Background and indications: Sciatic nerve block has been in use by anesthesiologists for over 90 years. The traditional approach has been to create landmarks over the gluteus and traverse this large muscle en route to the nerve. However, di Benedetto¹ described a somewhat more distal approach in which the nerve is blocked in the proximal thigh just as it leaves the pelvis. In di Benedetto’s¹ original description, the procedure was referred to as the subgluteus block, and will hereafter be referred to as the infragluteal approach to avoid confusion with the subgluteal space. When compared to the transgluteal approach, the infragluteal approach resulted in less patient discomfort and required less time with fewer needle punctures than the time-honored approach through the gluteus. Ultrasound has the potential to make the infragluteal sciatic block even more efficient with less discomfort for the patient. Sciatic block is provided for surgical procedures involving the distal femur, knee joint, leg, ankle, and foot.

Anatomy: Infragluteal sciatic block guided by landmarks and nerve stimulation relies on palpation of the greater trochanter and the ischial tuberosity, as the nerve lies approximately midway between them. The “groove” that lies between the hamstring muscles, which originate from the ischial tuberosity, and the lateral edge of the vastus lateralis muscle are then palpated. The nerve typically lies deep to this groove and is sought 4 cm below the line connecting the two bony landmark (Figs. 31.1 and 31.2).

With ultrasound, the same landmarks may be located. The ischial tuberosity and greater trochanter are readily imaged just proximal to the gluteal fold (Fig. 31.1); below this fold, the overlying gluteus maximus muscle is seen to thin out considerably. Deep to the gluteus, and superficial to the quadratus femoris muscle, lies the sciatic nerve at a depth of approximately 3 to 12 cm, depending on the patient’s habitus. The nerve itself has a fusiform or wedgeshaped appearance and is hyperechoic (Fig. 31.2). As one proceeds distally, the quadratus femoris disappears and the nerve becomes more round or oval and lies on the belly of the adductor magnus. Deeper, and lying somewhat more lateral than the nerve, the hyperechoic arc of the femur is evident. There are usually no significant vessels evident adjacent to the nerve at this level.

Patient position: Lateral decubitus position, with the affected side up or prone.

Transducer: 40 to 60 mm curved array oscillating at 2 to 5 MHz. 11 mm curved array oscillating at 6 to 10 MHz (smaller patients and children).