Background: The sciatic nerve is the terminal branch of the sacral plexus. It arises in the parasacral area at the back of the pelvis between the piriformis (posteriorly) and the pelvic fascia (anteriorly). It exits the pelvis through the greater sciatic foramen, just medial to the posterior border of ischium (PBI). The PBI forms the lower lateral bony edge of the greater sciatic foramen (Fig. 29.1). The sciatic nerve supplies the hip and knee joints, the hamstring muscle, and nearly the entire leg and foot. In its proximal course, the sciatic nerve is deep and difficult to identify; therefore, bones, which are easily identified sonographic landmarks, are used to localize the sciatic nerve. In the parasacral technique, the PBI is used to identify the sciatic nerve. Unlike other sciatic block techniques, the parasacral technique can block the entire sacral plexus as well. The technique described here is slightly distal to the technique described by Ben-Ari¹ and more proximal than the traditional transgluteal technique described by Labat.²

Indication: All lower limb surgeries (knee, below-knee, above-knee, and hip surgeries).

Transducer type: A curved probe (2 to 5 MHz).

Needle: Short-beveled, 12-cm insulated needle connected to a nerve stimulator unit. Longer needle may be required for morbidly obese patients.

Local anesthetics: 20 mL of 2% lidocaine, 0.5% ropivacaine. The selection of local anesthetic (LA) depends on the duration of surgery.

Patient position: Sims position.