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MBBS QUESTION #10147
Question 1
A 50-year-old man sustains a mid-shaft fracture of the femur. Radiographs at 6 weeks show a bridge of woven bone (external callus) at the fracture site. Which structure is primarily responsible for producing this bridging callus?
  • Periosteum✔️
  • Endosteum
  • Articular (hyaline) cartilage
  • Epiphyseal growth plate
Correct Answer Explanation
The inner (cambium) layer of the periosteum is richly osteogenic and proliferates rapidly after a fracture, laying down subperiosteal (external) callus that bridges the fracture ends. The endosteum contributes to internal callus formation, but bridging external callus is chiefly periosteal in origin — the basis for careful periosteal preservation during open fracture fixation.