What is wound healing & its phases of healing

Introduction

Wound Healing involves a complex collaboration between different cellular players like neutrophils, macrophages, lymphocytes, fibroblasts, and collagen, all working together to restore the natural structure and function of damaged tissue

Wound is a discontinuity or break in the surface epithelium.

When only the skin is involved, a wound heals simply. It is complex when it involves underlying nerves, vessels and tendons.

A closed wound can be classified as –

  • Contusion
  • Abrasion
  • Haematoma
Contusion

Can be minor soft tissue injury without break in the skin, or major such as when being run over by a vehicle.

Typically, it causes skin discoloration from trapped blood beneath the surface

Abrasion

In this wound, epidermis of the skin is scraped away exposing the dermis.

They are painful as dermal nerve endings are exposed. These wounds need cleaning, antibiotics and proper dressings.

Haematoma

This refers to collection of blood usually following injury. It can occur spontaneously in patients who have bleeding tendencies such as haemophilia.

Depending upon the site, it can be subcutaneous,intramuscular or even subperiosteal.

A knee joint haematoma may need to be aspirated followed by application of compression bandage.

Small haematomas get absorbed. If not, they can get infected

A open wound can be classified as –

  • Incised
  • lacerated
  • penetrating
  • crushed
Incised

They are caused by sharp objects such as knife, blade, glass, etc.

Such wounds boast sharp edges and minimal contamination.

Primary suturing is ideal for such wounds, as it gives a neat and clean scar.

Lacerated

They are caused by blunt injury such as fall on a stone or due to road traffic accidents (RTA). Edges are jagged.

The injury may involve only skin and subcutaneous tissue or sometimes deeper structures also.

Due to the blunt nature of the object, there is crushing of the tissue which may result in haematoma, bruising or even necrosis of the tissue.

These wounds are treated by wound excision and primary suturing provided they are treated within six hours of injury.

Penetrating

They are not uncommon.

Abdominal stabbings can seem minor but are serious because they might damage organs like the intestines, liver, spleen, or blood vessels, even with small cuts of just 1 or 2 cm

Medical professionals should admit and observe all penetrating abdominal wounds for at least 24 hours.

Layer by layer exploration and repair, though recommended, may not be possible at times due to oblique track of the wound.

Crushed

Blunt trauma from vehicle collisions, wall collapses, earthquakes, or industrial accidents causes these injuries.

These wounds pose a serious threat, leading to severe bleeding, tissue death, and blood vessel compression. Additionally, those injured are at higher risk for conditions like gas gangrene and tetanus.

Adequate treatment involves good debridement and removal of all dead and necrotic tissues.

Types of Healing

  1. primary healing
  2. secondary healing
1. Primary Healing

When clinicians use clips, sutures, or adhesive materials to primarily suture a wound, it promotes minimal scarring and is termed healing by first intention or primary healing.

2. Secondary Healing

When there is irrepairable skin loss or the wound becomes infected and breaks open, primary suturing is not possible. Healing by secondary intention occurs when wounds develop more scar tissue and take longer to heal. Ulcers follow the same healing process.

Phases of Wound Healing

Inflammatory Phase

It kicks off right after forming and goes on for 72 hours.

There is initial arteriolar vasoconstriction, thrombus formation, platelet aggregation due to endothelial damage and release of adenosine diphosphate (ADP).

Later vasodilatation and increased vascular permeability develops. Here haemostasis, coagulation and chemotaxis occur.

All these cause features of acute inflammation are rubor, calor, tumour, dolor and loss of function.

Proliferative Phase

It starts on the third day and goes on for 3 to 6 weeks.

There will be formation of granulation tissue and repair of the wound.

The Granulation tissue contains fibroblasts, neocapillaries, collagen, fibronectin and hyaluronic acid.

Remodelling Phase ( Maturation )

It begins at 6 weeks and lasts for 6 months to 1 or 2 years.

Collagen matures by cross-linking and rearranging its fibers along tension lines, which strengthens the scar.

As the wound heals, blood flow decreases. Fibroblasts and myofibroblasts work together to shrink the wound.

Type III collagen transforms into type I collagen, leading to the maturation of collagen.

Final matured scar is acellular and avascular.

Factors Affecting Wound Healing

  1. LOCAL FACTORS :
    • Infection
    • Presence of necrotic tissue and foreign body
    • Poor blood supply
    • Venous or lymph stasis
    • Tissue tension
    • Haematoma
    • Large defect or poor apposition
    • Recurrent trauma
    • X-ray irradiated area
    • Site of wound, e.g. wound over the joints and back has poor healing
    • Underlying diseases like osteomyelilis and malignancy
    • Mechanism and type of wound-incised/lacerated/crush/avulsion
  2. GENERAL FACTORS :
    • Age, obesity, smoking, alcohol, stress
    • Malnutrition, zinc, copper, manganese
    • Vitamin deficiency (Vil C, Vil A)
    • Anaemia, hypoxia
    • Malignancy
    • Uraemia
    • Jaundice
    • Diabetes, metabolic diseases
    • HIV and immunosuppressive diseases
    • Steroids and cytotoxic drugs

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