Patient Position: Supine with the thigh slightly externally rotated.

Indication: Surgery on the knee in conjunction with femoral nerve block.

Needle Size: 5-cm, 22-gauge insulated needle.

Surface Landmarks: Below the inguinal crease, 2 cm distal to pubic tubercle along the medial aspect of the thigh.

Ultrasound Landmarks: The lateral adductor brevis muscle. The anterior division of the obturator nerve usually lies superficial to the adductor brevis muscle. The posterior division of the nerve usually lies deep to the adductor brevis muscle. Both divisions produce broad, flat, hyperechoic images at the lateral border of the adductor brevis muscle. The obturator artery, which is sandwiched between the obturator internus and externus muscles.

Transducer Type: 5 to 8 MHz linear array.

Transducer Position: Axial or axial oblique along the medial aspect of the thigh, below the pubic ramus (Fig. 38-1).