Piriformis syndrome is a neuromuscular disorder caused by the compression or irritation of the sciatic nerve by the piriformis muscle. It is usually the result of a traumatic injury to the buttocks or hip region. The piriformis muscle is a long, narrow, pyramid-shaped muscle, located deep in the buttocks, that runs from the base of the spine to the top of the femur. Sciatic irritation causes nagging aches, pain, tingling and numbness in the area extending from the buttocks to the tibia.
Piriformis syndrome is a frequent cause of low back pain. Yoeman first described it in 1928, although the term itself wasn't introduced until 1947, when Robinson correctly identified sciatica as a symptom, not a disease. Diagnosis of the condition remains controversial among physicians because its definition and pathophysiology lack consensus.
The condition is caused by the irritation or compression of the proximal sciatic nerve by the piriformis muscle, which at the sacral vertebrae, runs through the sciatic notch and inserts at the greater trochanter of the femur. The piriformis muscle is used to help rotate the leg outwards.
It is particularly common among skiers, tennis players, long-distance bikers, and truck drivers. In addition, in as much as 20% of the population, the sciatic nerve passes through the piriformis muscle, contributing to the development of the condition.
Due to discrepancies in diagnosis, the incidence of piriformis syndrome ranges from very rare to being responsible for approximately 6% of sciatica cases. Women may be affected more frequently than men, with some reports suggesting a six-fold incidence among females. Some reports find that it is most commonly diagnosed in patients between 30 and 40 years old.
Causes and Symptoms
There is little consensus over the cause of piriformis syndrome. The syndrome is attributed to mechanical or chemical irritation of the sciatic nerve. Approximately 50% of patients have a history of buttocks, lower back or hip injury, although it is frequently diagnosed in people who sit for long periods of time, presumably because the position leads to compression of the sciatic nerve.
The release of chemical mediators, such as serotonin, prostaglandin E, bradykinin, and histamine, into the region surrounding the sciatic nerve during inflammation contributes to irritation.
Piriformis syndrome is characterized by chronic nagging pain, tingling or numbness starting at the buttocks and extending along the length of the thigh, sometimes descending to the calf. It may worsen with sitting, or with lower limb movement.
Piriformis syndrome is primarily a diagnosis of exclusion, aimed at identifying the piriformis muscle as the primary cause of the pain. Diagnoses should be made through a physical examination, and a complete neurologic examination.
Several maneuvers that contract or stretch the piriformis muscle can be performed. Freiberg's maneuver—an inward rotation of the thigh—stretches the piriformis muscle. In sitting patients, Pace's maneuver will elicit pain with the abduction of the affected leg. In Beatty's maneuver, the patient lies on a table on his non-affected leg, and the knee of the affected leg is bent knee and placed on the table. Raising the knee several inches off the table causes pain in the buttocks, and indicates piriformis syndrome
Imaging studies of the lower spine can exclude disc protrusion or degeneration, or osteoarthritis, hip and joint disease, and other spinal causes. Nerve conduction studies show delayed F waves and H reflexes.
The structure of the treatment team will vary on the severity of the condition and on the success of initial interventions. Generally the treatment team is composed of a physiotherapist and a massage therapist. In advanced cases that do not respond to mechanical or pharmacological therapy, surgery may be recommended.
Treatment for piriformis syndrome includes avoiding activities that aggravate the condition, such as running and bicycling. Patients who experience pain while sitting for long periods of time, should stand frequently, or raise the painful area from the seat.
Physiotherapy aimed at relaxing tight piriformis muscles, hip external rotators and adductors, strengthen hip abductors, or that increase the mobility of the sacroiliac joint can be beneficial. Home stretching routines can also be designed for the patient. Ultrasound has been effective for some patients.
Pharmacotherapy, including non-steroidal anti-inflammatory drugs, analgesics and muscle relaxants may help. An injection of corticosteroid into the piriformis muscle, close to the sciatic nerve, can also ease pain and reduce swelling. In severe cases, surgical resection of the piriformis muscle can be performed.
When piriformis syndrome is diagnosed and treated early, prognosis is good.
Other causes of sciatica must be ruled out. A rapid and accurate diagnosis of piriformis syndrome can localize the cause of the pain, and can prevent sentencing a patient to long-term chronic pain management.
DeLee, J. C. and D. Drez Jr. DeLee & Drez's Orthopaedic Sports Medicine, Principles and Practice, 2nd ed. Philadelphia: Saunders, 2003.
Papadopoulos, E. C. and Khan, S. N. "Piriformis syndrome and low back pain: a new classification and review of the literature." Orthopedic Clinics of North America 35 (January 2004).
"Piriformis Syndrome," Section 5, Chapter 62. In The Merck Manual of Diagnosis and Therapy. <http://www.merck.com>.
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Hannah M. Hoag, MSc