Abstract
Conflicting historical definitions of piriformis syndrome present a challenge to its proper identification and effective clinical approach. The objective of this chapter is to perform a comprehensive review of the pertinent literature to date, from the initial descriptions of the syndrome to the latest methods of management. A synthesis of the results helps to define the optimal criteria for diagnosis and the strength of evidence for both noninterventional and interventional treatment.
Keywords
Buttock pain, Diagnostic criteria, Piriformis syndrome, Sciatica
Introduction
Piriformis syndrome is a controversial cause of gluteal pain. Historically, piriformis syndrome has been a diagnosis that may account for as much as 6%–8% of patients seen for a complaint of sciatica (low back/leg pain in the distribution of the sciatic nerve) in the United States each year. The challenge surrounding the diagnosis and treatment of piriformis syndrome is to distinguish it from among the overlapping symptoms seen in other disorders involving the spine, hip, and pelvis. As such, it is generally recognized as a diagnosis of exclusion.
A definitive diagnosis of piriformis syndrome remains difficult because of evolving characterizations of this disease entity over time and the lack of a “gold standard” diagnostic test. A synthesis of the literature leads us to propose the new criteria for diagnosis shown in Box 24.1 .
- 1.
Marked pain in the gluteal region
- 2.
Pain may be focal or radiate into the posterior thigh
- 3.
Tenderness to palpation over the sciatic notch
- 4.
Active contraction or passive stretching of the piriformis muscle provokes concordant pain
- 5.
There is no alternative explanation for the pain
These criteria aim to provide a more clinically applicable approach to piriformis syndrome. Although there is a limited role for therapeutic injections or even surgery, the mainstay of treatment for this condition, once identified using these criteria, is properly directed physical therapy.
The goal of this chapter is to assist the clinician in defining and properly diagnosing this syndrome, to understand the strength of the evidence for proposed treatments, and then to apply an optimal approach to reducing pain and restoring function.
Presentation
Anatomy
The piriformis muscle originates from the anterior sacrum and sacroiliac joint, passes transversely through the greater sciatic foramen via the sciatic notch, and inserts on the greater trochanter ( Fig. 24.1 ). The muscle is innervated by the ventral rami of S1 and S2 (and L5 to a lesser extent), which join to form the nerve to the piriformis. The muscle receives its vascular supply predominantly from a branch off the inferior gluteal artery. When the hip is in extension, the piriformis muscle externally rotates the femur. When the hip is in flexion, the piriformis muscle acts as a weak hip abductor. In greater than 80% of the population, the sciatic nerve traverses beneath the piriformis muscle and exits the pelvis through the greater sciatic foramen. However, several cadaveric studies have demonstrated variable anatomy in a subset of individuals, including 10%–15% of the population with a split sciatic nerve, which travels both through and beneath the piriformis muscle. Less common variations include a split nerve traveling through and above the muscle, a complete nerve piercing through the muscle, and a complete nerve traversing above the muscle ( Fig. 24.2 ). It is unclear whether or not there is a correlation between these anatomic variants and the development of the syndrome.
Historical Features
Piriformis syndrome presents with a constellation of symptoms that often overlaps with other causes of gluteal pain, such as lumbosacral radiculopathy or sacroiliac joint dysfunction. “Typical” piriformis syndrome often presents as intermittent, sharp/shooting gluteal pain with or without radiation to the posterior thigh. Insidious onset of pain is the most common presentation, with acute pain (e.g., as the result of trauma) being far less common. Classically, the pain may be exacerbated by direct pressure to the region, prolonged sitting, rising from a seated position, stair climbing, and activation or stretching of the piriformis and surrounding musculature. Alleviating factors include changing to a nonpainful position and rest from provocative activity.
Physical Features
Physical examination for piriformis syndrome should evaluate for range of motion, strength, and functional movement patterns that may result in disproportionate strain of the piriformis muscle. The region over the sciatic notch must be palpated to elicit tenderness. A complete evaluation should include focused examination maneuvers that subject the piriformis muscle to active or passive stress. When performing the following tests, they are generally considered “positive” with reproduction of the patient’s concordant gluteal pain. The examination maneuvers are depicted in Fig. 24.3 .
The FAIR test (flexion, adduction, internal rotation) is performed in the supine or side-lying position. The examiner passively brings the patient’s affected side into 90 degrees of hip flexion and 60–90 degrees of knee flexion. The hip is then internally rotated and adducted to place tension on the piriformis muscle.
