A 32-year-old male farmer sustains a deep laceration to his forearm while working with farm tools. The wound is cleaned and sutured in the emergency department. On day 5 post-injury, the wound shows erythema, mild warmth, and a small amount of serous discharge. Histologically, the wound demonstrates prominent fibroblast proliferation, collagen deposition, and angiogenesis. Which phase of wound healing is predominant at this stage?

## Wound Healing Phases Timeline **Key Point:** Wound healing occurs in overlapping but distinct phases, each with characteristic histological and clinical features. ### Timeline of Wound Healing Phases | Phase | Onset | Peak | Duration | Key Features | |-------|-------|------|----------|---------------| | **Hemostasis & Inflammation** | 0–6 hours | 24–72 hours | 0–4 days | Platelet plug, fibrin clot, neutrophil infiltration, macrophage arrival | | **Proliferative** | 3–4 days | 5–21 days | 3–21 days | Fibroblast proliferation, collagen deposition, angiogenesis, granulation tissue | | **Remodeling** | 3 weeks | 3–12 months | 3 weeks–2 years | Collagen cross-linking, scar maturation, tensile strength increase | ### Clinical and Histological Findings at Day 5 At day 5 post-injury, the wound is transitioning from the inflammatory phase into the **proliferative phase**: 1. **Fibroblast proliferation** — Fibroblasts migrate into the wound and begin synthesizing collagen (Type III initially). 2. **Collagen deposition** — Active collagen synthesis is occurring; this is a hallmark of the proliferative phase. 3. **Angiogenesis** — New blood vessels form (granulation tissue), driven by VEGF and FGF. 4. **Mild inflammation persists** — Some erythema and serous discharge are expected as macrophages clear debris and secrete growth factors. **High-Yield:** The proliferative phase is characterized by the **3 C's**: **Collagen**, **Cell proliferation** (fibroblasts), and **Capillary formation** (angiogenesis). **Clinical Pearl:** The presence of granulation tissue (pink, friable, bleeds easily) is the hallmark of active wound healing in the proliferative phase. It appears clinically as a beefy red tissue filling the wound defect. ### Why Day 5 is Proliferative, Not Inflammatory Although some inflammatory signs persist (erythema, discharge), the **histological predominance of fibroblast proliferation, collagen deposition, and angiogenesis** definitively places this in the **proliferative phase**. The inflammatory phase (dominated by neutrophils and macrophages) peaks at 24–72 hours and begins to wane by day 5. [cite:Robbins 10e Ch 3]