a) Discuss the stages of fracture healing. [6]

Introduction: Fracture healing is a complex biological process that restores the structural and functional integrity of bone after injury. It involves a sequence of overlapping cellular and molecular events, broadly divided into distinct stages. Understanding these stages is critical for clinical management and predicting healing outcomes.

1. Inflammatory Stage (Reactive Phase)

Duration: Begins immediately after fracture, lasting approximately the first few days (1–7 days).

Pathophysiology:

• Fracture causes disruption to bone, periosteum, blood vessels, and surrounding soft tissues leading to hematoma formation at the fracture site.
• Broken blood vessels leak blood forming a fracture hematoma, which provides a scaffold and releases cytokines and growth factors such as platelet-derived growth factor (PDGF), transforming growth factor-β (TGF-β), and others.
• Inflammatory cells (neutrophils, macrophages) infiltrate, clearing debris, necrotic tissue, and bacteria.
• These cells release mediators that attract mesenchymal stem cells (MSCs) and initiate repair.

Clinical correlation: Initial swelling, tenderness, and local warmth occur due to inflammation.

2. Reparative Stage (Fibrocartilaginous and Bony Callus Formation)

Duration: Starts within days after injury and continues for several weeks (from approximately day 7 up to 3–4 weeks).

a) Soft Callus Formation (Fibrocartilaginous Callus)

• Mesenchymal stem cells differentiate into fibroblasts and…