Hip dysplasia is a condition in which the top portion of the thigh bone doesn't fit properly in the socket portion of the hip joint — either because it is out of place or it is not the correct shape. In many cases, this condition is present at birth. Some people may not be diagnosed during childhood, however, and only when symptoms appear later is the problem identified. Although some adults with hip dysplasia need surgery to correct the problem, total hip replacement isn’t always necessary.
Source: Mayo Clinic