Tibia Vara (Blount's Disease)
Proximal Tibial Physis Growth Disturbance
Types
Critical Must-Knows
- Pathophysiology: Compressive forces (Heuter-Volkmann law) on the posteromedial proximal tibial physis cause growth suppression.
- Risk Factors: Obesity (early walking), African American ethnicity.
- Infantile Blount's: Differentiate from Physiologic Bowing. Has Drennan Angle over 16°.
- Langenskiöld Classification: Describes the depression of the medial plateau. Stage VI = Physeal bar.
- Treatment: Bracing effective only in early Infantile (under 3 yrs). Surgery (Osteotomy) for all others.
Examiner's Pearls
- "Physiologic bowing usually resolves by age 2. Blount's PROgresses.
- "Metaphyseal-Diaphyseal Angle (Drennan): over 16° indicates Blount's; under 10° is physiologic.
- "Infantile Blount's has INTERNAL tibial torsion. Adolescent has MILD or neutral.
- "The epiphysis, physis, and metaphysis are ALL involved.
Blount's Pitfalls
Physiologic Bowing
Don't Overcall. Most bowing under 2 years is physiologic. Use Drennan angle (over 16) to differentiate.
Obesity
High Failure Rate. Obese patients have higher implant failure and recurrence rates. Correct the weight if possible.
Compartment Syndrome
Osteotomy Risk. High tibial osteotomy carries risk of compartment syndrome. Prophylactic release needed?
Peroneal Nerve
Nerve at Risk. Correction of varus (valgus osteotomy) stretches the peroneal nerve. Monitor post-op.
At a Glance: Infantile vs Adolescent Blount's
| Feature | Infantile (under 3 yrs) | Adolescent (over 10 yrs) |
|---|---|---|
| Laterality | Bilateral (50%) | Unilateral (90%) |
| Deformity | Severe Varus + Internal Torsion | Mild Varus + Leg Length Discrepancy |
| Physeal Bar | Common (Stage VI) | Rare |
| Drennan Angle | Over 16 degrees | Not used (Physis closed/closing) |
| Treatment | Brace → Osteotomy | Hemiepiphysiodesis or Osteotomy |
FATRisk Factors
Memory Hook:FAT and EARLY walking.
M-D-S-BLangenskiöld Classification
Memory Hook:Progression from beak to bar.
VARUSVARUS - Blount's Deformity Components
Memory Hook:VARUS corrects to NORMAL - correct all deformity components.
Overview and Epidemiology
Definition: Growth disorder of the proximal tibia primarily affecting the posteromedial physis, causing progressive varus, procurvatum, and internal rotation deformity.
Epidemiology:
- Infantile: Onset under 3 years. Often bilateral. Associated with early walking and obesity.
- Adolescent: Onset over 10 years. Often unilateral. Associated with obesity.
- Race: Much more common in African/Afro-Caribbean descent.
Pathophysiology (Heuter-Volkmann Law):
- Excessive compressive forces on the medial physis inhibit growth.
- The lateral physis continues to grow → Varus deformity.
- Also affects posterior aspect → Procurvatum (Extension deformity).
Pathophysiology and Mechanisms
Key Anatomy: Understanding the relevant anatomy is crucial for diagnosis and management. The structures involved include the osseous architecture and surrounding soft tissues.
Pathomechanics: The injury mechanism often involves specific loading patterns that disrupt the structural integrity.
Classification Systems
Infantile (under 3 years)
Bilateral involvement in 50% of cases. Associated with internal tibial torsion. Staged using Langenskiöld classification (I-VI) based on radiographic appearance of medial physis.
Adolescent (over 10 years)
More likely unilateral (90%). Less severe initial deformity but harder to treat due to less remodeling potential. Often associated with obesity and leg length discrepancy.
Clinical Assessment
Physical Examination:
- Gait: Varus thrust (lateral knee thrust) during stance phase.
- Deformity:
- Varus (Bow leg).
- Internal Tibial Torsion (Infantile).
- Leg Length Discrepancy (Affected side short).
- Obesity: Commonly BMI over 95th percentile.
Differentiating from Physiologic Bowing:
- Physiologic: Symmetrical, Gentle curve (femur and tibia), Resolves by age 2.
- Blount's: Abrupt angulation at proximal tibia, Asymmetric, Progressive, Lateral thrust.
Investigations (X-ray analysis)
Radiographic Parameters:
-
Metaphyseal-Diaphyseal Angle (Drennan Angle):
- Angle between line perpendicular to tibial diaphysis and line through metaphysis.
- Under 10 degrees: 95% chance Physiologic.
- Over 16°: 95% chance Blount's.
- 10-16°: Grey zone (Observe).
-
Langenskiöld Classification (Infantile):
- Describes morphology of medial metaphysis/epiphysis.
- Stage I-II: Irregular medial metaphysis / Beaking.
- Stage III-IV: Deepening of medial slope ("Step").
- Stage V: Double epiphysis sign.
- Stage VI: Bony bridge (Physeal Bar).
-
MRI: Evaluate for physeal bar (Stage VI) and intra-articular cartilage depression.
Management Algorithm
Infantile Blount's Management
Age under 3 Years (Stage I-II):
KAFO bracing with locked knee in extension, worn 23 hours per day. Approximately 50% success rate if started young and with unilateral disease.
Age over 3 Years or Stage III+:
Surgery indicated with High Tibial Osteotomy (HTO). Technique involves valgus correction, extension correction, and external rotation. Fixation with plate or external fixator (TSF/Ilizarov allows gradual correction). Aim to overcorrect to 5-10° valgus (physiologic for age).
