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oncology

Osteochondroma (Osteocartilaginous Exostosis)

intermediate
6 min
28 marks
6 questions
Clinical Scenario
A 14-year-old boy presents with a painless hard lump on the inner side of his right knee that he first noticed 2 years ago. It has gradually increased in size but is not painful. On examination, there is a firm, non-tender, immobile bony prominence on the medial aspect of the distal femur. Range of motion is full. X-ray shows a bony outgrowth from the metaphysis with cortical and medullary continuity with the parent bone.
AP radiograph of the distal femur demonstrating a pedunculated osteochondroma arising from the metaphysis. The lesion shows continuity of the cortex and medullary cavity with the parent bone (pathognomonic). The stalk points away from the adjacent joint. A cartilage cap (not visible on X-ray) overlies the bony exostosis. This is a solitary lesion in a skeletally immature patient.
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AP radiograph of the distal femur demonstrating a pedunculated osteochondroma arising from the metaphysis. The lesion shows continuity of the cortex and medullary cavity with the parent bone (pathognomonic). The stalk points away from the adjacent joint. A cartilage cap (not visible on X-ray) overlies the bony exostosis. This is a solitary lesion in a skeletally immature patient.

Source: PTPN11 Mutations in Metachondromatosis: Exostosis Imaging • PMC3077396 • CC-BY

Questions

Question 1 (4 marks)

Describe the clinical and radiographic features of osteochondroma.

Question 2 (5 marks)

What are the indications for treatment and surgical technique?

Question 3 (6 marks)

Describe hereditary multiple exostoses (HME).

Question 4 (5 marks)

How do you recognize malignant transformation?

Question 5 (4 marks)

What are the complications of osteochondroma?

Question 6 (4 marks)

Discuss outcomes and surveillance.

Exam Day Cheat Sheet

Must Mention

  • •Most common benign bone tumor
  • •Cortical + medullary continuity (pathognomonic)
  • •Cartilage cap: <1cm benign, >2cm concerning
  • •Growth stops at skeletal maturity
  • •HME: EXT1/2, autosomal dominant, 1-5% transformation
  • •Excise only if symptomatic

Common Pitfalls

  • •Missing continuity criterion
  • •Wrong cap thickness threshold
  • •Wrong transformation risk
  • •Operating unnecessarily
  • •Missing HME genetics
  • •Not knowing vascular complications