Causes

Abnormalities in the Annular Ring. Research has also focused on tears in the annular ring--the fibrous band that surrounds and protects the disk. The annular ring contains a dense nerve network and high levels of peptides that heighten perception of pain. Tears in the annular ring are a frequent finding in patients with degenerative disk disease. Some cases of chronic low back pain may be caused by inward growth of nerve fibers into the annular ring, which triggers pain within the intervertebral disk.

Muscle and Ligament Injuries

Other than age-related degenerative disk disorders, injuries in the muscles and ligaments supporting the back are the major causes of low back pain. Of note, is the iliac crest pain syndrome (iliolumbar syndrome), in which there are tears in the ligaments that help support the pelvic bone.

Spinal Stenosis

Spinal stenosis is the narrowing of the spinal canal. This typically develops as a person ages and the disks become drier and start to shrink. At some point in this process, any disruption, such as a minor injury that results in disk inflammation, can cause impingement on the nerve root and trigger pain. Pain from spinal stenosis can occur in both legs, or can present as sciatica. Spinal stenosis occurs mostly in the elderly with degenerative osteoarthritis, but it can sometimes be caused by other problems, including infection and birth defects.

Spondylosis and Spondylolisthesis

Spondylosis is a condition in which the fourth or fifth lumbar vertebrae degenerate or develop small fractures. This condition affects 4% to 6% of the general population, and the rates may be higher in certain populations. As it progresses, the spine can become unstable and lead to spondylolisthesis, in which one vertebra slips forward over the other and causes sciatica. The condition most often occurs in older individuals with women having a higher risk than men. It is also a common cause of back pain from stress fractures in young athletes and can also be due to inherited problems, injury, or bone disease.

Piriformis Syndrome

Some cases of sciatica pain may occur when a muscle located deep in the buttocks pinches the sciatic nerve. This muscle is called the piriformis. The resulting condition is called piriformis syndrome. Piriformis syndrome usually develops after an injury. In rare cases leg swelling, deep-vein blood clots, or both may occur. Piriformis syndrome is sometimes difficult to diagnose.

Ankylosing Spondylitis

Ankylosing spondylitis is a chronic inflammation of the spine that may gradually result in a fusion of vertebrae. Symptoms include a slow development of back discomfort, with pain lasting for more than three months. The back is usually stiff in the morning; pain improves with exercise. In severe cases, the patient must continually stoop over. It can be quite mild, however, and it rarely affects a person's ability to work. It occurs mostly in young Caucasians in their mid-twenties. The disease is more common in men, but about 30% of the cases are in women. Researchers believe that in most cases it is hereditary. About 20% of people with inflammatory bowel disease and about 20% of people with psoriasis develop a form of ankylosing spondylitis. There are few effective treatments for this potentially disabling disease, although etanercept (Enbrel) and infliximab (Remicade), anti-inflammatory agents known as TNF-blockers, are proving to be beneficial.

Miscellaneous Abnormalities

Any abnormality in joints, vertebrae, or nerve roots can cause back pain:

• The facet (z-joints) joints can wear down. In such cases, pain occurs on arching the back or when walking.
• In some cases a segment (consisting of two vertebrae and their common joint and disk) becomes unstable when its parts wear down.
• Injury to nerve roots, notably deep root ganglia (nerve cells in the spine whose fibers extend from skin to muscle tissue), may be important in some cases. Some patients may have scar tissue that traps the nerve roots in the lower spine and causes sciatica.