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Blount’s Disease

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Blount’s disease affects the inner edge of the upper shin bone at the knee growth plate (epiphyseal plate – runs horizontally across the knee), causing it to decrease its rate of growth in the portion of the growth plate that is closest to the leg’s inseam. The outside part of the growth plate continues to grow normally, leading to progressive bowing.

Blount’s disease affects two different age groups. There is infantile Blount’s, seen in young children, and adolescent Blount’s, seen in teenagers. In both groups, the children tend to be overweight for their age. This bowing deformity is always associated with internal tibial torsion (an inward direction of the ankle and foot relative to the direction of the knee). The left knee is aimed dead straight ahead, yet the ankle is directed toward the child’s right.{{more}}

If infantile Blount’s is diagnosed early enough, bracing can be instituted. We have had good results bracing children as young as two years old. Usually by the age of three, treatment will require a tibial osteotomy (surgery of the tibia) to straighten the lower extremity. Many will wait and “see how it goes”, and let the most effective bracing period go right by. In a special parallax-free three exposure x-ray of the full leg from hip to ankle, with the knee carefully aimed straight ahead , a line through hip and ankle centers ought to pass through knee center.

If that line passes outside the bone of the knee, then the angulation will worsen with time and not self-correct. We have seen no such reversals in that subset of children. We prefer to brace as bracing early not only works better but heads off the additional damage to the inner growth plate caused by the angular mechanical (nut cracker) compression caused by the bowed leg.

Depending on how crushed the growth plate is, the bowing may recur after surgery. Tibial osteotomy (tibia = shin bone, osteo = bone, tome = to cut) is also part of the treatment for the adolescent. There are many different techniques for performing the osteotomy. No matter what technique is chosen, the osteotomy must correct the bowing and twist (tibial torsion) at the same time. Bracing also attempts to correct both deformities at the same time.

X-rays are helpful for diagnosing Blount’s disease as well. But there is an important detail to be aware of when taking these x-rays. Usually an anterior -posterior (AP) view of the lower extremity is obtained with the knee pointed straight ahead (ignoring the foot direction). The growth plates are checked for any abnormality, such as is seen in rickets and other diseases.

Angle measurements about the proximal tibia as well as between the tibia and femur are made, which will help determine if Blount’s disease is present. Importantly, a line from the center of the hip joint to the center of the ankle joint is drawn as discussed above. This is the best prognosticator for progression.

This line is the weight bearing line of the lower extremity. If it passes completely beyond the knee joint substance, then whenever weight is placed on the leg it is passed from the hip to the ankle levered through the very medial part of the knee. The leverage amplifies the forces. This will tend to make the bowing worse over time, damaging the growth plate, and is an indication for treatment of the bowing.

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