At 14, Jamie was seriously overweight. Although she hated the term obese, she knew it probably applied. She also knew that her weight made it harder to do some things, like run the mile in PE and take her dog for long walks through the hilly town park.

But until she went to the doctor to see why her knee was hurting, she had no idea that being overweight was also causing another problem: Blount disease.

What Is Blount Disease?

Blount disease is a growth disorder that affects the bones of the lower leg, causing them to bow outward. It can affect people at any time during the growing process, but it's more common in kids under 4 and in teens. In younger kids both legs are often affected, but in teens it's usually just one.

To understand Blount disease, it helps to know about the tibia and the fibula — the two parallel bones that make up the lower leg. The fibula is the thinner bone located on the same side of the leg as your pinky toes. The larger bone, the tibia (or shin bone), is located on the same side as your big toes. When we stand, the tibia is the bone that bears most of our weight.

In kids and teens who are still growing, there is also a growth plate at the top of the tibia. This is called the physis and it's made out of cartilage, which is weaker than bone. The job of the physis is to allow the bone to lengthen and grow.

Sometimes, though, the physis has to bear more pressure than it can comfortably handle. This can start a series of events at the top of the tibia: The inner part, just below the knee, gets compressed. It may even stop making new bone. But the outer part continues to grow normally.

This uneven bone growth — coupled with increased pressure from above — causes the tibia to bow outward instead of grow straight. (Need a visual? Take a coffee stirrer and hold it upright — now push down gently from the top and imagine that's your tibia.)

Blount disease is very different from the type of bowlegs that are so common in babies and toddlers. Babies' legs are naturally bowed. But the bowing almost always straightens out on its own once a child starts walking between the ages of 1 and 2. Blount disease, on the other hand — whether it starts in early childhood or the teen years — will not correct itself over time and will only get worse if left untreated. That's why it's important to catch it early.

What Are the Symptoms?

The most obvious sign a person might have Blount disease is bowing of the leg below the knee. In young kids this is usually not painful, but for teens it can be (it may feel like a growing pain in the knee area). The pain may come and go. Most teens have already been taking over-the-counter pain relievers for it by the time they see a doctor.

A misaligned tibia can cause other problems, too, mainly due to a shift in the way the lower leg bears the weight of the body. For example, the tibia can actually start to rotate as well as bow, causing a condition called in-toeing (when the feet point inward instead of straight out).

Over time, Blount disease also can lead to arthritis of the knee joint and, in very severe cases, trouble walking. In rare cases, one leg may also become slightly shorter than the other.

What Causes Blount Disease?

Doctors believe the development of Blount disease is directly related to weight.

There are other underlying factors with Blount disease, though. In general, it's more common among girls, people of African heritage, kids who started walking at an early age, and those with a family member who also had it. Researchers are currently examining how the interplay of all these factors may contribute to the disease.

How Is It Diagnosed?

If your legs start bowing — especially if you also have knee pain that seems to be getting worse and can't be traced back to an injury — your doctor may consider Blount disease as a possibility. If so, your doc will refer you to an orthopedic specialist (a doctor who focuses on the treatment of bones).

The orthopedic doctor will do a complete physical exam and also take X-rays of your legs. X-rays help the doctor look for the abnormal bone growth patterns at the top of the tibia that are the telltale sign of Blount disease. They also help the doctor measure how severe the bowing is.

How Is it Treated?

How doctors treat Blount disease depends on how old the person is and how far the disease has progressed. Young kids may simply need to wear leg braces. Most older kids and teens will need to have surgery.

Many different types of surgeries can correct Blount disease — some involve cutting the tibia, realigning it, and holding it in place with a plate and screws; some involve removing the damaged growth plate; and some use an external device to hold the bones in place from the outside. If a person's toes turn in, surgeons must also correct the twist that's causing that, too.

Whichever method your surgeon recommends, the procedure will be done under general anesthesia (you will be completely asleep and won't feel a thing). Afterward, you'll probably need to wear some kind of cast and use crutches for a while. You'll also probably need physical therapy. The good news is, most teens make a complete recovery.

The Outlook

Most teens who have surgery to correct Blount disease soon find themselves returning to all their normal activities, even competitive sports. One lesson many people take away from dealing with Blount disease is the importance of keeping weight in a healthy range. Staying at a healthy weight can help protect bones and joints from excess wear and tear that can damage them over time.

If you would like help figuring out how to start on a safe diet and exercise plan, talk to your doctor.

Reviewed by: Alfred Atanda Jr., MD
Date reviewed: February 2010