(Continued from page 13)
described by Lasegue in 1870, with the first monograph being published in 1933 by Mixter and Barr. The disc has a very good nerve supply and a poor blood supply. And can be disrupted greatly leading to a "herniated disc" or herniated nucleus propulsus. This material can compress a nerve directly causing pain. The herniation also acts as a chemical irritant leading to an inflammatory reaction. This reaction not only can irritate the nerve root, it can also irritate the nerves to the disc, joints, muscles and skin. Sometimes material does not leave the confines of the annulus. Instead, the annulus may be torn, stretched or just chemically irritated from a nucleus propulsus that has degenerated and lost its water content. With time as the entire disc remains irritated, the chemosis will spread to the bones, causing Modic changes, facets causing hypertrophy and loss of synovium, to the nerve roots causing radiculopathy, to the innervating nerves causing discogenic pain and to the muscles causing spasms and pain.
Finally, the surrounding structures may play a role in low back pain. Not only can the skin cause pain, the internal organs can cause pain. The nerves from all of these structures, skin, muscles, tendons, ligaments, joints and bones travel to the spine before going to our brain to be perceived. If these structures are inflamed pain is felt. Likewise, the nerves can be inflamed without other causes. This is seen in diabetes and other types of peripheral neuropathy.
Understanding the anatomy allows one to correlate the patient's structural changes to their signs and symptoms. The side canals through which the nerve roots exit are called foramen. The smallest foramen at L5-S1 contains the largest nerve root. The largest foramen is at L1-2. In the foramen are several other structures; these are the connective tissue, ligamentum flavum, arteries, veins, lymphatics and sinuvertebral nerve. The nerve root and its coverings only occupy 35-45% of the space. The actual spinal nerve forms lateral to the foramen. The motor component sits anterior and inferior in the foramen. Posterior the foramen is bounded by the facet. Although the sinuvertebral nerve does not transmit sensation from the leg it does have a very important function when it comes to pain issues. The sinuvertebral nerve is the major sensory supply to the lumbar spine. The anterior and posterior divisions join the sympathetics. It enters the spinal canal through the foramen, around the pedicle to the posterior longitudinal ligament. It innervates the posterior longitudinal ligament, superficial annulus, epidural blood vessels, anterior dura, nerve root dural sleeve, posterior vertebral periosteum and posterior disk. The lateral disk is innervated by the ventral and grey rami while the anterior disk is innervated by the afferent sympathetics. The other nerves such as the posterior primary rami supply the facets, surface of the ligamentum flavum, the dorsal muscles, fascia, ligaments, blood vessels, periosteum and skin.
The disk is a universal joint that comprises 33% of the height of the spine. The outer layer, or annulus, is made of oblique concentric lamellae of fibrocartilage, which absorb stress by expansion and contraction. Ligaments surround the disk segment. The anterior ligament is broad and strong blending with the disk and filling in the bone concavity. The posterior longitudinal ligament is weak, smaller and at L5-S1 is one half its width. The ligaments act to strengthen the intervertebral joints and tend to reduce anterior shear forces. The blood supply is from the aorta but it is limited
(Continued on page 15)