Wound Healing

Wound healing is the coordinated restoration of tissue integrity after injury. It proceeds through overlapping phases, and failure at any stage produces a chronic wound, excessive scarring or dehiscence.

Phases

• Haemostasis (minutes to hours): vasoconstriction, platelet aggregation and fibrin clot formation. Platelet granules release PDGF, TGF-beta and fibronectin.
• Inflammation (days 1 to 4): neutrophils clear bacteria and debris in the first 48 hours, followed by macrophages (days 2 to 5), which orchestrate repair through growth factor release.
• Proliferation (days 4 to 21): fibroblasts deposit type III collagen, angiogenesis forms granulation tissue, keratinocytes migrate to re-epithelialise, and myofibroblasts drive contraction.
• Remodelling (3 weeks to 2 years): type III collagen is replaced by type I, cross-linking increases, and the scar reaches only about 70 to 80% of the original tensile strength.

Healing intentions

• Primary: edges apposed by sutures, staples or adhesive. Minimal scar.
• Secondary: left open to heal by granulation and contraction, used for contaminated wounds and abscess cavities.
• Tertiary (delayed primary): closure after 3 to 5 days once infection risk has passed.

Factors impairing healing

• Local: infection, ischaemia, tension, foreign body, necrotic tissue, haematoma, radiation, repeated trauma.
• Systemic: diabetes, malnutrition (protein, vitamin C, zinc), anaemia, smoking, advanced age, obesity, uraemia, jaundice, immunosuppression.
• Drugs: corticosteroids, chemotherapy, anticoagulants, NSAIDs, immunosuppressants, mTOR inhibitors.

Abnormal scarring

• Hypertrophic scars stay within the wound margin and regress over 1 to 2 years. Keloids extend beyond it, rarely regress and are commoner in darker skin. Contractures occur across joints.
• Chronic wounds fail to progress through healing within 4 to 6 weeks. Common types are venous, arterial, diabetic and pressure ulcers.

Normal healing: initial erythema, warmth and swelling for 3 to 5 days, followed by a firm healing ridge at 1 to 2 weeks, then scar maturation and blanching over months.

Complications and recognition

• Surgical site infection: spreading erythema, purulence, pain, fever, typically 3 to 7 days after surgery.
• Dehiscence: wound separation, often days 5 to 10. Serosanguinous drainage from an abdominal wound heralds fascial dehiscence.
• Seroma and haematoma: fluctuant collections that impede healing.
• Chronic wound signs: pale or friable granulation, undermined edges, rolled edges (consider malignancy), slough, exudate, odour, stalled size over 4 weeks.
• Hypertrophic scar and keloid: raised, pruritic, tender scar. Keloids follow minor insults such as piercing, with predilection for sternum, shoulders and earlobes.
• Marjolin ulcer: squamous carcinoma arising in chronic wounds or scars.
• Red flags: necrotising infection (pain out of proportion, crepitus, rapid spread), exposed bone or implant, non-healing wound beyond 12 weeks, and bleeding from friable margins.

Wound assessment is clinical and should document location, size, depth, tissue type, exudate, edges, surrounding skin and pain, with serial measurement and photographs.

Investigations

• Swab or tissue culture only when clinical infection is present. Deep tissue biopsy with quantitative culture (over 10^5 organisms per gram) when diagnosis is uncertain.
• CBC, glucose and HbA1c, albumin, prealbumin, ferritin, vitamin D, zinc and renal function.
• Ankle brachial index (and toe pressure, transcutaneous oxygen) for lower limb wounds. Healing is unlikely with transcutaneous oxygen below 30 mmHg.
• Duplex for venous reflux. Probe to bone test, radiograph or MRI for osteomyelitis.
• Biopsy of the edge for any ulcer unresponsive to 4 to 12 weeks of appropriate care, with atypical appearance, or long standing (malignancy, pyoderma gangrenosum, vasculitis).
• Wound scoring tools, for example TIME framework (tissue, infection, moisture, edge).

