Dictionary Thesaurus Word Dynamo Quotes Reference Translator Spanish

Piriformis syndrome

Piriformis syndrome is a neuromuscular disorder that occurs when the sciatic nerve is compressed or otherwise irritated by the piriformis muscle. This causes pain, tingling and numbness in the buttocks and along the course of the sciatic nerve. The syndrome may result from anatomical variations in the muscle-nerve relationship, or from overuse or strain.

Recent uncontrolled studies advanced theories behind the disorder. However, following a large scale formal prospective outcome trial using Class A study design as outlined by the American College of Physicians, the weight of the evidence-based medicine is that piriformis syndrome should be considered as a possible diagnosis when sciatica occurs without a clear spinal cause

The need for controlled studies is supported by studies of spinal disk disease that show a high frequency of abnormal disks in asymptomatic patients.

Pathophysiology

In 15% of the population the sciatic nerve passes through the piriformis muscle, rather than underneath it. These people have been reported by some studies to have a greater incidence of piriformis syndrome than does the general population. Some researchers discount the importance of this relationship in the etiology of the syndrome.

Inactive gluteal muscles also facilitate development of the syndrome. These are important in both hip extension and in aiding the piriformis in external rotation of the femur. A major cause for inactive gluteals is unwanted reciprocal inhibition from overactive hip flexors (psoas major, iliacus, and rectus femoris). This imbalance usually occurs where the hip flexors have been trained to be too short and tight, such as when someone sits with hips flexed, as in sitting all day at work. This deprives the gluteals of activation, and the synergists to the gluteals (hamstrings, adductor magnus, and piriformis) then have to perform extra roles they were not designed to do. Resulting hypertrophy of the piriformis then produces the typical symptoms.

Another purported cause for piriformis syndrome is stiffness, or hypomobility, of the sacroiliac joints. The resulting compensatory changes in gait would then result in shearing of one of the origins of the piriformis, and possibly some of the gluteal muscles as well, resulting not only in piriformis malfunction but in other low back pain syndromes as well.

Piriformis syndrome can also be caused by overpronation of the foot. When a foot overpronates it causes the knee to turn medially, causing the piriformis to activiate to prevent over-rotating the knee. This causes the piriformis to become overused and therefore tight, eventually leading to piriformis syndrome.

It is most frequently associated with falling injury.

Diagnosis

Piriformis syndrome is diagnosed by the presence of sciatica - radiating pain in the posterior thigh and lower leg - and the physical exam finding of tenderness in the area of the sciatic notch. Magnetic resonance neurography is a medical imaging technique that can show the presence of irritation of the sciatic nerve at the level of the sciatic notch where the nerve passes under the piriformis muscle. Neurography can also determine whether or not a patient has a split sciatic nerve or a split piriformis muscle - this may be important in getting a good result from injections or surgery. Image guided injections carried out in an Open MRI scanner can accurately relax the piriformis muscle to test the diagnosis. Other injection methods such as blind injection, flouroscopic guided injection, ultrasound, or EMG guidance can work but are not as reliable. Unlike spine injections, there is no bony target that can show up on X-ray, so fluoroscopy can't show the injection target. It has been difficult to achieve reliable injections with EMG and ultrasound because these methods are not specific to the piriformis muscle. CT guided injections can work well but provide a very high dose of radiation to the pelvis and there is no possibility of shielding sensitive tissues from the radiation.

Treatment

Treatment usually begins with stretching exercises and massage, and avoidance of contributory activities, such as running and bicycling. Some clinicians recommend formal physical therapy, including the teaching of stretching techniques, massage, and strengthening of the core muscles (abs, back, etc.) to reduce strain on the piriformis. Stretches exercises will target the piriformis, but may also include the hamstrings and hip muscles, in order to adequately reduce pain and increase range of motion.

Patients with piriformis syndrome may also find relief from ice and heat. Ice can be helpful when the pain starts, or immediately after an activity that causes pain. This may be simply an ice pack, or ice massage. Alternating heat and ice is often helpful.

Anti-inflammatory drugs and/or corticosteroid injections can be used. Rarely surgery may be recommended. The prognosis is generally good. Custom foot orthotics also help with both treatment and prevention. Gait correction can reduce the use of the piriformis, allowing the muscle to relax and heal itself. Ultrasound is another option, providing deeper heat than heat packs alone.

Minimal access surgery using newly-reported techniques has also proven successful in a large-scale formal outcome published in 2005.