This condition usually occurs during the teenage years when the thighbone is growing the most. Growth occurs at the growth plate in the upper neck portion of the thighbone, or femoral head. The upper neck portion of the thighbone slips from the growth plate, as seen on a hip x-ray. Children often limp or complain of thigh or knee pain. This may come on slowly or after an injury. The slip of the upper part of the head leads to chronic change in the bone and may lead to limping, long-term pain, and premature arthritis.