Congenital Pseudarthrosis of Tibia

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Congenital pseudarthrosis of the tibia (CPT) is a rare condition characterized by failure of the tibia to heal after fracture, resulting in a persistent nonunion. It is strongly associated with neurofibromatosis type 1 (NF1) and represents one of the most challenging conditions in pediatric orthopedics.

Epidemiology:

• Incidence: 1 in 140,000 to 250,000 live births
• Male to female ratio: 1.5:1
• Bilateral involvement: 10-15% of cases
• Left side slightly more common
• Strong association with NF1 (50-90% of cases)

Pathophysiology: CPT results from abnormal bone formation and healing. The exact mechanism is unknown but involves:

• Hamartomatous tissue at pseudarthrosis site (fibrous, non-ossifying)
• Abnormal periosteum (thickened, constrictive)
• Poor vascularity at pseudarthrosis site
• Abnormal bone biology (osteoclasts, osteoblasts dysfunction)
• NF1 gene mutation (when associated)

The condition represents a spectrum from anterior bowing (pre-fracture) to established nonunion (pseudarthrosis).

Normal Tibial Anatomy: The tibia is the primary weight-bearing bone of the lower leg. It has a triangular cross-section with anterior, medial, and lateral surfaces. The medullary canal contains bone marrow and provides a pathway for intramedullary fixation.

CPT Pathology: In CPT, there is:

• Anterior bowing: Characteristic deformity (anterolateral)
• Hamartomatous tissue: Fibrous, non-ossifying tissue at pseudarthrosis site
• Abnormal periosteum: Thickened, constrictive, prevents healing
• Narrowed medullary canal: In Type II, canal becomes sclerotic and narrowed
• Cystic lesions: In Type III, cystic changes precede fracture
• Established nonunion: In Type IV, complete pseudarthrosis with no healing potential

Pathophysiology: The hamartomatous tissue at the pseudarthrosis site prevents normal bone healing. The tissue is:

• Fibrous and avascular
• Contains abnormal cells (not true bone-forming cells)
• Creates a barrier to healing
• May be related to NF1 gene mutation (when associated)

NF1 Association: When CPT is associated with NF1:

• NF1 gene mutation affects bone biology
• Abnormal periosteal function
• Poor vascularity
• Worse prognosis than isolated CPT

Understanding the pathology helps guide treatment - excision of hamartomatous tissue is essential.

History:

• Anterior bowing noted at birth or early infancy
• May have history of minor trauma leading to fracture
• Family history of NF1 (if associated)
• Difficulty with weight-bearing or walking
• Previous treatment attempts (if established pseudarthrosis)

Physical Examination:

Inspection:

• Anterior (anterolateral) bowing of tibia
• May have visible pseudarthrosis site (if Type IV)
• Limb length discrepancy (if established)
• Ankle deformity (valgus, equinus)
• Assess for NF1 features:
  • Café-au-lait spots (over 6 spots over 1.5cm)
  • Axillary/inguinal freckling (Crowe's sign)
  • Neurofibromas
  • Lisch nodules (iris examination)

Palpation:

• Pseudarthrosis site may be palpable (Type IV)
• Anterior bowing may be felt
• Assess for mobility at pseudarthrosis (if present)

Range of Motion:

• Ankle: May have limited dorsiflexion (equinus)
• Knee: Usually normal
• Assess for contractures

Neurovascular:

• Usually normal
• Assess for NF1-related neuropathies (rare)

Associated Findings:

• Fibular involvement (common - may also have pseudarthrosis)
• Ankle deformity (valgus, equinus)
• Limb length discrepancy

Radiographs:

AP and Lateral Tibia:

• Assess anterior bowing (characteristic)
• Evaluate medullary canal (intact, narrowed, cystic, or nonunion)
• Measure bowing angle
• Assess for pseudarthrosis (Type IV)
• Evaluate fibula (may also be affected)

Full-Length Lower Limb:

• Measure limb length discrepancy
• Assess alignment
• Evaluate ankle deformity

CT Scan:

• May help assess medullary canal status
• Evaluate cystic lesions (Type III)
• Plan surgical approach

