discogenic low back pain and become sensitive in disc injury.