Fibular Hemimelia

Fibular hemimelia is the most common congenital long bone deficiency, characterized by partial or complete absence of the fibula. It represents a spectrum from mild hypoplasia to complete absence, with associated limb length discrepancy and foot deformities.

View larger

Epidemiology:

• Incidence: 1 in 40,000 live births
• Male to female ratio: 1.5:1
• Bilateral involvement: 9-52% of cases
• Right side slightly more common
• Most common long bone deficiency

Pathophysiology: Fibular hemimelia results from failure of normal fibular development during embryogenesis. The exact cause is unknown but may involve:

• Vascular insult during development
• Genetic factors (rare familial cases)
• Teratogenic exposure
• Failure of mesenchymal condensation

The condition represents a spectrum, with Achterman-Kalamchi classification describing severity based on fibular presence and foot status.

Normal Fibular Anatomy: The fibula is the lateral bone of the lower leg. It provides:

• Lateral stability to the ankle
• Muscle attachments (peroneals, flexor hallucis longus)
• Contributes to ankle mortise
• Minimal weight-bearing (10-15%)

Fibular Hemimelia Pathology: In fibular hemimelia, there is:

• Partial or complete absence of fibula
• Anteromedial tibial bowing (characteristic)
• Limb length discrepancy (main problem)
• Foot deformities (equinovalgus, absent rays, tarsal coalition)
• Ankle valgus (lateral tether absent)
• Knee problems (valgus, cruciate deficiency)

Pathophysiology: The absence of fibula causes:

• Loss of lateral support → ankle valgus
• Anteromedial tibial bowing (compensatory)
• Limb length discrepancy (fibula contributes to length)
• Foot deformities (lateral column affected)

Associated Musculoskeletal Findings:

• Anteromedial tibial bowing (characteristic)
• Tarsal coalition (common)
• Equinovalgus foot (most common)
• Absent lateral rays (common)
• Cruciate ligament deficiency
• Genu valgum
• Lateral femoral condyle hypoplasia
• PFFD (50% association)
• Coxa vara
• Acetabular dysplasia

Understanding the anatomy helps determine treatment - foot status is key, not fibula length.

The combination of a short lower limb, anteromedial bowing and a valgus foot has a focused differential. The discriminator is usually the radiographic status of the fibula, the apex/direction of any bowing, and the pattern of associated anomalies.

History:

• Shortened lower limb noted at birth
• May have foot deformity noted
• Family history (rare but may be present)
• Difficulty with walking or activities
• Previous treatment (if established case)

Physical Examination:

Inspection:

• Shortened lower limb
• Anteromedial tibial bowing (characteristic)
• Foot deformity (equinovalgus most common)
• Assess number of foot rays (toes)
• Assess for bilateral involvement
• Look for associated deformities (hip, knee, upper limb)

Palpation:

• Fibula may be absent or hypoplastic
• Anteromedial tibial bowing palpable
• Assess ankle stability
• Assess foot structure

Range of Motion:

• Ankle: May have limited motion, valgus deformity
• Knee: May have valgus, assess cruciate function
• Hip: Assess for PFFD, coxa vara
• Assess for contractures

Measurements:

• True leg length: ASIS to medial malleolus
• Apparent leg length: umbilicus to medial malleolus
• Tibial length: knee joint line to ankle
• Predict final LLD using multiplier method

Foot Assessment:

• Count functional rays (toes)
• Assess foot position (equinovalgus, equinovarus)
• Assess for tarsal coalition
• Assess ankle valgus angle

Associated Examination:

• Hips: Assess for PFFD (50% association)
• Knees: Assess for valgus, cruciate deficiency
• Upper limbs: Assess for ulnar hemimelia
• Other systems: Cardiac, renal (rare associations)

Radiographs:

AP and Lateral Lower Limb:

• Assess fibular presence/absence
• Evaluate anteromedial tibial bowing
• Measure limb length discrepancy
• Assess ankle valgus angle
• Evaluate foot structure (ray count, tarsal coalition)

Full-Length Standing Radiographs (Scanogram):

• Accurate LLD measurement
• Assess alignment
• Evaluate tibia-femur ratio
• Plan treatment

Foot Radiographs:

• Count functional rays
• Assess for tarsal coalition
• Evaluate foot structure
• Assess ankle valgus

CT Scan (if reconstruction considered):

• Detailed foot anatomy
• Assess tarsal coalition
• Plan foot centralization
• Evaluate ankle structure

Other Imaging:

• MRI: May assess soft tissue structures
• Ultrasound: Usually not needed

LLD Prediction:

• Multiplier method: Current LLD × multiplier = predicted final LLD
• Growth remaining method: More complex, accounts for growth
• LLD percentage is constant throughout growth

Reconstruction Complications:

Early:

• Infection (20-30% with external fixators)
• Wound healing problems
• Neurovascular injury
• Inadequate correction

