For 100 years now, since Legg-Calvé-Perthes (LCP) disease was first described, physicians have been searching for the cause of this condition. In this article, Dr. Harry Kim, an orthopedic surgeon from Texas Scottish Rite Hospital for Children reviews the current thinking on the etiology (cause) of LCP.
Perthes disease is a condition that affects the hip in children between the ages of four and eight. The condition is also referred to as Legg-Calve-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. The blood supply eventually returns, and the bone heals.
How the bone heals determines what problems the condition will cause in later life. Perthes disease may affect both hips. In fact, 10 to 12 percent of the time the condition is bilateral (meaning that it affects both hips). This condition can lead to serious problems in the hip joint later in life.
Clearly the problem is one of blood loss called ischemia. The area affected most is the head of the femur (thigh bone). This has been confirmed with today’s modern imaging studies. As a result of this blood loss, the bone dies and starts to collapse. Soon the smooth, round head of the femur starts to flatten and deform.
But what causes the decreased vascularity (blood flow) and can it be stopped before the damage is done? Dr. Kim tells us that many experts believe LCP is the result of several or even many factors. Another way to say this is that LCP is a multifactorial disease with both genetic and mechanical contributing
factors.
On the genetic side, it’s possible some children are more susceptible (more likely) than others to develop this problem. But it takes one or more “triggers” (environmental or external factors) to start the process.
Let’s back up and take a little closer look at the proposed causes of LCP. there are families with many members who have LCP as a result of a mutation in a particular gene. The affected gene controls the strength of collagen tissue. One miscoding in the gene and the hip joint cartilage and its blood vessels don’t form correctly.
Another biologic factor that contributes to some cases of LCP is a protein deficiency. Without the proper sequencing of these important proteins, affected individuals have abnormal coagulation (blood clotting). Abnormal blood clotting can cut off blood supply to the femoral head.
Other potential biologic factors that may be linked with LCP disease include low levels of abnormal insulin-like growth factor (IGF-1), low birth weight, and short body length at birth. Exposure to nicotine and other chemicals from tobacco is an important factor recently discovered. Likewise LCP may be triggered by exposure to tobacco if the mother smokes during pregnancy or the child is exposed to second hand smoke during infancy and early childhood.
With this much information in hand, further studies were done. Now there is some evidence that LCP can develop after a single episode of ischemia (blood loss) no matter what the cause. But the risk goes up with repeated (multiple) episodes of blood loss. If this proves to be true, then it is essential to predict, recognize, and stop all ischemic episodes.
Some experts suggest that one way to help prevent the damage done to the hip by this problem is to avoid mechanical pressure on the compromised blood vessels. That could mean keeping the child off his or her feet in a nonweight-bearing state. Limited weight-bearing will protect more than the blood vessels. Compression and load on the joint cartilage, growth plate, and bone will also be reduced.
Although these guidelines make sense, how much pressure and force are put on a child’s hips with different activities is not clear. Is running a bigger problem than walking? Is it how often the child is weight-bearing that makes a difference? Or could it be the number of steps taken each day should be limited? And how much does the child’s body weight play a role?
These are just some of the questions that need answers before early and more effective treatment can be prescribed for LCP disease. Many advances in research have been made over the last 100 years. Many more are expected in the next 100!