Physical Medicine and Rehabilitation for Piriformis Syndrome

Updated: Nov 09, 2018
  • Author: Milton J Klein, DO, MBA; Chief Editor: Ryan O Stephenson, DO  more...
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Overview

Background

Piriformis syndrome has been a controversial diagnosis since its initial description in 1928. [1] The condition, which can mimic a diskogenic sciatica, usually is caused by a neuritis of the proximal sciatic nerve. The piriformis muscle can either irritate or compress the proximal sciatic nerve due to spasm and/or contracture. Piriformis syndrome is also referred to as pseudosciatica, wallet sciatica, and hip socket neuropathy. [2]

In many musculoskeletal practices, piriformis syndrome can be considered a reasonable primary or secondary diagnosis if the symptoms, history, and physical examination are supportive. Due to the traumatic etiology of most cases, however, piriformis syndrome usually is associated with other, more proximal causes of low back pain, sciatica, or buttock pain (thereby further clouding the diagnosis).

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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. Branches from the L5, S1, and S2 nerve roots innervate the piriformis muscle, as demonstrated in the image below. Due to this innervation, a lower lumbar radiculopathy may cause secondary irritation of the piriformis muscle, which may complicate diagnosis and hinder patient progress.

Nerve irritation in the herniated disk occurs at t 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).

Many developmental variations of the relationship between the sciatic nerve in the pelvis and piriformis muscle have been observed. [3, 4, 5] 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. [6]

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:

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 [8] :

  • 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.

In an imaging study of 74 patients who demonstrated pathologies associated with piriformis syndrome, Vassalou et al found a greater incidence of secondary causes than primary etiologies, with the condition most often caused by space-occupying lesions in the piriformis area. The study, which employed magnetic resonance imaging (MRI) and/or computed tomography (CT) scanning, reported the most frequent imaging finding to be piriformis muscle enlargement. [9]

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Epidemiology

Frequency

United States

Given the lack of agreement on exactly how to diagnose piriformis syndrome, estimates of the frequency of sciatica caused by piriformis syndrome vary from rare to approximately 6% of sciatica cases seen in a general family practice. [10] More than 80% of adults have had at least 1 episode of disabling low back pain (LBP) in their lifetime. [11]

Mortality/Morbidity

Piriformis syndrome is not life-threatening, but it can have significant associated morbidity. The total cost of low back pain and sciatica is significant, exceeding $16 billion annually in direct and indirect costs.

Sex

Some reports suggest a 6:1 female-to-male ratio for piriformis syndrome.

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