Physical Medicine and Rehabilitation for Piriformis Syndrome

Pathophysiology

The piriformis muscle is flat, pyramid-shaped, and oblique. This muscle originates to the anterior of the S2-S4 vertebrae, the sacrotuberous ligament, and the upper margin of the greater sciatic foramen. Passing through the greater sciatic notch, the muscle inserts on the superior surface of the greater trochanter of the femur. With the hip extended, the piriformis muscle is the primary external rotator; however, with the hip flexed, the muscle becomes a hip abductor. The piriformis muscle is innervated by branches from L5, S1, and S2, as demonstrated in the image below.

Nerve irritation in the herniated disk occurs at the root (sciatic radiculitis). In piriformis syndrome, the irritation extends to the full thickness of the nerve (sciatic neuritis).

A lower lumbar radiculopathy may cause secondary irritation of the piriformis muscle, which may complicate diagnosis and hinder patient progress.

Many developmental variations of the relationship between the sciatic nerve in the pelvis and piriformis muscle have been observed.^{[2, 3, 4]} In approximately 20% of the population, the muscle belly is split, with 1 or more parts of the sciatic nerve dividing the muscle belly itself. In 10% of the population, the tibial/peroneal divisions are not enclosed in a common sheath. Usually, the peroneal portion splits the piriformis muscle belly, although in rare cases, the tibial division does so.

In a study of 200 pairs of sacral roots (100 patients, none of whom had piriformis syndrome) by Russell et al, T1-weighted magnetic resonance imaging (MRI) scans revealed that 199 of the S1 nerve roots (99.5%) were positioned above the piriformis muscle, while 150 of the S2 nerve roots (75%) traversed the muscle and 50 of them (25%) were located above it. The images also showed that 194 S3 nerve roots (97%) traversed the muscle and that 190 S4 nerve roots (95%) were below it. The piriformis muscles had an average size of 1.9 cm; in 19% of the study's patients, the muscle was asymmetrical by more than 3 mm.^[5]

Involvement of the superior gluteal nerve usually is not seen in cases of piriformis syndrome. This nerve leaves the sciatic nerve trunk and passes through the canal above the piriformis muscle.

Blunt injury may cause hematoma formation and subsequent scarring between the sciatic nerve and short external rotators. Nerve injury can occur with prolonged pressure on the nerve or vasa nervorum.

The etiology of piriformis syndrome can be divided into the following categories:

• Hyperlordosis
• Muscle anomalies with hypertrophy
• Fibrosis (due to trauma)
• Partial or total nerve anatomical abnormalities

Other causes can include the following:

• Pseudoaneurysms of the inferior gluteal artery adjacent to the piriformis syndrome
• Bilateral piriformis syndrome due to prolonged sitting during an extended neurosurgical procedure
• Cerebral palsy
• Total hip arthroplasty
• Fibrodysplasia ossificans progressiva (myositis ossificans)
• Vigorous physical activity
• Leg length discrepancy ^[6]

Piriformis syndrome remains controversial because, in most cases, the diagnosis is clinical, and no confirmatory tests exist to support the clinical findings.

Papadopoulos and colleagues proposed the following classifications for piriformis syndrome^[7] :

• Primary piriformis syndrome - This designation would apply to piriformis syndrome resulting from intrinsic pathology of the piriformis muscle itself, such as myofascial pain, anatomic variations, and myositis ossificans.
• Secondary piriformis syndrome (pelvic outlet syndrome) - This classification would encompass all other etiologies of piriformis syndrome, with the exclusion of lumbar spinal pathology.

Rehabilitation Program

Physical Therapy

Because there is no definitive method to accurately diagnose piriformis syndrome, treatment regimens are controversial and have not been subjected to randomized, blind clinical trials. Despite this fact, numerous treatment strategies exist for patients with this condition.

Functional biomechanical deficits associated with piriformis syndrome may include the following:

• Tight piriformis muscle
• Tight hip external rotators and adductors
• Hip abductor weakness
• Lower lumbar spine dysfunction
• Sacroiliac joint hypomobility

Functional adaptations to these deficits include the following:

• Ambulation with the thigh in external rotation
• Functional limb length shortening
• Shortened stride length

Once the diagnosis has been made, these underlying, perpetuating biomechanical factors must be corrected.

Consider the use of ultrasonography and other heat modalities prior to physical therapy sessions. Before piriformis stretches are performed, the hip joint capsule should be mobilized anteriorly and posteriorly to allow for more effective stretching. Soft-tissue therapies for the piriformis muscle can be helpful, including longitudinal gliding with passive internal hip rotation, as well as transverse gliding and sustained longitudinal release with the patient lying on his/her side. Addressing sacroiliac joint and low back dysfunction also is important.

A home stretching program should be provided to the patient. These stretches are an essential component of the treatment program. During the acute phase of treatment, stretching every 2-3 hours (while awake) is a key to the success of nonoperative treatment. Prolonged stretching of the piriformis muscle is accomplished in either a supine or an orthostatic position with the involved hip flexed and passively adducted/internally rotated.