Sciatica

Alternative names

Neuropathy - sciatic nerve; Sciatic nerve dysfunction

Definition

Sciatica is a condition involving pain, weakness, numbness, or tingling in the leg. It is caused by injury to or compression of the sciatic nerve.

Causes, incidence, and risk factors

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.

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

Symptoms

• Sensation changes
  o Of the back of the calf or the sole of the foot
  o Numbness, decreased sensation
  o Tingling, burning sensation
  o Pain, may be severe
  o Abnormal sensations
  
• Weakness of the knee or foot
  o Difficulty walking
  o Inability to move the foot (in severe cases)
  o Inability to bend the knee (in severe cases)
  

Signs and tests

Sciatica might be revealed by a neuromuscular examination of the legs by a physician. There may be weakness of knee bending or foot movement, or difficulty bending the foot inward or down. Reflexes may be abnormal, with weak or absent ankle-jerk reflex. Pain down the leg can be reproduced by lifting the leg straight up off the examining table.