# CIM Case: Congenital Pseudoarthrosis of Tibia ## Clinical Scenario **Patient:** 6-year-old boy **Presentation:** Fell at school, unable to weight-bear on left leg, closed injury to left tibia **Relevant history:** Parents noted progressive anterolateral bowing of the left leg since infancy, previous X-rays at age 2 showed cystic changes in the tibia, multiple café-au-lait spots noted since birth **Examination findings:** - Left leg shorter than right (2cm discrepancy) - Anterolateral bowing of left tibia - Mobile pseudoarthrosis at junction of middle and distal thirds - Multiple café-au-lait spots (>6, largest 4cm, coast of California borders) - Axillary freckling present - No skin nodules palpated - Intact sensation and pulses distally - Unable to weight-bear --- ## Investigations Provided ### Laboratory Results | Test | Result | Normal Range | Interpretation | |------|--------|--------------|----------------| | Haemoglobin | 125 g/L | 110-140 | Normal | | WCC | 7.2 x 10⁹/L | 5-13 | Normal | | Platelets | 310 x 10⁹/L | 150-400 | Normal | | Calcium | 2.40 mmol/L | 2.15-2.55 | Normal | | Phosphate | 1.5 mmol/L | 1.0-1.8 | Normal | | ALP | 250 U/L | 150-400 | Normal (child) | | Vitamin D | 85 nmol/L | >50 | Normal | ### Imaging **Image 1: AP and Lateral X-rays Left Tibia** **Radiological features:** - Anterolateral bowing at junction of middle and distal third - Complete fracture through area of cystic change - Atrophic bone ends with sclerotic margins - Tapered ("pencil-point") proximal fragment - Widened medullary canal at pseudoarthrosis site - Fibula also shows dysplastic changes - Cortical thickening proximally - No periosteal new bone **Image 2: Contralateral Tibia X-ray** **Findings:** - Normal tibial alignment - No dysplastic changes - Used for comparison and LLD assessment **Image 3: Previous X-rays (Age 2 years)** **Historical findings:** - Anterolateral bowing present - Cystic lesion in distal third of tibia - Thinned cortex overlying cyst - Findings consistent with pre-pseudoarthrosis ## Questions & Model Answers **Diagnosis: Congenital Pseudoarthrosis of Tibia (CPT) with Established Pseudoarthrosis - Crawford Type IV** **Also known as:** - Congenital anterolateral bowing with pseudoarthrosis - Neurofibromatosis-associated pseudoarthrosis **Association with Neurofibromatosis Type 1 (NF1):** | Feature | Percentage | |---------|------------| | CPT with NF1 | 50-90% of CPT cases have NF1 | | NF1 patients with CPT | 1-4% of NF1 patients develop CPT | | Bilateral CPT | Very rare, almost always with NF1 | **NF1 Diagnostic Criteria (NIH - need 2 or more):** | Criterion | This Patient | |-----------|--------------| | **≥6 café-au-lait spots** (>5mm pre-pubertal, >15mm post-pubertal) | Yes ✓ | | **≥2 neurofibromas** or 1 plexiform neurofibroma | No | | **Axillary/inguinal freckling** | Yes ✓ | | **Optic pathway glioma** | Unknown | | **≥2 Lisch nodules** (iris hamartomas) | Need ophthalmology | | **Distinctive osseous lesion** (sphenoid dysplasia, tibial dysplasia) | Yes - CPT ✓ | | **First-degree relative with NF1** | Unknown | **This Patient Meets NF1 Criteria:** - ≥6 café-au-lait spots with coast of California (smooth) borders ✓ - Axillary freckling ✓ - Tibial dysplasia (CPT) ✓ **Pathophysiology:** - Periosteal hamartoma tissue replaces normal periosteum - Abnormal osteoblast function - Poor vascularisation of pseudoarthrosis site - NF1 gene mutation affects neurofibromin → RAS pathway dysregulation > **Consultant Tip:** CPT is virtually pathognomonic of NF1 when unilateral. Always examine for café-au-lait spots and refer for formal NF1 assessment. **Crawford Classification of Congenital Pseudoarthrosis of Tibia:** | Type | Description | X-ray Appearance | Prognosis | |------|-------------|------------------|-----------| | **Type I** | Anterolateral bowing with dense cortex | Sclerotic, narrowed medulla | Good - may never fracture | | **Type II** | Anterolateral bowing with cystic lesion | Cyst with normal bone | Moderate - high fracture risk | | **Type III** | Anterolateral bowing with cyst at birth, fracture imminent | Cyst extending to cortex | Poor - will fracture | | **Type IV** | Established pseudoarthrosis | Atrophic ends, gap, sclerosis | Poor - difficult