Pain shooting down the leg is a common complaint causing people to seek medical care. The most likely cause of pain radiating into the leg is irritation of the spinal nerves at the lumbar spine level (sciatica). Another less common, and often missed, cause of sciatica is piriformis syndrome.
The piriformis (from Latin pirum forma –“pear–shaped”) muscle is connected to the sacrum (tailbone) on one side, and the greater trochanter of the femur on the other. The primary function of the piriformis muscle is external rotation of the leg, turning the foot outward. So how does the piriformis muscle cause sciatica symptoms? The rather simple explanation for this is the location of the muscle in relation to the sciatic nerve. The sciatic nerve runs just beneath the piriformis in most people, and in approximately 15 percent of the population the nerve passes straight through the muscle. Due to this relationship, spasms of the piriformis muscle can cause irritation or even entrapment of the sciatic nerve.
Symptoms of piriformis syndrome include shooting pain down the back of the leg (usually only on one side), numbness, tingling and rarely weakness. Due to the proximity of other nerves, piriformis spasm can also cause numbness in the groin area and even urinary/bowel incontinence. Aggravating factors include sitting on a hard surface for long periods, running and riding a bicycle. The muscle may be injured by direct trauma due to a fall onto the buttock, or subsequent bleeding after an injury that will then irritate the muscle. Other causes include the complex relationship between the piriformis and other muscles of the pelvis and the sacroiliac joint. Oftentimes, the cause of piriformis syndrome is unknown.
There is not a definitive way to diagnose the syndrome. Diagnosis begins with a complete history and physical exam. Indicators of piriformis syndrome are pain radiating down the back of the leg and tenderness at the base of the buttock (the “sciatic notch”). A diagnostic injection may be done to confirm the diagnosis; if the pain is relieved with the injection it is reasonable to conclude that the piriformis muscle is the pain generator. Radiographic studies are rarely helpful in making the diagnosis; although, they are important to eliminate other causes of buttock and leg pain. It is important to rule out the more common spinal nerve root irritation which can be done with a physical exam and an MRI of the lumbar spine.
Piriformis syndrome treatment is primarily with medications and physical therapy. Medications include anti–inflammatories and muscle relaxants. Stretching and physical therapy are the mainstay of treatment, because these modalities address the underlying cause – piriformis spasm. Physical therapy modalities include heat, ultrasound, massage and stretching. If pain is not relieved with conservative treatments, injection of the piriformis muscle may be done. Most commonly, local anesthetic (lidocaine) and steroid are injected to loosen up the muscle and decrease irritation of the sciatic nerve. Injections may be done with EMG or fluoroscopic guidance to ensure the medication is going into the muscle. Botulinum toxin (Botox) has also been injected into the piriformis muscle with success. In severe refractory cases, surgery is a last resort. Surgical correction involves cutting the muscle tendon at the attachment to the femur or cutting through the muscle itself to relieve pressure on the sciatic nerve.
Fortunately, piriformis syndrome generally responds well to physical therapy, pain medications and avoidance of aggravating factors. It is something to consider if you or someone you know is having pain down the back of their leg and the diagnosis is unclear or not responsive to typical sciatica treatment.
