POPLITEAL SCIATIC BLOCK AT A GLANCE
Indications: foot, ankle and Achilles tendon surgery
Transducer position: transverse over the popliteal fossa
Goal: local anesthetic spread surrounding the sciatic nerve within the epineural sheath
Local anesthetic: 15–20 mL
The anatomy of the sciatic nerve in the popliteal fossa is variable, and the division into the tibial nerve (TN) and common peroneal nerve (CPN) occurs at an inconstant distance from the popliteal crease (Figure 33G–1). With nerve stimulator–based techniques, larger volumes (eg, > 40 mL) of local anesthetic have been used to increase the chance of block success. However, US guidance reduces the volume required for reliable block because the injection can be halted once adequate spread is observed.
Cross-sectional anatomy of the sciatic nerve in the popliteal fossa. Shown are the common peroneal nerve (CPN), tibial nerve (TN), popliteal artery (PA), popliteal vein (PV), femur, biceps femoris muscle (BFM), semimembranosus muscle (SmM), and semitendinosus (StM) muscle. (Reproduced with permission from Hadzic A: Hadzic’s Peripheral Nerve Blocks and Anatomy for Ultrasound-Guided Regional Anesthesia, 2nd ed. New York: McGraw-Hill, 2011.)
The most common approaches to the popliteal sciatic block are the lateral approach, with the patient in the supine or lateral position, and the posterior approach in the prone or lateral position (Figure 33G–2). While the patient position and needle path differ between the two approaches, the rest of the technique details are similar.
The posterior approach to the US-guided popliteal sciatic block can be performed (A) with the patient in the lateral position, or (B) with the patient prone. (Reproduced with permission from Hadzic A: Hadzic’s Peripheral Nerve Blocks and Anatomy for Ultrasound-Guided Regional Anesthesia, 2nd ed. New York: McGraw-Hill, 2011.)
The injection of local anesthetic must occur within the sciatic nerve sheath that contains both components of the nerve.1-14 The injection is ideally accomplished at the position where both components of the nerve are within the sheath but slightly separated by adipose tissue, allowing for safe placement of the needle between them.15 Although the sciatic nerve block can be accomplished with an injection around either nerve component, injecting into the space between both is more common in clinical practice.16,17
Beginning with the transducer in the transverse position at the popliteal crease, the popliteal artery is identified, aided with color Doppler US when necessary, at a depth of approximately 3–4 cm. The popliteal vein accompanies the artery at it is positioned just superficial (posterior) to it. On either side ...