What is Piriformis Syndrome?
Piriformis syndrome is a neuromuscular condition where the piriformis muscle compresses the sciatic nerve in the deep gluteal space, causing buttock pain that radiates down the leg and mimics sciatica. 1, 2
Pathophysiology
The condition results from excessive tension or anatomical variations in the piriformis muscle that lead to sciatic nerve compression. 1 The piriformis muscle has an intimate anatomical relationship with the sciatic nerve, and while the nerve may pierce through the muscle in approximately 16% of healthy individuals, this anatomical variant does not appear to correlate with development of the syndrome. 2
The piriformis muscle's action on the hip varies with hip position: when the hip is flexed, it internally rotates and abducts the hip; in neutral position, it acts as an external rotator. 3 This biomechanical complexity contributes to the variable presentation of symptoms.
Clinical Presentation
The most common symptoms include:
- Buttock pain with external tenderness over the greater sciatic notch 2
- Pain radiating down the back of the affected lower limb along the sciatic nerve distribution 1, 4
- Aggravation of pain with sitting 2, 4
- Pain described as dull, aching, sharp, or electrical in character 5
Unlike true lumbar radiculopathy, piriformis syndrome typically does not cause specific dermatomal sensory loss or myotomal weakness. 5 Neurological examination results are usually normal, and straight leg raising tests are typically negative. 4
Diagnostic Challenges
Diagnosis is primarily one of exclusion due to the lack of validated and standardized diagnostic tests. 6 The condition is often misdiagnosed because symptoms overlap significantly with lumbar radiculopathy and other causes of sciatica. 5
Clinical examination findings include:
- Pain with flexion, adduction, and internal rotation of the hip (FAIR test) 4
- Positive Freiberg sign and Pace sign 4
- Direct palpation of the piriformis reproduces pain and symptoms 4
However, the FAIR test has limited clinical utility due to poor specificity. 5
Electrodiagnostic studies are typically normal and serve primarily to exclude other causes of symptoms rather than confirm piriformis syndrome. 2 Imaging studies like MRI are most useful when hip pain coexists with low back pathology to screen for significant pathology. 5
Epidemiology
The prevalence varies depending on diagnostic criteria used, but is estimated at 5-6% of all cases of low back, buttock, and leg pain, and up to 17% of patients with chronic low back pain. 2
Common Pitfalls
The condition is frequently misdiagnosed because it mimics L5-S1 disc lesions, but without the specific neurological deficits associated with true radiculopathy. 5 In long-standing cases, patients may develop compensatory gait patterns that further complicate the clinical picture. 5