The piriformis muscle is located deep in the buttock and is one of the external rotators of the hip. It originates from the front of the sacrum, passes through the greater sciatic foramen, and attaches to the top of the greater trochanter of the femur. Piriformis syndrome is a condition in which the piriformis muscle spasms and irritates the nearby sciatic nerve, causing pain, tingling, and numbness along the back of the leg and into the foot. There are several special tests that can be performed during a physical exam to help diagnose piriformis syndrome. These tests aim to recreate the patients’ symptoms by putting tension or stress on the piriformis muscle. The main special tests for piriformis syndrome are the FAIR test, Freiberg test, Pace test, Beatty test, and piriformis muscle stretch test.
FAIR Test
The FAIR test stands for Flexion, Adduction, Internal Rotation. It is one of the most common tests for piriformis syndrome. To perform this test, the patient lies on their back with the legs extended. The examiner lifts the affected leg up and flexes the hip to a 90 degree angle. They then adduct and internally rotate the hip while stabilizing the pelvis. Pain reproduction down the back of the leg suggests a positive test. Flexing, adducting, and internally rotating the hip puts a stretch on the piriformis muscle, irritating the sciatic nerve if piriformis syndrome is present.
Freiberg Test
The Freiberg test is also called the piriformis stretch test. With the patient lying on their back, the examiner lifts the affected leg straight up and then crosses it over the other leg so the ankle rests on the opposite knee. This causes external rotation and abduction of the hip, stretching the piriformis muscle. The test is positive if it reproduces the patient’s symptoms of buttock or leg pain. An alteration of this test involves flexing the unaffected hip to increase the stretch.
Pace Test
For the Pace test, the patient lies on their unaffected side with the affected hip and knee flexed to a 90 degree angle. Maintaining this hip flexion, the examiner then extends the flexed knee, forcing external rotation of the hip. The test tries to isolate the piriformis muscle. If it reproduces symptoms in the buttock or posterior leg, it is considered positive.
Beatty Test
The Beatty test has the patient lie on their back with the unaffected leg flat and the affected leg flexed at the hip and knee. The examiner places one hand under the flexed knee and the other hand on top of that knee. They then apply downward pressure through the knee, forcing internal rotation of the hip. This test can differentiate between piriformis syndrome and lumbar radiculopathy. Increased pain suggests piriformis irritation while relief of symptoms indicates lumbar involvement instead.
Piriformis Muscle Stretch Test
In the piriformis muscle stretch test, the patient lies on their back with both knees bent. The unaffected leg is used to stabilize the pelvis. The examiner lifts and lowers the affected leg repeatedly to stretch the piriformis muscle in different hip positions. This may include:
- Neutral hip rotation with knee bent to 90 degrees
- External hip rotation with knee bent to 90 degrees
- Internal hip rotation with knee bent to 90 degrees
- Neutral hip rotation with knee extended
Reproduction of sciatica symptoms during any of these stretches indicates a positive test for piriformis syndrome. Comparing symptoms in different hip positions can help identify exactly where the piriformis impingement on the sciatic nerve is occurring.
Interpretation of Special Tests
No single special test can definitively diagnose piriformis syndrome. The tests must be interpreted carefully in the context of the full clinical picture. Reproduction of the patient’s exact symptoms during a provocative test suggests piriformis involvement but does not rule out concomitant lumbar radiculopathy or other causes of sciatica. False positives and false negatives do occur. For example, 10-15% of normal individuals experience buttock pain during the FAIR test. Imaging like MRI may be needed to fully evaluate the lumbar spine, sacroiliac joint, hip, and sciatic nerve if the diagnosis remains uncertain after special testing.
Advantages and Disadvantages of Special Tests
Advantages:
- Non-invasive and do not require any equipment
- Inexpensive to perform
- Help distinguish piriformis syndrome from lumbar radiculopathy
- Can aid localization of the piriformis impingement
- May reduce need for imaging like MRI in some clear cut cases
Disadvantages:
- Prone to false positives and false negatives
- Difficult to interpret in isolation
- Do not always correlate with imaging findings
- User-dependent based on skill of examiner
- Pain provocation intolerable for some patients
When to Perform Special Testing
Special tests for piriformis syndrome should be considered when the patient presents with:
- Buttock pain
- Posterior thigh or leg pain following a sciatic nerve distribution
- Tingling, numbness, or weakness in the leg
- Symptoms aggravated by sitting, climbing stairs, squatting
- Limited hip internal rotation
It is important to correlate testing with a full history and physical exam to rule out lumbar stenosis, disc herniation, sacroiliac joint dysfunction, trochanteric bursitis, and other mimics of piriformis syndrome. Special tests are not diagnostic on their own but can aid clinical reasoning and localization prior to ordering advanced imaging.
Specificity and Sensitivity
No single special test for piriformis syndrome has perfect sensitivity or specificity. This means false positive and false negative results do occur. In general, the FAIR test is reported to have high sensitivity around 89-100% but only moderate specificity around 59-70% in various studies. The Freiberg piriformis stretch test has slightly lower sensitivity of 63-83% but higher specificity of 84-91%. Adding confirmatory lidocaine injection improves the accuracy somewhat for both tests. The Beatty test may have greater specificity up to 100% for differentiating piriformis syndrome from lumbar radiculopathy. However, formal studies on sensitivity and specificity for some of these less common tests remains limited in the literature.
Reliability
The reliability of special tests for piriformis syndrome depends on several factors:
- Careful patient selection using consistent inclusion/exclusion criteria
- Standardized patient positioning and test performance
- Avoiding co-contraction of surrounding hip external rotators
- Testing performed by an experienced examiner
- Accounting for patient effort and response bias
When these factors are controlled, several studies report acceptable reliability for common tests like the FAIR and Freiberg, with intra-tester kappa values ranging 0.63-0.93. However, outside of controlled studies, reliability drops off. In clinical practice, false positive rates up to 20% for the FAIR test and 10% for the Freiberg test have been described.
Performing Special Tests Correctly
To perform special tests for piriformis syndrome reliably:
- Follow standardized protocols for each test
- Stabilize pelvis and avoid compensatory motion
- Move affected leg through available range slowly to detect symptoms
- Watch for subtle signs like facial grimacing
- Perform active tests for patients able to cooperate
- Monitor and avoid aggravating other injuries
- Repeat test in slightly different positions to confirm
- Compare findings to unaffected side
Proper patient selection, positioning, stabilization, and slow controlled movement can optimize the utility of these special tests in identifying piriformis syndrome.
Conclusion
Special tests for piriformis syndrome provide useful diagnostic information during a physical exam. The FAIR, Freiberg, Pace, Beatty, and piriformis muscle stretch tests aim to recreate patients’ sciatica and buttock pain by putting tension on the piriformis muscle. No single test has perfect accuracy. False positives and negatives do occur. However, when combined with a full history and clinical picture, these provocative tests can aid in localizing the source of symptoms to the piriformis muscle versus lumbar spine pathology prior to advanced imaging. Controlled studies report acceptable reliability for the FAIR and Freiberg tests although this drops off in clinical practice. Strict protocols, patient stabilization, avoiding compensation, and monitoring for subtle signs can optimize the performance of special testing for piriformis syndrome.