It occurs when there is damage to the sciatic nerve, which is located in the leg and supplies the muscles of the back of the knee and lower leg. It supplies sensation to the back of the thigh, part of the lower leg, and the sole of the foot. Dysfunction of a single nerve group, such as the sciatic nerve, is classed as mononeuropathy .
Entrapment involves pressure on the nerve where it passes through a narrow structure.
This damage slows or prevents conduction of impulses through the nerve. The sciatic nerve is commonly injured by fractures of the pelvis or by gunshot wounds or other trauma to the buttocks or thigh. The nerve may be injured during intramuscular injections into the buttocks. It may also be injured by prolonged sitting or lying with pressure on the buttocks. It may be damaged by pressure from lesions such as a tumor , abscess , or bleeding in the pelvis.