During fracture healing, the transition from soft to hard callus is primarily driven by which cellular and molecular event?
- A Chondrocyte hypertrophy, vascular invasion, and mineralisation of cartilaginous matrix converting it to woven bone ✓
- B Osteoclastic resorption of woven bone followed by osteoblastic lamellar deposition
- C Periosteal stem cell differentiation into osteoblasts under cyclic compressive strain
- D Platelet-derived growth factor stimulating fibroblast-to-osteoblast transdifferentiation
Correct answer: A. Chondrocyte hypertrophy, vascular invasion, and mineralisation of cartilaginous matrix converting it to woven bone
Explanation
Secondary (indirect) fracture healing proceeds through a cartilaginous intermediate stage. During the transition from soft to hard callus, chondrocytes in the cartilaginous callus hypertrophy, deposit mineralised matrix, and undergo apoptosis. Vascular invasion then occurs, and osteoblasts replace the mineralised cartilage with woven bone — a process analogous to endochondral ossification. Osteoclastic remodelling converting woven to lamellar bone is a later (remodelling) phase, not the soft-to-hard callus transition.
Reference: Maheshwari Essential Orthopaedics, 6th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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