Can we use ''coin sign'' image to predict block success after performance of sciatic nerve block?

Ultrasound guidance during peripheral nerve block is a revolutionary approach in clinical practice. For a successful block, local anesthetics (LA) should surround the nerve circumferentially. Different definitions have been used to describe the ultrasound image for a successful block. For example, in the infraclavicular area, “U”-shaped LA distribution is suggested, whereas “doughnut sign” is recommended for small peripheral nerves of the body.[1,2]