Buttock pain, leg pain and weakness of muscles innervated by the sciatic nerve are often associated with a discogenic origin. However, other causes need to be considered, including compression of the sciatic nerve by the piriformis muscle, an external rotator, and extensor and abductor of the hip. The association of the piriformis and the sciatic nerve is significant. The muscle originates on the under side of the sacrum, traverses the buttock passing directly over the sciatic nerve and inserts into the greater trochanter. This triangular-shaped muscle with a very prominent tendon often has more than one muscle belly. The sciatic nerve usually passes freely beneath the muscle exiting along its lower edge. Ten percent of the time, the nerve will split into tibial and common peroneal branches with the peroneal branch weaving through the muscle bellies.
Problems arise when this anatomical configuration becomes inflamed. Although most often insidious in onset, this soft tissue problem can result from trauma, prolonged sitting, or over use. Buttock pain with sitting is one of the most consistent symptoms. Often the patient presents sitting on the opposite buttock, avoiding any pressure on the involved side. Motor weakness can occur along the sciatic nerve innervated muscle group. If the peroneal branch is significantly entrapped, weakness of the anterior tibialis muscle can develop to the point of complete foot drop. On examination, sciatic stretch signs such as sitting or supine straight leg raising seen with discogenic nerve compression are absent (pseudosciatica). Palpation of the buttock is associated with pain, often aggravated by flexion, adduction and internal rotation of the hip. Imaging studies are of limited value except to exclude other diagnostic entities. Diagnostic analgesic injections to the area are not 100 percent specific, but may be helpful.
Treatment includes behavior modification, physical therapy, and NSAIDs. With failure of conservative treatment and a high index of suspicion, surgical release and partial resection of the piriformis muscle can often provide significant relief if not complete resolution of symptoms.
MD News September 2008