The piriformis muscle originates on the anterolateral surface of the mid-portion of the sacrum and inserts on the superior medial aspect of the greater trochanter. When the hip is extended, the piriformis functions primarily as an external rotator of the thigh, with secondary contributions toward flexion. The muscle assists in abduction when the hip is flexed to 90 degrees. (3) The sciatic nerve has a variable relationship to the piriformis muscle. In the majority of the population, the sciatic nerve travels deep to the muscle. Approximately one fourth of the population is anatomically predisposed to piriformis syndrome because their sciatic nerve passes through the muscle, splits the muscle or both. (5,6)
Symptoms of piriformis syndrome may begin abruptly as the result of a traumatic event, or may develop slowly in response to repeated irritation. Piriformis muscle irritation and hypertonicity can result from a strain, a fall onto the buttocks or catching oneself from a “near fall”. In other instances, the process may begin following repetitive microtrauma, like long distance walking, stair climbing or from chronic compression- i.e.sitting on the edge of a hard surface or a wallet. (8,9)
Presenting complaints for piriformis syndrome include pain, paresthesia or numbness beginning in the gluteal region and radiating along the course of the sciatic nerve. Additional symptoms may develop from local trigger point referral into the proximal thigh, sacroiliac and hip regions. (9) Symptoms are often provoked by holding any one position for longer than 15-20 minutes- particularly prolonged sitting or standing. Positional changes may provide transient relief. Patients may report increasing discomfort when walking, running, stair climbing, riding in a car or arising from a seated position. Activities that involve hip internal rotation, like sitting cross-legged, may exacerbate symptoms (10).
Piriformis syndrome shares several common characteristics and may even co-exist with other lumbopelvic problems. The differential diagnosis for piriformis syndrome includes; hip pathology, fracture, lumbar compression fracture, discitis, trochanteric bursitis, sacroiliitis, sacroiliac joint dysfunction, lumbar radiculopathy, spinal stenosis and viscerosomatic referred pain.
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5. Beason LE, Anson B.J. The relation of the sciatic nerve and its subdivisions to the piriformis muscle. Anat Record. 1937;70:1-5.
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7. http://physioplus.blogspot.com/2008/09/piriformis-syndrome.html, retrieved 10/13
8. Foster MR. Piriformis syndrome. Orthopedics. 2002;25:821-825
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10. Magee DJ. Orthopedic Physical Assessment. 3rd ed. Philadelphia, Pa: WB Saunders Co; 1997.