Preparatory Mindset
Wound healing is the biology behind every incision and every injury. The exam tests: healing by primary vs secondary intention, the three phases of healing, factors that impair healing, and wound management (suture types, timing, dressing) (CM exam tested — NOT on PPT). The lab deck (换药/debridement/suturing) makes this a hands-on OSCE station too.
Exam mindset: know the phases (inflammatory → proliferative → remodeling/maturation), primary vs secondary vs tertiary (delayed primary) intention, and the local/systemic factors (infection, ischemia, malnutrition, steroids, diabetes, smoking). Know when to remove sutures by site.
Core Concepts
1. Phases of wound healing (MUST KNOW)
- Inflammatory phase (炎症期, days 0-4): hemostasis (platelet plug, clot), neutrophil & macrophage infiltration (debris removal), cytokine release (TGF-β, PDGF, VEGF). Macrophages are the master cells.
- Proliferative phase (增殖期, days 3-21): granulation tissue formation (new capillaries, fibroblasts, ECM), angiogenesis, epithelialization (from wound edges), wound contraction (myofibroblasts), collagen deposition (initially type III)
- Remodeling/maturation phase (塑形期, weeks 3-24+): collagen reorganization (type III → type I), cross-linking, scar strengthening (peak tensile strength ~80% of normal at 3 months; never reaches 100%), scar maturation/contraction
2. Healing by intention (MUST KNOW)
| Type | Description | Example | Result |
|---|---|---|---|
| Primary intention (一期愈合) | Clean, apposed wound edges; minimal tissue loss; suture closed | Surgical incision | Fast, minimal scar |
| Secondary intention (二期愈合) | Open wound, granulation from base, contraction & epithelialization | Burns, pressure sores, infected/dehisced wounds | Slow, larger scar |
| Tertiary / delayed primary (三期/延迟一期愈合) | Wound left open initially (contaminated), closed later (3-10 days) when clean | Contaminated traumatic wounds, battle injuries | Compromise: control infection then close |
3. Factors affecting wound healing (MUST KNOW)
Local factors:
- Infection (most important — prolongs inflammation, destroys tissue)
- Ischemia/poor blood supply (diabetes, peripheral vascular disease, radiation, tight sutures)
- Foreign bodies / necrotic tissue (delays healing — debridement)
- Wound tension, edema, repeated trauma
- Site (face heals fast; lower leg/feet slow — poor perfusion)
Systemic factors:
- Malnutrition (protein, vitamins C/A, zinc, iron deficiency)
- Diabetes (microvascular disease, immune dysfunction, hyperglycemia)
- Corticosteroids (inhibit inflammation & collagen synthesis)
- Immunosuppression/chemotherapy, radiation
- Smoking (vasoconstriction, ↓ O2 delivery)
- Age (slower healing in elderly)
- Chronic disease (renal failure, liver disease, malignancy)
4. Wound classification (surgical wounds — SSI risk)
| Class | Description | SSI risk |
|---|---|---|
| I Clean | No infection/inflammation; no entry into viscera | ~1-2% |
| II Clean-contaminated | Entry into respiratory/GI/GU tract under controlled conditions | ~5-10% |
| III Contaminated | Open fresh wounds; major spillage; acute non-purulent inflammation | ~15-20% |
| IV Dirty-infected | Established infection/perforation/purulence | ~30-40% |
5. Wound management (lab skills — MUST KNOW)
- Suture removal timing by site (MUST KNOW): face 4-5 days, scalp 5-7, trunk 7-10, upper limb 10-14, lower limb 14-21 (poor perfusion → longer); remove earlier if infection suspected (leave alternate sutures)
- Dressing change (换药) principles: aseptic technique; assess the wound (color, exudate, odor); clean with saline from center outward; apply sterile dressing; frequency per exudate
- Debridement (清创术) (lab P-7): remove devitalized tissue, foreign bodies, bacteria; irrigate copiously (saline, high pressure); achieve hemostasis; convert a contaminated wound to a clean one; close if clean & fresh (<6-8 h; longer or heavily contaminated → leave open/delayed primary)
- Suture techniques (lab P-6): interrupted, continuous/running, mattress (horizontal/vertical), subcuticular, purse-string; deep tension sutures for wound support
- Bowel anastomosis (lab P-8): end-to-end small bowel anastomosis — single or double layer, inversion of mucosa, tension-free, good blood supply
- Drains: indicate deep/abscess/leak; remove when output low or as planned
6. Abnormal healing & complications
- Wound dehiscence (裂开): sudden opening (often day 5-10), risk factors (infection, malnutrition, steroids, ↑ intra-abdominal pressure, poor technique) → support, re-closure or heal by secondary intention
- Wound infection (SSI): erythema, pus, fever (day 5-7) → open, drain, culture, antibiotics
- Hypertrophic scar vs keloid: keloid = scar beyond the original wound margin (genetic, more in darker skin, earlobes/sternum); hypertrophic = within the wound, regresses
- Chronic wound: pressure sore, diabetic foot ulcer, venous ulcer — treat cause (offload, revascularize, compression), debridement, infection control, moist wound environment
High-Yield Points
- Three phases: inflammatory (0-4d) → proliferative (3-21d) → remodeling (3w-24w+)
- Primary = surgical closure; Secondary = open/granulation; Tertiary = delayed primary closure
- Wound tensile strength peaks at ~80% of normal (3 months), never 100%
- Infection = most important local factor; steroids/diabetes/smoking/malnutrition = systemic factors
- Suture removal: face 4-5, scalp 5-7, trunk 7-10, upper limb 10-14, lower limb 14-21 days
- Debridement: remove devitalized tissue; irrigate; convert contaminated → clean; close if <6-8 h fresh
- SSI classes I-IV; wound infection usually day 5-7
- Keloid: grows beyond wound margin (vs hypertrophic within)
- Wound dehiscence day 5-10 — risk factors & management
Topic Summary
Wound healing proceeds through inflammation (hemostasis, neutrophils/macrophages), proliferation (granulation tissue, angiogenesis, epithelialization, contraction), and remodeling (collagen III→I, scar strengthening to ~80% at 3 months). Healing is primary (clean closure), secondary (open granulation), or tertiary/delayed primary (contaminated wound closed later). Local factors (infection most important, ischemia, foreign bodies) and systemic factors (malnutrition, diabetes, steroids, smoking, age) determine outcome. Manage wounds with aseptic dressings, timely debridement (convert contaminated to clean), appropriate sutures (removal by site: face 4-5 days to lower limb 14-21 days), and recognize complications (dehiscence day 5-10, SSI day 5-7, keloid vs hypertrophic scar).
LMCHK OSCE Practice
- Wound assessment: inspect (erythema, swelling, discharge, dehiscence), describe the healing phase, and decide primary vs secondary healing.
- Dressing change demonstration: aseptic technique — wash hands, sterile gloves, saline cleaning center-outward, sterile dressing; explain the frequency.
- Suture technique: perform interrupted & mattress sutures on a pad; state removal times by site; explain why lower limb sutures stay longer.
- Debridement station: describe the steps (irrigate, excise devitalized tissue, achieve hemostasis, decide closure timing) — for a fresh (<6 h) vs delayed/contaminated wound.
- Keloid vs hypertrophic scar: identify and explain the difference (beyond the wound margin = keloid; risk factors).
- Pressure sore staging & management: stage I-IV, offloading, wound care, nutrition.
- Wound infection recognition: signs of SSI and first-line management (open, culture, drainage).