Figure 2.

Patient and transducer positions for performance of each ultrasound-guided right-sided obturator nerve block technique. The dotted lines indicate the inguinal crease. (a) The patient is placed in the supine position with his hip slightly abducted and externally rotated. In the distal approach for obturator nerve block, the transducer is placed medial to the femoral vein, along the inguinal crease, perpendicularly to the skin. A needle is inserted from the point indicated by the red circle, in-plane with the transducer, in a medial-to-lateral direction. (b) The transducer is tilted cranially from the position shown in Figure 2(a) to obtain an ultrasound image similar to that in Figure 3(b). A needle is inserted from the point indicated by the yellow circle in an anterior-to-posterior direction using out-of-plane ultrasound guidance in the approach devised by Taha [23]. In the approach used by Lin et al. [42], a needle is inserted from the point indicated by the red circle, in a lateral-to-medial direction, using in-plane ultrasound guidance. (c) The technique described by Akkaya et al. [35] can be performed with the patient in a supine position and his/her leg straight. The transducer is placed in the sagittal plane on the inguinal crease between the femoral vein and the pubic tubercle. A needle is inserted from the point indicated by the red circle, in-plane with the transducer, in an inferior-to-superior direction. (d) In the approach devised by Yoshida et al. [31], the patient is placed in the lithotomy position. The transducer is placed immediately lateral to the perineum on the medial aspect of the thigh along the extended line of the inguinal crease and orientated cephalad. A needle is inserted 2-3 cm cephalad from the anterior side of the transducer (red circle) and advanced in-plane with the transducer in an anterior-to-posterior direction. ASIS, anterior superior iliac spine.