- Indications: foot and ankle surgery; analgesia following knee surgery
- Transducer position: transverse on the lateral aspect of thigh or over popliteal fossa
- Goal: local anesthetic spread surrounding the sciatic nerve within epineural sheath
- Local anesthetic: 20–30 mL
Cross-sectional anatomy of the sciatic nerve in the popliteal fossa. Shown are common peroneal nerve (CPN), tibial nerve (TN), popliteal artery (PA), popliteal vein (PV), femur, biceps femoris (BFM), semimembranosus (SmM) and semitendinosus (StM) muscles.
Performance of a sciatic block above the popliteal fossa benefits from ultrasound guidance in several ways. The anatomy of the sciatic nerve as it approaches the popliteal fossa can be variable, and the division into the tibial nerve (TN) and common peroneal nerve (CPN) occurs at a variable distance from the crease. Knowledge of the location of the TPN and CPN in relation to each other is beneficial in ensuring the anesthesia of both divisions of the sciatic nerve. Moreover, with nerve stimulator–based techniques, larger volumes (e.g., >40 mL) of local anesthetic often are required to increase the chance of block success and rapid onset. A reduction in local anesthetic volume can be achieved with ultrasound guidance because the injection can be halted once adequate spread is documented. The two approaches to the popliteal sciatic block common in our practice are the lateral approach with patient in supine (more commonly, oblique position) and the posterior approach (Figure 40-2). It should be noted that with the lateral approach, the resulting ultrasound image is identical to the image in the posterior approach. Both are discussed in this chapter. Only the patient position and needle path differ between the two approaches; the rest of the technique details
Posterior approach to ultrasound-guided popliteal sciatic block can be performed with the patient in the oblique position (A) or with the patient prone (B).
With the posterior and the lateral approaches, the transducer position is identical; thus the sonographic anatomy appears the same. However, note that although the image appears the same, there is a 180° difference in patient orientation. Beginning with the transducer in the transverse position at the popliteal crease, the popliteal artery is identified, aided with the color Doppler ultrasound when necessary, at a depth of approximately 3 to 4 cm. The popliteal vein accompanies the artery. On either side of the artery are the biceps femoris muscles (lateral) and the semimembranosus and semitendinosus muscles (medial). Superficial (i.e., toward the skin surface) and lateral to the artery is the tibial nerve, seen as a hyperechoic, oval, or round structure with a stippled or honeycomb pattern on the interior (Figure 40-3A and B). If difficulty in identifying the nerve ...