Radiographic evaluation of bowed legs in children.
Radiographic screening is widely used to distinguish between Blount disease (infantile tibia vara) and physiologic bowing. Thirteen children with Blount disease, evaluated before 3 years of age, with initial radiographs showing no sign of Langenskiold changes, were compared with 50 children with physiologic bowing, also evaluated before 3 years of age with similar radiographic studies. Screening test accuracy was determined retrospectively for measurement of the mechanical axis, the tibial metaphyseal-diaphyseal angle (TDMA), and the epiphyseal-metaphyseal angle (EMA). A radiographic screening method combining the TMDA and the EMA, using cutoff values of 10 degrees and 20 degrees respectively, exhibited the best combination of sensitivity, specificity, and positive predictive value, correctly identifying all cases of Blount disease and 40 of 50 cases of physiologic bowing. Our data suggest that children between 1 and 3 years of age with TMDA <10 degrees, or TMDA > or =10 degrees and EMA < or =20 degrees, are at less risk for development of Blount disease. Children with TMDA > or =10 degrees and EMA >20 degrees are at greater risk for development of Blount disease and should be followed closely.