Research has shown us that Legg-Calvé-Perthes occurs more often in certain geographical areas. For example, children in Northern Europe have the highest rate of occurrence while children around the equator have the lowest incidence. Why is that?
Well, first, what is Legg-Calvé-Perthes disease (also known as Perthes disease)? Perthes is a condition that affects the hip in children between the ages of four and eight. The condition is referred to as Legg-Calvé-Perthes disease in honor of the three physicians who each separately described the disease.
In this condition, the blood supply to the growth center of the hip (the capital femoral epiphysis) is disturbed, causing the bone in this area to die. There is also an imbalance between the bone building cells (bone deposition) and bone breakdown (bone resorption). The blood supply does eventually return and the bone heals.
How the bone heals determines what problems the condition will cause later in life. Understanding the effects on the bone cells during the early days of this disease helps direct treatment. A three-tier surgical approach has been proposed starting with preventive surgery to preserve the round head of the femur (thigh bone).
The surgeon may use one of several techniques to “contain” the head of the femur in the socket in order to help keep the round shape. This approach is meant to prevent deformity of the femoral head and works best for older children (age six and older). Younger children are more likely to respond well to conservative (nonoperative) care and don’t need corrective surgery.
The second surgical approach is called remedial surgery. The goal is damage control after the disease process has already started to change the bone structure. In other words remedial surgery is to minimize the effects of the deformity that has already occurred (e.g., fragmentation and/or collapse of the femoral head). The child must have good bone quality that can hold up under the stress and pressure of weight bearing. Reducing pain and improving function is possible.
The third tier of treatment referred to as salvage surgery is done to reshape the femoral head and reform the acetabulum (hip socket). This more extensive reconstructive (“joint preserving”) surgery is used for patients who have joint deformity. They are usually older and may even be adults for this type of treatment. They often also have damage to the surrounding cartilage and soft tissues.
Children who do not receive treatment early enough or for whom treatment is not effective may eventually develop degenerative arthritis. Structural changes may be too great for reconstructive surgery. That’s when total hip replacement may be indicated. Saving the joint helps put off hip joint replacement for as long as possible. Studies have shown that people with long-term degenerative effects of Perthes who have total hip replacement before age 40 report a reduced quality of life.
Despite this understanding of a three-tiered approach to Perthes disease, there is still much to be discovered to create the best results. For example, the amount of femoral rotation and the angle of the bone as the femoral head fits into the socket may make a difference in outcomes. How much of the femoral head should be covered by the socket is another area that requires further study.
Knowing that excessive bone resorption is part of the early damage associated with Perthes has led scientists to look for ways to prevent this from happening. Medications (by mouth or by injection directly into the hip) such as bisphosphonates to prevent bone loss are being used in animal studies. These drugs may help decrease bone deformity while the body heals itself and restores blood flow to the area. Other biologic therapy to prevent bone loss is also being investigated.
Now back to the original question. Why do more children in northern latitudes develop Perthes (e.g., northern Europe)? Researchers have uncovered two possible environmental factors: second hand smoke from cooking stoves and tobacco as well as lower socioeconomic status. Children in families with lower incomes appear to be at greater risk. Although these variables have been uncovered, the exact way in which these things contribute to Perthes disease remains unknown.