What replaces the cartilaginous callus during bone healing?

• A. Bony Callus
• B. Fibrocartilage
• C. Hyaline Cartilage
• D. Osteoid

Answer: (A)

When a fracture heals, the initial soft callus is a fibrocartilaginous tissue that acts as a temporary bridge. As healing advances, this cartilaginous scaffold is replaced by bone through endochondral ossification. Blood vessels invade the site, osteoprogenitor cells become osteoblasts, and they lay down osteoid that mineralizes into woven bone. This new tissue forms the hard, or bony, callus that stabilizes the fracture. Over time, this bony callus is remodeled into mature bone.

That’s why the correct concept is the bony callus. The soft fibrocartilaginous tissue is the preceding stage, not the replacement; hyaline cartilage isn’t the typical replacement stage here, and osteoid is the unmineralized bone matrix laid down before mineralization, whereas the actual replacement is mineralized bone forming the bony callus.