"Si" (四), four; "du" (瀆), water channel. The depression between two bones of forearm resembles a water channel. In ancient times, the four major rivers—Jiang (Yangtze River), Huai (Huai River), He (Yellow River), and Ji (Ji River)—were referred to as the four water channels, symbolizing that the meridian qi permeates and irrigates more extensively at this point.

bubble_chart Location

Sidu (TE9) acupoints
(adapted from "Meridians and Acupoints")

• Zhenjiu Jiayi Jing: "On outer side, 5 cun distal to elbow, in the depression".

bubble_chart Anatomy

• Muscles: radial side, extensor digiti minimi, extensor digitorum; ulnar side, extensor carpi ulnaris; deeper, extensor pollicis longus and abductor pollicis longus.
• Nerve: posterior cutaneous nerve of forearm; deeper, posterior interosseous nerve plexus of forearm .
• Vessel: deep layer, posterior interosseous arteries and veins of forearm.

bubble_chart Manipulation

Perpendicular insertion is 0.5~1.5 cun, Moxibustion with moxa cone is 3~5 cun, moxibustion with moxa stick is used for 5~15 minutes.

bubble_chart Efficacy

Improve hearing, clear throat.

• Classical: deafness, toothache, pharyngeal swelling, cheek ulcers, mumps, pain in arm and shoulder.
• Modern: wrist droop, forearm paralysis, weakness in wrist extension, finger spasms, sensation of foreign object in throat, head fullness and pain.

bubble_chart Combinations

• Sudden deafness: Tianyou (TE16), Sidu (TE9).
• Headache: Taiyang (EX-HN5), Sidu (TE9).
• Forearm pain and weakness in wrist extension: Quchi (LI11), Sidu (TE9).