Background and indications: The sciatic nerve gives off four branches below the knee that must be blocked for surgery of the ankle or foot. These are the sural nerve, the superficial and deep peroneal nerves, and the posterior tibial nerve. In addition, the saphenous nerve, a branch of the femoral nerve, must also be anesthetized when surgery on the ankle or foot is planned. The superficial peroneal and sural nerves are very small and difficult to image on ultrasound. Because they are superficial, most practitioners prefer to block these with skin infiltration. The deep peroneal nerve runs along the anterior surface of the tibia, deep to the extensor retinaculum (Fig. 33.1). The posterior tibial nerve can be found posterior to the medial malleolus near the posterior tibial artery (Fig. 33.2). The saphenous nerve can be found next to the saphenous vein, usually posterior to the vein (Fig. 33.3). Ankle block is indicated for surgery on the foot below the ankle.

Anatomy: The deep peroneal nerve can often be found lateral to the anterior tibial artery. The nerve has a round or oval hyperechoic appearance (Fig. 33.1). The posterior tibial nerve can be found posterior to the posterior tibial artery, where it has a round hyperechoic appearance (Fig. 33.2