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Congenital Pseudarthrosis Tibia

  • Also known as
    • Anterolateral bowing

Definition

  • Anterolateral bowing.
    • True bone dysplasia with non union or potential non union through a hamartomatoUsually area in the tibia.
    • not present at birth
    • really a fibrous non-union of a pathological fracture
  • The defect in the bone is filled with mature, fibrous connective tissue.
  • The name is, therefore, a misnomer since, by definition, a pseudarthrosis has a cleft lined by fibrocartilage containing fluid and bounded by a capsule.
  • Bowing usually at junction of Mid / Distal 1/3

Epidemiology

  • Rare
  • 1:200 000
  • M = F
  • 50% have Neurofibromatosis type 1
  • 1-3% of Neurofibromatosis have CPT

Aetiology

  • Cause unknown
  • Theories include:
    1. Intrauterine fracture
    2. Localised vascular abnormality
    3. Constriction due to proliferating fibrous tissue
    4. Localised lesions Eg fibrous Dysplasia

Pathology

  • HamartomatoUsually cuff present at site of lesion site
  • Even with Neurofibromatosis, no clear histol evidence that fibrous tissue is Neurofibromatosis

Classification

Crawford Classification of Congenital Tibia Pseudarthrosis
Type Description
1 Non-dysplastic
  • Increased cortical density
  • Dense medullary canal
2 Dysplastic  
a
  • Wide medullary canal
  • Failure of tubulation
b
  • Cystic lesion before fracture or canal enlargement from a previoUsually fracture
c
  • Fracture, Cysts & Frank pseudarthrosis; Narrowed ends of fragments

Boyd Classification of Congenital Pseudarthrosis of the Tibia
Type Description
1
  • Congenital anterior bowing
  • Defect present in tibia on x-ray
  • Other Congenital defects may be present
  • Rare
2
  • Congenital anterior bowing
  • Hourglass constriction of tibia
  • Spontaneously fracture or 2° minor trauma
  • Usually < 2 yrs when fracture
  • Tapered, rounded & sclerotic
  • Medial cavity on XR
  • Most commmon & worst prognosis
  • Prognosis worse with Neurofibromatosis
  • 1/2 of cases
3
  • Fracture develops at site of bone cyst
  • Usually near junction of mid/ distal 1/3
  • Anterior bowing precedes or follow fracture
4
  • Sclerotic bony segment initially present at junction of mid/ distal 1/3
  • Segment may produce complete or partial obliteration of medial canal
  • No narrowing of tibia
  • Fracture develops like stress fracture
5
  • Congenital dysplastic tibia
  • Mild bowing
  • ± Pseudarthrosis
6
  • Intraosseous Neurofibromatosis or Schwannoma
  • ± Pseudarthrosis
  • Very rare


Natural History

  • If have Neurofibromatosis – virtually all will fracture by 2y
  • reasonable to bypass graft prophylactically involved segment if has Neurofibromatosis

Management

  • No fracture ie Type I or IIA
    • brace all
    • If have Neurofibromatosis -> discuss prophylactic bypass graft +/- excision
  • Fracture ie Type II B&C
    • usually excise segment, graft & rod
    • several options with rod
    • Sheffield growing rod through ankle joint
    • Steinman pins etc in tibia
      • 40-80% success
  • Difficult to treatment
    • Won't heal by POP alone
    • Pre fracture treatment = Preventative bracing
    • After fracture, treatment is surgical
      • Usually ~ 2yo
      • Try to avoid surgery till older
    • problem is one of malalignment & ongoing stress riser
  • Surgery Timing Controversial
    • More delay = shorter underdeveloped leg
    • Older pt = Increased union rate
    • ? Brace till large enough or first controlled by AFO & then surgery
  • Bone Grafting
    • Can be done prophylactically in concavity of bowed tibia
    • In combination
  • IM Rod
    • First approach once fractured
    • Most reliable technique
    • 60% union rate
  • Vascularised Free Fibular Graft
    • Pseudarthrosis segment resected
    • Contralateral fibula unless Ipsilateral Fibula OK
    • Hold with Ilizarov or External Fixateur
    • Good results reported ~ 80%
    • Advantages:
      • 1° bone lengthening
      • Defect correction
      • Rapid union
    • Disadvantages
      • Tech demanding
      • Requires microsurgery
      • Operation on normal leg
  • Major problem is valgus
    • Usually defects of Normal ankle joint 2° overgrowth of distal tibial epiphysis
      • Distal fibula acts as tether
      • Treatment with tibial / Fibular synostosis
      • Avoid by using ipsilateral fibula
      • Only possible if fibula not involved
  • Ilizarov Tech
    • Pseudarthrosis resected
    • Corticotomy of proximal metaphysis performed
    • 3-level ring fixator applied
    • Middle tibial segment moved distally to provide metaphyseal lengthening & Pseudarthrosis compression
    • Allows: Bone lengthening
        • Correct of defect
        • High union rates
  • Amputation
    • “hould not be the operation of first resort or last resort
    • Several lesions with poor prognosis
    • Make early decision
    • Boyd or Syme have excellent outcome in this group

Prognosis

  • Varies by type
  • Worse with
    • Congenital / early onset
    • Shortening
    • Tapering
    • Sclerosis
  • Failure of surgery with graft resorption
    • Amputation in 50%
  • Remember 25% of patients with Neurofibromatosis1 develop CNS Glioma
    • Coast of Maine café au lait spots (irreg outline)
    • associated with Albright’s syndrome
      • Triad
        • precocious puberty
        • polyostotic fibrous dysplasia
        • café au lait spots
  • Malignant transformation rate – 4% of fibrous dysplasia
  • Malignant transformation rate in fibrous dysplasia is <1%
    • Coast of California (smooth outline)
    • café au lait spots associated with neurofibromatosis

Webpage Last Modified: 15 October, 2011
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