A 34-year-old pregnant woman in the maternity ward was experiencing considerable pain during labor. Her obstetrician decided to perform a caudal epidural block within the sacral canal. What are the most important bony landmarks used for the administration of such anesthesia?

The sacral cornua lie on either side of the sacral hiatus, from which one can gain access to the sacral canal. This is the best landmark for administration of anesthesia. The ischial tuberosities are more commonly used as landmarks for a pudendal nerve block. The ischial spines cannot be palpated. The posterior superior iliac spines, though palpable, are not proximal enough for an epidural block within the sacral canal. The coccyx is not part of the sacral canal.