Dr. Kevin Yip

Dr Kevin Yip
Orthopaedic Surgeon
MBBS(UK), FRCS(EDIN), FAM(SING), FHKCOS(ORTHO)

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Fibrous Cortical Defect/Nonossifying Fibroma

Basics
Description
  • NOF is a common developmental abnormality in children and adolescents with open physes; it is not seen in adults.
    • Despite the name, this condition mineralizes and disappears with skeletal maturity.
    • When the lesion is very small, it is called a fibrous cortical defect.
    • Occurs eccentrically in the metaphyses of long bones, most commonly in the distal femur, proximal tibia, or distal tibia
  • The lesion is seen in children and adolescents, but not in adults.
  • Staging (as with other benign lesions):
    • Stage 1: Latent (~96%)
    • Stage 2: Active (~2-3%)
    • Stage 3: Aggressive (<1%)
  • Natural history:
    • Active stage 2 during childhood
    • Becoming latent stage 1 at skeletal maturation
  • Synonyms: Benign metaphyseal cortical defect; Metaphyseal fibrous defect; Benign fibrous histiocytoma; Fibrous xanthoma
Epidemiology
A common skeletal lesion
 
Incidence
Estimated to occur in 35% of healthy children with open physes
 
Etiology
The cause is hypothesized to be a focal area of increased periosteal resorption during growth.
 
Associated Conditions
  • NF:
    • NOF-appearing lesions may be found (~5%).
  • Jaffe-Campanacci syndrome:
    • Rare, congenital disorder
    • Multiple NOFs (widespread and symmetric)
    • Cafe-au-lait pigmentation
    • Nonskeletal abnormalities
    • Mental retardation
Diagnosis
Signs and Symptoms
  • Most lesions are asymptomatic and are found incidentally on radiographs.
  • Occasionally, the condition is painful if a pathologic fracture occurs through the lesion or if such a fracture is impending.
Physical Exam
  • Usually, the lesion is nontender.
  • No swelling or tenderness should be present with weightbearing, unless a fracture is impending.
  • NOF-like lesions may occur in NF.
  • Jaffe-Campanacci syndrome
Tests
Imaging
  • On plain radiographs, a lytic (radiolucent) lesion is seen eccentrically in the metaphyses of long bones (usually the distal femur, proximal tibia, or distal tibia).
    • Based in the cortex
    • Overlying cortex if thinned
    • Surrounded by a scalloped, reactive rim of sclerotic (radiopaque) bone
    • Often appears multiloculated, producing a bubbling appearance
    • Ranges in size from a few millimeters to a few centimeters
    • Usually solitary
    • If a bone scan is obtained, the lesion will appear hot early on from the reactive rim of bone.
      • As the lesion heals, the bone scan will become normal.
Pathological Findings
  • The lesion is filled with fibrous connective tissue arranged in a whirled, starry night pattern.
  • Also seen are multinucleated giant cells, foam-filled histiocytes, and hemosiderin pigmentation.
  • Cystic spaces are not typical.
Differential Diagnosis
  • Chondromyxoid fibroma
  • Giant cell tumor
  • Fibrous dysplasia
Treatment
General Measures
  • In general, full, unrestricted activity is allowed.
  • If weightbearing pain develops, AP and lateral radiographs should be obtained to look for stress fractures.
  • MRI is effective in detecting stress fractures.
Medication
  • The treatment for large lesions is radiographic monitoring according to the physician’s judgment because the lesion is self-healing at skeletal maturity.
  • Patients with large lesions should be seen every 6 months.
    • This monitoring may continue until growth is complete.
  • If >50% of the cortex is involved, and the patient is symptomatic (pain), a pathologic fracture is possible.
    • In this case, treatment is surgery with curettage and bone grafting.
    • If the lesion is small and asymptomatic (<25% of the width of the cortex), no monitoring is needed.
  • No restrictions are placed on activity unless a pathologic fracture is impending (>50% of the cortex is involved in a symptomatic child), in which case the child should be nonweightbearing or have protected weightbearing on the affected extremity.
Surgery
  • For impending pathologic fracture, curettage (scraping the lesion) followed by bone grafting (placing bone graft into the lesion) should be performed.
  • Internal fixation usually is not necessary.
Follow-up
Prognosis
All these lesions are self-healing at skeletal maturity.
 
Complications
  • Pathologic fracture is seen rarely.
  • Pathologic fractures usually occur only in lesions involving >50% of the cortex in symptomatic patients or in patients who have had severe trauma.
Patient Monitoring
  • Serial radiography:
    • AP and lateral views of the affected part
Miscellaneous
Codes
ICD9-CM
213.9 Fibrous cortical defect
 
Patient Teaching
  • Tell children that they must report pain or limp to their parents.
  • Reassure the child and parents regarding the benign nature of the lesion, the natural course of self-healing, and the prevalence of the lesion in healthy children (35%).
  • If the lesion is small, no follow-up is needed.
  • If it is large, follow-up should be obtained every 6-12 months.
FAQ
Q: If a child has a large NOF and is completely asymptomatic, is protected weightbearing or surgery necessary?
A: In general, if the child is completely asymptomatic, protected weightbearing is not necessary. A small risk of fracture is likely with trauma. Surgery is not necessary.
 
Q: What are the disadvantages of surgery?
A: A major disadvantage is the scar and the need for protected weightbearing for 3-6 months after surgery.

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