Blount Disease (Tibia Vara)

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
   • Higher prevalence in children of African and Hispanic descent
   • 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

Global epidemiology:

• Prevalence varies markedly by population - higher in populations of African and Afro-Caribbean descent and in regions where early walking is common
• Relatively rare in Northern European/Caucasian populations
• Incidence rising worldwide in parallel with the childhood obesity epidemic, especially the adolescent (late-onset) form
• Male predominance (approximately 3:1)

Risk factors:

• Early walking (before 10 months)
• Obesity (especially adolescent form; BMI is an independent predictor of being listed for surgery)
• African or Hispanic descent
• Vitamin D deficiency (controversial)
• Mechanical stress on the immature medial physis

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

The Langenskiöld classification (1952, revised 1964) describes six progressive stages of infantile Blount disease based on the radiographic appearance of the proximal medial tibial metaphysis and epiphysis. It is the gold standard classification used worldwide.

Critical for surgical decision-making: Stages I-III may respond to bracing; Stages IV-VI require surgery.

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Drennan's Metaphyseal-Diaphyseal Angle (MDA) - the single most important measurement:

• Measured on standing AP radiograph
• Angle between a line tangent to the medial and lateral metaphyseal beaks and a line perpendicular to the longitudinal axis of the tibial shaft
• Under 11 degrees: physiologic, likely to resolve
• 11-16 degrees: gray zone, predictive of progression, close monitoring
• Over 16 degrees: diagnostic of pathologic tibia vara

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Tibiofemoral angle (TFA):

• Angle between the femoral and tibial axes
• Normal at age 2-3 years: 0-5 degrees valgus
• Blount disease: progressive varus (10-30 degrees or more)
• Measured on standing long-leg radiograph

Levine and Drennan groups (alternative framing of the MDA):

• Group 1: physiologic (MDA under 11 degrees)
• Group 2: indeterminate/at risk (MDA 11-16 degrees, monitor closely)
• Group 3: pathologic (MDA over 16 degrees, Blount disease confirmed)

Modified (type A/B/C) classification (LaMont 2019): A 3-tier system based on the morphology of the metaphyseal/epiphyseal slope that correlates with recurrence better than Langenskiöld - type C (vertical down-sloping epiphysis and metaphysis) carries the worst prognosis.

Presenting complaint:

• Parents notice bowed legs that are not improving or are worsening
• 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

Red flags for an 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)

Physical Examination

Gait assessment (most important):

• Lateral thrust gait: dynamic varus thrust during stance phase, indicating functional medial compartment insufficiency and predicting 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)
• Assess asymmetry if unilateral (compare knee heights)

Rotational profile:

• Internal tibial torsion: thigh-foot angle (normally 10 degrees external) - present in 60-80% of cases
• Femoral version: check internal rotation in the prone position

Other examination:

• Varus stress test: increased medial gapping suggests LCL laxity; fixed varus = bony deformity (advanced disease)
• Leg length (true: ASIS to medial malleolus)
• Knee ROM and ligament stability
• Neurovascular status and exclusion of neuromuscular disorder
• General exam: BMI/obesity assessment, height/weight percentiles, signs of rickets (widened wrists, costochondral beading) or skeletal dysplasia

Standing anteroposterior (AP) radiograph - gold standard:

• Must be weight-bearing for accurate alignment; include both knees for comparison
• Key measurements: MDA (Drennan), tibiofemoral angle, 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; obtain when planning surgery
• Identifies femoral vs tibial contribution to deformity and measures true leg length discrepancy
• Mechanical axis deviation (MAD): distance from knee centre to the mechanical axis

Lateral radiograph: assess for procurvatum (anterior bowing) and tibial slope - useful for surgical planning.

