What is It?
In 1910, Drs. Legg, Calve', and Perthes independently described a disorder of the hip in young children. Many theories have been proposed as to the cause including inflammation, infection, trauma, and even "hip problems" noted at birth. The most popular theory at the present time is that for some unknown reason, there is a temporary loss of the blood supply to the femoral head (ball portion of the hip joint). In the growing child, the two major components of the hip joint are the ball (femoral head) and the socket (acetabulum). These two structures are pictured in figure (1). The femoral head in the growing child has several distinct zones, figure (2). The metaphysis is the spongy bone area in the femoral neck or that portion of bone next to the femoral head. The physis is the growth center of the femur (thigh bone). It is composed of bone forming cells that enable the bone to grow in length. The epiphysis is located between the physis and the acetabulum (socket), and it actively contributes to the growth of the femoral head (ball portion). As stated earlier, for some unknown reason, there is a temporary interruption in the blood supply to the epiphyseal, physeal, and sometimes metaphyseal portion of the femur of the hip joint. This is shown by the stippled area in figure (3). When this happens, a part or all of the area involved temporarily dies. It is important to understand that the acetabulum (socket) is not affected or involved in this loss of blood supply.

Who Is Affected?
Perthes disease most commonly is seen in the 4-8 year age group, but children age 2 years up to teenagers, can be involved. Boys are involved more than girls by a ratio of 4 or 5 to 1. Perthes can involve both hips in 10-12% of the youngsters but does not occur simultaneously at the exact same stage. Reports exist showing positive family histories (up to 20%), but it has never been proven to be inherited. Generally speaking, children with Perthes disease tend to be shorter in stature than average.

How Is It Detected?
Children with Perthes disease most commonly have a limp that has been slow and intermittent in its appearance. Pain is not usually a major factor, and often seems more activity related. Because of slow onset and minimal pain, if any, it may be months before the parents seek help in determining the cause of the problem. Often, children will complain of knee pain, when the problem is located in the hip. Initially, the doctor, during examination, will find a child that limps, has loss of motion about the hip, and in cases of longer duration, evidence of muscle wasting or atrophy about the involved hip and thigh.