Sciatic nerve block: Anatomy

The sciatic nerve can be blocked above the level of the knee joint. If ultrasound imaging is used, the sciatic nerve can be consistently found at the top center of the popliteal fossa just lateral to the popliteal pulse, before its division into the tibial and common peroneal nerves. The classic intertendinous technique involves the identification of the popliteal triangle, which is defined by the tendon of biceps femoris laterally, the tendons of the semitendinosus and semimembranosus medially, and the popliteal fossa crease. Generally, the nerve can be identified 7 cm above the popliteal crease, at the midpoint between the tendons, or 9 cm above the popliteal crease, 1 cm lateral to the midline of the triangle. The sciatic nerve can also be blocked proximally via a posterior approach, classically described by Labat. The landmarks for the classical approach by Labat are determined by first drawing a line from the greater trochanter to the posterior superior iliac spine. A second line is drawn from the greater trochanter to the sacral hiatus. From the midpoint of the posterior superior iliac spine line, another line is drawn perpendicularly to the meet the sacral hiatus line. The intersection of the perpendicular line and the sacral hiatus line is the needle insertion point. Summary of key anatomical landmarks for sciatic nerve identification:

POPLITEAL APPROACH

• Semimembranosus/semitendinosus tendons (medial)
• Biceps femoris tendon (lateral)
• Popliteal crease (inferior)
• Popliteal artery (medial, visualized by ultrasound)

POSTERIOR APPROACH

• Posterior superior iliac spine
• Greater trochanter
• Sacral hiatus