Wound Healing

Phases of Healing - Stitching It Up

📌 Mnemonic: Heavy Inflammation Produces Remodeling.

• 1. Hemostasis (Immediate):
  • Vasoconstriction, platelet aggregation (plug).
  • Coagulation cascade activation → Fibrin clot. Key: Thrombin.
• 2. Inflammation (Day 1-6):
  • Neutrophils (PMNs, 24-48 hrs): Debris/bacteria clearance.
  • Macrophages (Day 2-3+): Crucial; phagocytosis, release GFs (PDGF, TGF-$\beta$).
• 3. Proliferation (Day 4 - Wk 3):
  • Fibroblasts: Collagen III synthesis, GFs (FGF).
  • Angiogenesis (VEGF), granulation tissue.
  • Epithelialization (EGF, KGF).
  • Wound contraction (myofibroblasts).
• 4. Remodeling (Wk 3 - 1yr+):
  • Collagen III → Collagen I (organized).
  • ↑ Tensile strength (max ~80% of original).
  • Scar formation & maturation. Apoptosis of cells.

⭐ Absence of macrophages severely impairs wound healing, highlighting their critical role.

Wound Closure Types - Sealing the Deal

• Primary Intention:
  • Clean wound, edges apposed (surgical incision).
  • Closure: Sutures, staples, adhesives.
  • Minimal scar, rapid healing.
• Secondary Intention:
  • Wound left open (infected wounds, ulcers).
  • Heals by granulation, contraction, epithelialization.
  • Larger scar, slower healing.
• Tertiary Intention (Delayed Primary Closure):
  • Initially open (contaminated wound); debride, manage infection.
  • Surgical closure after 3-5 days.
  • Reduced infection risk.

⭐ Tertiary intention (Delayed Primary Closure) is typically performed 3-5 days post-injury, allowing for initial debridement and infection control.

Factors in Healing - Boost or Bust

• Systemic Factors:
  • Boost:
    • Nutrition: Protein, Vit C, A, Zinc, Copper
    • Good oxygenation & perfusion
    • Growth factors (PDGF, FGF, EGF)
    • Hormones: Insulin, Growth Hormone
  • Bust:
    • Age (↑), Diabetes Mellitus, Obesity
    • Malnutrition (Vit C**↓, Protein↓, Zinc↓**)
    • Hypoxia, Ischemia
    • Drugs: Corticosteroids, Chemotherapy, NSAIDs
    • Smoking, Uremia, Jaundice
    • Severe stress (**↑**cortisol)
• Local Factors:
  • Boost:
    • Moist environment (occlusive dressings)
    • Good blood supply
    • Absence of infection
  • Bust:
    • Infection (most common cause of delay)
    • Foreign body, Necrotic tissue
    • Poor perfusion (e.g., PAD), Edema, Hematoma
    • Radiation injury
    • Excessive tension/movement
    • Desiccation or Maceration

⭐ Infection is the single most common and important cause of delayed wound healing.

Problematic Healing - Scars & Setbacks

• Hypertrophic Scars:
  • Raised, red, often pruritic; within wound margins.
  • Type III collagen ↑; may regress spontaneously.
• Keloids:
  • Extend beyond margins; thick, rubbery, often painful/pruritic.
  • Type I & III collagen ↑↑; high recurrence.
  • Sites: earlobes, sternum. Darker skin predisposition.
• Atrophic Scars:
  • Depressed, thin; loss of collagen/elastin (e.g., acne, striae).
• Other Setbacks:
  • Wound Dehiscence: Edges separate. Risks: infection, tension, poor nutrition.
  • Contractures: Limit movement, deformity. Common post-burns, over joints.
  • Chronic Wounds: Fail to heal > 3 months. E.g., diabetic, venous ulcers.

⭐ Marjolin's Ulcer: SCC in chronic non-healing wounds, old burn scars, or sinus tracts; often aggressive.

High‑Yield Points - ⚡ Biggest Takeaways

• Healing phases: Inflammation (PMNs, Mφ), Proliferation (fibroblasts, new vessels), Remodeling (collagen I).
• Platelets release growth factors (PDGF, TGF-β), initiating the healing cascade.
• Macrophages are critical for debridement and promoting tissue repair.
• Fibroblasts produce collagen type III, later replaced by stronger collagen type I.
• Myofibroblasts cause wound contraction, reducing defect size.
• Final tensile strength is approximately 80% of normal skin.
• Healing impaired by: infection, ischemia, diabetes, malnutrition, corticosteroids.