LOCATION
Level with the 4th posterior sacral foramen, 1.5 cun lateral to the medial sacral crest.
Features
-/-
Body Inches (cun)
Each person has his/her own personal body inches.
One cun is equal to the width of the Knuckle of the thumb.
Nerves, vascular
Inferior gluteal nerve, the lateral branch of the posterior branch of the third and fourth sacral nerves, the inferior gluteal nerve and the arteries and veins under the gluteal nerve, and the internal arteries and veins of the pudendal region.
Indication
Lumbosacral pain，sciatica pain，uterus meningitis，anal pain/muscle spasm，pediatric paralysis sequelae，paralysis of the lower limbs，urinary retention. Secondary point for KI related gynecological disorders: menstrual problems, leukorrhea, pelvic inflammatory disease, enometriosis.
Combinations
Low back pain：BL 30 & BL 40.
Difficulty in urination：BL 30 & BL 25 & BL 36.
Chronic ipelvic inflammation：BL 30 & EX-CA1 & SP 10 & SP 06.
Leukorrhea，irregular menstruation，Spermatorrhea：BL 30 & BL 23 & SP 06.
Hemorrhoids：BL 30 & BL 57 & EX-UE2.
Prolapse of the anus：BL 30 & GV 01 & BL 57.
穴位
在骶部，當骶正中嵴旁1.5寸，平第四骶後孔。
特點
-/-
同身寸
針灸取穴比量法。出自《千金要方》。
是指以患者本人體表的某些部位折定分寸，
作为量取穴位的長度單位。
穴區神經血管
臀下皮神經，第三、四骶神經後支的外側支，臀下神經和臀下動、靜脈，陰部內動、靜脈。
適應症
腰骶，痛坐骨神經痛，子宮內膜炎，肛門諸肌痙攣，小兒麻痺後遺症，下肢癱瘓，尿瀦留等。
穴位配伍療法
背連腰痛：1.白環俞 2.委中
大小便不利：1.白環俞 2.大腸俞 3.承扶
慢性盆腔炎：1.白環俞 2.子宮 3.血海 4.三陰交
白帶，月經不調，遺精：1.白環俞 2.腎俞 3.三陰交
痔瘡：1.白環俞 2.承山 3.二白
脫肛：1.白環俞 2.長強3.承山