The piriformis muscle is a small external rotator muscle on the back of the hip joint deep to the large and powerful gluteal muscle which power hip movement stability of the pelvis. The sciatic nerve lies in close proximity to this muscle as it exits the pelvis and descends down the back of the leg. In some patients, an anatomical variation exists where the nerve passes through two heads of the piriformis muscle. Piriformis syndrome occurs when the sciatic nerve is compressed or otherwise irritated as it passes adjacent or through the muscle. Like carpal tunnel syndrome where the median nerve is compressed by ligaments in the wrist, this is considered to be an "entrapment neuropathy."
The symptoms of piriformis syndrome may mimic those of conventional sciatica caused by a herniated disc in the lower back. These include back pain, buttock pain, leg pain numbness and tingling. Pain may be precipitated or aggravated by activities that stretch or require contraction of the piriformis muscle.
The diagnosis of piriformis syndrome can be a challenge as there are limited reproducible physical exam tests or imaging studies that reliably detect its presence. Therefore it is sometimes considered a diagnosis of exclusion when sciatic like symptoms are present in the absence of a cause attributed to lumbar spine problems. Because of the absence of reliable imaging or other diagnostic studies, piriformis syndrome is often misdiagnosed and treated as other causes of hip and leg pain leading to frustration on the part of the patient, physician and therapist. The role of diagnostic imaging largely resides in rule out other diagnoses.
Piriformis syndrome is thought to relate weak or underactive gluteal muscles. This can occur from inactivity (prolonged sitting) as well as from activities that favor hip flexion over hip abduction. These include activities that favor forward movement like running. The ration of hip flexion to hip abduction increases, the piriformis muscle has to work harder to compensate for the underactive gluteal muscles. Hypertrophy or enlargement of the muscle can lead to nerve compression both through stronger muscle contraction, greater muscle bulk but also a tighter muscle.
The goal of treatment of properly diagnosed piriformis syndrome is to address these specific deficits. Stretching tight muscles on the back of the hip may relieve pressure on the nerve. Hip abductor strengthening may also improve the ration of strength between flexion and abduction and reduce the stress on the piriformis muscle. Deep tissue massage, myofascial release techniques and other inflammation reducing modalities can also help alleviate the symptoms. Obvious to the treatment objectives is to avoid the offending activity that appears and cause or aggravate the symptoms.
When these methods fail, injection therapy of either cortisone or Botulinum toxin (BOTOX) has been described. This should be done under ultrasound guidance to visualize the nerve and prevent damage to the nerve from direct injection. The goal of a cortisone injection is to reduce local inflammation of the nerve caused by the entrapment. Botox on the other hand temporarily paralyzes the muscle to prevent entrapment that worsens with muscle spasm and contraction.
Finally, surgical treatment may be considered as a last resort. Surgery entails release of the tendon from its insertion on the back on the femur bone. This eliminates tension on the muscle and thereby reduces pressure on the nerve. It is critical that all other diagnoses have been considered and ruled out prior to undertaking surgical treatment. Selective injection of the sacroiliac and hip joints may be advisable to rule out pain arising from either of these locations. MRI imaging of the hip and spine is also advisable to rule out other sources of compression on the sciatic nerve.