Juvenile Blount's disease: bilateral case with asynchronous onset.

We encountered a rare case of bilateral juvenile Blount's disease diagnosed as unilateral at the onset. The patient was a 9-year-old girl who visited our outpatient clinic with pain and deformity in the left knee. Examination of the left knee showed severe varus deformity. Correction of the varus deformity and tibial shortness was carried out at the same time by the callotasis method using an Orthofix external fixator. During follow-up the varus deformity in her right knee gradually progressed. At 18 months after the initial surgery, the right varus deformity and tibial shortness were corrected at the same time by the callotasis method using an Orthofix external fixator; proximal epiphysiodesis was also performed. The coronal-plane alignment of both knees remains good. In cases with bilateral involvement of Blount's disease, the onset of the deformity is usually nearly synchronous. In some cases, however, it begins unilaterally, as with this patient, so it is essential to check both sides by means of tomography or magnetic resonance imaging and not just radiography. Moreover, we must be careful to plan the treatment in such a case so as to anticipate possible leg-length discrepancy problems.