Structure pierced to give caudal anaesthesia is?

Caudal anesthesia is popular in pediatric anesthesia and is paicularly useful when sacral anesthetic spread is desired (e.g., perineal, anal, rectal procedures). Caudal anesthesia requires identification of the sacral hiatus. The sacrococcygeal ligament (i.e., extension of ligamentum flavum) overlies the sacral hiatus between the two sacral cornua. To facilitate locating the cornua, the posterior superior iliac spines should be located and, by using the line between them as one side of an equilateral triangle, the location of the sacral hiatus should be approximated. After the sacral hiatus is identified, the index and mid-dle fingers of the palpating hand are placed on the sacral cornua, and after local infiltration, the caudal needle (or Tuohy needle if a catheter is to be placed) is inseed at an angle of approximately 45 degrees to the sacrum. While the needle is advanced, a decrease in resistance to needle inseion should be appreciated as the needle enters the caudal canal. The needle is then redirected so that the angle of inseion relative to the skin surface is decreased.