Blount Disease (Tibia Vara)

The OnePagerSummary above provides a comprehensive at-a-glance overview of Blount disease including the Langenskiöld classification, key statistics, must-know concepts, and exam pearls.

Blount disease (tibia vara) is a pathologic growth disturbance of the medial aspect of the proximal tibial physis, resulting in progressive genu varum deformity. It represents a failure of normal endochondral ossification at the medial metaphysis.

Two distinct clinical entities:

1. Infantile form (most common):

   • Onset before age 4 years
   • Often bilateral (60-80%)
   • More common in early walkers
   • African and Hispanic descent (3-4x higher)
   • Better response to conservative management

2. Adolescent form:

   • Onset after age 8-10 years
   • Usually unilateral (80%)
   • Strong association with obesity
   • Less predictable, worse prognosis
   • Requires surgical management

Australian epidemiology:

• Rare in Caucasian Australian population
• Higher prevalence in Aboriginal and Torres Strait Islander children
• Increasing incidence correlating with childhood obesity epidemic
• Male predominance (3:1 ratio)

Risk factors:

• Early walking (before 10 months)
• Obesity (especially adolescent form)
• African or Hispanic descent
• Vitamin D deficiency (controversial)
• Mechanical stress on immature physis

The condition is progressive if untreated, leading to permanent deformity, lateral thrust gait, lateral compartment osteoarthritis, and functional disability.

Physis anatomy:

• Proximal tibial physis contributes 55-60% of tibial growth
• Medial and lateral physeal growth should be symmetric
• Growth rate approximately 6mm per year (3mm medial, 3mm lateral)
• Peak growth velocity in infancy and early adolescence

Normal lower limb alignment evolution:

• Birth: 10-15 degrees varus (physiologic)
• Age 12-18 months: Neutral mechanical axis
• Age 2-4 years: 10-12 degrees valgus (physiologic)
• Age 6-7 years: 5-7 degrees valgus (adult alignment)

Mechanical axis:

• Line from femoral head center to ankle center
• Normally passes through medial tibial spine (or just lateral)
• In Blount disease, passes medial to knee (medial compartment overload)

Hueter-Volkmann principle:

• Increased compression → decreased growth
• Decreased compression → increased growth
• Medial physeal compression from mechanical overload → growth suppression
• Creates vicious cycle: varus → increased medial stress → more varus

Histologic findings:

• Disorganized physeal architecture (loss of columnar arrangement)
• Fibrocartilaginous tissue replacing normal physeal cartilage
• Thickened periosteum on medial aspect
• Metaphyseal cartilage islands (failure of resorption)
• Progressive changes from Stage I to Stage VI

Mechanical factors:

• Early walking increases medial compartment stress
• Obesity dramatically increases joint reaction forces
• Internal tibial torsion increases frontal plane moment arm
• Creates asymmetric loading of medial physis

Progressive deformity components:

1. Varus angulation (primary deformity)
2. Internal tibial torsion (60-80% of cases)
3. Procurvatum (anterior bowing) in advanced cases
4. Medial physeal bar formation (Stage VI)
5. Leg length discrepancy (lateral overgrowth)

Presenting complaint:

• Parents notice bowed legs that are not improving or are worsening
• Child has abnormal gait (waddling, lateral thrust)
• Knee or leg pain in older children (uncommon in infantile form)
• Concerns about shoe wear (lateral sole wear)

Age at presentation:

• Infantile form: Typically 18 months to 3 years (after walking established)
• Adolescent form: 8-15 years (often coincides with growth spurt)

Key history questions:

• Age of first walking (under 10 months = risk factor)
• Birth weight and current weight (obesity assessment)
• Unilateral vs bilateral deformity
• Progressive or static deformity
• Family history of bowed legs or metabolic bone disease
• Dietary history (vitamin D, calcium intake)
• Previous bracing or treatment

Associated symptoms:

• Pain uncommon in infantile form
• Adolescent form may have knee pain (medial compartment overload)
• Difficulty running or sports participation
• Cosmetic concerns

Red flags for alternative diagnosis:

• Short stature (consider skeletal dysplasia)
• Other joint involvement (consider skeletal dysplasia)
• Pathologic fractures (consider rickets or metabolic disease)
• Developmental delay (consider genetic syndrome)

