Definition

Piriformis syndrome describes a clinical variations of this relationship have been well documented (Fig. 58.1). Cadaver studies have described situation whereby the piriformis muscle is compressing the sciatic nerve, resulting in a sciatic neuropathy. The piriformis muscle and sciatic nerve both exit the pelvis through the greater sciatic notch. Numerous anatomic the sciatic nerve passing below the piriformis muscle, through the muscle belly, as a divided nerve above and through the muscle, and as a divided nerve through and below the muscle [1,2]. More recently, a case report of piriformis syndrome described a fifth variation of an undivided nerve passing above an undivided piriformis muscle [3]. Yeoman [4] was the first to describe the relationship of these two structures in 1928, and Robinson [5] first coined the term piriformis syndrome in 1947.

Although the anatomic relation of these two structures is well documented, this remains a controversial diagnosis. There is no consensus among clinicians on the validity of this entity and therefore no documentation of the incidence [6]. Some authors suggest that piriformis syndrome is responsible for up to 36% of low back pain and “sciatica” cases, whereas others found the piriformis to be culpable in less than 1% of sciatica cases [7,8]. Nevertheless, Goldner [9] estimated an incidence of less than 1% in an orthopedic practice. Prevalence is difficult to identify because the diagnosis is one of exclusion and based on clinical findings [10].

Sciatic neuropathy related to piriformis syndrome may be a result of intrinsic injury to the piriformis muscle (primary syndrome) or a compression at the pelvic outlet (secondary syndrome) [11]. Secondary causes of piriformis syndrome can include superior and inferior gluteal artery aneurysm, benign pelvic tumor, endometriosis, and myositis ossificans. Often, a history of minor trauma may be described, such as falling onto the buttock [12].

Symptoms

The patient with piriformis syndrome will complain of buttock pain with or without radiation into the leg. Sitting on hard surfaces will exacerbate the symptoms of pain and occasional numbness and paresthesias without weakness. This may be seen in chronic as well as in acute situations. Activities that produce a motion of hip adduction and internal rotation, such as cross-country skiing and the overhead serve in tennis, may also exacerbate the symptoms [13,14]. Because of the relationship of the piriformis muscle with the lateral pelvic wall, patients may also experience pain with bowel movements, and women may complain of dyspareunia [15].

Physical Examination

The physical examination will reveal normal neurologic findings with symmetric strength and reflexes. Tenderness to palpation is experienced from the sacrum to the greater trochanter, representing the area of the piriformis muscle [16]. A palpable taut band is tender with both rectal and pelvic examination because the piriformis muscle sits in the deep pelvic floor [14]. Passive hip abduction and internal rotation may compress the sciatic nerve, reproducing pain (a Freiberg sign). Contraction of the piriformis with resistance to active hip external rotation and abduction may also reproduce pain or asymmetric weakness (a Pace sign) [17]. A positive result of the straight-leg test may also be appreciated [18]. Rectal examination may be performed to palpate a taut band. See Table 58.1.