to heal | **This Patient: Crawford Type IV (Established Pseudoarthrosis)** **Other Classification Systems:** **Boyd Classification:** | Type | Description | |------|-------------| | **Type 1** | Defect with tapered bone ends | | **Type 2** | Hourglass constriction, most common | | **Type 3** | Cyst at distal third | | **Type 4** | Sclerotic segment | | **Type 5** | Dysplastic fibula | | **Type 6** | Intraosseous neurofibroma | **Prognostic Factors:** | Factor | Better Prognosis | Worse Prognosis | |--------|------------------|-----------------| | **Age at fracture** | >5 years | <2 years | | **Type** | Type I-II | Type III-IV | | **Bone quality** | Hypertrophic | Atrophic | | **Location** | Proximal | Distal | | **Associated fibula** | Normal | Also dysplastic | | **NF1 status** | No NF1 | Confirmed NF1 | **This Patient's Prognosis:** - Crawford Type IV - established pseudoarthrosis - Age 6 years - moderate - Atrophic bone ends - unfavourable - Fibula also involved - unfavourable - Confirmed NF1 - unfavourable - **Overall: Guarded prognosis, likely to require multiple surgeries** > **Consultant Tip:** Crawford Type IV with NF1 and fibular involvement has the worst prognosis. Counsel the family about likely need for multiple surgeries and possible eventual amputation. **Goals of Treatment:** | Goal | Priority | |------|----------| | **Achieve union** | Primary | | **Maintain alignment** | Essential | | **Preserve limb length** | Important | | **Prevent refracture** | Long-term | | **Avoid amputation** | Ultimate | **Conservative Management (Pre-fracture Only):** | Method | Indication | |--------|------------| | **Clamshell orthosis** | Pre-fracture, Crawford I-II | | **Total contact AFO** | Protect against fracture | | **Activity modification** | Reduce impact loading | **Surgical Principles:** | Principle | Rationale | |-----------|-----------| | **Resect pseudoarthrosis** | Remove abnormal tissue | | **Stimulate healing** | Bone graft, biologics | | **Rigid fixation** | Intramedullary preferred | | **Protect until solid** | Prolonged immobilisation | **Surgical Options:** | Technique | Advantages | Disadvantages | |-----------|------------|---------------| | **IM nail + bone graft** | Stable fixation, alignment | 50-60% union | | **Vascularised fibula graft** | Best union rates (85%) | Complex, morbidity | | **Ilizarov/external fixation** | Compression, lengthening | Pin infections, compliance | | **Combined techniques** | Synergistic benefits | Complex | **Recommended Approach for This Patient:** ``` Established Pseudoarthrosis (Crawford IV) ↓ Resect pseudoarthrosis tissue (including periosteal hamartoma) ↓ Intramedullary rodding (Williams/Fassier-Duval rod) ↓ Bone graft (autograft + consider BMP-2) ↓ Consider vascularised fibula graft if primary fails ↓ Post-op: Long leg cast → AFO protection until maturity ``` **Biologics:** | Agent | Role | |-------|------| | **BMP-2** | May improve union rates, off-label use | | **Bone marrow aspirate** | Autologous cells | | **PRP** | Limited evidence | > **Consultant Tip:** There is no universally successful treatment. Families must understand that multiple surgeries are likely, and amputation remains a possibility in refractory cases. **Intramedullary Rodding Technique:** **Preoperative Planning:** | Step | Consideration | |------|---------------| | **Imaging** | Full-length films, contralateral for comparison | | **Rod sizing** | Williams rod or Fassier-Duval telescoping rod | | **Graft source** | Iliac crest autograft, consider allograft | | **Consent** | Discuss refracture, LLD, amputation risk | **Surgical Technique:** **Step 1: Approach and Exposure** - Anterolateral incision over pseudoarthrosis - Expose pseudoarthrosis site - Identify and protect neurovascular structures **Step 2: Pseudoarthrosis Resection** | Structure to Remove | Rationale | |---------------------|-----------| | **Fibrous tissue** | Non-healing tissue | | **Sclerotic bone ends** | Back to bleeding bone | | **Abnormal periosteum** | Hamartomatous tissue | | **Interposed soft tissue** | Block to healing | **Step 3: Prepare Bone Ends** - Resect to healthy bleeding bone - May require 1-3cm resection - Creates fresh bone surfaces **Step 4: Intramedullary