Gait assessment (most important):

• Lateral thrust gait: Dynamic varus thrust during stance phase
• Indicates functional medial compartment insufficiency
• Predictor of progression
• Waddling gait if bilateral
• Reduced cadence and stride length

Standing alignment:

• Intercondylar distance: Measure between medial femoral condyles with ankles together
• Normal under 6 cm in young children
• Over 6-8 cm suggests pathologic bowing
• Asymmetry if unilateral (compare knee heights)

Varus stress test:

• Apply varus force to knee in extension
• Increased medial gapping suggests LCL laxity (chronic lateral stretch)
• Fixed varus = bony deformity (advanced disease)

Rotational profile:

• Internal tibial torsion: Thigh-foot angle (normally 10 degrees external)
• Present in 60-80% of Blount disease cases
• Femoral version: Check internal rotation in prone position
• May have combined femoral anteversion

Leg length measurement:

• True leg length: ASIS to medial malleolus
• Apparent leg length: Umbilicus to medial malleolus
• Leg length discrepancy common (affected side may be shorter or longer)

Knee examination:

• Range of motion: Usually full, unless severe deformity
• Ligament stability: LCL may be attenuated
• Tenderness: Medial metaphysis (uncommon)

Neurologic examination:

• Document distal neurovascular status
• Exclude cerebral palsy or neuromuscular disorder

General examination:

• BMI calculation and obesity assessment
• Height and weight percentiles
• Signs of rickets (widened wrists, costochondral beading)
• Signs of skeletal dysplasia

Standing anteroposterior (AP) radiograph:

• Gold standard for diagnosis and staging
• Must be standing (weight-bearing) for accurate alignment assessment
• Include both knees for comparison
• Key measurements:
  • Metaphyseal-diaphyseal angle (MDA) - Drennan angle
  • Tibiofemoral angle (TFA)
  • Intercondylar distance
• Langenskiöld staging based on medial metaphyseal changes
• Look for: Medial beaking, metaphyseal defect, physis widening, epiphyseal wedging

Standing long-leg radiograph (full-length):

• Mechanical axis alignment - line from femoral head to ankle
• Should be obtained when planning surgery
• Identifies femoral vs tibial contribution to deformity
• Measures true leg length discrepancy
• Mechanical axis deviation (MAD): Distance from knee center to mechanical axis

Lateral radiograph:

• Assess for procurvatum deformity (anterior bowing)
• Evaluate tibial slope
• Less critical for diagnosis but useful for surgical planning

Oblique views:

• Occasionally helpful for evaluating physeal bar in Stage VI
• Not routinely required

Follow-up imaging schedule:

• Initial diagnosis: Standing AP both knees
• If under 3 years with Stage I-II and bracing: Repeat every 3-4 months
• If observation: Repeat every 6 months until skeletal maturity
• Post-operative: Immediate, 6 weeks, 3 months, then every 6 months

CT scan:

• Indications:
  • Suspected physeal bar (Stage VI)
  • Pre-operative planning for complex deformity
  • Assessment of three-dimensional deformity
• Can create 3D reconstructions
• Quantify physeal bar size and location
• Radiation concern in young children

MRI:

• Indications:
  • Evaluate physeal bar without radiation (preferred in children)
  • Assess cartilaginous structures not visible on radiograph
  • Differentiate Blount from focal fibrocartilaginous dysplasia
• T2-weighted sequences best for physis evaluation
• Can show physeal cartilage irregularities in early disease

Ultrasound:

• Limited role
• Can assess medial physeal cartilage in infants
• Not routinely used in clinical practice

Nuclear medicine:

• Not indicated

Routine bloods (to exclude metabolic causes):

• Serum calcium: Normal in Blount, low in rickets
• Serum phosphate: Normal in Blount, low in rickets
• Alkaline phosphatase: Normal in Blount, elevated in rickets
• 25-OH vitamin D: Rule out vitamin D deficiency rickets
• Parathyroid hormone (PTH): Elevated in rickets if secondary hyperparathyroidism

Indications for laboratory testing:

• Atypical presentation (younger than 18 months, short stature)
• Radiographic features suggestive of metabolic disease (widened physis, metaphyseal fraying throughout skeleton)
• Family history of metabolic bone disease
• Dietary concerns (inadequate vitamin D, calcium)

Not routinely required if classic Blount disease presentation and radiographic findings.

