Sciatica Health Article

Definition

Sciatica describes pain or discomfort in the distribution of the sciatic nerve or its components. This nerve runs from the lower part of the spinal cord, down the back of the leg, to the foot. Injury to, or pressure on, the sciatic nerve can cause the characteristic pain of sciatica—a sharp or burning pain that radiates from the lower back or hip, following the path of the sciatic nerve to the foot.

Description

The sciatic nerve is the largest and longest nerve in the body. It supplies sensation from the lower back to the foot. The nerve originates in the lumbar region of the spinal cord. As it branches off from the spinal cord, it passes between the bony vertebrae (the component bones of the spine) and runs through the pelvic girdle (hipbones). The nerve passes near the hip joint and continues down the back of the leg to the foot.

Sciatica is a fairly common disorder. Approximately 40% of the population suffers from it at some point in their lives; however, only about 1% experience any sensory or motor deficits. Sciatic pain has several root causes, and its treatment is directed to the underlying problem.

Of the identifiable causes of sciatic pain, lumbosacral (LS) radiculopathy and back strain are the most frequently suspected. The LS area is the lower part of the spine, and radiculopathy describes pain radiating from pressure on a spinal nerve roots. This area between the vertebrae (hard bones) is cushioned with a disk of shockabsorbing tissue. The spinal canal, comprising the spinal cord and other nerve roots, is hollow and lies in the middle of the spinal column. It is the disks between the vertebrae that enable the back to bend or flex.

A "ring" of cartilage, gristle-like in character, is found the outer edge of the disk (the annulus). The disk's center (nucleus) is a substance like gel. When a disk ruptures, or herniates, it does so because of wear-and-tear, excessive weight, poor posture, injury (perhaps due to improper lifting), or disease. The center nucleus pushes the outer edge of the disk into the spinal canal, putting pressure on the nerves. The spinal nerve root may become compressed by the shifted tissue or the vertebrae. This compression of the nerve root sends a pain signal to the brain. Although the injury is actually suffered by the nerve roots, the pain may be perceived as originating anywhere along the sciatic nerve. Further, if fragments of the disk lodge in the spinal canal, the nerves that control bowel and urinary functions may be damaged. Incontinence may result.

Sciatica is largely a symptom of a herniated disk. However, compression of the sciatic nerve can also present as muscle spasms in the lower back (back strain). In this case, pressure is placed on the sciatic nerve. In rare cases, infection, cancer, bone inflammation, or other diseases may cause pressure. Another possible cause of sciatica is piriformis syndrome.

As the sciatic nerve passes behind the hip joint, it shares the space with several muscles. One of these muscles, the piriformis muscle, is closely associated with the sciatic nerve. In some people, the nerve actually runs through the muscle. If this muscle is injured or has a spasm, it places pressure on the sciatic nerve, in effect, compressing it.

In many sciatica cases, the specific cause is never identified. About half of affected individuals recover from an episode within a month. Some cases persist and may require aggressive treatment. In other cases, the pain returns or becomes chronic.