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

What is the diagnosis and what is the association with neurofibromatosis?

Describe the Crawford classification and its prognostic significance.

What are the principles of management and treatment options?

Describe the intramedullary rodding technique for CPT.

What is the role of vascularised fibula graft?

What are the complications and what are the indications for amputation?

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

CPT is strongly associated with NF1 - screen all patients
Crawford Type IV has worst prognosis - counsel family
Pseudoarthrosis tissue must be resected - abnormal biology
IM rod should cross the ankle - protect distal tibia
Vascularised fibula graft has best union rates - consider if conventional fails
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

Neurofibromatosis Type 1
Tibial Bowing in Infancy
Paediatric Non-union
Vascularised Bone Grafting
Limb Lengthening in Children
Paediatric Amputation

Congenital Pseudoarthrosis of Tibia