Radiographic characteristics of lower-extremity bowing in children.

Lower-extremity bowing is common in infants and children and can result from a variety of conditions. At radiography, developmental bowing shows varus angulation centered at the knee, "metaphyseal beaking," thickening of the medial tibial cortices, and tilted ankle joints. Tibia vara (Blount disease) demonstrates genu varum and depression of the proximal tibia medially. Congenital bowing manifests as posteromedial bowing with cortical thickening along the concavity of the curvature and, in some cases, diaphyseal broadening. In rickets, radiographic changes occur primarily at sites of rapid growth and are predominantly metaphyseal, with widening of the zone of provisional calcification. Achondroplasia is characterized by shortening and thickening of the long bones with metaphyseal flaring and cupping. In neurofibromatosis, there may be anterolateral bowing of the tibia, and there is often focal narrowing and intramedullary sclerosis or cystic change at the apex of the angulation. The tibia is typically involved at the junction of the middle and distal thirds. Osteogenesis imperfecta demonstrates bowing from softening due to osteoporosis and multiple fractures and typically involves the entire skeleton. In camptomelic dysplasia, lower-extremity bowing is associated with a short trunk, short limbs, and deficiencies in pelvic bone development. Recognition of these pathologic conditions is important for differentiating those that will resolve spontaneously from those that require surgery or other treatment.