An 18-month-old early-walking boy has bilateral bowlegs. Radiographs show steep medial sloping of the proximal tibial metaphyses with medial beaking and irregular ossification confined to the tibia, sparing the femora. Which feature best distinguishes this condition from physiological genu varum?

• A Lateral cortical thickening of the distal femur
• B Symmetrical varus that increases with weight bearing and resolves by age 4
• C Widening of the intercondylar notch
• D Medial metaphyseal beaking with irregular ossification of the proximal tibial epiphysis ✓

Explanation

Infantile Blount's disease (tibia vara) shows Langenskiold changes: medial depression and beaking of the proximal tibial metaphysis, irregular widening of the physis medially, and later a step in the medial epiphysis. Physiological genu varum is symmetrical, involves femur and tibia evenly, shows smooth metaphyseal borders, and self-corrects by about 3 to 4 years. Varus that worsens progressively past the expected resolution age should prompt consideration of Blount's disease.

Reference: Tachdjian's Pediatric Orthopaedics, 5th ed.

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