Doctors aren't sure what causes this to happen. Hip dislocation occurs in about one per cent of all newborns. Infants are routinely screened for hip problems at birth. When hip dislocation is present at birth, the risk of another problem called congenital muscular torticollis (CMT) is much higher.

In CMT, the sternocleidomastoid muscle (SCM) is contracted or stuck in a shortened position. This pulls the head and neck to one side. The head is often tilted and rotated. Boys are more likely than girls to have both DDH and CMT.

There could be a genetic factor as some of these problems tend to run in families. with the gender gap, there may also be a hormonal factor. Less often there is a movement disorder and the child is born with other developmental disabilities.