## Fracture Healing Stages — Timeline and Features Fracture healing progresses through four overlapping stages: ### Stage 1: Inflammatory Phase (0–3 weeks) - Fracture hematoma forms immediately - Inflammatory cells (neutrophils, macrophages) infiltrate - Angiogenesis begins - Fibrocartilaginous callus starts forming - **Duration: Overlaps with early callus formation** ### Stage 2: Soft Callus Formation (1–4 weeks) - **Key feature at 3 weeks: This is the primary stage occurring** - Hyaline cartilage and fibrocartilage replace the hematoma - Woven bone (immature, non-lamellar) begins to form - Osteoblasts and chondroblasts proliferate from periosteum and endosteum - Angiogenesis and neovascularization are active - **Callus is NOT yet rigid — still cartilaginous** ### Stage 3: Hard Callus Formation (3–12 weeks) - Cartilaginous callus is gradually replaced by woven bone - Rigid bony bridge forms - Fracture becomes mechanically stable ### Stage 4: Remodeling Phase (Months to years) - Woven bone is replaced by lamellar bone - Hematoma is completely resorbed - Medullary canal is restored **Key Point:** At 3 weeks, the fracture is in the **soft callus stage**. The hematoma is being replaced, not completely resorbed. A rigid bony bridge does NOT yet exist — that occurs in the hard callus stage (weeks 3–12). **High-Yield:** The **soft callus is cartilaginous and NOT rigid**. Complete resorption of hematoma and formation of a rigid bony bridge are features of the **hard callus stage**, which occurs AFTER 3 weeks. **Clinical Pearl:** Radiographically, at 3 weeks you see early callus bridging the fracture, but the callus is still mostly cartilaginous. Mechanical testing would show the fracture is still weak — it gains strength progressively as woven bone replaces cartilage.
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