DDH is a treatable condition that affects some babies and when untreated as a child will lead to significant problems later in life. The hip includes the ball of the thighbone (femur) and the socket where the ball fits. The socket is called the acetabulum. In babies born with DDH, the ball of the thighbone slips in and out of the socket. This repetitive instability gradually wears down the lining of the ball and socket, or cartilage, leading to arthritis.