Follow-up imaging schedule:

• Initial diagnosis: standing AP both knees
• Under 3 years with Stage I-II on bracing: repeat every 3-4 months
• Observation: every 6 months until skeletal maturity
• Post-operative: immediate, 6 weeks, 3 months, then every 6 months

MRI (preferred for physeal assessment in children):

• Evaluate physeal bar without radiation
• Assess cartilaginous structures not visible on radiograph
• Differentiate Blount from focal fibrocartilaginous dysplasia (FFCD)
• T2-weighted sequences best for the physis; can show early physeal cartilage irregularities

CT:

• Suspected physeal bar (Stage VI) and pre-operative planning for complex deformity
• 3D reconstructions to quantify physeal bar size and location
• Radiation concern in young children

Ultrasound: limited role; can assess medial physeal cartilage in infants but not routine.

Nuclear medicine: not indicated.

Routine bloods (to exclude metabolic causes - mainly rickets):

• Serum calcium / phosphate: normal in Blount, low in rickets
• Alkaline phosphatase: normal in Blount, elevated in rickets (very low in hypophosphatasia)
• 25-OH vitamin D: rule out vitamin D deficiency rickets
• Parathyroid hormone (PTH): elevated in rickets with secondary hyperparathyroidism

Indications for laboratory testing:

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

Not routinely required with a classic Blount presentation and typical radiographic findings.

Key points: age under 3 years is critical for bracing success; Stage IV or higher = surgery regardless of age; MDA over 16° = diagnostic; overcorrect to 5-10° valgus to prevent recurrence.

Observation - for physiologic genu varum (under 2 years, MDA under 11 degrees) and borderline cases (MDA 11-16 degrees). Clinical and radiographic review every 6 months; monitor for increasing MDA or advancing Langenskiöld stage; counsel on natural history and weight management.

Bracing (KAFO) - indications (all criteria must be met):

• Infantile Blount disease (onset before age 4 years)
• Age under 3 years (preferably 1-3 years)
• Langenskiöld Stage I or II (occasionally Stage III if very young)
• MDA 11-16 degrees (some authorities include up to 20 degrees)
• Compliant family (must wear 23 hours daily)

Contraindications: age over 3-4 years, Langenskiöld Stage IV or higher, adolescent form, fixed deformity.

Orthosis and protocol:

• KAFO (knee-ankle-foot orthosis) producing a valgus force, extending from upper thigh to ankle, custom-molded
• Wear 23 hours per day (remove for bathing only)
• Duration 12-24 months; night-time only bracing is ineffective
• Serial clinical and radiographic monitoring every 3-4 months

Success criteria: MDA improvement (decrease 5+ degrees), less varus tibiofemoral angle, no stage progression; goal MDA under 11 degrees.

Failure indicators (proceed to surgery): progression of MDA after 6-12 months, advancement of Langenskiöld stage, age reaching 4 years without improvement, non-compliance.

Expected success rate: Stage I-II under age 3 years = 60-80%; Stage III = 20-40%; Stage IV or older children = essentially 0%.

Absolute indications:

• Langenskiöld Stage IV or higher (medial metaphyseal overgrowth)
• Failed bracing after 6-12 months in an appropriate candidate
• Age over 4 years at presentation (bracing unlikely to succeed)
• Adolescent Blount disease (all cases require surgery)
• Progressive deformity with functional impairment (lateral thrust gait)

Relative indications: Stage III approaching age 4, MDA over 20 degrees even if young, severe mechanical axis deviation, unilateral disease.

Goals of surgery: correct varus (restore mechanical axis), address internal tibial torsion, correct procurvatum, restore symmetric physeal growth (in growing children), and prevent recurrence.

Surgical timing and age considerations:

• Under 4 years: optimal remodeling but high recurrence (30-50%) - overcorrect to 10 degrees valgus, counsel about likely repeat surgery; consider gradual correction with an external fixator.
• Age 4-8 years: osteotomy preferred; moderate recurrence (15-20%); guided growth an option if significant growth remains and deformity is moderate. Age 5 is a critical transition - recurrence risk falls sharply beyond it.
• Age 8-12 years: osteotomy or guided growth depending on severity/growth remaining; recurrence under 20%; the adolescent form typically presents here.
• Adolescent (12+ years): acute osteotomy preferred (limited growth); recurrence under 10%; accurate correction essential; may need bar resection if Stage VI.

