Suggested Technique

The subgluteal region has a “bright triangle” consisting of the hyperechoic sciatic nerve and adjacent tendons of the semitendinosus-biceps and semimembranosus. These proximal tendons can appear similar to the sciatic nerve on ultrasound scans. The sciatic nerve is always lateral to these ischiocrural tendons. The semimembranosus tendon is characterized by a large, flat proximal aponeurosis. The semitendinosus muscle forms a conjoint tendon with the biceps femoris that points to the medial aspect of the sciatic nerve. Short-axis view with sliding of the transducer is usually better than long-axis view to confirm nerve identity and distinguish it from the adjacent tendons.

Prone position allows the most stable access for proximal sciatic nerve block. In-plane technique from the lateral side of the leg is a relatively easy approach to proximal sciatic block. If prone positioning is difficult, lateral approach can be used for this block. A broad linear probe (5-cm footprint or larger) is best to provide a large field of view for this block because working room is not limited in this region.

Anatomic variation of the sciatic nerve in the subgluteal region primarily consists of identification of separate contributions from the common peroneal and tibial nerves.^2,3 This indicates proximal division of the sciatic nerve by the piriformis muscle. If the anomaly is correctly identified, multiple-injection technique guided by ultrasound provides complete sciatic block.

The sciatic nerve lies between the greater trochanter (lateral) and the ischial tuberosity (medial). These bony reference points are useful proximal landmarks for sciatic block in the gluteal region.⁴ In some patients the inferior gluteal artery can be identified on the medial side of the proximal sciatic nerve.