Expansion
Haemostasis, inflammation, proliferation and remodelling
Expansion
- Haemostasis (immediate): vasoconstriction, platelet plug, fibrin clot
- Inflammation (0 to 3 days): neutrophils then macrophages, which are the key orchestrating cell, clearing debris and releasing growth factors
- Proliferation (3 days to 3 weeks): granulation tissue with angiogenesis, fibroblast migration, type III collagen deposition, and re-epithelialisation
- Remodelling (3 weeks to a year or more): type III replaced by type I collagen, cross-linking, and wound contraction by myofibroblasts
Strength: about 10 per cent at one week (hence suture removal timing), 70 to 80 per cent at three months, and it never exceeds about 80 per cent of normal.
Primary intention: clean apposed edges, minimal granulation tissue, fine scar. Secondary intention: open wound, abundant granulation tissue, marked contraction, larger scar.
Impaired healing: infection (the commonest cause), poor blood supply, diabetes, malnutrition, vitamin C deficiency, zinc deficiency, steroids, chemotherapy, radiotherapy, smoking, foreign body and mechanical stress.
Excessive healing: hypertrophic scar stays within the wound boundary; keloid extends beyond it and recurs after excision.