Blount's Disease Classification
Blount's disease (tibia vara) is classified primarily by age at clinical onset into three distinct forms: infantile (0-3 years), juvenile (4-10 years), and adolescent (11 years and older), with the Crawford radiographic classification system being the most frequently utilized for staging disease severity. 1, 2
Age-Based Classification
The age-based classification system divides Blount's disease into distinct categories that have important prognostic and treatment implications:
Infantile Tibia Vara (Early-Onset)
- Age of onset: 0-3 years 2, 3
- Often bilateral presentation 4
- Manifests in the first few years of life with progressive tibial bowing 4
- Associated with early walking and obesity 4
- Progresses to more severe deformities, including depression of the medial tibial plateau 4
Juvenile Tibia Vara (Late-Onset)
- Age of onset: 4-10 years 2, 3
- Can be unilateral or bilateral 4
- Characterized by a high rate of recurrence (50%) following surgical correction in males with clinical onset ≤10 years of age 2
- Appears in obese children, predominantly affecting black children 2, 3
Adolescent Tibia Vara (Late-Onset)
- Age of onset: 11 years and older 2, 3
- Often unilateral presentation 4
- Clinical characteristics include: black race (consistent finding), 2:1 male predominance, normal height, marked obesity (mean BMI 41 kg/m²), and knee pain as primary presenting complaint 1, 2
- Females and males with onset >11 years have no recurrences after surgical correction, unlike the juvenile group 2
Radiographic Classification Systems
Crawford Classification (Most Frequently Utilized)
The Crawford classification is the most commonly used radiographic staging system and divides congenital pseudarthrosis of the tibia into two main types 1:
Type I
- Anterolateral bowing of the tibia with a narrow canal due to increased cortical thickness 1
Type II (Subdivided into IIA, IIB, and IIC)
- Type IIA: Anterolateral bowing with widening of the tibial canal and a tubulation defect 1
- Type IIB: Anterolateral bowing with a cystic lesion, indicating an impending fracture or healing from a previous fracture 1
- Type IIC: Anterolateral bowing with a frank fracture and pseudoarthrosis, with or without cystic change 1
Langenskiöld Radiographic Staging
While not detailed in the provided evidence, the Langenskiöld classification stages infantile tibia vara from I-VI based on progressive radiographic changes, with stages I-III being amenable to conservative or minimally invasive treatment 5.
Key Radiographic Features by Age Group
Infantile Form
- Typical roentgenographic findings with abrupt angulation of the proximal tibia into varus 3
- Epiphyseal wedging and metaphyseal beaking 4
Late-Onset Forms (Juvenile and Adolescent)
- Epiphyses are wedge-shaped due to medial flattening 2
- Physes are irregular in thickness 2
- Minimal, if any, increased prominence of the proximal medial metaphysis 2
- Average genu varum deformity of 19 degrees (range 10-45 degrees) 2
Additional Classification Considerations
Other Classification Systems
Multiple classification systems exist including Anderson, Boyd, Choi et al., and Paley classifications, though these are primarily descriptive and not specifically treatment-guiding 1.
Etiology-Based Categories
Tibia vara can be classified by etiology 3:
- Developmental (Blount's disease)
- Post-traumatic
- Post-infectious
- Focal fibrocartilaginous dysplasia (rare, 8 reported cases) 3
Clinical Pitfalls
The juvenile form (ages 4-10) has the highest recurrence rate after surgical correction (50% in males), making age at presentation a critical prognostic factor 2. This contrasts sharply with adolescent-onset disease where recurrence is rare, emphasizing that treatment planning must account for age-specific risks rather than treating all late-onset disease uniformly.