Background and indications: Ultrasound-guided block of the sciatic nerve can be conducted from the anterior aspect of the patient as well as from the lateral or posterior positions. When the block is conducted from the anterior approach (at the level of the lesser trochanter), it is too distal to be of use in hip surgery. However, the anterior approach allows the patient to remain supine. This is especially advantageous in patients who have fractures of the lower extremity. Anterior sciatic block is used for surgery of the distal posterior thigh, posterior knee, leg, or foot.

Anatomy: From the anterior approach, the sciatic nerve lies deep and medial to the femur (Fig. 30.1). The nerve is bounded laterally by the gluteus maximus muscle and medially by the biceps femoris and semimembranosus/semitendinosus muscles (frequently referred to as the hamstring muscles). Just anterior to the nerve lies the adductor magnus muscle. Medial to the nerve, and quite superficial in the thigh at these levels, the femoral vessels and nerve can be seen (Fig. 30.1). On ultrasound, the sciatic nerve will appear as a hyperechoic oval or round structure (Fig. 30.2). In some patients, the obturator artery and nerves can also be seen lying deep to the adductor longus and between the adductor brevis and adductor magnus muscles (Fig. 30.3).

Patient position: The patient remains supine. The thigh is externally rotated, and the knee is flexed. The leg should be externally rotated so that the sciatic nerve is rotated to a position medial to the femur.

Transducer: 60 mm curved array oscillating at 2 to 5 MHz.