Guiding Piriformis Injections with Sciatic Nerve Stimulator
The sciatic nerve travels underneath the piriformis muscle in the deep buttock area. In some people, the nerve passes through the muscle belly. Prolonged or repeated contractions of the piriformis muscle compresses or irritates the sciatic nerve enough to cause pain, numbness, and tingling in the buttock. The symptoms may travel down the leg along the pathway of the sciatic nerve. This condition is called piriformis syndrome.

Treatment for piriformis syndrome starts with analgesics (pain relievers) and physical therapy. The therapist helps the patient change posture that might be contributing to the problem. Stretching the piriformis muscle often helps, as well as mobilizing the sciatic nerve. The therapist guides the patient through these steps, but in some cases, the painful symptoms persist.

Doctors turn to injections of the piriformis next. Steroids, local anesthetics (numbing agents), and botulinum toxin (BOTOX) may be used. BOTOX is a paralyzing agent that works temporarily to help stop muscle contractions of the piriformis.

It's best to use guided injection for this treatment. Computed tomography (CT scans) or fluoroscopy (real-time X-ray) show the surgeon where the needle is in relation to the soft tissues and bones. But not all centers have such advanced technology available. And even if they do, the cost may be prohibitive for such a minor procedure.

This is where nerve stimulation can help guide the injection. The authors of this study made careful assessment of the patient's anatomy and found the ideal place to insert the needle through the buttocks. A drawing of the landmarks used to find the insertion point is provided. The tip of the needle was placed just behind the sciatic nerve. The needle was connected to a nerve stimulator.

The nerve was stimulated using this technique. When the surgeon could tell he was on the sciatic nerve by stimulating it, then he moved the needle back a few centimeters into the piriformis muscle. A special dye was injected to make sure the piriformis muscle was being injected.

This low-cost, low-tech method of identifying the right anatomical spot for the injection was tested first on a small (pilot) group of 18 patients. Once the researchers were sure the method worked, they did a larger double-blind study with 80 people. Double-blind means that the patients and the staff giving the injections did not know which injection the patient was getting.

The patients were divided into two groups randomly. One group received a numbing agent (bupivacaine) combined with saline (a salt solution). The second group was injected with bupivacaine and a second agent (clonidine). Clonidine is actually a blood pressure medication. But it works for pain because it also blocks pain messages from being delivered to the brain via the spinal cord.

Based on results, the patients could have up to four injections. Success was measured by pain scores recorded by the patient while walking, sitting, and lying down. They kept a diary and filled out charts to write down when they needed additional pain relievers, what type they took, how much pain they were in (intensity), and how long the pain lasted (duration).

The patients who got bupivacaine combined with clonidine clearly had the best results. Almost half of this group was pain free by the end of the first week (after only one injection). This compared with none in the group receiving just the bupivacaine.

A second injection gave even more patients in the bupivacaine/clonidine group pain relief. Only two patients in the bupivacaine/saline group reported reduced pain after the second injection. At the end of four weeks, 92 per cent of the bupivacaine/clonidine group was pain free (compared to only 24 per cent in the bupivacaine/saline group). And the bupivacaine/clonidine group used far fewer extra pain medications compared with the bupivacaine/saline group.

There are many theories as to why the addition of clonidine makes such a difference. Some experts suggest it has an impact on the immune system, reducing local inflammation of the sciatic nerve. Others think clonidine can alter nerve impulses, possibly even affecting how the spinal cord works.

It's also possible that the effect takes place in the piriformis muscle, not in the nervous system. Injection leads to muscle relaxation, which then takes pressure off the entrapped nerve. Even a short period of time with the nerve and motor unit interrupted could alter the pain-spasm cycle. And in the meantime, blood flow is restored allowing tissue healing.

The authors concluded that nerve stimulator guidance of injections for piriformis syndrome can be done safely and yield very good results. The combined bupivacaine clonidine solution works better than just bupivacaine alone. Repeated injections may be needed. Using clonidine also has few to no side effects.
Zoher Naja, MD, et al. The Effectiveness of Clonidine-Bupivacaine Repeated Nerve Stimulator-guided Injection in Piriformis Syndrome. In The Clinical Journal of Pain. March-April, 2009. Vol. 25. No. 3. Pp. 199-205.