Review Question - QID 220855

The patient presents with infantile Blount's disease, characterized by a progressive, often asymmetric varus deformity of the proximal tibia that does not spontaneously resolve after age 2–3. The presence of a metaphyseal-diaphyseal angle (MDA) greater than 16 degrees on radiographs most reliably distinguishes infantile Blount's disease from physiologic genu varum (Answer 2).

Infantile Blount's disease is a progressive, asymmetric varus deformity of the proximal tibia presenting before age 4. This most commonly occurs in children with risk factors such as obesity and early ambulation. Infantile Blount's is distinguished from physiologic genu varum by its lack of spontaneous resolution and characteristic radiographic findings. The current treatment algorithm is both age and severity-dependent: for children under 3 years with a mild deformity (Langenskiöld stage I–II), bracing may be attempted, but surgical intervention (most commonly proximal tibial osteotomy) is indicated for progressive or severe cases, especially after age 3 or in those with symptomatic changes. Growth modulation techniques, such as lateral tension band plating, are increasingly used in select cases, while gradual correction with external fixation is reserved for multiplanar or recurrent deformities. In advanced disease with medial tibial epiphysiodesis, combined procedures including epiphysiodesis and osteotomy may be required. The American Academy of Pediatrics recommends regular follow-up until skeletal maturity due to the risk of recurrence and complications such as limb length discrepancy and early osteoarthritis.

Brooks and Gross review the evaluation and management of genu varum in children, emphasizing the importance of distinguishing physiologic genu varum, which typically resolves spontaneously. This is in contrast to pathologic causes of varus deformity, such as infantile Blount disease and various metabolic and genetic etiologies of deformity (e.g., rickets, achondroplasia, renal osteodystrophy, osteogenesis imperfecta). The authors note that idiopathic Blount’s is the most common pathologic etiology, with management strategies tailored to patient age and disease stage. Radiographic assessment with standing lower limb films is essential for diagnosis and surgical planning, as deformity may involve the distal femur or proximal tibia. The authors conclude that when surgical intervention is indicated, restoration of the mechanical axis is the primary goal.

Jamil and colleagues conducted a systematic review to clarify knee measurement values in children aged 0–3 years with normal alignment, physiologic bowing, and pathologic bowing. They found that after 19 months of age, children with normal alignment no longer have measurable intercondylar distance (ICD) or clinical tibiofemoral varus. In contrast, children with pathologic genu varum have significantly higher ICD and radiologic tibiofemoral angles (rTFA) compared to those with physiologic bowing, with an ICD greater than 4 cm at 18 months, suggesting a pathologic process. The review concludes that children older than 18 months with persistent or pronounced varus should be monitored closely, and that ICD and clinical tibiofemoral angle are more useful than rTFA for early detection of pathologic bowing.

Figure A: AP radiograph of the bilateral knees demonstrating characteristic findings of infantile Blount's, including medial metaphyseal beaking and fragmentation of the proximal tibia with asymmetric varus deformity.

Incorrect Answers:
Answer 1: While early walking may be a risk factor for infantile Blount's, walking at 15 months is within the normal range and not diagnostic. This feature is nonspecific and can be seen in normal development.
Answer 3: This describes physiologic genu varum, which typically presents with symmetric, resolving bowing.
Answer 4: A normal ICD after age 18 months is typical of resolved physiologic genu varum rather than infantile Blount's.
Answer 5: Leg length discrepancy is not a consistent or early finding in either physiologic or pathologic genu varum, and its absence does not help distinguish between these processes.