Wound Healing

Types of Wound Healing: 

• Primary:

  • Direct approximation of wound edges w\in hours of wound creation
  • Example: sutures, stables, skin grafts
  • Contraindications: bites, infections, crush injuries, > 6-8 hrs since injury, retained foreign body

• Secondary:

  • Wound left open to heal spontaneously: epithelialization, contraction, granulation
  • Requires dressing changes
  • Inferior cosmetic result

• Delayed primary:

  • When the wound is left open (debridement, packing, antibiotics) to control infection and form granulation tissue for a few days, then the wound can be closed (suturing, graft, flap)

 

Classification of Wound Healing: 

	Definition	Example	Risk of infection
Clean	Operative, non-traumatic, no inflammation, no break in technique, no entering of resp\GI\GU	Thyroidectomy, hip replacement	<2%
Clean-contaminated	Operative, non-traumatic, entering resp\GI\GU w\out significant spillage	Tonsillectomy, cholecystectomy	5-10%
Contaminated	Operative w\ major break in technique, traumatic, entering resp\GI\GU w\ gross spillage, evidence of inflammation	Large bowel resection, biliary or GU surgeries w\ infected bile or urine	15%
Dirty	Operative, traumatic, fecal contamination, foreign body, necrosis, pus, perforation	Empyema, abscess I&D, wound debridement	40%

 

Stages of Wound Healing: 

• Inflammatory (1-6 days): limits damage and prevents further injury:

  • Hemostasis: vasoconstriction + platelet plug (within minutes)
  • Vasodilation and increased permeability:
  • Cell migration: margination, diapedesis, chemotaxis

• Proliferative (day 4 – week 3):

  • Matrix formation:
    • Fibroblast migration (7 day)
    • Collagen synthesis (D5-wk3); mainly type III here -> tensile strength begins to inc at D4-5
    • Glycosaminoglycan production
  • Angiogenesis: VEGF\NO
  • Epithelialization: begins 24-48 h

• Remodeling (week 3 – 1 year):

  • Collagen: increased collagen synthesis and organization (type I replaces type III, until normal 4:1 ratio is achieved)
  • Contraction: due to myofibroblasts
  • Scar formation and remodeling: begins at D21

 

Factors Affecting Wound Healing:

Local	Systemic
–   Blood\oxygen supply (atherosclerosis, Raynaud’s, scleroderma, PVD) –   Retained foreign body –   Infection (inc risk due to hematoma\seroma) –   Temperature –   Radiation	–   Age –   Hereditary conditions: collagen vascular diseases (EDS, progeria, Werner syndrome) –   Nutritional (proteins, vit C) –   Smoking –   Chronic ds (DM, Ca, CVD) –   Immunodeficiency (steroids, chemo, radio)

 

Abnormal Wound Healing:

Hypertrophic scar	Keloid
–   Elevated, but remains w\in borders of original scar –   Type III collagen oriented parallel to epidermal surface + abundant myofibroblasts and collagen –   Associated w\ poor technique during suturing –   Site: flexor surfaces –   More common than keloids, less likely to recur after therapy	–   Scar growing outside original wound borders –   Disorganized type I & III collagen, hypocellular collagen bundles –   Related to genetic and endocrine influences (inc in preg and puberty) –   Site: sternum, shoulder, face, earlobes –   More resistant to therapy

 

Random notes:

 

 

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Download the PDF version: here

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References:

• Salah Aldekhayel’s lecture
• Essentials of plastic surgery
• Toronto notes