The Lasègue maneuver describes the passive flexion of the hip to 90 degrees and then extending the knee to create neural tension on the sciatic nerve. Note that this is distinct from the straight leg raise test, which involves passively raising the affected limb (with the knee already extended) to reproduce pain in the 30–70 degree range.
The Freiberg maneuver involves passive internal rotation of the extended hip joint, placing tension on the piriformis muscle.
The Beatty maneuver places the patient in the lateral decubitus position, with the affected side up and the knee resting on the examination surface. The piriformis muscle is then activated as the patient abducts the hip, holding the knee “several inches” off the examination surface.
The Pace maneuver activates the piriformis muscle through resisted active abduction of the hip in the seated position.
Guide to the clinician
Piriformis syndrome presents as insidious-onset gluteal pain that is exacerbated by the activation or stretching of the muscle. Variable anatomic relationships between the piriformis and sciatic nerve have been described and are proposed to predispose a subset of the population to this syndrome. Various diagnostic maneuvers for piriformis syndrome have been described, including the FAIR test, as well as the Lasègue, Freiberg, Beatty, and Pace maneuvers. It should be noted that none of these described maneuvers have been validated in the literature.
Diagnostic Criteria
Throughout the history of piriformis syndrome, there have been multiple proposed definitions of this condition. To date, they remain controversial, with blurred diagnostic criteria. In the following discussion, we highlight two historically important definitions that are often referenced in the literature. In addition, we propose a new set of criteria for piriformis syndrome that emphasizes a myofascial pain component, is more clinically applicable, and better reflects our current understanding of this disease entity.
Robinson
In the early 20th century, the source for sciatic-type pain was disputed. A seminal paper in 1934 by Mixter and Barr described “sciatica” as being caused by intervertebral disc herniation. In that era, other competing theories regarding the etiology of sciatica included the sacroiliac joint, an intrinsic disorder of the sciatic nerve itself, or compression by the piriformis muscle. As early as 1928, the literature had described a relationship between the piriformis muscle, the sciatic nerve, and sciatic-type pain, with detailed analyses of hip and pelvis anatomy using cadavers and radiographs.
It was not until 1947 that the term “pyriformis [sic] syndrome” was first used by Robinson to describe the particular type of sciatic pain caused by “an abnormal condition of the pyriformis muscle” as opposed to pathology originating in the lumbosacral spine. Robinson initially described the syndrome as having six “cardinal features,” including a history of trauma to the sacroiliac/gluteal region, pain in the region of the sacroiliac joint/piriformis muscle radiating down the lower limb causing difficulty with ambulation, symptom exacerbation with bending/lifting, a “sausage-like” mass that is tender to palpation, a positive Lasègue sign, and gluteal atrophy. Although Robinson’s labeling of piriformis syndrome was seminal, the clinical field has largely moved on from his description.
Stewart
In 2003, Stewart characterized piriformis syndrome as a sciatic neuropathy with five strict criteria. He defined the syndrome as requiring signs/symptoms of sciatic nerve damage, electrodiagnostic evidence of such damage, normal imaging studies of the back/pelvis/sciatic notch, sciatic compression by the piriformis muscle confirmed by surgical exploration, and relief of symptoms after surgical decompression. Given the exceptionally restrictive requirements of both electrodiagnostic and surgical confirmation, piriformis syndrome is an exceedingly rare phenomenon under Stewart criteria, with only six documented cases meeting all five criteria.
Proposed New Criteria
Millions of people with gluteal pain are diagnosed with “piriformis syndrome” every year, which is in stark contrast to the rarity of true sciatic neuropathy caused by impingement by the piriformis muscle. This discrepancy stems in part from the historical application of “piriformis syndrome” in reference to piriformis-mediated true sciatic neuropathy (e.g., axonal injury), sciatic neural tension at the level of the piriformis, or piriformis-mediated myofascial pain, the last which may be conceptualized as “piriformis myalgia.” As such, we propose new, modern criteria for piriformis syndrome (see Box 24.1 ), which provide a basis for clinically relevant identification and treatment of the spectrum of this syndrome, from the myofascial to neuropathic variants.
Guide to the clinician
The criteria set by Robinson (1947) and Stewart (2003) are generally not used in everyday practice. Our new criteria ( Box 24-1 ) capture the myofascial and neuropathic variants of piriformis syndrome:
- 1.
Marked pain in the gluteal region
- 2.
Pain may be focal or radiate into the posterior thigh
- 3.
Tenderness to palpation over the sciatic notch
- 4.
Active contraction or passive stretching of the piriformis muscle provokes concordant pain
- 5.
There is no alternative explanation for the pain.
