During childhood a growth plate exists between the neck and the ball (head) of the femoral bone. This is called the physis (picture). The growth plate is made of cartilage and during adolescence this area is weak. Occasionally the growth plate is weak enough that the head of the femur slips on the neck. This is called a slipped upper femoral epiphysis (SUFE) or slipped capitol femoral epiphysis (SCFE).
SUFE is generally thought to be quite rare (2 per 100,000 children). However, minor slips may be unrecognised, presenting in adult life with hip pain, impingement(link) or arthritis. The classical age of presentation is 12-14yrs in girls and 12-16 years in boys. Boys are more frequently affected than girls and in 25% of cases both hips are involved although generally not at the same time.