The ultrasound prober location and gray-scale and color Doppler images. (a) The ultrasound transducer is placed at the midpoint of the line connecting the greater trochanter (red circle) and the posterior superior iliac spine (yellow circle). The green arrow indicates the direction of ultrasound transducer movement. (b) The ultrasound image when the transducer is placed at the midpoint of the line connecting the greater trochanter and the posterior superior iliac spine. Hip bone is seen as hyperechoic specular reflectors (yellow triangle). (c) The final position of ultrasound transducer placed and a lateral to medial approach injection. (d) The ultrasound image when the transducer shifts to the lesser sciatic notch. Blue and green arrows indicate sacrospinous and sacrotuberous ligaments, respectively. The red arrow indicates ischial tuberosity. The internal pudendal artery (blue Doppler signal) lies in the corner between the coccygeus and internal obturator muscles. The white arrow indicates needle trajectory and injection point. (e) The ultrasound image after anesthetic injection around the internal pudendal artery. The pentagram represents the spread of local anesthetics.