The hip joint is created as a ball and socket joint. In DDH, the hip socket may be shallow, letting the ball of the long leg bone, also known as the femoral head, slip in and out of the socket. The ball may move partially or completely out of the hip socket. The greatest incidence of DDH occurs in first-born females with a history of a close relative with the condition. Hip dysplasia is considered a multifactorial trait.
Multifactorial inheritance means that many factors are involved in causing a birth defect.
The factors are usually both genetic and environmental. There appears to be a different threshold of expression, which means that one gender is more likely to show the problem than the other gender. For example, hip dysplasia is nine times more common in females than males. One of the environmental influences thought to contribute to hip dysplasia is the baby s response to the mothers hormones during pregnancy. Once a child has been born with hip dysplasia, the chance for it to happen again in a male or female child is about 6 percent overall.