A 35-year-old male presents with a closed fracture of the mid-shaft femur sustained 6 weeks ago. Radiographs show early callus formation with bridging of the fracture site. Regarding the stages of fracture healing, all of the following occur during the inflammatory phase EXCEPT:

Explanation

## Stages of Fracture Healing: Inflammatory Phase **Key Point:** The inflammatory phase occurs in the first 1–2 weeks after fracture and is characterized by hemostasis, inflammation, and cellular recruitment — NOT bone formation. ### Timeline of Fracture Healing | Phase | Duration | Key Events | |-------|----------|------------| | **Inflammatory** | 0–2 weeks | Hematoma formation, fibrin clot, vascular permeability ↑, cytokine/growth factor release, immune cell recruitment | | **Soft Callus (Reparative)** | 2–6 weeks | Cartilage and woven bone formation by osteoblasts and chondrocytes; angiogenesis | | **Hard Callus (Remodeling)** | 6 weeks–months | Woven bone → lamellar bone; callus resorption; restoration of mechanical strength | ### What Happens in the Inflammatory Phase 1. **Hemostasis & Fibrin Deposition** - Platelets aggregate and form a clot - Fibrin matrix acts as scaffold - Increased vascular permeability allows fluid exudation 2. **Cellular Recruitment** - Neutrophils arrive within hours (peak at 24–48 hours) - Macrophages arrive by day 3–5 - These cells clear debris and secrete growth factors 3. **Cytokine & Growth Factor Release** - **PDGF** (platelet-derived growth factor) from platelets - **TGF-β** (transforming growth factor-beta) from damaged cells - **IL-1, IL-6, TNF-α** from inflammatory cells - These recruit osteoblasts and promote angiogenesis 4. **Osteoblast Activation** (begins late in inflammatory phase, peaks in soft callus phase) - Osteoblasts are recruited but do NOT form woven bone until the **soft callus phase** (weeks 2–6) **High-Yield:** Formation of woven bone occurs during the **soft callus (reparative) phase**, NOT the inflammatory phase. This is a classic NEET PG trap. **Clinical Pearl:** If you see a fracture at 6 weeks with "early callus formation," the patient has already transitioned from inflammatory → soft callus phase. The inflammatory phase is complete. **Warning:** Do not confuse osteoblast *recruitment* (inflammatory phase) with osteoblast *bone formation* (soft callus phase).