eMedicine Specialties > Physical Medicine and Rehabilitation > Lower Limb Musculoskeletal Conditions

Piriformis Syndrome

Author: Milton J Klein, DO, MBA, Consulting Physiatrist, Sewickley Valley Hospital, Allegheny General Hospital, Harmarville Rehabilitation Center, Ohio Valley General Hospital, and Aliquippa Community Hospital
Contributor Information and Disclosures

Updated: Nov 6, 2008

Introduction

Background

Piriformis syndrome has been a controversial diagnosis since its initial description in 1928.¹ The condition usually is caused by a neuritis of the proximal sciatic nerve. The piriformis muscle can either irritate or compress the proximal sciatic nerve due to spasm and/or contracture, and this problem can mimic a diskogenic sciatica. Piriformis syndrome is also referred to as pseudosciatica, wallet sciatica, and hip socket neuropathy.

Related eMedicine topics:
Chronic Pelvic Pain
Piriformis Syndrome [Sports Medicine]

Pathophysiology

The piriformis muscle is flat, pyramid-shaped, and oblique. This muscle originates to the anterior of the S2-S4 vertebrae, the sacrotuberous ligament, and the upper margin of the greater sciatic foramen (see Image 1). Passing through the greater sciatic notch, the muscle inserts on the superior surface of the greater trochanter of the femur. With the hip extended, the piriformis muscle is the primary external rotator; however, with the hip flexed, the muscle becomes a hip abductor. The piriformis muscle is innervated by branches from L5, S1, and S2.

A lower lumbar radiculopathy may cause secondary irritation of the piriformis muscle, which may complicate diagnosis and hinder patient progress.

Many developmental variations of the relationship between the sciatic nerve in the pelvis and piriformis muscle have been observed.² In approximately 20% of the population, the muscle belly is split with 1 or more parts of the sciatica nerve dividing the muscle belly itself. In 10% of the population, the tibial/peroneal divisions are not enclosed in a common sheath. Usually, the peroneal portion splits the piriformis muscle belly, although in rare cases, the tibial division does so.

Involvement of the superior gluteal nerve usually is not seen in cases of piriformis syndrome. This nerve leaves the sciatic nerve trunk and passes through the canal above the piriformis muscle.

Blunt injury may cause hematoma formation and subsequent scarring between the sciatic nerve and short external rotators. Nerve injury can occur with prolonged pressure on the nerve or vasa nervorum.

The etiology of piriformis syndrome can be divided into the following categories:

• Hyperlordosis
• Muscle anomalies with hypertrophy
• Fibrosis (due to trauma)
• Partial or total nerve anatomical abnormalities

Other causes can include the following:

• Pseudoaneurysms of the inferior gluteal artery adjacent to the piriformis syndrome
• Bilateral piriformis syndrome due to prolonged sitting during an extended neurosurgical procedure
• Cerebral palsy
• Total hip arthroplasty
• Myositis ossificans
• Vigorous physical activity

Piriformis syndrome remains controversial because, in most cases, the diagnosis is clinical, and no confirmatory tests exist to support the clinical findings.

Papadopoulos and colleagues proposed the following classifications for piriformis syndrome³ :

• Primary piriformis syndrome - This designation would apply to piriformis syndrome resulting from intrinsic pathology of the piriformis muscle itself, such as myofascial pain, anatomic variations, and myositis ossificans.
• Secondary piriformis syndrome (pelvic outlet syndrome) - This classification would encompass all other etiologies of piriformis syndrome, with the exclusion of lumbar spinal pathology.

Frequency

United States

Given the lack of agreement on exactly how to diagnose piriformis syndrome, estimates of the frequency of sciatica caused by piriformis syndrome vary from rare to approximately 6% of sciatica cases seen in a general family practice. Approximately 90% of adults have had at least 1 episode of disabling low back pain (LBP) in their lifetime.

Mortality/Morbidity

Piriformis syndrome is not life-threatening, but it can have significant associated morbidity. The total cost of low back pain and sciatica is significant, exceeding $16 billion in direct and indirect costs.

Sex

Some reports suggest a 6:1 female-to-male ratio for piriformis syndrome.

Clinical

History

Piriformis syndrome often is not recognized as a cause of low back pain (LBP) and associated sciatica. This clinical syndrome is due to a compression of the sciatic nerve by the piriformis muscle; it is identical in clinical presentation to LBP with associated L5, S1 radiculopathy due to diskogenic and/or lower lumbar facet arthropathy with foraminal narrowing. Not uncommonly, patients demonstrate both of these clinical entities simultaneously. This diagnostic dilemma highlights the need for patients with LBP and associated radicular pain to undergo a complete history and physical examination, including a digital rectal examination.

Many cases of refractory trochanteric bursitis are observed to have an underlying occult piriformis syndrome due to the insertion of the piriformis muscle on the greater trochanter of the hip. If a patient's trochanteric bursitis and piriformis syndrome are treated inadequately, both conditions remain resistant to medical management.

Physical

Examination findings may include the following:

• Piriformis muscle spasm often is detected by careful, deep palpation.
• A digital rectal examination may reveal a tenderness on the lateral pelvic wall that reproduces symptoms.
• The reproduction of sciatica-type pain with weakness results from resisted abduction/external rotation (Pace test).
• The Freiberg test is another diagnostic sign that elicits pain upon forced internal rotation of the extended thigh.
• The Beatty maneuver reproduces buttock pain by selectively contracting the piriformis muscle.⁴ The patient lies on the uninvolved side and abducts the involved thigh upward; this activates the ipsilateral piriformis muscle, which is a hip external rotator and, when the hip is flexed, an abductor.
• A painful point may be present at the lateral margin of the sacrum.
• Shortening of the involved lower extremity may be seen.
• The patient may have difficulty sitting due to an intolerance of weight bearing on the buttock.
• The patient may have the tendency to demonstrate a splayed foot on the involved side when in the supine position.
• Piriformis syndrome alone is rarely the cause of a focal neuromuscular impairment; either a sciatic mononeuropathy or an L5-S1 radiculopathy can mimic both of these conditions, obscuring diagnosis of piriformis syndrome.
• A Morton foot may predispose the patient to developing piriformis syndrome. The prominent second metatarsal head destabilizes the foot during the push-off phase of the gait cycle, causing foot pronation and internal rotation of the lower limb. As a compensatory mechanism, the piriformis muscle (external hip rotator) reactively contracts repetitively during each push-off phase of the gait cycle , leading to piriformis syndrome.

Causes

Approximately 50% of patients with piriformis syndrome have a history of trauma, with either a direct buttock contusion or a hip/lower back torsional injury. The remaining 50% of cases are of spontaneous onset, so the treating physician must have a high index of suspicion for the problem, lest it be overlooked.

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