DDH is a congenital (present at birth) condition of the hip joint, occurring once in every 1,000 babies. The hip joint is as a ball and socket. In DDH the hip socket may be too shallow. In severe cases the ball of the femur can slip either partially or completely out of the socket. Mild DDH may not be picked up until adulthood when the hip becomes painful. The issue is that with a shallow socket, the forces going through the hip are concentrated over a smaller area, causing increased wear and arthritis.