Does piriformis syndrome exist?

Even though the concept of piriformis syndrome (PS) was proposed 8 decades ago, (1) the existence of PS is still controversial. (2, 3)  The diagnosis of PS is based on knowledge of anatomy, clinical findings, and anecdote, rather than firm evidence.  The fuzzy criteria for diagnosing PS has made it difficult to perform randomized double blind studies on this syndrome.  So there is little evidence available regarding the best methods to diagnose and treat it.   In spite of the lack of evidence, there are plenty of assumptions, speculations, and treatment protocols purposed for this malady. 

Anatomy and Pathophysiology

The piriformis is a flat, pear-shaped (literal translation from Latin: piri-pear, formis-shape) muscle that originates on the anterior sacrum and the sacrotuberous ligament.  From its origin on the pelvis, it passes through the sciatic notch and inserts into the greater trochanter of the femur.  The sciatic nerve passes between the piriformis and the ilium (figure 1).  The purposed theory is that a taut or anomalous piriformis (figure 2) will compress the sciatic nerve and cause sciatic neuralgia that may mimic disc-related sciatica.   Myofascial manipulation, therapeutic modalities, ergonomic modification, and stretching (figure 3) have been recommended by a host of lecturers, authors, and clinicians as the treatment of this spectral diagnosis.

Occurrence

Even if we disregard the controversy over the existence of piriformis syndrome and the lack of a firm diagnostic test, studies place the probable occurrence of PS from rare (4) to about 6% (5) of the sciatica cases.  Other studies show that patients who meet their definition of PS to be higher. (6)  Surprisingly a more common source of non-nerve root compression sciatica is gynecological conditions such as ovarian cysts, pregnancy, and endometriosis. (5)

Variations in the anatomy of the sciatic nerve and piriformis exist (7), but are not necessarily related to being symptomatic. 

Diagnosis

There are no practical laboratory, radiographic, or electrodiagnostic tests recommended for PS at this time. Therefore, diagnosis is based on clinical observations and history.  The diagnosis of PS should be made after excluding other sources of sciatic pain.  First, look to the spine for causation of sciatica, then to non-nerve root compression causes. Differential diagnosis for non-nerve root compression sciatica should also include gynecological disorders, space-occupying lesions, and myofascial entrapments (such as PS).

Treatment

Since spinal conditions are a more common source of sciatica than piriformis syndrome, the practitioner should avoid treatments that could provoke spinal sources of sciatica (spinal flexion and axial compression).  The patient should likewise avoid any motion or activity that provokes or peripheralizes the sciatica.

Treatment recommendations by a host of authors include myofascial release, stretching, massage, ergonomics, modalities, trigger point

Conclusion

Nerve root compromise, not piriformis syndrome, is responsible for most cases of sciatic neuralgia.  Female patients may have a gynecological source of sciatica.  Other sources of sciatic compression include space occupying lesions.  Clinicians should not cling to the diagnosis of PS so closely that they become blinded to more probable sources of sciatic neuralgia.

Just because a patient has sciatica and tenderness near the site of the piriformis or the doctor believes he feels a tightness or trigger point in the PS, it does not indicate that the patient has PS.  Even though PS is less common than other types of sciatic neuralgia it is reasonable to believe that entrapment along the length of the sciatic nerve may be possible.  Treatment protocols for PS may be beneficial for a subset of patients with buttocks pain and sciatica absent other probable causes.

Does Piriformis syndrome exist?  A better question would be:  Is piriformis syndrome over diagnosed?

(1)   Yeoman W. The relation of arthritis of the sacroiliac joint to sciatica. Lancet. 1928;ii:1119-22.

(2)   Stewart JD. The piriformis syndrome is overdiagnosed Muscle Nerve. 2003 Nov; 28(5):644-6.

(3)   Silver JK, Leadbetter WB. Piriformis syndrome: assessment of current practice and literature review. Orthopedics. 1998;21:1133–1135

(4)   Bernard TN, Kirkaldy-Willis WH. Recognizing specific characteristics of nonspecific low back pain. Clin Orthop. 1987;217:266–280

(5)   Yoshimoto M, Kawaguchi S, Takebayashi T, et al. Diagnostic features of sciatica without lumbar nerve root compression. J Spinal Disord Tech. Jul 2009;22(5):328-33.

(6)   Fishman LM, Dombi GW, Michaelsen C, et al: Piriformis syndrome. diagnosis, treatment, and outcome: a 10-year studyArch Phys Med Rehabil  2002; 83:295-301.

(7)   Bergman RA, Afifi AK, Miyauchi R.  Variations in relation of sciatic nerve to m. piriformis.  Illustrated encyclopedia of human anatomic variation: opus III: Nervous system   http://www.anatomyatlases.org