What is the FIRST stage in the healing of a bone fracture or an extraction socket?

Correct answer: C. Haematoma formation

• A. HARD CALLUS forms from about 3–6 weeks as osteoblasts mineralise the soft callus into disorganised WOVEN bone.
• B. REMODELLING is the final stage, running for months to years as osteoclasts and osteoblasts convert woven bone into mature LAMELLAR bone along lines of stress.
• C. CORRECT. HAEMATOMA FORMATION is the initiating event. Torn vessels bleed into the defect and the clot both fills the space and, critically, delivers platelets and inflammatory cells that release growth factors (PDGF, TGF-beta, BMPs) to orchestrate everything that follows. In an extraction socket the clot is the scaffold on which all subsequent healing depends — its loss produces ALVEOLAR OSTEITIS.
• D. SOFT CALLUS forms at roughly 1–3 weeks, when fibroblasts and chondroblasts replace the granulation tissue with fibrocartilage. It comes after the haematoma and inflammatory phase.

Note: That is incorrect: haematoma formation is stage ONE of the classic four-stage sequence (haematoma/inflammation → soft callus → hard callus → remodelling). Expect this concept to be tested through extraction socket healing, where clot protection is the whole basis of post-operative instructions.