Late:

• Persistent LLD (may need additional lengthenings)
• Ankle problems (instability, stiffness, arthritis)
• Knee problems (valgus, cruciate deficiency)
• Foot problems (deformity recurrence, tarsal coalition)
• Contractures (ankle, knee)
• Hardware problems

Lengthening Complications:

• Pin site infection (common)
• Stiffness (ankle, knee)
• Contractures
• Delayed union
• Premature consolidation
• Nerve injury (peroneal most common)
• Refracture

Syme Amputation Complications:

Early:

• Wound healing problems (5-10%)
• Heel pad migration (if not properly fixed)
• Infection (rare)

Late:

• Heel pad migration (may need revision)
• Bony overgrowth (may need revision)
• Prosthetic fitting problems (rare)

Prevention:

• Careful patient selection
• Meticulous surgical technique
• Aggressive physical therapy (reconstruction)
• Long-term bracing (reconstruction)
• Realistic expectations

Syme Amputation:

Immediate:

• Pain management
• Wound care
• Cast 2-3 weeks

After Healing:

• Prosthetic fitting (6-8 weeks)
• Gait training
• Return to activities

Long-term:

• Prosthetic adjustments as child grows
• Monitor for heel pad migration
• Monitor for bony overgrowth

Reconstruction:

Immediate:

• Pain management
• Wound care
• Cast or external fixator care

Lengthening Phase:

• Pin site care (daily cleaning)
• Distraction protocol (1mm/day)
• Physical therapy (critical)
• Regular radiographs

After Union:

• Protected weight-bearing
• AFO long-term
• Physical therapy
• Gradual return to activities

Long-term Follow-up:

• Annual assessment until skeletal maturity
• Monitor LLD progression
• Assess function
• Address complications

Functional Outcomes:

Syme Amputation:

• Excellent function in 80-90%
• Running, sports possible with prosthesis
• Minimal restrictions
• High patient satisfaction
• Single surgery, short treatment

Reconstruction:

• Variable function (60-70% good outcomes)
• Often residual LLD (2-5cm)
• Ankle problems common (instability, stiffness)
• May need AFO long-term
• Multiple surgeries (2-4 lengthenings)
• Long treatment course (10-15 years)

Quality of Life:

• Syme: Excellent quality of life, high satisfaction
• Reconstruction: Variable, depends on outcome
• Both groups function well overall
• Psychosocial support important

Predictors of Success:

• Appropriate patient selection
• Syme: Proper technique, heel pad preservation
• Reconstruction: Motivated family, adequate rays, manageable LLD

Long-term:

• Syme: Prosthetic adjustments as child grows, otherwise stable
• Reconstruction: May need additional procedures, ankle problems may worsen
• Both: Most function independently

Unresolved questions:

• No validated, disease-specific patient-reported outcome measure for fibular hemimelia exists; cross-study comparison is limited
• The genetic/embryological basis is still unclear (vascular insult vs mesenchymal condensation failure); most cases remain sporadic and unexplained
• Whether proactive cruciate reconstruction at the time of lengthening should be routine (versus reactive) is not yet supported by high-level evidence

Global epidemiology:

• Most common congenital long-bone deficiency; reported birth prevalence approximately 1 in 40,000 (longitudinal limb deficiencies overall ~1 per 20,000)
• Male predominance (~1.5:1); right side slightly more common; bilateral in roughly 10-25% of series
• Predominantly sporadic - the large majority are isolated with no Mendelian inheritance; rare familial/syndromic cases exist
• Strongly co-segregates with ipsilateral femoral deficiency (PFFD) and cruciate/lateral femoral condyle dysplasia

Side-by-side practice positions (no single global guideline exists):

Registry and outcome notes:

• No dedicated arthroplasty-style registry exists for fibular hemimelia; evidence is from single-centre series and pooled cohorts
• Comparative cohort data (amputation vs reconstruction) show comparable quality-of-life and function in mid-childhood, shifting practice toward shared decision-making
• Long-term registries of paediatric limb reconstruction track lengthening index, complication and re-operation rates rather than implant survival

High- vs limited-resource variation:

• High-resource settings: magnetic intramedullary lengthening nails (e.g. PRECICE), staged SUPERankle reconstruction, gait labs, and lifelong prosthetic upgrades make reconstruction feasible
• Limited-resource settings: external-fixator (Ilizarov) lengthening or early Syme/Boyd amputation with a durable end-bearing stump is often the most reliable, cost-effective route to independent ambulation
• Prosthetic access and the ability to fund multiple childhood prosthesis changes materially influence whether amputation is the pragmatic choice

Counselling essentials (universal):

• Major, often irreversible decision - informed consent and realistic expectations are mandatory
• Document foot ray count, predicted final LLD, and ankle/knee stability
• No "wrong" choice between a well-executed amputation and a well-executed reconstruction; follow to skeletal maturity