Congenital Pseudarthrosis of Tibia

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

Differential Diagnosis of Anterolateral Tibial Bowing

Anterolateral bowing is the key discriminator - posteromedial bowing is a benign, self-correcting entity and must NOT be confused with CPT.

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

CPT is a low-volume, heterogeneous condition with no randomised trials - almost all evidence is Level III/IV. The following remain genuinely contested.

1. Is there a single "gold standard" operation? Three strategies dominate: intramedullary rodding (Charnley-Williams), Ilizarov/circular fixation, and vascularized fibular graft (VFG). The Rastogi systematic review favours combined IMR plus Ilizarov and VFG over either alone, but no head-to-head trial exists. The newer cross-union (4-in-1) technique reports the best early union and lowest refracture, yet rests on small series with short follow-up. The honest exam answer is that practice is converging on combined biological and mechanical strategies rather than any one named operation.

2. Role of biological adjuncts (BMP, bisphosphonates). The anabolic (BMP) plus anti-catabolic (bisphosphonate) concept is biologically rational given the NF1 bone phenotype, but evidence is limited to small series. rhBMP use in skeletally immature children is off-label, and a survival benefit over meticulous resection and stable fixation alone is unproven.

3. Prophylactic rodding of pre-fracture bowing (Crawford I/II). Bracing reliably delays but does not prevent fracture. Whether to insert a prophylactic telescoping rod before the first fracture is debated - it may protect the limb, but commits a young child to ankle-spanning hardware and revisions, and some series show fracture still occurs.

4. Timing of amputation. After repeated failed reconstructions with severe LLD and a stiff, deformed ankle, amputation can outperform a non-functional salvaged limb. The number of attempts before recommending amputation is not standardised and is individualised to function, family wishes and psychosocial factors.

5. Refracture and retained hardware. Refracture rates of 30-50% mean "union" is not the endpoint. Whether a load-sharing rod should be retained permanently to skeletal maturity (supported by Johnston's long-term data) versus removed is debated.

Global Epidemiology:

• Incidence approximately 1 in 140,000 to 250,000 live births (rare worldwide)
• NF1 prevalence in CPT pooled at 55% across the literature, but up to 84% in cohorts using strict NIH criteria with serial follow-up, because NF1 features often emerge after the CPT diagnosis (Van Royen 2016)
• Anterolateral bowing presents in infancy; bilateral disease in 10-15%

Guidance and Consensus (no formal single-society guideline exists):

Registries:

• No dedicated CPT implant registry exists given rarity. Evidence is driven by pooled systematic reviews (e.g. Rastogi 2022, 1227 patients) and multicentre paediatric collaboratives rather than arthroplasty-style national registries.
• NF1 disease registries and rare-disease networks increasingly capture orthopaedic outcomes.

High- vs Limited-Resource Practice Variation:

• High-resource settings: microsurgical VFG, BMP adjuncts, modern telescoping rods, cross-union, and combined IMR plus Ilizarov are feasible; early referral to specialist limb-reconstruction centres.
• Limited-resource settings: vascularized transfer and BMP may be unavailable; emphasis falls on non-vascularized autograft with IM rodding or Ilizarov, longer bracing, and earlier consideration of amputation with prosthetic fitting where multiple reconstructions are not feasible.

Multidisciplinary Team (universal): Paediatric orthopaedic surgeon, microsurgeon/plastic surgeon, clinical geneticist, physiotherapist, orthotist/prosthetist, and psychological support for child and family.

Counselling and Consent (universal):

• High failure rate and likelihood of multiple operations
• Realistic union expectations and 30-50% refracture risk even after union
• Amputation framed as a functional treatment option, not a failure
• Long-term follow-up to skeletal maturity for refracture, LLD and ankle deformity