Chapter 38

Distal sciatic nerve block (popliteal fossa block) is a relatively simple technique that results in reliable surgical anesthesia of the calf, tibia, fibula, ankle, and foot.1,2 Consequently, this technique is used primarily for anesthesia or analgesia for foot, ankle, and lower-leg surgery.3 The sciatic nerve can be approached from either the posterior approach described by Rorie,3 or the lateral approach, which eliminates the need to reposition patients in the supine position.1 With the lateral popliteal fossa block, patients remain supine for the block and catheter placement, rather than being prone and then turning supine after the block is placed. Both approaches provide equivalent surgical anesthesia after nerve blockade.1 With both approaches, catheters can be inserted to provide prolonged postoperative analgesia; catheters, however, are more easily secured in the lateral position. Because of the slower resolution of neural blockade in the lower extremity, popliteal fossa block performed with long-acting local anesthetics such as ropivacaine can provide 12–24 hours of analgesia after foot surgery. The remarkable safety of the block has been demonstrated in numerous studies.3,4

Analgesia with lower-extremity blocks typically lasts longer than analgesia with ankle block. For instance, McLeod found that lateral popliteal fossa block with 0.5% bupivacaine lasted 18 hours when compared with ankle block, which lasted only 6.2 hours.5 Popliteal fossa block has also been used as an effective analgesic technique in children.6 In a study of the efficacy of the popliteal sciatic nerve blockade (0.75 mL/kg of ropivacaine 0.2%) after foot and ankle surgery, 19 of 20 children required no analgesic agents during the first 8–12 hours postoperatively. Blocking the sciatic nerve in the popliteal fossa is an excellent choice for foot and ankle surgery.1 When used as a sole technique in outpatients, popliteal fossa block provides excellent anesthesia and postoperative analgesia, allows use of a calf tourniquet, and is devoid of disadvantages of neuraxial blockade.7

### Indications & Contraindications

The popliteal block is one of the most commonly used regional anesthesia techniques in regional anesthesia practice. Common indications include corrective foot surgery, foot debridement, short saphenous vein stripping, repair of the Achilles tendon, and others.8 As opposed to the more proximal block of the sciatic nerve, popliteal fossa block anesthetizes the leg distal to the hamstring muscles, allowing patients to retain knee flexion.9,10

### Functional Anatomy

The sciatic nerve is a nerve bundle consisting of two separate nerve trunks, the tibial and common peroneal nerves. A common epineural sheath envelops these two nerves at their outset in the pelvis.11 As the sciatic nerve descends toward the knee, the two components eventually diverge in the popliteal fossa, giving rise to tibial and common peroneal nerves (Figure 38–1). This division of the sciatic nerve occurs usually between 50 and 120 mm proximal to the popliteal fossa crease.

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