Anterior approach to the sciatic nerve block: the effects of leg rotation.

In the anterior approach to the sciatic nerve block, the femur often obstructs the passage of the needle toward the sciatic nerve. In this study, by using a human cadaver model, we assessed how internal and external rotation of the leg influences the accessibility of the sciatic nerve with the anterior approach. Ten lower extremities from five adult cadavers were studied. Needles were used to simulate the anterior approach to the sciatic nerve block. The effect of leg rotation on the needle plane required to reach the sciatic nerve was studied with legs in the neutral position and then with internal and external rotation (45 degrees) of the legs. During needle placement in the neutral position, the needle could not be fully advanced to the level of the sciatic nerve because of obstruction by the lesser trochanter in 80% of attempts. Medial redirection of the needle (10 degrees--15 degrees) allowed it to pass the lesser trochanter but brought the tip of the needle too medial to the sciatic nerve. Internal rotation of the leg facilitated passage of all needles inserted at the level of the lesser trochanter. We conclude that internal rotation of the leg may significantly facilitate needle insertion in the anterior approach to sciatic block.