- 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
