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Piriformis Syndrome

  • Author: Shishir Shah, DO; Chief Editor: Sherwin SW Ho, MD  more...
 
Updated: Aug 19, 2015
 

Background

Low back pain (LBP), is ubiquitous. An estimated 30-45% of persons aged 18-55 years have some form of back pain in their lifetime. LBP most commonly involves one of the following conditions: sciatic nerve entrapment, herniated nucleus pulposus, direct trauma, muscle spasm due to chronic or overuse injury, or piriformis syndrome.

Piriformis syndrome (see the image below) is characterized by pain and instability. The location of the pain is often imprecise, but it is often present in the hip, coccyx, buttock, groin, or distal part of the leg. The history and physical findings are key elements in differentiating the more common forms of LBP and piriformis syndrome. The literature and general knowledge on piriformis syndrome is limited, compared with that of sciatica or disc herniation. However, the common findings associated with piriformis syndrome are agreed upon.

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).

Yeoman first described piriformis syndrome in 1928 as periarthritis of the anterior sacroiliac joint. The history of this condition stems from one of many causes of lower back and leg pain. Many patients who underwent unsuccessful surgery in the lumbosacral region were later found to have piriformis syndrome.

For patient education resources, see the Osteoporosis and Bone Health Center and Back, Ribs, Neck, and Head Center, as well as Back Pain.

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Epidemiology

Frequency

United States

The female-to-male incidence ratio of piriformis syndrome is 6:1. In one study at a regional hospital, 45 of 750 patients with LBP were found to have piriformis syndrome. Another author estimated that the incidence of piriformis syndrome in patients with sciatica is 6%.

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Functional Anatomy

The function of the piriformis muscle is to externally rotate and abduct the thigh. The sacral plexus is closely associated with the anterior surface of the piriformis muscle. The lumbosacral trunk and the ventral rami of the first 3 sacral nerves form the sacral plexus. The sciatic nerve passes inferior to the piriformis muscle.

The sciatic nerve exits the pelvis via 4 routes: (1) The nerve passes anteriorly to the piriformis between the rims of the greater sciatic foramen. (2) The peroneal portion of the sciatic nerve passes through the piriformis; the tibial portion passes anterior to the piriformis muscle. (3) The peroneal branch of the sciatic nerve loops above and posterior to the piriformis muscle, whereas the tibial branch passes anterior to the piriformis muscle. (4) The undivided sciatic nerve penetrates the piriformis muscle.

Dysfunction of the piriformis muscle can cause signs and symptoms of pain in the sciatic nerve distribution, that is, in the gluteal area, posterior thigh, posterior leg, and lateral aspect of the foot.[1]

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Sport-Specific Biomechanics

Gait mechanics help in demonstrating the physiologic features of piriformis hypertrophy. When a person takes a step forward, the extremity moves from external rotation to internal rotation, and the piriformis muscle lengthens. This stretching is followed by reflex contraction. A second contraction in the initially stretched piriformis muscle occurs when the opposite foot swings forward. This gait pattern leads to hypertrophy, and the dual contraction is further exacerbated by the stretching of the piriformis muscle on the side of a shortened leg.

More commonly, piriformis syndrome is secondary to inflammation due to gluteal trauma or spasm. The effect of this inflammatory process on the sciatic nerve is chemical rather than mechanical. Several theories suggest that the following are key factors in the muscle hyperfunction or spasm that leads to an interstitial myofibrositis: extravasation of blood; release of serotonin from platelets; and prostaglandin E, serotonin, bradykinin, and histamine release.

Although no general consensus about the etiology and pathophysiology of piriformis syndrome exists, many physicians and physical therapists attribute this syndrome to a specific mechanism involving the sciatic nerve. For example, Benson and Schutzer attributed the syndrome to blunt trauma to the buttocks that results in hematoma formation and subsequent scarring between the sciatic nerve and the short external rotators.[2] Entrapment of the sciatic nerve at the sciatic trunk (where it leaves the pelvis and crosses the greater sciatic notch) is an infrequent cause. This entrapment can also occur as a result of an enlarged hypertrophic piriformis, an inflamed piriformis muscle, tumors, cysts, and pseudoaneurysms.

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Contributor Information and Disclosures
Author

Shishir Shah, DO Consulting Staff, Comprehensive Woundcare, Banner Baywood Hospital

Shishir Shah, DO is a member of the following medical societies: American Academy of Family Physicians, American Medical Association, American Osteopathic Association

Disclosure: Nothing to disclose.

Coauthor(s)

Thomas W Wang, MD Consulting Staff, Department of Occupational Medicine, Kaiser-Permanente

Thomas W Wang, MD is a member of the following medical societies: American Academy of Family Physicians

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Russell D White, MD Clinical Professor of Medicine, Clinical Professor of Orthopedic Surgery, Department of Community and Family Medicine, University of Missouri-Kansas City School of Medicine, Truman Medical Center-Lakewood

Russell D White, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Family Physicians, American Association of Clinical Endocrinologists, American College of Sports Medicine, American Diabetes Association, American Medical Society for Sports Medicine

Disclosure: Nothing to disclose.

Chief Editor

Sherwin SW Ho, MD Associate Professor, Department of Surgery, Section of Orthopedic Surgery and Rehabilitation Medicine, University of Chicago Division of the Biological Sciences, The Pritzker School of Medicine

Sherwin SW Ho, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, Arthroscopy Association of North America, Herodicus Society, American Orthopaedic Society for Sports Medicine

Disclosure: Received consulting fee from Biomet, Inc. for speaking and teaching; Received grant/research funds from Smith and Nephew for fellowship funding; Received grant/research funds from DJ Ortho for course funding; Received grant/research funds from Athletico Physical Therapy for course, research funding; Received royalty from Biomet, Inc. for consulting.

Additional Contributors

Joseph P Garry, MD, FACSM, FAAFP Associate Professor, Department of Family Medicine and Community Health, University of Minnesota Medical School

Joseph P Garry, MD, FACSM, FAAFP is a member of the following medical societies: American Academy of Family Physicians, American Medical Society for Sports Medicine, Minnesota Medical Association, American College of Sports Medicine

Disclosure: Nothing to disclose.

References
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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).
 
 
 
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