About Perthes Disease
What is Perthes Disease?
Perthes disease is a childhood hip disorder caused by a disruption of blood flow to the ball (called femoral head) of the hip joint. The loss of blood flow produces the death of bone in the femoral head, which is referred to as "avascular necrosis" or "ischemic necrosis" of the femoral head. The basic anatomy of the hip is shown in the illustration to the right.
Perthes disease is also referred to as Legg-Calvé-Perthes disease or Legg-Perthes disease. The names come from the three men who first reported the disease in 1910 – Arthur Legg (USA), Jacques Calvé (France), and Georg Perthes (Germany).
What causes it?
We do not know what causes the disruption of blood flow to the femoral head. Perthes disease does not have a strong genetic inheritance, and in fact, only about 5 percent of the patients have a family member with the condition. It also does not appear to be caused by direct hip injury.
Some studies have shown an association between Perthes disease and following factors:
exposure to cigarette smoking, rare blood clotting disorders, hyperactivity and attention deficit disorder, and minor congenital abnormalities like inguinal hernias and undescended testes.
Who gets it?
Perthes disease affects a wide age range of children (ages of 2 to 15) but the most common age range is between 4 and 9. Boys are four times more likely affected than girls. Ten percent of patients will have Perthes in both hips (referred to as bilateral disease). Usually one side is affected first and then the oher side will get the disease a few years later.
There is some variation in the frequency of Perthes disease between different regions and ethnic groups.
What are the symptoms?
In general, Perthes disease produces symptoms that have a gradual onset. Pain and limping are two common symptoms. The limping is often worse with activity or at the end of the day and often usually improves with rest. Pain is usually not specific to the hip. More often, children experience thigh or knee pain which delays proper diagnosis. Parents may notice that the movement of the affected hip is less than the unaffected side.
What is the progression of Perthes?
Perthes disease goes through 4 stages numbered 1 to 4. These are called Waldenström radiographic stages as it was first described by Dr Waldenström using x-rays. The duration of each stage is different with the stage 3 being the longest. Younger patients (those less than 6 years old when the disease began) tend to move through the stages faster and have better outcomes. Note that older patients (those over age 11) may not go through the stages as described below.
- Stage 1 is called the Initial or avascular necrosis stage
On x-rays, the femoral head looks whiter and smaller than the unaffected side due to the disruption of blood flow that causes bone death. Early flattening of the top of the femoral head or fracture line (called subchondral fracture or crescent sign) can be seen. This stage generally is less than one year.
- Stage 2 is called the fragmentation or resorptive stage
In this stage, the femoral head looks irregular and broken up (fragmented) with a more flattened appearance. These x-ray irregularities are due to the dead bone being removed by the healing process creating areas without bone (seen as dark areas on x-rays). The removal of the dead bone is called resorption and thus this stage is sometimes referred to as the resorptive stage. The femoral head can also appear to be moving out of the socket (called lateral subluxation or extrusion). This stage generally lasts 1 to 1 1/2 years.
- Stage 3 is called the reossification stage
In this stage, new bone (seen as increased white appearance of the femoral head) starts to fill in the areas where the dead bone has been removed. The newly-formed bone can be seen along the outer perimeter of the femoral head that gradually fills in towards the central area. Because the new bone is filling in, this stage is called the ossification stage. This stage is usually the longest stage and can take 2-3 years.
- Stage 4 is called the healed stage
In this stage, the appearance of the bone in the femoral head looks similar to the normal side. It is homogeneous and the irregular, fragmented appearance is no longer seen. The affected femoral head, however, can be enlarged (called coxa magna), flattened (coxa plana), and have a short, broad neck (coxa breva). The final shape of the femoral head at this stage (the degree of flattening or deformity) and how it fits the socket largely determines the long-term outcome. This is the stage where Stulberg radiographic classification is applied (see "Prognosis").