Ultrasound-guided lateral approach for sciatic nerve block: a comparison with the anterior approach

INTERVENTION: To perform a sciatic nerve block using the anterior approach To perform a sciatic nerve block using the lateral approach CONDITION: Disease on distal to the knee requiring orthopedic surgery PRIMARY OUTCOME: Incidence of posterior femoral cutaneous nerve block at 30 min after execution of a sciatic nerve block SECONDARY OUTCOME: 1. Incidence of sensory block by a sciatic nerve block within 30 min after execution of a sciatic nerve block; 2. Incidence of motor block by a sciatic nerve block within 30 min after execution of a sciatic nerve block; 3. Time required to identify the sciatic nerve under ultrasound; 4. Distance from the skin to the sciatic nerve; 5. Needle distance under the skin when the tip of the needle reaching the sciatic nerve; 6. Time required to perform a sciatic nerve block; 7. Incidence of adverse effects caused by a sciatic nerve block INCLUSION CRITERIA: 1. Patients undergoing a unilateral lower extremity surgery on distal to the knee under general anesthesia combined with peripheral nerve blocks 2. American Society of Anesthesiologists PS 1‐3 3. Written informed consent is provided