The examiner will expect you to differentiate Blount disease from other causes of genu varum in children.

Peroneal nerve palsy:

• Most feared complication of proximal tibial osteotomy
• Incidence 1-5% depending on technique
• Usually neurapraxia (stretching injury) that recovers over 3-6 months
• Risk factors: Lateral closing wedge, excessive acute lengthening, fibular osteotomy
• Prevention: Careful surgical technique, protect nerve, limit acute lengthening
• Management: Document immediately post-op, foot-drop brace (AFO), monitor for recovery, EMG at 6 weeks if no recovery

Compartment syndrome:

• Rare but devastating if missed
• Risk increased with excessive soft tissue dissection or acute lengthening
• Presents with pain out of proportion, pain with passive stretch, tense compartments
• High index of suspicion in immediate post-operative period
• Management: Immediate fasciotomy if suspected - do NOT delay

Vascular injury:

• Very rare
• Anterior tibial artery at risk with proximal fibular osteotomy
• Popliteal vessels at risk if posterior dissection
• Prevention: Know anatomy, minimize dissection
• Management: Vascular surgery consultation if suspected

Wound complications:

• Infection, dehiscence, hematoma
• More common with external fixator (pin sites)
• Increased risk in obese patients
• Prevention: Meticulous technique, minimize soft tissue stripping, prophylactic antibiotics
• Management: Antibiotics for infection, debridement if necessary

Hardware issues:

• Screw or plate breakage (rare in acute phase)
• Prominent hardware causing irritation
• Loss of fixation if inadequate construct

Recurrence of deformity:

• Most common complication especially if operated under age 4 years
• Incidence 30-50% if surgery before age 4, 15-20% if age 4-8, under 10% if after age 8
• Due to ongoing asymmetric physeal growth
• Prevention: Overcorrect to 10 degrees valgus, consider lateral epiphysiodesis, delay surgery if possible
• Management: Monitor annually, repeat osteotomy if significant recurrence

Physeal bar formation:

• Occurs if physis violated during surgery or from progressive disease (Stage VI)
• Results in growth arrest and progressive angular deformity
• Prevention: Avoid crossing physis with hardware, meticulous surgical technique
• Management: Physeal bar resection if under 50% and growth remaining, otherwise osteotomy or accept deformity

Leg length discrepancy:

• Can result from lateral physeal arrest (intentional hemiepiphysiodesis) or asymmetric growth
• Also from acute lengthening if opening wedge osteotomy
• Prevention: Measure carefully, correct to neutral if symmetric growth expected
• Management: Shoe lift if mild (under 2 cm), contralateral epiphysiodesis if moderate (2-4 cm), lengthening if severe (over 4 cm)

Malunion:

• Under-correction (persistent varus)
• Over-correction (excessive valgus)
• Residual rotational deformity (internal tibial torsion)
• Prevention: Accurate pre-operative planning, intra-operative alignment verification
• Management: Revision osteotomy if symptomatic or significant (over 10 degrees from target)

Nonunion:

• Rare in children (excellent healing potential)
• More common if opening wedge without bone graft
• Risk factors: Inadequate fixation, infection, smoking (adolescents)
• Management: Revision surgery with bone graft and stable fixation

Osteoarthritis:

• Long-term complication if deformity not corrected
• Medial compartment overload leads to early degenerative changes
• Lateral compartment also at risk from chronic lateral thrust
• Prevention: Early correction of deformity to restore mechanical axis
• Management: Joint preservation strategies (osteotomy), eventual arthroplasty if severe

Failed bracing:

• Most common "complication" of conservative approach
• Progression of deformity despite appropriate bracing
• Delayed definitive treatment may worsen prognosis
• Prevention: Early recognition of failure (3-6 months), prompt conversion to surgery

Skin complications from brace:

• Pressure sores, skin breakdown
• Particularly in obese patients
• Prevention: Proper brace fitting, regular skin checks, hygiene
• Management: Temporary removal for healing, refit brace

Psychosocial impact:

• Cosmetic concerns from deformity
• Social isolation from bracing (full-time wear)
• Reduced activity participation
• Management: Family support, realistic expectations counseling, transition to surgery if appropriate

