Ultrasound-Guided Obturator Nerve Block: A Focused Review on Anatomy and Updated Techniques

Figure 3

Ultrasound images obtained during obturator nerve block. (a) A preprocedure view of the distal approach, which is obtained with the transducer located as in Figure 2(a). The anterior branch of the obturator nerve is located at the hyperechoic thick fascia between the adductor brevis muscle and the pectineus (arrows) or adductor longus (open triangles) muscles. The posterior branch of the obturator nerve lies within the fascia between the adductor brevis and adductor magnus muscles (closed triangles). A needle is introduced into these fasciae in a medial-to-lateral (red dotted lines) or lateral-to-medial direction under in-plane ultrasound guidance. (b) A preprocedure view obtained with the transducer located as in Figure 2(b). A hyperechoic structure with an acoustic shadow (arrows) represents the superior pubic ramus. The target for injection of local anesthetic is the fascia, which is seen as contiguous with the superior pubic ramus and located between the pectineus and obturator externus muscles (open triangles). In the approach used by Taha [23], a needle is introduced into this plane under out-of-plane ultrasound guidance (yellow dotted line). In the approach used by Lin et al. [42], a needle is inserted into this plane under in-plane ultrasound guidance in a lateral-to-medial direction (red dotted line). (c) A preprocedure view obtained with the transducer located as in Figure 2(c). Hyperechoic thick fascia between the pectineus and obturator externus muscles (open triangles) is seen inferior to a hyperechoic structure with an acoustic shadow, which represents the superior pubic ramus (arrows). A needle is inserted into this fascia under in-plane ultrasound guidance in an inferior-to-superior direction (red dotted line). (d) A preprocedure view obtained with the transducer located as in Figure 2(d). The obturator externus muscle is seen superficial to the superior pubic ramus (arrows) and the pectineus muscle is seen anterior to the obturator externus muscle. A hyperechoic thick fascia between the pectineus and obturator externus muscles (open triangles) is the target plane. As a needle is inserted 3 cm cephalad from the anterior side of the transducer and advanced in-plane with the transducer toward this fascia in this case (red dotted line), the needle-ultrasound beam angles come to be almost perpendicular. AL, adductor longus muscle; AB, adductor brevis muscle; AM, adductor magnus muscle; PE, pectineus muscle; OE, obturator externus muscle; SPR, superior pubic ramus; GR, gracilis muscle.

(a)

(b)

(c)

(d)