Piriformis Syndrome

Information on Piriformis Syndrome

Get the correct diagnosis on the sciatic nerve pain you’re experiencing.

Piriformis Syndrome may be responsible for 0.3% to 6% of all cases of low back pain and/or sciatica, which with estimated new cases of low back pain and sciatica at 40 million annually, the incidence of piriformis syndrome would be roughly 2.4 million per year.
Piriformis syndrome has symptoms that include pain, tingling, or numbness in the buttock and down the leg which may get worse after sitting for prolonged periods. The piriformis muscle is located in the buttock region and can irritate the nearby sciatic nerve and cause pain, numbness, and tingling along the back of the leg and into the foot (similar to sciatic pain). The sciatic nerve runs just adjacent to the piriformis muscle, which functions as an external rotator of the hip. Whenever the piriformis muscle is irritated or inflamed, it also affects the sciatic nerve, which then results in sciatica-like pain. Causes of piriformis syndrome are unknown, but suspected causes include a muscle spasm in the piriformis muscle itself, tightening or swelling of the muscle in response to injury or spasm, or bleeding in the area of the piriformis syndrome.
The diagnosis of piriformis syndrome is not easy. Other conditions that can also mimic the symptoms of piriformis syndrome include lumbar canal stenosis, disc inflammation, or pelvic causes. The treatment for piriformis syndrome is much less invasive and severe than the treatment of herniated lumbar discs. However, many doctors never consider piriformis syndrome as a possible diagnosis. Many physicians who are aware of it are uncertain how to properly diagnose and treat it.
Dr. Aaron Filler credits the advent of MR Neurography and open MR-injection techniques with new large-scale outcome as leading to the successful diagnosis and treatment of many more piriformis syndrome sufferers.

Anatomy of Piriformis Muscle and Sciatic Nerve

This drawing illustrates the important anatomy for piriformis syndrome.
The nerve-related leg pain of Sciatica is often due to piriformis muscle syndrome. Unlike the sciatica from a herniated disk, there is often little or no back pain while buttock pain predominates. The pain is worse when sitting, relieved by standing or walking, and often extends no farther down the leg than the ankle or mid-foot. When toes are involved, it usually affects all five toes.
This drawing illustrates the important anatomy for piriformis syndrome and shows how certain leg positions pull the piriformis muscle up against the sciatic nerve causing buttock pain and radiating leg pain.

Anatomy of Piriformis Muscle and Sciatic Nerve

Animation: Critical physical exam for muscle based piriformis syndrome.
The patient’s foot is placed lateral to the contralateral knee. Resisted abduction or adduction against the examiner’s hand may reproduce the symptoms. Straight leg raising is typically negative.
There is often relief obtained by traction on the involved leg, particularly by pulling upwards at a ten to twenty degree angle and towards the contralateral side by a similar amount. The distribution of symptoms typically involves both L5 (big toe) and S1 (small toe) components because this a pan-sciatic syndrome. The symptoms often progress no further than the ankle in distinction to sciatica from a lumbar disk which typically radiates into the toes.

Image Anatomy for Injections

Animation: This T1 weighted axial MRI scan shows the anatomy used to guide the injection of the piriformis muscle in an Open MRI scanner.

Diagnosis of Piriformis Syndrome

MR Neurography Image Findings in Piriformis Syndrome

Image Findings from MR Neurography
Animation: These images demonstrate image findings observed in severe cases of piriformis syndrome when MR Neurography is used with soft tissue MR pelvis imaging protocols.
(A) Coronal T2-weighted neurographic image section. The yellow arrows indicate the sciatic nerves at the point of passage through the sciatic notch – the sciatic nerve on the left
(B) Axial T1-weighted MR image showing asymmetry in the size of the piriformis muscles. This may reflect either hypertrophy on the right or atrophy and spasm on the left. Muscle spasm may change the shape and hardness of a muscle without altering its total volume.
(C) Curved reformat image of the sacral spinal nerves, lumbo-sacral plexus and proximal sciatic nerves again showing the hyperintensity consistent with irritation of the left sciatic nerve and its antecedents.
(D) Axial T2-weighted image showing hyperintensity and loss of fascicluar detail in the left sciatic nerve at the point of passage through the sciatic notch.

Treatment of Piriformis Syndrome

Outpatient minimally invasive surgical treatment

New minimal access, outpatient surgery greatly improves outcome and reduces recovery time
Animation: Elements of piriformis surgery including incision locations.
Piriformis surgery is now a small procedure which can be carried out under local anaesthetic as an outpatient.
Traditional piriformis surgery is a large and debilitating operation but no patient should be having these operations today. There were two types of traditional piriformis surgery, one involves a large lateral hip incision similar to the approach used for a hip replacement surgery. The second involves a very large incision and involves completely detaching all of the gluteal muscles from the iliac crest. Both of these types of surgery result in weeks of debilitation, walking on crutches and pain, with only limited success treating the original problem.
The new type of “minimal access surgery” developed at NIMA by Dr. Aaron Filler involves only a small incision, and in most cases can be performed on an outpatient basis. Large scale formal outcome trials involving hundreds of patients with follow-up out to eight years show no detectable effect on normal walking in any of the patients – this a great change from the traditional surgery that often leaves permanent problems with gait. Recovery takes only a few days in most patients.
Those patients who have positive physical exam findings, positive MR neurography findings and a clear positive response to MRI guided piriformis injection have had a 85% to 90% good to excellent outcome.

Open MRI Guided Injection of the Piriformis Muscle

Piriformis Injections
Animation: Open MRI provides the necessary accuracy and reliability to safely inject the piriformis muscle with therapeutic and diagnostic agents.
The piriformis muscle is a relatively small structure located as far as eight inches below the surface of the buttock. If a blind injection misses the muscle, the injection test is meaningless. Immediately deep to the piriformis muscle is the sciatic nerve and the colon so misplacement of the needle may lead to significant complications.
Dr. Aaron Filler’s use of open MRI image guidance makes this a safe, reliable and accurate procedure. In these images, the physician’s finger is seen indicating the angle of approach in the first image. In subsequent views, local anesthetic is injected in the skin and then a titanium Lufkin needle is introduced and advanced into the piriformis muscle. An injection of Marcaine (10cc of 0.5% solution of this long-acting local anesthetic) and 1cc of steroid medication is then seen darkening the interior of the muscle in the last two image frames.
These flash MRI images each take about 12 seconds to complete. In about 20% of cases the injection is therapeutic and the piriformis syndrome resolves completely and permanently. In others, the injection needs to repeated in a few months, and in still others, it last only a few days. In this category, surgery may be required to maintain the pain relief.
Thanks to Dr. Filler’s technique, piriformis surgery is now a small procedure which can be carried out under local anesthetic as an outpatient.
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