Mondo Description Asternia, also known as a complete congenital sternal cleft, is a condition in which a bone called thesternum does not form properly.The sternumusuallyconnects to the ribs to form the ribcage. Individuals with asternia are missing this bone and may appear to have a rut or trench under the skin in the middle of the chest. Most individuals with asternia have no symptoms, though some may have difficulty breathing. Asternia is sometimes associated with other conditions, such as heart problems. The cause of asternia is currently unknown. Treatment consists of surgery to close the gap between the ribs.