What are the causes, incidence, and associated abnormalities of congenital pseudoarthrosis of the tibia?

Congenital Pseudoarthrosis of the Tibia: Causes, Incidence, and Associated Abnormalities

Congenital pseudoarthrosis of the tibia (CPT) is a rare pediatric orthopedic condition characterized by anterolateral bowing of the tibia with high rates of pathologic fracture and non-union, most commonly associated with neurofibromatosis type 1 and requiring combined surgical approaches for optimal outcomes. 1

Incidence and Epidemiology

• CPT is an extremely rare condition, with very few cases reported per year 2
• Most commonly presents in the pediatric population under 10 years of age 2
• Typically manifests as anterolateral bowing of the tibia with high risk of fracture and non-union

Causes and Pathophysiology

Primary Causes:

• Neurofibromatosis Type 1 (NF1): The most common underlying cause, with approximately 50-60% of CPT cases associated with NF1 1
• Fibrous hamartoma: Abnormal tissue growth at the pseudarthrosis site that prevents normal bone healing
• Vascular insufficiency: Poor blood supply to the affected area contributes to impaired healing

Pathological Features:

• Anterolateral bowing of the tibia that progresses to fracture
• Sclerotic bone ends with narrowing of the medullary canal
• Fibrous tissue interposition between bone fragments
• Biologically and mechanically inferior bone quality, even after healing 3

Associated Abnormalities

Skeletal Abnormalities:

• Fibular involvement: Persistent fibular pseudarthrosis is present in up to 90% of cases 4
• Ankle valgus deformity: Common complication affecting 45-50% of patients 4
• Limb length discrepancy: Mean shortening of 2.6 cm, with some cases experiencing up to 8 cm discrepancy 4
• Tibial deformities: Anterior or medial bowing ranging from 5-28 degrees 4

Systemic Associations:

• Neurofibromatosis Type 1: Characterized by café-au-lait spots, neurofibromas, and other manifestations
• Ankle and foot dysfunction: Limited range of motion and stiffness, particularly when transarticular rods are used 4
• Growth disturbances: Affecting the tibia and surrounding structures

Complications and Challenges

• Refracture: The most common and serious complication after primary healing 5

  • Rates vary by treatment technique: 85% for intramedullary rods alone, 81% for Ilizarov alone, 60% for combined techniques, 45% for vascularized fibular grafting, and 22.5% for cross-union 1
  • Can occur up to 18 years after initial fusion 3

• Non-union: Varies by technique with rates of 16.4% for intramedullary rods alone, 12.3% for Ilizarov alone, 6% for combined techniques, and 7.3% for vascularized fibular grafting 1

• Ankle stiffness: More common with intramedullary rod fixation techniques 1

• Progressive deformities: May develop throughout growth period, requiring long-term monitoring 4

Management Considerations

• Operative management is indicated for all patients over 2 years old (100% consensus agreement) 3, 1
• Complete excision of the pseudarthrosis site with sufficient autogenous bone grafting is essential (100% consensus agreement) 3, 1
• Combined fixation approach using both external fixation (Ilizarov) and intramedullary fixation achieves the highest union rates (84% primary union) and lowest complication rates 1
• Long-term follow-up until skeletal maturity is crucial due to the risk of late refracture 3

Emerging Approaches

• Cross-union technique: Creates tibiofibular fusion to increase stability, with 100% primary union rate and lower refracture rates (22.5%) 6
• Adjunctive therapies: Various biological approaches including bone morphogenic proteins and bisphosphonates are being investigated, though current evidence does not strongly support their routine use 3, 1

CPT remains one of the most challenging conditions in pediatric orthopedics, requiring a sophisticated surgical approach and long-term monitoring to address both the primary pathology and associated complications.