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.

Why the tibia matters. The tibia normally carries roughly 85-90% of axial load and stabilises both the knee (proximal articulation with the femur via the medial tibial plateau and cruciates) and the ankle (distal articulation with the talus). Its loss therefore produces a predictable triad of problems whose location depends on which part of the tibia is missing.

Consequences by deficiency pattern:

The decisive structures are therefore the proximal tibial anlage (bony or cartilaginous), the patella and an active quadriceps mechanism - their presence determines whether a stable knee can be salvaged. The fibula is almost always present and frequently becomes the load-bearing strut after reconstruction.

Associated findings (tibial hemimelia is rarely isolated): foot deformity (usually equinovarus), marked limb-length discrepancy, ipsilateral hand/upper-limb anomalies, bifid or duplicated femur (Gollop-Wolfgang complex), and a recognised autosomal-dominant familial form. A systematic survey for associated anomalies is mandatory.

The short, varus, externally deformed leg of tibial hemimelia overlaps clinically with several other congenital long-bone deficiencies. The discriminators below are high-yield.

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

Global epidemiology

• Incidence approximately 1 per 1,000,000 live births - one of the rarest long-bone deficiencies, roughly 25-30x less common than fibular hemimelia.
• Slight male predominance; bilateral in around 30%; right and left affected equally.
• Rarely isolated - associated limb (hand ectrodactyly, bifid femur/Gollop-Wolfgang), and occasional syndromic or autosomal-dominant familial forms; a deliberate anomaly survey is mandatory.

Practice positions across regions (no single society publishes a dedicated tibial hemimelia guideline given rarity; positions are derived from major paediatric limb-deficiency literature):

Registry note: congenital limb-deficiency surveillance networks (e.g. EUROCAT in Europe, ICBDSR internationally) capture birth-prevalence data, but no arthroplasty-style implant registry exists for this reconstructive paediatric condition - outcome evidence rests on single-centre case series (level IV), not registry or randomised data.

High- vs limited-resource practice variation

• High-resource: MRI/ultrasound staging, multidisciplinary teams (paediatric orthopaedics, radiology, prosthetics, physiotherapy, psychology, genetics), and the option of multi-stage reconstruction with growth-friendly lengthening.
• Limited-resource: imaging access may be confined to plain radiographs, biasing toward early amputation; prosthetic durability, follow-up logistics and cost favour a single definitive procedure.

Counselling and governance (universal): informed consent for an irreversible decision (amputation vs reconstruction), documented knee/quadriceps assessment, US/MRI confirmation of the anlage before committing, balanced discussion of both pathways with realistic outcome expectations, and structured follow-up to skeletal maturity for limb-length management and prosthetic adjustment.