Review Question - QID 218582

This patient has Infantile Blount's disease, but given his relatively advanced age (>=4), he is indicated for surgical management with a proximal tibia/fibular valgus osteotomy.

Infantile Blount's disease is a pathologic condition which causes progressive genu varum in children, most commonly ages 2-5 years old. The pathophysiology is incompletely understood, but likely relates to mechanical overload of the medial tibial physis in susceptible individuals. Blount's can be quantified radiographically using the metaphyseal-diaphyseal (Drennan) angle, where >16º is considered abnormal and likely to progress. The Langenskiold classification is also used to describe the degree of epiphyseal-metaphyseal growth disturbance (Illustration A). In children <3 years old, brace treatment with a knee ankle foot orthosis (KAFO) is indicated in Langenskiold type I or II disease. In stages III-VI or any children >3 years old, surgical management with proximal tibia/fibular valgus osteotomy is recommended.

Davids et al. reviewed the clinical evaluation of bowed legs in children, noting that it is important to be able to differentiate between physiologic and pathologic bowing. They do not recommend routine radiographs, but do recommend the "cover up," test to identify young children who are at high risk for infantile tibia vara. They concluded that the cover up test had a high positive and negative predictive value for infantile tibia vara.

Scott et al. evaluated body mass index as a prognostic factor in development of infantile Blount's disease. They noted that patients with an elevated BMI had a higher risk for developing Blount's. They created a criteria for diagnosing Blount's which included a Drennan angle > 10º and a BMI >=22, which had high sensitivity, specificity, and predictive values.

Levine et al. were instrumental in the early radiographic evaluation of tibia vara. They developed the metaphyseal-diaphyseal angle by creating an intersection through the proximal tibial metaphysis and a line perpendicular to the long axis of the tibial diaphsysis. They noted that deformity in the proximal tibia is more commonly pathologic and they used an angle > 11º as a cutoff for patients most at risk.

Illustration A demonstrates stages I-VI of the Langenskiold Classfication. Illustration B demonstrates the "cover up test," for evaluating Infantile Blount's.

Incorrect Answers:
Answer 1: Observation is not appropriate for a 4 year-old patient with infantile Blount's disease, despite type II Langenskiold classification.
Answer 2: Ankle foot orthosis (AFO) would not appropriately address the knee pathology, even in cases where brace treatment was appropriate.
Answer 3: KAFO would be indicated in patients <3 years old with Langenskiold type I or II disease.
Answer 5: In infantile Blount's disease, the pathology is centered on the proximal tibia, therefore a distal femur osteotomy is not appropriate.