Course
The symptoms of piriformis syndrome often improve with the avoidance of exacerbating activities and correction of relevant strength and/or flexibility deficits. A majority of cases respond to conservative management, including physical therapy and pharmacologic therapy. Interventional management (e.g., injection therapy) is available but not commonly used. Surgical options are entertained only very rarely for recalcitrant cases.
Differential Diagnosis
Before arriving at the diagnosis of piriformis syndrome, a wide differential for conditions causing gluteal pain should be considered. Pain in the gluteal region may not only be generated locally, but also be referred from the surrounding structures. Given the extensive differential, it is helpful to categorize the differential diagnosis of gluteal pain by whether or not there is concomitant back pain.
The presence of low back pain suggests pathology involving the lumbosacral spine and its supporting structures. Crucially, pain accompanied by true neurologic deficit (e.g., weakness, sensory disturbance, abnormal reflexes), particularly in a myotomal or dermatomal distribution, should prompt further workup for a neuropathic process (e.g., lumbosacral radiculopathy or neurogenic claudication secondary to spinal stenosis). Bony sources for low back pain include facet arthropathy, spondylolysis, spondylolisthesis, sacroiliac joint dysfunction, and sacral stress fracture. Soft tissue sources for low back pain include lumbar discogenic pain, iliolumbar ligament sprain, muscular strain, and myofascial pain with active trigger points.
In the absence of low back pain, gluteal pain is likely generated by local buttock, hip, or pelvic structures. As with low back pain, the presence of neurologic deficit should prompt evaluation for a neuropathic process (e.g., lumbosacral plexopathy, sciatic neuropathy, or other peripheral mononeuropathy). Neurologic signs and symptoms should not be present in piriformis-mediated myofascial pain.
In considering the broad differential for piriformis syndrome, posterior buttock pain may originate from muscular strain (e.g., gluteal muscles, piriformis, proximal hamstring), ischial bursitis, or ischiofemoral impingement syndrome. Pain at the ischial tuberosity suggests proximal hamstring tendinopathy or ischial bursitis. Ischiofemoral impingement syndrome is a rare impingement phenomenon involving the quadratus femoris muscle as it passes through the ischiofemoral space and may be provoked with the ischiofemoral impingement test (pain with passive extension of the neutral/adducted hip with the patient in the lateral position) and/or the long stride walking test (pain with terminal hip extension during long-stride walking).
Lateral buttock/hip pain may indicate greater trochanteric pain syndrome (GTPS) or iliotibial (IT) band syndrome. GTPS encompasses disorders of the gluteus medius/minimus, trochanteric bursitis, and external snapping hip. Single leg standing and squatting may reveal static or dynamic unleveling of the pelvis, suggesting gluteus medius/minimus dysfunction with or without associated bursitis. IT band syndrome most often presents with pain distally and may also involve discomfort of the anterolateral hip. Examination maneuvers for IT band syndrome include Ober test and Noble compression test. External snapping hip refers to maltracking of the gluteus maximus or IT band complex over the greater trochanter.
Medial hip/buttock pain suggests pathology of the hip joint, gluteus maximus, adductor muscles, or sacrotuberous ligament. Anterior hip/groin pain suggests intraarticular hip pathology, such as osteoarthritis, labral tears, femoroacetabular impingement, femoral stress fracture, or avascular necrosis. In select cases, intraarticular hip pathology can also cause pain in the posterior hip/buttock or through the anterior thigh to knee. Extraarticular sources for anterior pain include hip flexor tendinopathy (e.g., iliopsoas, rectus femoris), osteitis pubis, or athletic pubalgia. Note that the FAIR test is also used in the examination of the hip joint; however, in the case of intraarticular hip pathology, the maneuver typically reproduces anterior/groin pain, as opposed to posterior pain as with piriformis syndrome.
Rare Conditions
When evaluating a patient with gluteal pain and back pain, it is important to consider rare but serious conditions, such as infections (e.g., epidural abscess), cancer (e.g., multiple myeloma), or acute neurologic compromise (e.g., cauda equina syndrome). “Red flag” signs and symptoms include fever, unexplained weight loss, loss of bowel/bladder control, perineal sensory disturbance, and nocturnal pain. Vertebral compression fractures should be considered in patients of advanced age, with poor bone health or recent trauma. In patients with suboptimal bone health, such as those with osteoporosis, a history of chronic corticosteroid use, or suspected female athlete triad, it is important to consider pelvic insufficiency fractures or bone stress injuries as a source for pain. The literature also describes rare piriformis syndrome secondary to space-occupying lesions (e.g., intrapiriformis lipoma ).
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