Tibial Hemimelia

Tibial hemimelia is a rare congenital deficiency characterized by partial or complete absence of the tibia. It is much rarer than fibular hemimelia and represents one of the most challenging conditions in pediatric orthopedics, with treatment decisions based primarily on knee functionality.

Epidemiology:

• Incidence: 1 in 1,000,000 live births (very rare)
• Male to female ratio: 1.5:1
• Bilateral involvement: 30% of cases
• Right and left sides: Equal distribution
• Much rarer than fibular hemimelia (1:40,000)

Pathophysiology: Tibial hemimelia results from failure of normal tibial 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 from complete absence (Type IA) to partial presence (Type IB-IV), with Jones classification describing severity based on tibial presence and knee functionality.

Normal Tibial Anatomy: The tibia is the primary weight-bearing bone of the lower leg. It provides:

• Primary weight-bearing (85-90% of load)
• Knee joint stability (proximal articulation with femur)
• Ankle joint stability (distal articulation with talus)
• Muscle attachments (tibialis anterior, posterior, etc.)

Tibial Hemimelia Pathology: In tibial hemimelia, there is:

• Partial or complete absence of tibia
• Fibula usually present (but may be abnormal)
• Knee instability (if proximal tibia absent)
• Ankle instability (if distal tibia absent)
• Limb length discrepancy (main problem)
• Foot deformities (common)

Pathophysiology: The absence of tibia causes:

• Loss of primary weight-bearing bone
• Knee instability (if proximal tibia absent)
• Ankle instability (if distal tibia absent)
• Limb length discrepancy
• Foot deformities

Associated Findings:

• Foot deformities (common)
• Limb length discrepancy
• Fibular abnormalities (may be present but abnormal)
• Other limb anomalies (rare)

Understanding the anatomy helps determine treatment - knee functionality is key.

History:

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

Physical Examination:

Inspection:

• Shortened lower limb
• Assess for tibial presence (may not be palpable)
• Foot deformity (common)
• Assess for bilateral involvement
• Look for associated deformities

Palpation:

• Tibia may be absent or hypoplastic
• Assess fibula (usually present)
• Assess knee stability
• Assess ankle stability
• Assess foot structure

Range of Motion:

• Knee: Assess stability and function (critical)
• Ankle: May have limited motion, instability
• Assess for contractures

Measurements:

• True leg length: ASIS to medial malleolus
• Apparent leg length: umbilicus to medial malleolus
• Assess knee function (critical)

Knee Assessment (Critical):

• Assess quadriceps function
• Assess knee stability
• Assess passive motion
• Non-functional knee (Type IA) = amputation
• Functional knee (IB/II) = synostosis possible

Foot Assessment:

• Assess foot structure
• Assess for deformities
• Assess for preservation possibility

Associated Examination:

• Other limbs: Assess for other anomalies
• Other systems: Rare associations

Radiographs:

AP and Lateral Lower Limb:

• Assess tibial presence/absence
• Evaluate proximal tibia (if present)
• Evaluate distal tibia (if present)
• Assess fibula (usually present)
• Measure limb length discrepancy
• Assess knee joint
• Assess ankle joint

Full-Length Standing Radiographs:

• Accurate LLD measurement
• Assess alignment
• Evaluate knee and ankle

Foot Radiographs:

• Assess foot structure
• Evaluate deformities

Ultrasound (Critical for Type IB):

• Essential to differentiate Type IB from IA
• Assess for proximal tibial cartilage (Type IB)
• If cartilage present = Type IB (preserve knee)
• If no cartilage = Type IA (amputation)

MRI (if USS inconclusive):

• Detailed assessment of proximal tibia
• Assess cartilage presence
• Differentiate Type IB from IA

Key Point: USS/MRI essential for Type IB vs IA differentiation - cannot rely on X-ray alone (cartilage not visible on X-ray).

Synostosis Complications:

Early:

• Infection (rare)
• Wound healing problems
• Neurovascular injury (rare)

Late:

• Nonunion (may need revision)
• Malalignment
• Knee instability (if synostosis fails)
• Hardware problems

Amputation Complications:

Early:

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

Late:

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

Prevention:

• Careful patient selection
• Meticulous surgical technique
• Proper imaging (USS/MRI for IB vs IA)
• Realistic expectations

Synostosis:

Immediate:

• Pain management
• Wound care
• Cast 6-8 weeks

After Union:

• Protected weight-bearing
• Physical therapy
• Prepare for Syme amputation

After Syme:

• Prosthetic fitting
• Gait training
• Return to activities

Amputation (Type IA):

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 complications
• Regular follow-up

Functional Outcomes:

Type IA (Amputation):

• Good function with prosthesis
• Single surgery
• Early treatment allows development
• Minimal restrictions

Type IB/II (Synostosis + Syme):

• Preserves knee function
• Good prosthetic function
• Two-stage procedure
• Better than amputation if knee functional

Type III/IV:

• Variable outcomes
• Depends on specific anatomy

Quality of Life:

• Both groups function well overall
• Prosthetic function good
• Psychosocial support important

Predictors of Success:

• Appropriate patient selection
• Proper imaging (IB vs IA differentiation)
• Meticulous surgical technique
• Early treatment

Long-term:

• Prosthetic adjustments as child grows
• Most function independently
• Regular follow-up needed

Healthcare System:

• Tibial hemimelia management requires specialized pediatric orthopedic centers
• USS/MRI imaging available for proper classification
• Public hospital system provides comprehensive care
• Multidisciplinary teams available (orthopedics, prosthetics, psychology)

Multidisciplinary Care:

• Pediatric orthopedic surgeon (primary)
• Radiologist (USS/MRI for Type IB vs IA differentiation)
• Prosthetist (for amputation cases)
• Physiotherapist (rehabilitation)
• Psychologist (support for child and family)
• Social worker (financial and social support)

Medicolegal Considerations:

• Informed consent critical - major decision (amputation vs synostosis)
• Proper imaging essential - USS/MRI for Type IB vs IA differentiation
• Documentation of knee functionality assessment
• Family counseling about both options
• Long-term follow-up until skeletal maturity

Prosthetic Services:

• Available through public and private providers
• Regular adjustments needed as child grows
• Functional prostheses for activities and sports
• High-quality prostheses available

Research and Outcomes:

• Australian centers follow international guidelines
• Registry data helps track long-term outcomes
• Quality of life studies important for treatment decisions