Rodding** | Technique | Details | |-----------|---------| | **Rod type** | Williams rod or Fassier-Duval | | **Entry point** | Through ankle (retrograde) and proximal tibia (antegrade) | | **Cross ankle** | Essential to protect distal segment | | **Cross knee** | May be needed for proximal lesions | **Step 5: Bone Grafting** | Graft Type | Source | |------------|--------| | **Autograft** | Iliac crest (cancellous) | | **Allograft** | Supplement if needed | | **BMP-2** | Off-label, may improve union | **Step 6: Fibula** | Situation | Management | |-----------|------------| | **Normal fibula** | Usually leave alone | | **Dysplastic fibula** | May need resection or osteotomy | | **Intact and preventing reduction** | Osteotomy | **Postoperative Protocol:** | Phase | Duration | Management | |-------|----------|------------| | **Cast immobilisation** | 3-6 months | Long leg cast | | **Transition to brace** | Until maturity | Custom AFO | | **Weight-bearing** | Protected until union | PWB → FWB | | **Follow-up** | Every 3 months | X-rays, assess union | > **Consultant Tip:** The rod must cross the ankle joint to protect the distal tibia from refracture. Use telescoping rods (Fassier-Duval) to accommodate growth. **Vascularised Fibula Graft (VFG) for CPT:** **Indication:** | Scenario | Role of VFG | |----------|-------------| | **Primary treatment** | Some centres use as first-line | | **Failed conventional surgery** | Most common indication | | **Large bone defect** | >3cm gap after resection | | **Atrophic non-union** | Poor local biology | **Advantages:** | Benefit | Mechanism | |---------|-----------| | **Living bone** | Brings blood supply | | **Osteogenic** | Active bone formation | | **Highest union rates** | 80-90% in best series | | **Structural support** | Strong cortical bone | | **Hypertrophy** | Graft enlarges over time | **Disadvantages:** | Issue | Consideration | |-------|---------------| | **Technical complexity** | Requires microvascular expertise | | **Donor site morbidity** | Pain, weakness, valgus ankle | | **Long operative time** | 6-10 hours | | **Microsurgical failure** | 5-10% vascular thrombosis | | **Still may refracture** | 20-30% need reoperation | **Technique Overview:** | Step | Details | |------|---------| | **Harvest** | Contralateral fibula (6-8cm segment) | | **Pedicle** | Peroneal artery and veins | | **Inset** | Into tibial defect after pseudoarthrosis resection | | **Fixation** | IM rod or plate | | **Anastomosis** | To posterior tibial or peroneal vessels | **Outcomes:** | Outcome | Rate | |---------|------| | **Primary union** | 70-85% | | **Union after revision** | 85-95% | | **Refracture** | 15-25% | | **Amputation avoided** | 85-90% | **Alternative: Free Fibula + IM Rod (Combination Technique)** - VFG wrapped around IM rod - Provides both structural support and biology - May have best outcomes **Considerations for This Patient:** - Age 6 - reasonable candidate - Failed previous surgery - not applicable (first presentation) - May consider if conventional surgery fails - Discuss with family as potential future option > **Consultant Tip:** Vascularised fibula graft has the best union rates but is technically demanding. Reserve for failed conventional treatment or large defects. **Complications of CPT Treatment:** **Early Complications:** | Complication | Management | |--------------|------------| | **Wound infection** | Antibiotics, debridement | | **Hardware failure** | Revision | | **Graft resorption** | Repeat grafting | | **Vascular injury** | Repair, fasciotomy if needed | **Late Complications:** | Complication | Incidence | Management | |--------------|-----------|------------| | **Refracture** | 30-50% | Repeat surgery, protection | | **Non-union** | 15-40% | Revision, VFG | | **Leg length discrepancy** | Common | Lengthening, epiphysiodesis | | **Angular deformity** | Common | Corrective osteotomy | | **Ankle stiffness** | Common | Physio, rarely fusion | | **Growth arrest** | If physis damaged | Monitor, address LLD | **Refracture:** | Factor | Description | |--------|-------------| | **Incidence** | 30-50% even after successful union | | **Timing** | Any time, often within 2 years | | **Prevention** | Protective bracing