A 68-year-old woman with chronic kidney disease (eGFR 28 mL/min/1.73 m²) and type 2 diabetes mellitus undergoes emergency repair of a perforated duodenal ulcer. On postoperative day 12, the surgical wound shows delayed epithelialization with minimal granulation tissue formation. Serum creatinine is 3.2 mg/dL, and vitamin C level is 0.4 mg/dL (normal: 0.6–2.0 mg/dL). Which phase of wound healing is MOST SIGNIFICANTLY impaired in this patient?

Explanation

## Wound Healing Phases and Vitamin C Deficiency ### Clinical Context This patient presents with **delayed granulation tissue formation** on postoperative day 12, which is the hallmark of impaired **fibroplasia phase** (days 3–21). The key clues are: - Low vitamin C (0.4 mg/dL — scurvy range) - Chronic kidney disease (reduced vitamin C absorption and increased urinary losses) - Minimal granulation tissue on day 12 (should be robust by this time) ### The Four Phases of Wound Healing | Phase | Timeline | Key Events | Vitamin C Role | |---|---|---|---| | **Haemostasis & Inflammation** | 0–5 days | Platelet plug, fibrin clot, neutrophil infiltration | Minimal role | | **Fibroplasia & Angiogenesis** | 3–21 days | Collagen deposition, neovascularization, granulation tissue | **CRITICAL — cofactor for prolyl/lysyl hydroxylase** | | **Remodelling & Maturation** | 21 days–2 years | Collagen cross-linking, scar maturation, tensile strength | Important but not rate-limiting | | **Epithelialization** | Concurrent with all phases | Re-epithelialization from wound edges | Supported by collagen scaffold | ### Key Point: **Vitamin C is essential for collagen hydroxylation**, the critical step in collagen stabilization and cross-linking. Without it, collagen molecules cannot form stable triple helices, and granulation tissue cannot form. ### High-Yield: **Vitamin C deficiency specifically impairs the fibroplasia phase** because: 1. Prolyl hydroxylase and lysyl hydroxylase require ascorbic acid as a cofactor 2. Without hydroxylation, collagen is unstable and rapidly degraded 3. Granulation tissue (which is 70% collagen) cannot form 4. This manifests as **delayed healing with minimal granulation tissue** — exactly this patient's presentation ### Clinical Pearl: Chronic kidney disease patients are at high risk for vitamin C deficiency due to: - Reduced dietary intake - Increased urinary losses (water-soluble vitamin) - Malabsorption from uraemia - Dialysis-related losses ### Mnemonic: **VitC = Collagen Cross-linking** - **V**itamin C → Hydroxylase cofactor - **C**ollagen → Prolyl/lysyl residues hydroxylated - **C**ross-linking → Stable triple helix formation - **C**ollagen → Granulation tissue scaffold ### Why NOT the Other Phases? - **Haemostasis & Inflammation (0–5 days):** This phase is largely intact; the patient has normal coagulation and inflammatory response. Vitamin C plays a minor role here. - **Remodelling & Maturation (21+ days):** While vitamin C is involved, this phase hasn't begun yet (patient is only on day 12). The acute problem is lack of granulation tissue formation. - **Epithelialization:** This is concurrent with all phases, but epithelialization DEPENDS on a collagen scaffold (granulation tissue). Without collagen, epithelialization cannot proceed — the primary defect is collagen synthesis, not epithelialization itself. [cite:Robbins and Cotran Pathologic Basis of Disease 10e Ch 3]