Osteochondroma

• Cartilage-capped bony projection
• Commonest benign tumour of bone

Incidence

• Accounts for 45% of benign bone tumours
• 12% of all bone tumours
• Males slightly more than Females
• Age 10 – 40 (most present under 20 years old)
• May be solitary or multiple (diaphysial aclasis)
• Any bone developing by enchondral ossification may be involved

Clinically

• Usually presents in the second decade, if not sooner
• Presents with lump or interference of tendon function
• Pain is not common, unless there is a fracture or an inflamed overlying bursa
• 50% are located in distal femur, upper tibia or proximal humerus
• Lesions enlarge during skeletal growth, then become latent
• Arise from metaphyseal part of the bone, move toward the diaphysis with growth and usually angle away from the growth plate

TrevorsDisease : Osteochondroma on epiphysial side of the growth plate

Diaphysial Aclasis

• Also known as Multiple Hereditary Exostosis (MHE)
• Autosomal dominant
• Disordered enchondral growth
• Multiple osteochondromas plus disordered metaphyseal growth
• Characteristics
  • Short stature
  • Bowing of limbs, esp. in forearm (50%) and ankle (45%)
  • Multiple osteochondromas
• Osteochondromas are usually sessile and large
• Treat individual lesions as necessary and observe for malignant change
• Risk of malignant transformation is10% overall or 0.25% per lesion
• Chance of malignant changes is higher in proximal lesions
• Annual examination and radiography is necessary

X-Ray

• Bony overgrowth, starting from metaphysis, projecting toward diaphysis
• Medullary canal of affected bone usually flows into the lesion
• Suspicious radiologic changes
  • Mineralisation of cartilage cap
  • Destruction of subchondral bone
  • Inhomogeneous density changes

CT Scan

• Useful for evaluation of painful or enlarging lesions
• Shows cartilage cap calcification

Bone Scan

• Bone scan shows activity at the tip, during growth period
• Increased activity on bone scan after maturity suggests malignant change

Pathology

• Normal bone covered by a cap of normal cartilage
• Developmental abnormality of juxta-epiphysial area
• May be sessile or pedunculated
• Average thickness of the cap is
  • 10-20 mm in growing child
  • 2-3 mm after maturity
• Cartilage cap resembles layers of the normal growth plate
• A bursa usually covers the lesion

Treatment

• Nil, unless symptomatic
• Indications of excision
  • Neurovascular compression
  • Limitation of ROM
  • Growth disturbance
  • Muscle irritation
  • Inflamed overlying bursa
• Extra-capsular marginal excision (recurrence 2%) is procedure of choice
• Excision, if necessary, is best done in second decade
• Decreased risk of recurrence, if excised after maturity

Prognosis

• Risk of malignant change 
  • Less than 1% (0.25%) in a solitary lesion
  • 10% in diaphysial aclasis
• Sarcomatous change are usually low grade
• Findings suggestive of sarcomatous change :
  • Enlarging mass
  • New-onset pain, esp. in absence of mechanical factor
  • Cartilage cap larger than 8 cm in diameter
  • Cartilage cap thicker than 1 cm thick (>2 cm strongly suggestive)
  • Positive bone scan after maturity
  • X-Ray
    • Fluffy outline (calcification)
    • Destruction of subchondral bone
    • Inhomogeneous density changes

References

• Lonner J.H, Steiner G.C and Kenan S : Cartilage-forming Tumors. In Spivak JM, Di Cesare PE, Feldman DS : Orthopedics; A Study Guide; 1999
• Frassica F.J, Frassica D.A and McCarthy E.F : Orthopedic Pathology. In Mark D. Miller : Review of Orthopedics; 2008