Key Facts

Understanding wound healing physiology is fundamental to surgical practice. Identifying and addressing factors that impair healing optimises patient outcomes.

Epidemiology

Chronic wounds affect ~2-4% of the population. NHS spends ~£5 billion/year on wound management. ~200,000 patients have chronic leg ulcers. Surgical site infections affect ~3-5% of surgical wounds.

Aetiology

Types of wound:

• Incisional (surgical), laceration, abrasion, contusion, puncture, avulsion, burn
• Acute wounds: Expected to heal through normal phases
• Chronic wounds: Fail to progress through normal healing — stuck in inflammatory phase (e.g., venous ulcers, diabetic ulcers, pressure ulcers)

Pathophysiology

Phase 1 — Haemostasis (minutes):

• Vasoconstriction → platelet aggregation → fibrin clot → coagulation cascade

Phase 2 — Inflammation (days 1-5):

• Neutrophils (first 24-48 hours) → macrophages (day 2-5; KEY orchestrating cell)
• Phagocytosis, debridement, cytokine release (TGF-β, PDGF, VEGF)

Phase 3 — Proliferation (days 5-21):

• Fibroblasts → collagen synthesis (predominantly type III initially → type I replaces over months)
• Angiogenesis → granulation tissue formation
• Epithelialisation from wound edges/adnexal structures
• Wound contraction (myofibroblasts)

Phase 4 — Remodelling (weeks to ≥1 year):

• Type III collagen replaced by type I collagen
• Cross-linking increases tensile strength
• Maximum strength ~80% of normal skin at 3 months

Normal Healing

• Progressive wound closure, decreasing inflammation
• Clean, pink granulation tissue
• Contracting wound edges (secondary intention)
• Decreasing pain and exudate

Impaired Healing

• Wound dehiscence (partial or complete)
• Chronic non-healing wound (>6 weeks without healing)
• Excessive exudate, necrotic tissue, biofilm
• Surrounding cellulitis (infection)

Abnormal Scarring

• Hypertrophic scar: Raised, red, stays within wound boundaries; may improve over 1-2 years
• Keloid scar: Extends beyond original wound; does not regress spontaneously; more common in darker skin, earlobes, sternum, shoulders
• Contracture: Excessive wound contraction → functional limitation (especially over joints)

Red Flags

• Wound dehiscence post-laparotomy with pink serous discharge ('pink fluid') — may herald evisceration
• Non-healing wound in elderly or diabetic — exclude malignancy (Marjolin's ulcer — SCC arising in chronic wound)
• Rapidly spreading cellulitis around wound — consider necrotising fasciitis

Bedside

• Wound assessment: Size, depth, tissue type (granulation, slough, necrotic), exudate, edges, surrounding skin
• Wound swab: If clinical infection suspected (not routine — treat clinically)
• ABPI: For leg ulcers — venous (>0.8) vs arterial (<0.5)

Bloods

• FBC: Infection, anaemia
• CRP: Infection
• HbA1c, glucose: Diabetes optimisation
• Albumin, pre-albumin: Nutritional status
• U&Es: Renal function

Imaging

• Duplex US: Venous ulcers (assess venous insufficiency)
• X-ray: Osteomyelitis, foreign body
• MRI: Deep infection, osteomyelitis
• Biopsy: Non-healing wound >6 weeks — exclude malignancy

Optimise Healing Factors

• Nutrition: Adequate protein, calories, vitamin C (collagen synthesis), zinc
• Glycaemic control: HbA1c <58 mmol/mol
• Smoking cessation: Nicotine causes vasoconstriction, reduces oxygen delivery
• Remove/reduce: Steroids, immunosuppressants where possible
• Offloading: Pressure ulcers and diabetic foot ulcers
• Treat infection: Antibiotics only for clinical infection (cellulitis, systemic sepsis)

Wound Management

• Debridement: Sharp, autolytic (hydrogels), mechanical, enzymatic, biological (larval)
• Dressings: Match to wound type — alginate (exudative), foam (moderate exudate), hydrocolloid (low exudate), hydrogel (dry/necrotic)
• Negative pressure wound therapy (NPWT/VAC): Promotes granulation, reduces oedema; useful for complex wounds
• Compression: For venous ulcers (only if ABPI >0.8)

Surgical

• Skin grafting: Split-thickness (SSG) or full-thickness (FTSG) for wounds unable to close
• Flap reconstruction: For complex wounds requiring tissue bulk
• Fasciotomy: Compartment syndrome

Referral Criteria

• Non-healing wound >6 weeks — tissue viability/wound specialist
• Suspected malignancy — biopsy and 2WW
• Complex wounds — plastic surgery
• Diabetic foot — MDT diabetic foot team

• Primary intention wounds: Heal within 1-2 weeks
• Secondary intention: Variable — weeks to months depending on size, depth, patient factors
• Venous ulcers: ~70% heal within 6 months with compression; recurrence common
• Diabetic foot ulcers: ~50% heal within 20 weeks; ~15% lead to amputation
• Pressure ulcers: Prevention is more effective than treatment; mortality ~25-33% in hospitalised patients with Grade IV
• Wound strength: Never exceeds ~80% of original tissue

Phases of Wound Healing

Factors Impairing Wound Healing