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 similar in clinical presentation to LBP with associated L5, S1 radiculopathy due to diskogenic and/or lower lumbar facet arthropathy with foraminal narrowing. (The image below demonstrates the origins of both conditions.) 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.
Nerve irritation in the herniated disk occurs at the root (sciatic radiculitis). In piriformis syndrome, the irritation extends to the full thickness of the nerve (sciatic neuritis).
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:
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Piriformis muscle spasm often is detected by careful, deep palpation.
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The reproduction of sciatica-type pain with weakness results from resisted abduction/external rotation (Pace test). [3]
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The Freiberg test is another diagnostic sign that elicits pain, upon forced internal rotation of the extended thigh. [4]
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The Beatty maneuver reproduces buttock pain by selectively contracting the piriformis muscle. [5] 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.
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Some specialists may include a digital rectal examination, which may reveal a tenderness on the lateral pelvic wall that reproduces piriformis symptoms; this procedure is less commonly performed, as it is uncomfortable and leads to a nonspecific finding.
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A painful point may be present at the lateral margin of the sacrum.
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Shortening of the involved lower extremity may be seen.
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The patient may have difficulty sitting due to an intolerance of weight bearing on the buttock.
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The patient may have the tendency to demonstrate a splayed foot on the involved side when in the supine position.
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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.
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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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Nerve irritation in the herniated disk occurs at the root (sciatic radiculitis). In piriformis syndrome, the irritation extends to the full thickness of the nerve (sciatic neuritis).
