THE PIRIFORMIS SYNDROME

Although one of the more frequent causes of pain in the distribution of the sciatic nerve is a herniated lumbar disc, intraspinal lesions, lumbar stenosis, pelvic masses, and diabetic neuropathy may produce sciatica-like symptoms. An additional cause of such symptoms is entrapment of the sciatic nerve at the point of exit deep to the piriformis muscle, and this should be included as part of the differential diagnosis, especially in strength athletes. The other causes of sciatic pain should be excluded before this diagnosis is made.

The relationship of the piriformis muscle to sciatic pain apparently was first described by Yoeman, in 1928. He stated that any lesion of the sacro-iliac joint may be associated with an inflammatory reaction of the piriformis muscle, which could compress the sciatic nerve. Robinson, who probably was the first to describe the piriformis syndrome as a separate entity, listed six cardinal features: (1) A history of a traumatic injury to the sacro-iliac and gluteal region; (2) pain in the region of the sacro-iliac joint, greater sciatic notch, and piriformis muscle, extending down the lower limb and causing difficulty in walking; (3) acute exacerbation of the symptoms by lifting or stooping; (4) a palpable, sausage-shaped mass over the piriformis muscle, during an exacerbation of symptoms, that is markedly tender to pressure (this is pathognomonic of the syndrome); (5) a positive straight-leg-raising test; and (6) gluteal atrophy, depending on the duration of symptoms.

The sciatic nerve is formed by the fourth and fifth lumbar and the first, second and third sacral-nerve roots. It emerges from the pelvis into the gluteal region through the greater sciatic notch. At the distal edge of the notch, the nerve passes deep to the piriformis muscle and over the gemelli and internal obturator muscles.

The nerve lies adjacent to the sharp edge of the sciatic notch, so any increase in lordosis with compensatory flexion of the hip tightens the rotator group of muscles and draws the nerve trunk firmly against the rim of bone. One anatomical variation is the passage of all or part of the sciatic trunk through or over the piriformis muscle. Passage of the nerve through the tendinous portions of the muscle probably increases the occurrence of sciatica in patients who have the piriformis syndrome. Hypertrophy of the piriformis muscle, as is often the case in athletes, increases the chances of compression of the sciatic nerve.

Knowledge of the anatomy of the sciatic nerve and its relationship to the piriformis muscle and gluteal vessels makes it easier to understand the clinical picture of entrapment of the nerve. Anatomical variation in this region is frequent enough to make recognition of this syndrome difficult and uncertain. In some patients, symptoms may develop due to the process of an atypical fibrous band containing a group of small vessels. The etiology of the lesion producing the symptoms may be confirmed at the time of an operation. It is possible and necessary to suspect the presence of an anatomical variation without an operation. The diagnosis of a piriformis syndrome should be entertained in any athlete, including bowlers.

The sciatic nerve can be compressed under several different circumstances. Patients who are bedridden or comatose often lie in one position, with the hips hyperextended, and this may compress the nerve. Similarly, in patients who remain under general anesthesia or who sit in an awkward position for a prolonged period, symptoms of compression of the sciatic nerve can develop. Fibrosis after deep muscular injection in the buttock, and a hematoma after a fracture of or an operation on the hip, after a fall on the buttocks, or after prolonged use of anticoagulants, can compress the sciatic nerve. Scarring in the region of the ischial tuberosity, a pelvic mass (for example, endometriosis) near the greater sciatic notch, an aneurysm of the superior or inferior gluteal artery, or anatomical variation of these vessels can all compress the nerve.

Non-operative measures that may be tried in patients who have piriformis syndrome include physiotherapy, especially stretching of the piriformis muscle, administration of analgesics, administration of non-steroidal anti-inflammatory agents, deep tissue massage, application of ultrasonic waves, and injection of local anesthetics and corticosteroids.

Operative treatment, if necessary, rarely consists of sectioning of the piriformis muscle at its tendinous origin, release of fibrous bands or com-pressing vessels, and external neurolysis. The functional loss after transection of the piriformis muscle is slight, since there are three stronger short external rotators of the hip, but it is unknown whether this would produce significant weakness of athletes.

It cannot be overemphasized that the diagnosis of piriformis syndrome is entirely clinical and one of exclusion. Despite the difficulty of obtaining confirmation of this diagnosis, it should be included in the differential diagnosis when a patient has pain along the sciatic nerve.

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