until maturity | | **Management** | Often repeat surgery needed | **Leg Length Discrepancy:** | Cause | Management | |-------|------------| | **Bone resection** | Creates immediate LLD | | **Growth arrest** | Progressive LLD | | **Shortening** | Expected 2-5cm at maturity | | **Treatment options** | Lengthening, contralateral epiphysiodesis, shoe raise | **Indications for Amputation:** | Indication | Rationale | |------------|-----------| | **Multiple failed surgeries** | Usually >3-4 procedures | | **Severe LLD** | >10cm, unmanageable | | **Severe ankle stiffness** | Non-functional limb | | **Chronic pain** | Quality of life | | **Family/patient preference** | After informed discussion | **Amputation Outcomes:** | Aspect | Consideration | |--------|---------------| | **Level** | Below-knee (Syme's or transtibial) | | **Function** | Excellent with prosthesis | | **Sports** | Full participation possible | | **Psychology** | Often liberating after years of treatment | **Timing of Amputation Discussion:** | When to Discuss | Context | |-----------------|---------| | **At diagnosis** | Part of informed consent | | **After 2-3 failed procedures** | Realistic option | | **When family ready** | Patient-centred decision | **This Patient's Prognosis:** - First surgery - proceed with IM rod + grafting - Expect possible refracture - Brace until skeletal maturity - May need 2-4 surgeries total - Amputation rate in series: 10-20% > **Consultant Tip:** A well-done below-knee amputation often provides better function than a limb salvaged after multiple surgeries. Discuss early, decide together. --- ## Key Teaching Points ### Pattern Recognition **This pattern suggests Congenital Pseudoarthrosis of Tibia:** - Anterolateral bowing of tibia from infancy - Fracture at junction of middle and distal third - Café-au-lait spots (NF1 association) - Atrophic bone ends on X-ray - Often fibula also involved - Progressive deformity before fracture **NF1 Features to Look For:** | Feature | This Patient | |---------|--------------| | Café-au-lait spots (≥6) | Yes ✓ | | Coast of California borders | Yes ✓ | | Axillary freckling | Yes ✓ | | Tibial dysplasia | Yes ✓ | | Neurofibromas | Not yet (develop later) | | Lisch nodules | Need slit-lamp | ### Critical Management Points 1. **CPT is strongly associated with NF1** - screen all patients 2. **Crawford Type IV has worst prognosis** - counsel family 3. **Pseudoarthrosis tissue must be resected** - abnormal biology 4. **IM rod should cross the ankle** - protect distal tibia 5. **Vascularised fibula graft has best union rates** - consider if conventional fails 6. **Amputation is a valid option** - discuss early, decide together --- ## Common Examiner Follow-ups **Q: "What is the natural history if untreated?"** Without treatment: - Progressive deformity and shortening - Recurrent fractures - Severe leg length discrepancy - Non-functional limb - Eventually requires amputation The condition does NOT heal spontaneously - the abnormal periosteum prevents union. --- **Q: "What is the Farmer procedure?"** The Farmer procedure (or cross-union technique): - Vascularised contralateral fibula transfer - Fibula is transposed with its blood supply intact (rotation plasty concept) - Used when ipsilateral fibula is also dysplastic - Provides structural support and blood supply - Now largely replaced by free vascularised fibula graft --- **Q: "What is the role of BMP in CPT?"** BMP-2 (bone morphogenetic protein-2): - Off-label use in CPT - May improve union rates when added to bone graft - Studies show benefit in some series - Concerns about cost, off-label status, cancer risk in NF1 - Used as adjunct, not primary treatment - Dose: Variable, typically 1.5-12mg --- **Q: "Why does the rod need to cross the ankle?"** The distal tibial segment in CPT is: - Small and fragile - At high risk of refracture - Protected by rod extending into talus/calcaneus - Crossing ankle provides mechanical protection - Accept some ankle stiffness for limb salvage - May be removed at skeletal maturity if stable --- ## Related Topics - Neurofibromatosis Type 1 - Tibial Bowing in Infancy - Paediatric Non-union - Vascularised Bone Grafting - Limb Lengthening in Children - Paediatric Amputation