What Is Blount's Disease?

A Cause of Bowed Legs in Children

Blounts Disease
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Bowed legs can be common in young children, but most often kids grow straight as time goes on. It's normal as kids start walking, in their first years of life, to have bowing of their legs. But over time, the legs should straighten out. However, there are conditions that can cause abnormal alignment of the lower extremity, leading to progressive bowing of the legs that does not spontaneously resolve.

One of the most common in children is a condition called Blount's disease. Blount's disease is a problem that causes abnormal growth and alignment of the legs.

There are two primary types of Blount's disease: infantile and adolescent. The infantile Blount's disease in typically diagnosed in kids age 2 to 5, whereas adolescent is found in early teenage children. There is also a less-common type of this condition called juvenile Blount's disease, or intermediate Blount's disease, as it occurs in ages between infantile and adolescent Blount's.

Infantile Blount's Disease

Infantile Blount's is a condition that causes bowed legs in toddler aged children. It is about twice as common in boys than girls, and often occurs in both knees. The condition causes an abnormality of the growth plate on the top of the shin bone, the tibia. The cause of the problem is not known, but the condition causes a deceleration of growth in a portion of the growth plate (but not all of it) so the growth of the tibia becomes asymmetric—as a result the bone bows as the outside grows faster than the inner side.

While the cause of infantile Blount's disease is not known, there are some known risk-factors, including:

  • Early walking age
  • Obesity and large stature
  • Black or hispanic children
  • Vitamin D deficiency

There are several conditions that can look like Blount's disease, including a persistent bowing of the legs that is normal in younger children, rickets, and other systemic conditions that can lead to an abnormal stature.

Left untreated, infantile Blount's disease can lead to abnormalities of gait, and ultimately to knee joint problems including meniscus tears and knee arthritis. Most often young children, under the age of 4, are treated non-surgically to determine if the condition is going to be persistent or spontaneously resolve. Many doctors recommend bracing, although it has never been demonstrated that bracing truly alters the course of the condition. Some doctors believe that the patients who improve with braces would have likely improved without bracing.

Surgical options vary substantially, but a surgical approach in generally recommended for children with progressive Blount's disease over the age of 4 years. Most commonly, the bone is broken (an osteotomy), realigned, and held in a new position to correct the deformity. The new position is actually an overcorrection to hopefully lead to a straight leg upon completion of growth. Determining how to best reset the position of the extremity is challenging and best accomplished by a surgeon with a lot of experience treating Blount's disease.

Adolescent Blount's Disease

Adolescent Blount's disease shares many characteristics with the infantile form, but also has some distinctions.

Foremost, adolescent Blount's is almost always the result of obesity, and the condition is becoming more common with the increasing problem of childhood obesity. While the cause is not entirely clear, it is suspected to be the result of damage to the growth plate from increase body weight that the growth plate cannot tolerate.

Bracing has not been shown to be effective in adolescent Blount's and is not used. Surgery is the standard treatment for adolescents with a significant bowed leg deformity from Blount's disease. The most common surgery is to break the bone and reset it, although unlike the younger patients, the alignment should not be overcorrected.

In addition, some surgeons will stop the growth, a procedure called an epiphysiodesis, at the remaining growth plate to ensure further deformity does not occur.

Sources: 

Birch JG. "Blount disease" J Am Acad Orthop Surg. 2013 Jul;21(7):408-18.

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