Immediate (recovery room): neurovascular assessment - especially peroneal nerve (document dorsiflexion, first web space sensation, pulses); multimodal analgesia; ice and elevation. Confirm alignment (target 5-10 degrees valgus) and hardware position on immediate radiographs.

Immobilization and weight-bearing: long leg cast or hinged knee brace for ~6 weeks. Non-weight-bearing for 2-4 weeks if opening wedge with graft, then progress to partial and full weight-bearing by 6-8 weeks once union is confirmed.

Follow-up:

• Week 2: wound check, suture removal
• Week 6: clinical and radiographic review; remove cast if union evident; begin gentle ROM and progress weight-bearing
• Month 3: confirm union and alignment; return to sport typically 3-4 months
• Month 6, 12, then annually until skeletal maturity: monitor for recurrence (especially if operated young), measure MDA, watch for physeal bar and leg length discrepancy

Procedure-specific:

• Guided growth: radiographs every 3-4 months; remove plate once corrected (12-24 months); monitor 6-12 months for rebound
• External fixator: scheduled adjustments, daily pin-site care, watch for pin-site infection; frame removal at consolidation (3-6 months)

Rehabilitation progresses through protection (0-6 weeks), early mobilization (6-12 weeks), strengthening (3-6 months), and return to activity (6+ months), with gait re-education to correct any lateral thrust.

Peroneal nerve palsy:

• Most feared complication of proximal tibial osteotomy; incidence 1-5% depending on technique
• Usually a neurapraxia that recovers over 3-6 months
• Risk factors: lateral closing wedge, excessive acute lengthening, proximal fibular osteotomy
• Management: document immediately post-op, foot-drop brace (AFO), monitor for recovery; EMG at 6 weeks if no recovery

Compartment syndrome:

• Rare but devastating; risk rises with extensive soft-tissue dissection or acute lengthening
• Presents with pain out of proportion and pain on passive stretch
• Immediate fasciotomy if suspected - do NOT delay

Vascular injury: very rare; anterior tibial artery at risk with proximal fibular osteotomy. Know the anatomy; vascular consultation if suspected.

Wound complications / hardware issues: infection, dehiscence, haematoma (more common with external fixator pin sites and in obese patients); loss of fixation or prominent hardware.

Recurrence of deformity - the most common long-term complication, driven by ongoing asymmetric physeal growth:

• 30-50% if surgery before age 4 years, 15-20% age 4-8, under 10% after age 8
• Prevention: overcorrect to ~10 degrees valgus, consider lateral epiphysiodesis, delay surgery where feasible
• Management: monitor annually, repeat osteotomy if significant

Physeal bar formation: from violation of the physis at surgery or progressive disease (Stage VI), causing growth arrest and progressive deformity. Avoid crossing the physis with hardware; treat with bar resection if under 50% and growth remains, otherwise osteotomy.

Leg length discrepancy: from lateral physeal arrest, asymmetric growth, or acute lengthening. Manage with shoe lift (under 2 cm), contralateral epiphysiodesis (2-4 cm), or lengthening (over 4 cm).

Malunion: under-correction (residual varus), over-correction (excessive valgus), or residual internal tibial torsion. Revision osteotomy if symptomatic or more than 10 degrees from target.

Nonunion: rare in children; more likely with opening wedge without graft. Treat with revision and bone graft.

Osteoarthritis: long-term medial compartment degeneration if deformity is uncorrected; prevent by restoring the mechanical axis early.

Failed bracing: the commonest "complication" of the conservative approach - progression despite appropriate bracing delays definitive treatment. Recognize failure early (3-6 months) and convert to surgery.

Skin complications from the brace: pressure sores and skin breakdown, particularly in obese patients. Ensure proper fit and regular skin checks.

Psychosocial impact: cosmetic concern, reduced participation, and the burden of full-time bracing. Provide family support and realistic counselling.