Infantile Blount Disease Prognosis:

• Bracing success (Stage I-II, under age 3 years): 60-80% achieve correction
• Surgical outcomes: 85-90% satisfactory alignment at maturity if operated appropriately
• Recurrence rates:
  • Surgery under age 4 years: 30-50% recurrence
  • Surgery age 4-8 years: 15-20% recurrence
  • Surgery after age 8 years: under 10% recurrence
• Long-term function: Excellent if treated early and appropriately
• Osteoarthritis risk: Low if corrected before persistent lateral thrust develops

Adolescent Blount Disease Prognosis:

• Bracing: Ineffective (0% success)
• Surgical outcomes: 85-90% satisfactory short-term alignment
• Recurrence: Lower than infantile (8-10%) due to less remaining growth
• Long-term function: Good but higher rate of early osteoarthritis due to pre-existing overload
• Obesity management: Critical for long-term success but difficult to achieve

Factors Affecting Prognosis:

• Age at treatment: Younger = better bracing response, but higher surgical recurrence
• Langenskiöld stage: Higher stage = worse natural history, more complex surgery
• Obesity: Strong negative prognostic factor, increases recurrence risk
• Compliance: Critical for both bracing and post-operative rehabilitation
• Bilateral vs unilateral: Bilateral infantile often responds better to bracing

The following topics are frequently tested in Orthopaedic exams related to Blount disease:

Epidemiology in Australia:

Blount disease is relatively rare in the Australian population but shows specific patterns:

• Lower overall prevalence compared to North American and African populations
• Higher incidence in Aboriginal and Torres Strait Islander children
• Increasing incidence correlating with childhood obesity epidemic
• More common in tropical northern Australia where early walking is prevalent

Australian Treatment Considerations:

• Bracing access: KAFO braces require specialist orthotist prescription
• Monitoring: Follow-up through major pediatric orthopaedic centers
• Surgical access: Proximal tibial osteotomy available at all tertiary pediatric centers
• Regional considerations: Remote communities may have delayed presentation

Key Australian Guidelines:

• Royal Australasian College of Surgeons (RACS) supports Ponseti-type principles for conservative management
• Australian Orthopaedic Association guidelines align with international standards for surgical timing
• NDIS may provide funding for bracing and therapy in eligible children

Culturally Appropriate Care:

• Consider traditional practices and family involvement in Indigenous communities
• Ensure appropriate interpreter services for CALD families
• Weight management counseling should be culturally sensitive

Blount disease (tibia vara) is a pathologic growth disturbance of the medial proximal tibial physis resulting in progressive genu varum deformity. Two distinct forms exist: infantile (onset under 4 years, often bilateral) and adolescent (onset after 8 years, obesity-related, usually unilateral).

Key diagnostic features:

• Drennan's metaphyseal-diaphyseal angle (MDA): Over 16 degrees diagnostic
• Langenskiöld classification (Stages I-VI): Stage IV (medial metaphyseal overgrowth) is threshold for surgery

Management:

• Observation: Physiologic genu varum with MDA under 11 degrees
• Bracing (KAFO): Age under 3 years, Stage I-II, MDA 11-16 degrees, 23 hours daily for 12-24 months (60-80% success)
• Surgery: Stage IV or higher, failed bracing, age over 4 years, all adolescent Blount disease

Surgical options:

• Proximal tibial valgus osteotomy (workhorse) - correct to 5-10 degrees valgus
• Guided growth (8-plate) for selected early cases with growth remaining
• External fixator for severe/complex deformity or very young children

Complications:

• Recurrence (30-50% if surgery under age 4 years)
• Peroneal nerve palsy (2-4% incidence)
• Long-term osteoarthritis if uncorrected

Critical exam points:

• Differentiate from physiologic genu varum using MDA and age
• Stage IV = surgery mandatory
• Overcorrect to 5-10 degrees valgus to prevent recurrence
• Address internal tibial torsion (present in 60-80%)
• Recurrence counseling essential when operating on young children

Blount disease requires early recognition, appropriate conservative management when indicated, and timely surgical intervention for progressive or advanced disease. Long-term monitoring until skeletal maturity is essential, particularly in children operated at young ages due to high recurrence risk.