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Miscellaneous dermatology

Wound Healing

Objectives

  • Revise biology of wound healing.

Key points

  • Partial thickness wounds regenerate more rapidly than full thickness wounds.
  • Injury results in haemostasis, inflammation, proliferation, and repair.
  • Keratinocytes migrate and proliferate in a single layer before keratinisation.
  • Dermal injury is repaired by granulation tissue, then a collagen matrix (scar).
  • Damaged hair follicles, sweat glands and melanocytes may not be replaced.
  • Chronic wounds are those that persist for longer than 4 weeks.
  • A moist environment promotes wound healing.
  • Patient factors delaying wound healing include smoking, diabetes, poor nutritional state and other illness.
  • Local factors delaying wound healing include inadequate perfusion, wound infection and skin disease.

Introduction

Skin generally heals rapidly to restore barrier function after injuries such as cuts, abrasions, thermal burns, puncture wounds and blisters.

The severity of a wound depends on its surface area and depth. Partial thickness wounds can recruit new keratinocytes from adjacent adnexal tissue and can regenerate much more rapidly than full thickness wounds of the same surface area where regeneration of epithelium arises only from keratinocytes on the wound edges. Damage to the dermis can be repaired but results in altered tissue i.e. a scar.

Injury results in epidermal and dermal repair: haemostasis, inflammation, proliferation, and repair. Haemostasis creates a protective wound scab beneath which cell migration and movement of the wound edges can occur. Inflammation brings nutrients to the area of the wound, removes debris and bacteria, and provides chemical stimuli for wound repair. Repair begins immediately after wounding and proceeds rapidly through the processes of epithelialisation, fibroplasia, and capillary proliferation into the healing area.

Wounds can be classified as either acute or chronic. Acute wounds are sometimes defined as those that follow the normal phases of healing; they are expected to show signs of healing in less than 4 weeks and include postoperative wounds. Chronic wounds are those that persist for longer than 4 weeks and are often of complex poorly understood origin.

Acute surgical wound after curettage of pyogenic granuloma

Chronic pressure ulceration

Venous ulceration healing with granulation tissue


Epidermal repair

Dermal repair

Moist wound healing

A moist environment is beneficial compared with a dry wound. Moist wounds:

Adverse factors

Delayed wound healing is more likely in some patients.

Patient factors

Local factors