Limb Length Discrepancy

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Blount Disease

Blount disease is a growth disorder that affects the bones of the lower leg, causing them to curve outward. There are two types: infantile, which affects young children usually before age 4; and adolescent, which affects older kids and teens. In young kids, up to 70% of cases are bilateral (meaning both legs are affected), while teens are more likely to have the condition in just one leg.

Blount disease is different from bowleggedness, which is so commonly found in babies and toddlers. Due to the position of the fetus in the womb before birth, babies' legs are naturally bowlegged. This curvature usually straightens out once babies begin to walk.

But in a child with Blount disease the curvature will not correct itself over time and will only get worse if left untreated. That's why an early diagnosis is important.

Understanding Blount Disease

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

Kids and teens who are still growing also have a growth plate at the top of the tibia called the physis, which is made out of cartilage and is weaker than bone. The job of the physis is to allow the bone to lengthen and grow.

Sometimes, though, when the physis is subjected to more pressure than it can comfortably handle, it starts off a series of events at the top of the tibia. The inner part, just below the knee, gets compressed and may even stop making new bone, while the outer part continues to grow normally. This uneven bone growth — combined 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. See the bend?)

Risks Factors

The development of Blount disease is sometimes related to a child's weight, especially among teens. Most kids who get it are overweight or obese or have recently undergone a period of rapid weight gain. It is also more common in girls, people of African heritage, kids who started walking at an early age, and those with a family member who had the condition.

Signs and Symptoms

The most obvious symptom of Blount disease is a bowing of the leg below the knee. In young children this is usually not painful, though it can sometimes affect the way they walk. For preteens and teens, the discomfort can be worse and, at first, can be mistaken for growing pains.

A bowing tibia also can cause other problems 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 inward, causing a condition called intoeing (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. Rarely, one leg may also become slightly shorter than the other.

Diagnosis

If your child's legs are bowed — and especially if your child is also complaining of knee pain that seems to be worsening over time and can't be traced back to an injury — the doctor may suspect Blount disease and refer you to an orthopedic doctor, who specializes in the treatment of bones.

The orthopedic doctor will perform a complete physical exam and also take X-rays of your child's legs. He or she will look for the telltale signs of Blount disease, which are abnormal bone growth patterns at the top of the tibia. The X-rays will let the doctor take several different measurements of your child's leg to determine how severe the bowing is and what the best treatment plan would be.

It's important to realize that some mild bone changes can be difficult to spot in kids younger than 2, and it's often hard to tell whether a toddler has normal, age-appropriate bowing that will self-correct or a developing case of Blount disease. Close follow-up is necessary, and usually by age 3 it's easier for a doctor to make a diagnosis.

Treatment

The treatment of Blount disease depends on how old your child is and how far the disease has progressed. Kids younger than 2 might just need careful monitoring until doctors are sure the bowing is due to Blount disease and not a part of normal development.

Severe bowing and bowing in kids between 2 and 4 years old might require leg braces known as KAFOs (knee-ankle-foot orthotics). KAFOs, which go from the thigh to the toes, are created specially for kids using a mold of their leg. Over time, the devices gradually shift the leg bones to a straighter, more aligned position.

For older kids and teens, or kids for whom bracing doesn't work, surgery is often necessary. Many different types of surgery are used to correct Blount disease:

  • An osteotomy is a procedure where the bone is cut, realigned, and fixed internally with plates and screws.
  • A hemi-epiphysiodesis is a procedure to stop the growth of the normal half of the physis to allow the diseased side to catch up and straighten out the leg.
  • A Taylor Spatial Frame is an external fixation device that holds the bones in place from the outside while correcting the bowing and rotation of the leg.

Whichever method the surgeon recommends, the procedure will be done under general anesthesia, which means your child will be sedated and asleep and won't feel a thing during surgery. Afterward, your child might need to wear a cast and/or use crutches for a while. Physical therapy also might be necessary.

Outlook

Most kids who undergo treatment for Blount disease do extremely well and make a complete recovery.

Overall, it's important for parents to monitor the factors that might have contributed to their child's condition. For example, if a child is overweight, helping him or her maintain a healthy weight can go a long way toward sparing bones and joints from excess wear and tear, and prevent other long-term complications of weight gain (like type 2 diabetes and heart disease).

If you need help figuring out how to get your child on the road to a healthier lifestyle that includes a balanced diet and exercise, talk to your doctor.

Reviewed by: Kerry L. Loveland, MD
Date reviewed: June 2013