Acute wound care

• Control bleeding, irrigate with 100 to 500 mL warm saline or potable water under low pressure, remove foreign material, and debride devitalised tissue.
• Local anaesthesia with lidocaine 1% (maximum 4.5 mg/kg plain, 7 mg/kg with adrenaline).
• Close clean wounds within 6 to 8 hours (face up to 24 hours). Heavily contaminated, bite, crush or delayed wounds are left open or closed by delayed primary closure.
• Suture selection: nylon or polypropylene 5-0 to 6-0 on face (remove at 3 to 5 days), 4-0 to 3-0 on trunk and limbs (7 to 14 days, 10 to 14 over joints and back). Absorbable polyglactin 4-0 to 3-0 for deep layers. Tissue adhesive for low tension wounds, and staples for scalp and trunk.
• Tetanus: tetanus toxoid vaccine if last dose over 10 years ago (5 years for dirty wounds). Tetanus immunoglobulin 250 units IM for dirty wounds with unknown or incomplete vaccination.
• Antibiotic prophylaxis is not routine. Use it for bites, heavily contaminated wounds and open fractures: amoxicillin-clavulanate 875/125 mg twice daily for 3 to 5 days, or cefazolin 2 g IV for open fractures.

Moist wound healing and dressings

• Maintain a moist, clean, warm environment. Choose by wound type: hydrocolloids for light exudate, foam for moderate exudate, alginates and hydrofibre for heavy exudate or bleeding, hydrogel for dry slough, silver or iodine (cadexomer) for critical colonisation, and non-adherent contact layers for fragile skin.
• Negative pressure wound therapy at 75 to 125 mmHg continuous for complex wounds, open abdomen, and grafts, after debridement. Avoid over malignancy, untreated osteomyelitis or exposed vessels.
• Debridement: sharp, enzymatic (collagenase), autolytic, larval, or hydrosurgical.

Optimising host factors

• Smoking cessation, glycaemic control (HbA1c below 8%, glucose 140 to 180 mg/dL perioperatively), nutrition (protein 1.25 to 1.5 g/kg/day, calories 30 to 35 kcal/kg/day), correct anaemia and treat vascular disease.
• Supplement only when deficient: vitamin C 500 mg twice daily, zinc sulfate 220 mg daily for 10 to 14 days, vitamin A 10,000 units for steroid-induced impairment.
• Offload pressure, apply compression (30 to 40 mmHg) for venous ulcers, and revascularise ischaemic limbs.

Infection

• Superficial cellulitis: flucloxacillin 500 mg to 1 g four times daily, or cefalexin 500 mg four times daily, for 5 to 7 days. MRSA risk: doxycycline 100 mg twice daily or trimethoprim-sulfamethoxazole 160/800 mg twice daily.
• Severe or deep infection: piperacillin-tazobactam 4.5 g IV every 6 hours with vancomycin 15 to 20 mg/kg every 8 to 12 hours, plus urgent surgical debridement for necrotising infection.

Adjuncts for refractory wounds

Skin substitutes and grafts, platelet-rich plasma, becaplermin 0.01% gel for diabetic foot ulcers, hyperbaric oxygen (2.0 to 2.5 atmospheres, 90 minutes daily) for selected diabetic foot, radiation injury and necrotising infection.

Scar management

• Silicone gel or sheeting daily for 12 weeks or longer, sun protection, massage, and pressure garments for burns.
• Hypertrophic scars and keloids: intralesional triamcinolone 10 to 40 mg/mL every 4 to 6 weeks, 5-fluorouracil 50 mg/mL intralesional, cryotherapy, pulsed dye laser, and excision with postoperative radiotherapy or steroid injection for keloids (recurrence over 50% with excision alone).

Follow-up

Review chronic wounds weekly to fortnightly. Failure to reduce wound area by 40% at 4 weeks predicts non-healing, which calls for reassessment of cause, biopsy and specialist referral.