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The sciatic nerve divides into tibial and peroneal nerves at a variable level, typically 7–10 cm above the flexion crease, but occasionally as high as the buttock, or below the knee joint.
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It emerges in the popliteal fossa between the biceps femoris laterally, and the semitendinosus/semimembranosus medially.
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- Surgery of the lower leg, ankle, and foot (in combination with a saphenous block if the skin of the anteromedial aspect of the lower leg or the medial aspect of the ankle or foot is involved)
- Isolated tibial nerve block for postoperative analgesia after knee surgery (in combination with a continuous femoral block, and GA/spinal for anesthesia, especially if a thigh tourniquet is to be used)
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- Posterior approach:
- Patient prone or in lateral decubitus, lying on the nonoperative side
- Mark the flexion crease and the muscles on each side (biceps femoris laterally, semitendinosus and semimembranosus medially)
- Draw a perpendicular extending cephalad, about 1 cm lateral to the center of the flexion crease line. The needle insertion point is 7 cm cephalad to the flexion crease
- Insert a 50 mm needle aiming 45° cephalad, setting the PNS at 1.2 mA, 2 Hz, 0.1 millisecond, and elicit a response in the tibial or peroneal innervation territory
- If a tibial response is obtained, adjust needle position while decreasing current. If a response is still present at 0.4 mA, aspirate and then inject one half of the local anesthetic (typically 10–15 mL) in a fractionated fashion, and redirect needle laterally to obtain a peroneal response. In a similar fashion, inject 10–15 mL of local anesthetic
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