Blount Disease

• Etiology:
  — Developmental disorder with disrupted endochondral ossification of the medial proximal tibial physis leading to abnormal development of the proximal medial tibial epiphysis and metaphysis
  — Risk factors of early ambulation and obesity suggest biomechanical component of stress to medial compartment of knee
• Imaging Radiograph:
  — Tibia has increased metaphyseal-diaphyseal angle (Drennan) of greater than 11 degrees (less than 11 degrees is physiologic bowing, borderline is 8-11 degrees)
  — Widened medial tibial physis
  — Medial tibial metaphysis is depressed and beaked and irregular and fragmented
  — Abnormal and delayed ossification of the medial tibial epiphysis
  — Angular deformities of genu varum on standing AP radiograph (mostly from tibia)
  — Procurvatum of tibia on lateral radiograph
  — Internal rotation of tibia and lateral subluxation of tibia
• Imaging MRI: Medial proximal tibia is location of:
  — Physis has widening and downsloping and physeal bar
  — Metaphysis has irregularity, downsloping, and increased signal intensity on T2WI
  — Tibial epiphyseal cartilage: Far medial is thick, central mid-coronal is thin leading to increased joint space
  — Medial meniscus is thickened with or without abnormal signal
  — Angular deformities of medial and posterior downsloping
  — Soft tissues: Perichondral membrane is thickened
• DDX: Physiologic bowing which shows a curved tibia while Blount disease has sharp angle at medial tibial epiphysis
• Complications: Limb shortening leading to limb length discrepancy if asymmetric or unilateral
• Treatment:
• Clinical:
  — Infantile or early onset form in less than 4 years (usually bilateral)
  — Late onset form in greater than 4 years (usually unilateral)

Radiology Cases of Blount Disease