Chapter 147. Popliteal Blocks

Anatomy (Figure 147-2):

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.

It emerges in the popliteal fossa between the biceps femoris laterally, and the semitendinosus/semimembranosus medially.

Indications:

• 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)

Contraindications:

None specific.

Technique using NS:

• 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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