Relative tibial and femoral varus as a predictor of progression of varus deformities of the lower limbs in young children.

Many young children present to pediatric orthopaedic surgeons with genu varum and mild beaking of the medial metaphysis on x-ray. Predicting whether these deformities will progress is challenging. In addition, there is no consensus as to whether these children should all be classified as having Blount disease. To avoid this latter problem, the authors included in this study all children presenting with bowed legs, regardless of diagnosis. With the aim of improving the ability to predict progression, the authors tested the hypothesis that patients with progression have more tibial than femoral varus. The authors reviewed 173 varus limbs of 98 patients younger than 4 years old. The authors determined the angular deformity in both femur and tibia by measuring the angles between their mechanical axes and the transverse axis of the knee, and determined the contribution of tibial deformity as a percentage of the total (%DT). The metaphyseal-diaphyseal angles of the tibia (MDA) were also measured to compare the value of that test with the %DT. There were 22 limbs with progressive and 141 limbs with resolving varus. Both the MDA and %DT were significantly different between groups. Tibial varus was found to exceed femoral varus in all patients with progression and also in several patients whose deformity resolved spontaneously. Although more specific and more sensitive than the MDA, the %DT is a good, but not perfect, predictor of progression. However, all patients in this series with both a %DT >50% and an MDA of 16 degrees or greater went on to progress. Using both of these tests together may therefore provide the surgeon with a reliable indicator of the children who would benefit from surgical correction.