Move the probe with a parallel shift medial to the ischiocavernosus muscle in the anterior perineal triangle until the superficial and deep transverse muscles are visualized.

Proximal sciatic nerve block is indicated:

– for surgical anaesthesia with peripheral nerve blocks that includes surgery of the thigh or knee

– for surgical anaesthesia with peripheral nerve blocks that includes a thigh tourniquet

– as an alternative to popliteal sciatic nerve block when that is not feasible

Proximal sciatic nerve blocks are:

– the subgluteal approach

– the anterior approach combined with a saphenous nerve block (SPEDI)

– the parasacral parallel shift approach to block the sacral plexus (as an alternative to subgluteal approach or
SPEDI – single penetration dual injection)

Parras T & Blanco R: Bloqueo pudendo ecoguiado (Ultrasound guided pudendal block). Cirugia Mayor Ambulatoria 18(1): 31-35 (2013)

http://www.asecma.org/attachments/article/162/06_18_1_FC_Parras.pdf

Parras T & Blanco R: Bloqueo perineal guiado con ultrasonidas.
Revista de anestesia regional e terap

The internal pudendal artery can be visualized in transverse view with Color Doppler at the level of the ischial tuberosity.

The needle is inserted with in-plane technique from the medial end of the probe aiming just lateral to the artery. 10 mL of local anaesthetic is injected bilaterally.

The internal pudendal artery can be visualized with Color Doppler in longitudinal view deep to the deep transverse perineal muscle. The artery can be tracked posteriorly towards the ischial tuberosity. The pudendal nerve runs alongside the internal pudendal artery either medial or lateral to the artery.

Place the patient supine with the pelvis elevated by a pillow. Hips and knees are flexed and the thighs are abducted with external rotation.

Place the linear high-frequency probe on a line between the scrotum/mons pubis and the lateral border of the anus on top of the ischiopubic ramus. Visualize the ischiocavernosus muscle on top of the ischiopubic bone.

Alcocks canal (synonym: pudendal canal) is a fascial compartment on the lateral wall of the ischioanal fossa that contains the pudendal nerve, the internal pudendal artery and the internal pudendal vein.

The pudendal nerve runs alongside the internal pudendal artery in the Alcocks canal along the medial margin of the inferior pubic ramus deep to the muscles of the superficial pelvic floor.

In the ilioanal fossa below the levator ani, the pudendal nerve has three branches: the inferior rectal branch, the perineal branch, and the dorsal nerve of the penis (blue arrow).

The pudendal nerve origins from the spinal nerves S2-S4 and whirls around the ischial spine.