Piriformis muscle injection is a useful diagnostic and therapeutic procedure for myofascial pain.
After informed consent is obtained, the patient is placed in the lateral Sims’ position. The piriformis muscle is palpated from the sacrum toward the hip. The injection sites are identified as points of maximal tenderness to deep palpation, reproducing the patient’s pain complaint. This may or may not result in referred pain. The patient is prepared in a standard aseptic fashion over an area large enough to allow palpation of landmarks, and sterile technique is used throughout the procedure. A 1½-in. (4-cm), 21- to 25-gauge needle is inserted at the point of maximal tenderness and advanced to the area of the trigger point. After negative aspiration, the trigger point area is injected with 4 mL of local anesthetic (Fig. 67-31).
FIGURE 67-31. Piriformis trigger points and referred pain patterns.
The referred pain pattern for the piriformis muscle often involves the buttocks, iliosacral region, and posterior hip. The patient should be familiar with the stretching program for the piriformis muscle and be instructed in a home program. Failure to include a home stretching program usually results in short-term relief.
Attention to the anatomy of the sciatic nerve in this region will prevent intraneural injection; otherwise, significant complications are uncommon with trigger point injections. Severe pain on injection suggests the possibility of an intraneural injection, and the needle should be repositioned immediately. Temporary lower extremity weakness is possible from regional spread of the local anesthetic.