What is Blount disease (tibia vara), its clinical presentation, diagnostic work‑up, and management options for infantile and adolescent forms?

Blount Disease (Tibia Vara): Clinical Overview and Management

Definition and Pathophysiology

Blount disease is a growth disorder characterized by progressive varus angulation ("bowing") of the proximal tibia due to abnormal development of the medial aspect of the proximal tibial physis. 1 The condition results from diminished physeal growth medially, leading to an abrupt tibial angulation into varus at the proximal end. 2, 3

The disorder manifests as a multi-planar deformity including:

• Pronounced tibia varus (primary deformity) 1
• Proximal tibial procurvatum 1
• Internal tibial torsion 1
• Limb length discrepancy 1
• Depression of the medial tibial plateau in severe cases 1
• Compensatory deformities in the distal femur and distal tibia 1

Clinical Presentation

Two Distinct Forms

Infantile (Early-Onset) Blount Disease:

• Presents between ages 1-4 years 3
• Often bilateral 1
• Progresses to more severe deformities including medial tibial plateau depression 1
• Mean BMI in one series was approximately 41 kg/m² 4

Late-Onset Blount Disease:

• Subdivided into juvenile (ages 4-10) and adolescent (ages 11+) forms 1, 3
• Often unilateral 1
• Appears in obese children, particularly Black children between ages 6-15 years 3
• Strongly associated with severe obesity (mean BMI ~41 kg/m²) 4

Key Risk Factors

Higher BMI is the most significant modifiable risk factor, with severe pediatric obesity substantially increasing Blount disease risk. 4, 5 Additional associations include:

• Early walking 1
• Vitamin D deficiency 1
• Hereditary factors 1
• Mechanical stress from obesity 5

Diagnostic Work-Up

Clinical Assessment

Examine specifically for:

• Visible tibial bowing with varus angulation 5, 6
• Measurement of intercondylar distance to quantify deformity severity 7
• Gait abnormalities 1
• Limb length discrepancy 1
• Knee pain (though leg deformity is the primary presentation, not isolated knee pain) 6

Radiographic Evaluation

Obtain standing anteroposterior and lateral radiographs of both lower extremities to assess:

• Medial proximal tibial angle (MPTA) 8
• Mean axis deviation (MAD) 8
• Posterior proximal tibial angle 8
• Joint line congruence angle (JLCA) 8
• Langenskiold staging (stages I-VI based on physeal changes) 2

Common pitfall: Do not focus solely on knee radiographs when evaluating leg pain in obese children—always obtain hip radiographs to exclude slipped capital femoral epiphysis, which frequently refers pain to the knee and is commonly missed. 6

Laboratory Evaluation

Consider metabolic work-up in persistent or atypical cases: 7

• Serum phosphate
• Alkaline phosphatase
• 25-hydroxyvitamin D levels
• Parathyroid hormone
• FGF23 (if X-linked hypophosphatemia suspected)

X-linked hypophosphatemia (XLH) can mimic Blount disease with severe leg bowing and should be considered when biochemical abnormalities show hypophosphatemia, elevated alkaline phosphatase, and elevated FGF23. 7 Genetic testing for PHEX gene mutations may be necessary in suspected hereditary conditions. 7

Management Strategy

Non-Operative Management

Observation alone is appropriate only in:

• Very young children (<2 years) with mild deformity 9
• Cases where metabolic causes (vitamin D deficiency, XLH) are identified and treated first 7, 5

Weight loss programs should be initiated in all obese patients as they demonstrate pain reduction (effect size 0.20) and physical function improvement (effect size 0.23), though effects are modest. 5 Weekly supervised sessions for 8 weeks to 2 years with explicit weight-loss goals can achieve mean weight loss of -4.0 kg. 5

Surgical Management

Surgery is indicated when non-operative treatment fails and deformity progresses, as untreated disease results in pain, gait abnormalities, premature medial compartment knee arthritis, and limb length discrepancy. 1

Surgical Options Based on Age and Severity:

For Growing Children with Remaining Growth Potential:

Guided growth techniques (hemi-epiphysiodesis) should be initiated early—after 12 months if deformity persists despite maximized medical therapy. 4 This approach:

• Corrects deformity at the physis before significant diaphyseal deformity develops 4
• Normalizes forces across physes and joints, promoting normal growth 4
• Does not require immobilization 4
• Provides uniplanar coronal correction (limitation: does not correct tibial medial torsion) 4
• Can successfully correct recurring genu varum even after prior epiphyseolysis 2

Monitor closely for overcorrection if plates remain in situ too long; rebound deformity after plate removal is rare but reported. 4

For Advanced Deformity or Near Skeletal Maturity:

Osteotomy with correction is the definitive treatment:

1. Acute correction with internal fixation 4

   • Performed at site(s) of major deformity
   • Corrects in all three planes
   • Higher complication rate (57% experience at least one complication; 29% recurrent deformity) 4

2. Gradual correction with external fixation (Ilizarov or Taylor Spatial Frame) 8

   • Both methods significantly improve MPTA, MAD, and JLCA 8
   • No significant difference in outcomes between Ilizarov and TSF 8
   • Effective regardless of infantile vs. adolescent type or prior surgical failure 8
   • Most common complication: superficial pin-site infection 8
   • Mean follow-up shows maintained correction at 34 months 8

Delay osteotomy for residual deformity until skeletal maturity when possible, as surgery in young children with poor metabolic control has notable recurrence rates. 4 Exception: Perform earlier if major deformities induce severe knee instability. 4

Combined Techniques:

For complex cases, combine:

• Excision of abnormal physeal tissue 1
• External and/or intramedullary fixation 1
• Autogenous bone grafting 1
• Physeal bar resection or physeal distraction as needed 1

Post-Operative Management

Document axis correction at 12 months post-operatively using radiographic measurements (MPTA, MAD, JLCA). 4 Perform functional assessment using validated tools such as the Pediatric Outcomes Data Collection Instrument (PODCI) or 6-minute walk test. 4

Follow frequently until skeletal maturity to optimize clinical outcomes and detect recurrence early. 9 At transition to adult services, obtain full orthopedic clinical and radiographic assessment to define residual deformity. 4

Prognosis and Complications

Untreated Blount disease leads to:

• Abnormal gait and decreased mobility 7
• Progressive joint damage and early osteoarthritis 7
• Decreased growth velocity and disproportionate short stature 7
• Chronic pain and functional impairment 1

With appropriate surgical intervention, both Ilizarov and TSF achieve significant improvement in limb mechanical axis and tibial alignment, with correction maintained at final follow-up regardless of prior surgical failures. 8