Sciatica

Sciatica is a form of peripheral neuropathy. It occurs when there is damage to the sciatic nerve, located in the back of the leg. This nerve controls the muscles of the back of the knee and lower leg and provides sensation to the back of the thigh, part of the lower leg and the sole of the foot. Incomplete damage to the sciatic nerve may appear identical to damage to one of the branches of the sciatic nerve (tibial nerve dysfunction or common peroneal nerve dysfunction).

A problem in a single nerve group, such as the sciatic nerve, is classified as a mononeuropathy. The usual causes are direct trauma (often due to an injection into the buttocks), prolonged external pressure on the nerve, and pressure on the nerve from nearby body structures. It can also be caused by entrapment -- pressure on the nerve where it passes through a narrow structure. The damage slows or prevents conduction of impulses through the nerve.

The sciatic nerve is commonly injured by fractures of the pelvis, gunshot wounds, or other trauma to the buttocks or thigh. Prolonged sitting or lying with pressure on the buttocks may also injure it. Systemic diseases, such as diabetes, can typically damage many different nerves, including the sciatic nerve. The sciatic nerve may also be harmed by pressure from masses such as a tumor or abscess, or by bleeding in the pelvis.

In many cases, no cause can be identified.

More information about Sciatica

Note: A ruptured lumbar disk in the spine may cause symptoms that simulate the symptoms of sciatic nerve dysfunction.

The sciatic nerve is the largest and longest nerve in the body. About the thickness of a person's thumb, it spans from the lower back to the foot. The nerve originates in the lower part of the spinal cord, the so-called lumbar region. 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, or hip bones. The nerve passes through the hip joint and continues down the back of the leg to the foot.

Sciatica is a fairly common disorder and approximately 40% of the population experiences it at some point in their lives. However, only about 1% have coexisting sensory or motor deficits. Sciatic pain has several root causes and treatment may hinge upon the underlying problem.

Of the identifiable causes of sciatic pain, lumbosacral radiculopathy and back strain are the most frequently suspected. The term lumbosacral refers to the lower part of the spine, and radiculopathy describes a problem with the spinal nerve roots that pass between the vertebrae and give rise to the sciatic nerve. This area between the vertebrae is cushioned with a disk of shock- absorbing tissue. If this disk shifts or is damaged through injury or disease, the spinal nerve root may be compressed by the shifted tissue or the vertebrae.

This compression of the nerve roots sends a pain signal to the brain. Although the actual injury is to the nerve roots, the pain may be perceived as coming from anywhere along the sciatic nerve.

The sciatic nerve can be compressed in other ways. Back strain may cause muscle spasms in the lower back, placing pressure on the sciatic nerve. In rare cases, infection, cancer, bone inflammation, or other diseases may be causing the pressure. More likely, but often overlooked, is the piriformis syndrome. As the sciatic nerve passes through 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 can linger a few weeks longer and may require aggressive treatment. In some cases, the pain may return or potentially become chronic.