Introduction
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 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.
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.
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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%.
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.
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.1 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.
Clinical
History
Patients with piriformis syndrome have the following symptomatic history:
- Chronic pain in the buttocks
- This pain may radiate to the lower leg and worsens with walking or squatting.
- This pain may imitate LBP.
- Pain with bowel movements
- Pain in the labia majora in women; pain in the scrotum in men
- Dyspareunia in women
- Pain when getting up from bed
- Pain exacerbated by hip adduction and internal rotation
- Intolerance to sitting
Physical
Piriformis syndrome is a diagnosis of exclusion.
- At physical examination, the most important factor that differentiates sciatic pain from piriformis syndrome is the absence of neurologic deficit in piriformis syndrome.
- Herniation or disc compression results in intraneural derangement of the nerve root structure, whereas piriformis syndrome causes a qualitative epineural irritation.
- In piriformis syndrome, the only true-positive sign is tenderness over the gluteal region.
- The pain can be reproduced with maximum elongation of the piriformis muscle in flexion, adduction, and internal rotation of the hip.
- Weakness can be observed with resisted external rotation and abduction of the hip.
- Several authors describe the use of the following signs in diagnosing piriformis syndrome:
- Lasegue sign: Pain is present in the vicinity of the greater sciatic notch during extension of the knee with the hip flexed to 90 º, tenderness to palpation of the greater sciatic notch is noted.
- Pace sign: Pain and weakness are present on resisted abduction-external rotation of the thigh.
- Freiberg sign: Pain occurs with passive internal rotation of the extended thigh when the patient is supine.
- Robinson, who first described the syndrome, stated that piriformis syndrome had 6 cardinal features:
- Positive Lasegue sign
- Sausage-shaped mass over the piriformis muscle
- Gluteal atrophy in chronic cases
- Trauma to the region
- Pain in the sacroiliac joint region, gluteal muscles, or greater sciatic notch
- Pain exacerbated by lifting and relieved by traction on the affected extremity
- Beatty reproduced the pain of piriformis syndrome in the following way2 :
- The patient lies with the painful side up and the involved leg flexed.
- The knee of the affected side rests on the table. Pain in the buttocks is reproduced when the patient lifts the leg and knee slightly above the table.
- Other authors conclude that pain can be reproduced in the lateral pelvic wall by means of rectal or pelvic examination.
Causes
- Trauma to the buttocks or gluteal region is the most common cause of piriformis syndrome.
- Skiers, truck drivers, tennis players, and long-distance bikers are at high risk.
- In Morton foot, the prominent head of the second metatarsal causes foot instability and a reactive contraction of the external rotators of the hip during gait.
- Spinal stenosis can lead to bilateral piriformis tenderness.
- Anatomic variations of the divisions of the sciatic nerve above, below, and through the belly of the piriformis muscle may be causative factors.
More on Piriformis Syndrome |
 Overview: Piriformis Syndrome |
| Differential Diagnoses & Workup: Piriformis Syndrome |
| Treatment & Medication: Piriformis Syndrome |
| Follow-up: Piriformis Syndrome |
| References |
| Next Page » |
References
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Further Reading
Keywords
piriformis syndrome, hip pocket neuropathy, sciatic neuritis, wallet neuritis, lower back pain, low back pain, LBP, periarthritis of the anterior sacroiliac joint, piriformis muscle, piriformis hypertrophy, sciatic nerve entrapment, herniated nucleus pulposus, muscle spasm due to chronic or overuse injury, sciatica, Morton foot, spinal stenosis, nerve entrapment syndromes
