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Brown: Atlas of Regional Anesthesia, 3rd ed., Copyright © 2006 Saunders, An Imprint of Elsevier
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The obturator nerve emerges from the medial border of the psoas muscle at the pelvic brim and travels along the lateral aspect of the pelvis anterior to the obturator internus muscle and posterior to the iliac vessels and ureter. It enters the obturator canal cephalad and anterior to the obturator vessels, which are branches from the internal iliac vessels. In the obturator canal, the obturator nerve divides into anterior and posterior branches ( Fig. 15-1 ). The anterior branch supplies the anterior adductor muscles and sends an articular branch to the hip joint and a cutaneous area on the medial aspect of the thigh. The posterior branch innervates the deep adductor muscles and sends an articular branch to the knee joint. An accessory obturator nerve may be found in 10% of patients.

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Figure 15-1  Obturator nerve: functional anatomy.


The patient lies supine, with the legs positioned in a slightly abducted position. The genitalia should be protected from antiseptic solutions.

Needle Puncture.

The pubic tubercle should be located and an X marked 1.5 cm caudad and 1.5 cm lateral to the tubercle ( Fig. 15-2 ). The needle is inserted at this point; and at a depth of approximately 1.5 to 4 cm it contacts the horizontal ramus of the pubis. The needle is then withdrawn, redirected laterally in a horizontal plane, and inserted 2 to 3 cm deeper than the depth of the initial contact with bone. The needle tip now lies within the obturator canal ( Fig. 15-3 ). With the needle in this position, 10 to 15 mL of local anesthetic solution is injected while the needle is advanced and withdrawn slightly to ensure development of a “wall” of local anesthetic in the canal.

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Figure 15-2  Obturator nerve anatomy: oblique view.

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Figure 15-3  Obturator nerve block: technique.

Potential Problems.

The obturator canal is a vascular location; thus, the potential exists for intravascular injection or hematoma formation, although these possibilities are more theoretical than clinical concerns.

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