Surgical Technique
High Tibial Osteotomy (Acute)
Indications: Infantile Blount's, Moderate deformity.
- Access: Curved incision proximal tibia.
- Fibulectomy: Often needed (mid-shaft) to allow correction.
- Osteotomy: Curved (Dome) or Wedge below tuberosity.
- Correction:
- Valgus (Correct varus).
- External Rotation (Correct torsion).
- Extension (Correct procurvatum often neglected).
- Fixation: Plate or Pins/Cast.
- Decompression: Prophylactic anterior compartment fasciotomy usually done.
Complications
Complications
| Complication | Risk Factor | Management |
|---|---|---|
| Recurrence | Obesity, Incomplete correction | Repeat Osteotomy / Guided Growth |
| Compartment Syndrome | Acute Osteotomy | Fasciotomy |
| Peroneal Nerve Palsy | Acute Valgus correction | Nerve release / Gradual correction |
| Physeal Arrest | Implant crossing physis | Bar resection |
| DVT | Obesity, Adolescents | Prophylaxis |
Postoperative Care
Protocol:
- Immobilization: Initial splinting/casting to protect the repair/fracture.
- Rehabilitation: Gradual Range of Motion (ROM) and strengthening as healing progresses.
- Weight Bearing: Progression depends on stability of fixation and healing.
Outcomes and Prognosis
Infantile Blount Disease:
- Langenskiöld I-II: Excellent prognosis with guided growth (85-90% success)
- Langenskiöld III-IV: Good prognosis with osteotomy (75-85% success)
- Langenskiöld V-VI: Fair prognosis, higher recurrence rates (20-40%)
- Recurrence risk: 10-25% overall, higher with obesity and late treatment
Adolescent Blount Disease:
- More challenging to treat with higher recurrence rates (25-40%)
- Obesity significantly impacts outcomes and implant durability
- Taylor Spatial Frame may have better outcomes in complex cases
Factors Affecting Outcome:
- Age at treatment (earlier = better for infantile)
- Body mass index (obesity = worse outcomes)
- Langenskiöld stage at presentation
- Compliance with postoperative bracing/weight bearing restrictions
Evidence Base
Drennan Angle
- Defined Metaphyseal-Diaphyseal Angle (MDA).
- Over 11 degrees usually progresses (original paper).
- Current consensus: over 16 degrees is pathologic, under 10 is benign.
Bracing Efficacy
- KAFO bracing effective in Langenskiöld I-II if under 3 years old.
- Ineffective in obese children or older children.
Obesity and Outcomes
- Obesity is strongly associated with Blount's.
- Higher rate of implant failure and recurrence in obese adolescents.
- External fixator (TSF) may be better for large limbs.
Guided Growth for Blount Disease
- 8-plate or staples effective for Langenskiold Stage I-II
- Average correction time 12-18 months
- Works best in children under 6 years
- Recurrence rate 15-20% in infantile form
Taylor Spatial Frame vs Acute Osteotomy
- TSF allows multiplanar correction in complex adolescent cases
- Lower recurrence rate than plate fixation in obese patients
- Pin site infection in 30% but usually minor
- Better correction of internal tibial torsion
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
The Bow-Legged Toddler
"Is this Blount's or Physiologic?"
The Obese Adolescent
"What is your management plan?"
MCQ Practice Points
Drennan Angle
Q: What Drennan angle strongly suggests Blount's disease? A: Over 16 degrees (under 10 is physiologic).
Pathology Location
Q: Which part of the physis is affected in Blount's? A: Posteromedial proximal tibial physis. (Leads to Varus + Procurvatum/Internal Rotation).
Treatment Age
Q: Up to what age is bracing effective in Infantile Blount's? A: Generally up to age 3. After age 3 or Stage III, surgery is usually required.
Langenskiöld VI
Q: What characterizes Langenskiöld Stage VI? A: Formation of a bony Physeal Bar (bridge) across the medial physis.
Infantile vs Adolescent
Q: How does infantile Blount's differ from adolescent Blount's? A: Infantile Blount's (under 3 years) is bilateral in 50%, has internal tibial torsion, and uses Langenskiöld staging. Adolescent Blount's (over 10 years) is unilateral in 90%, has leg length discrepancy, and less remodeling potential making it harder to treat.
Surgical Approach
Q: Why is Taylor Spatial Frame preferred in obese adolescent Blount's? A: TSF allows gradual multiplanar correction (varus, rotation, length), provides stable fixation in large limbs, and has lower risk of peroneal nerve palsy and compartment syndrome compared to acute osteotomy correction.
Australian Context
- Indigenous Health: Higher prevalence of deformities in some populations? (Less data than US).
- Obesity: Increasing rates of childhood obesity making this more common.
High-Yield Exam Summary
Key Features
- •Posteromedial physis growth arrest
- •Obesity and early walking are risk factors
- •Internal tibial torsion (infantile)
- •Drennan Angle over 16 degrees diagnostic
- •African American ethnicity more common
Classification
- •Infantile (under 3 years): Bilateral 50%
- •Adolescent (over 10 years): Unilateral 90%
- •Langenskiöld I-II: Beaking
- •Langenskiöld III-IV: Step-off
- •Langenskiöld V-VI: Bar formation
Treatment
- •KAFO brace if under 3 years (Stage I-II)
- •Osteotomy if over 3 years or Stage III+
- •TSF for obese or complex deformity
- •Hemiepiphysiodesis for mild adolescent
- •Overcorrect to 5-10 degrees valgus
Complications
- •Compartment syndrome - prophylactic fasciotomy
- •Peroneal nerve palsy - stretch injury
- •Recurrence - higher with obesity
- •Physeal arrest from implant
- •DVT risk in obese adolescents