An uncommon cause of sciatica, piriformis syndrome is caused by entrapment and compression of the sciatic nerve by the piriformis muscle at the level of the sciatic notch (Fig. 126.1). Patients suffering from piriformis syndrome complain of pain that begins in the buttocks and radiates into the affected leg all the way to the foot. There is associated numbness and dysesthesias as well as weakness in the distribution of the sciatic nerve. As the syndrome progresses, the patient may experience altered gait as a result of the pain and weakness associated with the compromise of the sciatic nerve. This alteration of gait will often cause secondary sacroiliac, low back, and hip pain, which may serve to confuse the diagnosis. Untreated, atrophy of the muscles innervated by the sciatic nerve may result. Piriformis syndrome is the clinical constellation of symptoms that occurs when the sciatic nerve is compressed and/or entrapped at the level of the piriformis muscle. The cause of this sciatic nerve compromise can be from a variety of pathologic processes: direct trauma to the nerve; compression of the nerve by tumor, hematoma, or mass; and compression of the nerve by hypertrophied or anomalous piriformis muscle (Fig. 126.2).

Patients suffering from piriformis syndrome will exhibit tenderness on palpation of the sciatic notch. A positive straightleg raising test is often present as is a positive Tinel sign when the sciatic nerve is percussed at the sciatic notch. The pain of piriformis syndrome may be elicited by the piriformis syndrome provocation test. To perform the piriformis syndrome provocation test, the patient is placed in the modified Sims position with the affected leg superior. The hip of the affected leg is then flexed ˜50 degrees, and while stabilizing the pelvis, the affected leg is pushed downward (Fig. 126.3). The test is considered positive if the patient’s pain symptomatology is reproduced. On palpation of the piriformis muscle, a swollen, indurated muscle belly may be appreciated. Weakness of the affected gluteal muscles and muscle wasting may be identified in more advanced cases of untreated piriformis syndrome.

Piriformis syndrome is frequently misdiagnosed as lumbar radiculopathy or is attributed to primary hip pathology, leading to both diagnostic and therapeutic misadventures. Plain radiographs of the hip will help identify primary hip pathology, and electromyography will help distinguish the compromise of sciatic nerve function associated with piriformis syndrome from radiculopathy. Most patients who suffer from lumbar radiculopathy have back pain associated with reflex, motor, and sensory changes that are associated with back pain, whereas patients with piriformis syndrome have only secondary back pain and no reflex changes. Furthermore, the motor and sensory changes of piriformis syndrome are limited to the distribution of the sciatic nerve below the sciatic notch. Lumbar radiculopathy and sciatic nerve entrapment may coexist as the so-called “double crush” syndrome, and this can further confuse the clinical picture. Based on the patient’s clinical presentation, additional testing may be indicated, including complete blood cell count, uric acid, sedimentation rate, and antinuclear antibody testing. Magnetic resonance imaging or computed tomography scanning of the lumbar spine is indicated if a herniated disc, a spinal stenosis, or a space-occupying lesion is suspected (Fig. 126.4). The injection technique described below can be utilized as both a diagnostic and a therapeutic maneuver.

The sciatic nerve provides innervation to the distal lower extremity and foot with the exception of the medial aspect of the calf and foot, which are subserved by the saphenous nerve. The largest nerve in the body, the sciatic nerve is derived from the L4, L5, and the S1-S3 nerve roots. The roots fuse in front of the anterior surface of the lateral sacrum on the anterior surface of the piriformis muscle. The nerve travels inferiorly and leaves the pelvis just below the piriformis muscle via the sciatic notch (see Figs. 126.1 and 126.5). Just beneath the nerve at this point is the obturator internus muscle. The sciatic nerve lies anterior to the gluteus maximus muscle; at this muscle’s lower border, the sciatic nerve lies halfway between the greater trochanter and the ischial tuberosity. The sciatic nerve courses downward past the lesser trochanter to lie posterior and medial to the femur (Fig. 126.6). In the midthigh, the nerve gives off branches to the hamstring muscles and the adductor magnus muscle. In most patients, the nerve divides to form the tibial and common peroneal nerves in the upper portion of the popliteal fossa, although in some patients these nerves can remain

separate through their entire course. The tibial nerve continues downward to provide innervation to the distal lower extremity, whereas the common peroneal nerve travels laterally to innervate a portion of the knee joint and, via its lateral cutaneous branch, provide sensory innervation to the back and lateral side of the upper calf.