[Ultrasound-guided posterior approach to block the sciatic nerve at the popliteal fossa].

The recent introduction of ultrasound guidance for locating peripheral nerves and nerve plexi has allowed injection of anesthetic agents to block the sciatic nerve at the popliteal fossa proximal to division, thus preventing damage to adjacent structures, repeated punctures, and multiple nerve stimulations to verify anesthetic diffusion around the nerve. We report the case of a 23-year-old man, ASA I, who underwent reduction and osteosynthesis of a fractured right fibula. Ultrasound was used to guide the needle after identification of the sciatic nerve 10 cm from the knee fold and 3.5 cm deep. When the point of the needle was near the nerve, the nerve stimulator was switched on to 0.5 mA, and when no response was obtained the current was increased to 1.5 mA. The needle was moved slightly (1-2 mm) to produce a plantar flexion (tibial component) that persisted until stimulation had been reduced to 0.4 mA, at which time 30 mL of 1.5% mepivacaine was injected. The sonographic image during injection showed that the anesthetic had surrounded the nerve (donut sign). The motor and sensory block of the sciatic nerve was complete and no adverse events occurred during or after surgery. We conclude that the combination of ultrasound guidance and nerve stimulation allows the sciatic nerve to be located easily. The approach to the point before division of the sciatic nerve can be guaranteed so that puncture of neighboring vessels can be avoided and optimal anesthesia provided.