MRI:

• Assess soft tissue (hamartomatous tissue)
• Evaluate vascularity
• Plan vascularized fibula transfer

NF1 Workup (if suspected):

• Genetic testing (NF1 gene mutation)
• Ophthalmology examination (Lisch nodules)
• Family history assessment
• Dermatology assessment (café-au-lait spots, neurofibromas)

Bone Scan:

• May assess vascularity at pseudarthrosis site
• Less commonly used now

Early Complications:

Surgical:

• Infection (5-10%)
• Wound healing problems
• Neurovascular injury (microsurgery)
• Graft failure (vascularized fibula)
• Hardware problems

Late Complications:

Nonunion:

• Persistent pseudarthrosis (30-50% failure rate)
• May require multiple surgeries
• Amputation after 3-4 failures

Deformity:

• Recurrent anterior bowing
• Ankle deformity (valgus, equinus)
• Limb length discrepancy

Growth Disturbance:

• Shortening of affected limb
• May require lengthening procedures

Ankle Problems:

• Stiffness (IM rod through ankle)
• Deformity (valgus, equinus)
• May require ankle fusion

Donor Site (Vascularized Fibula):

• Fibular nonunion (rare)
• Ankle instability (if too much fibula removed)
• Peroneal nerve injury

Prevention:

• Careful patient selection
• Meticulous surgical technique
• Adequate excision of hamartomatous tissue
• Stable fixation
• Long-term bracing
• Realistic expectations

Immediate Postoperative:

• Pain management
• Neurovascular monitoring (especially microsurgery)
• Wound care
• Immobilization (cast, external fixator)

Casting Phase:

• Long leg cast 3-6 months
• Non-weight bearing initially
• Serial radiographs to assess healing
• Cast changes if needed

After Union:

• Protected weight-bearing
• Gradual return to activities
• Long-term PTB brace (full-time initially, then part-time)
• Activity modification (avoid high-impact sports)

Long-term Follow-up:

• Annual assessment until skeletal maturity
• Monitor for refracture
• Assess limb length discrepancy
• Evaluate ankle function
• Address complications as they arise

Bracing:

• PTB orthosis long-term
• May need until skeletal maturity
• Prevents refracture
• Activity modification

Functional Outcomes:

Union Rates:

• Vascularized fibula transfer: 50-70%
• Autogenous iliac crest: 30-50%
• Ilizarov: 40-60%
• Overall: 50-70% with best treatment

Predictors of Success:

• Early treatment (before multiple fractures)
• Adequate excision of hamartomatous tissue
• Vascularized bone graft
• Stable fixation
• NF1-negative (better than NF1-positive)

Predictors of Failure:

• NF1 association (worse prognosis)
• Multiple previous surgeries
• Large defect
• Poor vascularity
• Inadequate excision

Quality of Life:

• Most patients function well after union
• May have activity limitations
• Ankle problems common
• Limb length discrepancy may require lengthening
• Psychosocial support important

Long-term:

• Refracture risk: 20-30% even after union
• Long-term bracing often needed
• Ankle problems may require fusion
• Limb length discrepancy may worsen
• Regular follow-up essential

Healthcare System:

• CPT management requires specialized pediatric orthopedic centers
• Vascularized fibula transfer requires microsurgery expertise
• Public hospital system provides comprehensive care
• Multidisciplinary teams available (orthopedics, genetics, plastic surgery)

Multidisciplinary Care:

• Pediatric orthopedic surgeon (primary)
• Plastic surgeon (microsurgery for vascularized fibula)
• Geneticist (NF1 diagnosis and counseling)
• Physiotherapist (rehabilitation, bracing)
• Prosthetist (if amputation required)
• Psychologist (support for child and family)
• Social worker (financial and social support)

Medicolegal Considerations:

• Informed consent critical - high failure rate, multiple surgeries likely
• Realistic expectations essential - 50-70% union rate, 20-30% refracture risk
• Documentation of NF1 assessment and implications
• Family counseling about amputation as treatment option (not failure)
• Long-term follow-up until skeletal maturity

Research and Outcomes:

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