## Inflammatory Phase of Fracture Healing **Key Point:** The inflammatory phase is the immediate response to fracture, lasting 24–72 hours, dominated by cellular cleanup and cytokine signalling. ### Cellular Events in the Inflammatory Phase | Phase | Duration | Key Cells | Primary Events | |-------|----------|-----------|----------------| | **Inflammatory** | 0–3 days | Neutrophils, macrophages, platelets | Hemostasis, debris removal, cytokine release | | **Soft Callus** | 3–21 days | Fibroblasts, chondrocytes, osteoblasts | Cartilage and fibrous tissue formation | | **Hard Callus** | 3 weeks–4 months | Osteoblasts, osteocytes | Woven bone deposition and mineralization | | **Remodelling** | Months–years | Osteoclasts, osteoblasts | Conversion to lamellar bone, restoration of architecture | **High-Yield:** Neutrophils arrive first (within hours), followed by macrophages. Macrophages release **TNF-α**, **IL-1**, and **IL-6**, which trigger osteoblast recruitment and angiogenesis. **Clinical Pearl:** The inflammatory phase is essential for healing — suppressing inflammation too early (e.g., excessive NSAIDs in the first 2 weeks) can impair callus formation. ### Why the Correct Answer Neutrophils and macrophages are the hallmark cells of the inflammatory phase. They phagocytose dead tissue, bacteria, and clot, and secrete growth factors (VEGF, FGF, TGF-β) that recruit fibroblasts and osteoblasts for the next phase. 
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