Obturator Nerve Block: From Anatomy to Ultrasound Guidance

Abstract

To the Editor: Recently, Fujiwara et al.1 described the use of ultrasound imaging in the identification and block of the obturator nerve. Despite the clinical relevance of the study, we have some concern about the anatomy of the obturator nerve at the inguinal region level. The obturator nerve, as it exits the pelvis and at the level of the obturator externus, divides into an anterior branch, which is located superficially, and a posterior branch, which is situated at a deeper anatomic level.2 Cadaveric studies have also confirmed a large degree of anatomic variability in the obturator nerve anatomy, such that in 50% of individuals the common obturator nerve divides into superficial and deep branches at the level of the obturator foramen whereas in the majority of others a multiple branching pattern occurs throughout its anatomic course.3–5 In the report by Fugiwara et al.,1 the authors suggest that the common obturator nerve is located in between three muscles including the adductor longus (anteriorly), adductor brevis (posteriorly), and pectineus muscle (laterally). However, this description seems not to be anatomically correct since at this point the nerve has been already bifurcated into anterior and posterior branches and possibly into further divisions.6 Thus, the authors more likely identified and blocked one of the obturator nerve branches and not the common obturator nerve. Additionally, according to the images provided, the anatomic location of the common obturator nerve seems to be very superficial, approximately 1–2 cm from skin surface. Those images are possibly in contrast with the location of the common obturator nerve, that anatomically lies at a deeper level, in a very close relationship to the obturator externus muscle.5 We conclude that, due to complicated anatomy and the high anatomic variability of the obturator nerve, additional studies are needed to delineate the precise ultrasound anatomy of this nerve. Sofia Anagnostopoulou, MD, PhD Department of Anatomy School of Medicine University of Athens Georgia Kostopanagiotou, MD, PhD 2nd Department of Anesthesiology School of Medicine University of Athens Attikon Hospital Tilemachos Paraskeuopoulos, MD Department of Anatomy School of Medicine University of Athens Anastasia Alevizou, MD Department of Anesthesiology General State Hospital of Athens Athens, Greece, EU Theodosis Saranteas, MD, DDS, PhD 2nd Department of Anesthesiology School of Medicine University of Athens Attikon Hospital Athens, Greece, EU [email protected]