RESUMO
OBJECTIVE: To identify the optimal site for piriformis muscle injection, using easily detectable sacroiliac joint as a landmark, under fluoroscopic guidance. METHOD: We examined the anatomic relationships of the sciatic nerve, piriformis muscle and sacroiliac joint in 18 buttocks from 9 cadavers. The distance from the inferior margin of the sacroiliac joint to the piriformis muscle at the crossing point with the sciatic nerve, and the width of the sciatic nerve at that point were measured. We assessed the depth of the piriformis muscle and the sciatic nerve using ultrasonography in asymptomatic controls. RESULTS: The mean distance from the inferior margin of the sacroiliac joint to the piriformis muscle at the crossing point with the sciatic nerve was 15.7+/-3.4 (12~22) mm laterally and 16.5+/-4.1 (10~25) mm caudally. The mean width of the sciatic nerve at that point was 15.4+/-3.7 (12~22) mm. Ultrasonographic findings revealed the mean distance as 4.48+/-0.49 cm from the skin to the surface of the piriformis muscle and as 5.68+/-0.62 from the skin to the surface of the sciatic nerve. CONCLUSION: The most optimal injection site for piriformis syndrome was located 15.6+/-3.4 (12~22) mm laterally and 16.5+/-4.1 (10~25) mm caudally from the inferior margin of the sacroiliac joint.