Blount disease is an asymmetrical disorder of proximal tibial growth that produces a three-dimensional deformity. Tibia vara is the main component of the deformity. Blount disease exists as two clinical variants, infantile or early-onset, and adolescent or late-onset, defined based on whether the first manifestations develop before or after 10 years of age. The pathophysiological mechanisms are unclear. In the Americas and Caribbean, Blount disease chiefly affects black obese children. Without treatment, the prognosis is often severe, particularly in the infantile form due to the development of medial tibial epiphysiodesis at about 6 to 8 years of age. In other parts of the world, the associations with black ethnicity and obesity are less obvious and the prognosis is often less severe. A consensus exists about the optimal treatment in two situations: before 4 years of age, progressive Blount disease should be corrected, preferably by a simple osteotomy; and once medial tibial epiphysiodesis has developed, both a complementary epiphysiodesis and gradual external fixator correction of the other alignment abnormalities, rotational deformity, and limb length are required. After 4 years of age, the outcome in the individual patient is difficult to predict. Magnetic resonance imaging supplies information on the morphology and vascularisation of the growth regions, thereby helping to guide treatment decisions. In the adolescent form, morbid obesity limits the treatment options. Untreated Blount disease in adults is rarely encountered. A more common occurrence is the presence of residual abnormalities at skeletal maturity in patients treated for Blount disease in childhood. Premature osteoarthritis may develop. In this situation, osteotomy may delay the need for total knee arthroplasty.

The treatment of infantile Blount's disease remains controversial. The progressive development of epiphysiodesis of the medial tibial physis induced a complex deformity of the lower limb such as severe genu varum, joint incongruity, torsion instability and leg length discrepancy with major functional consequences. Nine knees on eight children (average age was 7 years and 2 months) were treated by a one-time procedure using a specific external fixator that combined elevation of the medial tibial plateau, axial correction in the valgus, complete sterilization of the upper tibial growth cartilage, leg lengthening anticipation and de-rotation if necessary. Magnetic resonance imaging was useful to describe the deformity and to prepare for surgery. Corrections were progressively obtained through the physis plan by means of short incisions and the use of a specific external fixator. The primary results at an average of 24 months were good with a low rate of complications but final evaluation will be conducted at the end of the children's growth period.

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