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 Blou nt disease, evaluated before 3 years of age, with initial radiographs showi ng no sign of Langenskiold changes, were compared with 50 children with phy siologic bowing, also evaluated before 3 years of age with similar radiogra phic studies. Screening test accuracy was determined retrospectively for me asurement 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 a nd 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 sugge st that children between 1 and 3 years of age with TMDA <10<degrees>, or TM DA greater than or equal to 10 degrees and EMA less than or equal to 20 deg rees, are at less risk for development of Blount disease. Children with TMD A greater than or equal to 10 degrees and EMA >20 degrees are at greater ri sk for development of Blount disease and should be followed closely.