PHASES OF WOUND HEALING

The wound healing process is a dynamic process which can be divided into three phases

and it’s not linear and often wounds can progress both forwards and back through the phases

depending upon various factors such as infection, or other causes of wound chronicity.

The phases of wound healing are inflammatory phase, proliferation phase and maturation

phase. The first phase is the body’s natural response to injury. After initial injury, the blood

vessels there will contract and a clot is formed to achieve hemostasis. Then, dilation of blood

vessels will occur to allow cytokines, antibodies, white blood cells, growth factors, enzymes and

nutrients to reach the area. Release of vasoactive substances from stromal mast cells will make

small vessels permeable to molecular and cellular mediators of the inflammatory response. It is

at this stage that signs of inflammation can be seen (erythema, heat, edema, pain). Chemotaxis

results in migration and concentration of polymorphonuclear leukocytes that digest bacteria,

foreign debris, and necrotic tissue with lysosomal enzymes.

Then, in the second phase, the injured area is reconstructed with new granulation tissues

consisting of collagen and extracellular matrix, into which angiogenesis develop. The color and

condition of the granulation tissue can be the indicator of how the wound is healing. Dark

granulation tissue can mean poor perfusion, ischemia or infection at the wound site. Healthy

granulation tissue is pink/ red in colour, and doesn’t bleed easily. To achieve this, it is important

that the fibroblasts receive adequate oxygen and nutrient supply from the vessels.

Third phase will occur after the wound has closed and comprises of remodeling of

collagen (type 3, type 1 predominate in skin and aponeurosis). Both number of blood vessels and

cellular activity will decrease in this phase. Approximately 80 percent of the original strength of

the tissue is obtained by six weeks after surgery, but the diameter and morphology of collagen

fibers do not have the appearance of normal skin until about 180 days.

WOUND HEALING : PRIMARY AND SECONDARY INTENTION

(a) Healing by first intention/1 o union

Clean or uninfected wound , surgically incised Without much loss from cells/tissue wound edges approximated by surgical sutures Sequence:

initial hemorrhage (blood clots → seals wound against dehydration + infection) → acute inflammatory response → epithelial changes (basal cells proliferate + migrate towards incisional space, forms scab - separate viable dermis & necrotic material, multilayered new epidermis formed (Day 5) → organization (fibroblasts invade on Day 3, collagen fibrils form on Day 5 until healing, scar tissue with scanty cellular and vascular elements are formed in Week 4)

(b) Healing by second intention/2 o union

open with large tissue defect (+/- infection) extensive loss of cells/tissues wound not approximated by surgical suture, but left open Sequence:

Initial hemorrhage → inflammatory phase → epithelial changes → granulation tissues (main healing process - mature scar is pale and white due to more collagen, less vascularity, hair follicles/sweat glands NOT replaced) → wound contraction (myofibroblasts contract wound to 1/3 or 1/4 of original size)

Presence of infection- Bacterial contamination delays the process of healing due to release of bacterial toxins that provoke necrosis, suppuration and thrombosis. - Surgical removal of dead and necrosed tissue, (debridement) helps in this condition.

Difference in sequence:→ 2o union has larger tissue defect, slower, ugly scar formed, more inflammation + granulation tissue + scarring→ wound contraction only in 2o union

Difference in overall

Primary Union Secondary Union

Clean Unclean

Usually not infected +/- infection

Margins surgical clean Irregular margin

Sutures used Sutures not used

Scanty granulation tissue at incised gap

Exuberant granulation tissue to fill gap

Neat linear scar Contracted irregular wound

Complications infrequent Common complications Infection of wound - delay healing Implantation (epidermal) cyst Rust coloured pigmentation (hemosiderin) Deficient scar formation - inadequate

granulation tissue formation Incisional hernia/wound dehiscence Hypertrophied scars/keloid (excessive, ugly,

painful scars) Excessive contraction - Duputyren’s

contracture Neoplasia – Squamous cell carcinoma in

Marjolin’s ulcer

WOUND CLOSURE

Primary wound closure is preferred to close an open wound if possible. Suture is made to bring the skin edges together, and patient only need to keep the suture clean and dry.

Pros

1. A wound closed primarily heals much more quickly and with less pain.2. Primary closure involves fewer problems with abnormal scarring3. All vital, underlying structures are covered.

Contraindications to Primary Wound Closure

Concern about wound infection is the main reason not to close a wound primarily. If infection develops, the resultant deformity may be worse than that caused by the initial injury alone. The following circumstances are associated with an unacceptably high risk of infection:

1. An acute wound > 6 hours old (with the exception of facial wounds)2. Foreign debris in the wound that cannot be completely removed (e.g., a wound with a lot

of embedded dirt that you cannot clean completely)3. Active oozing of blood from the wound4. Dead space under the skin closure5. Too much tension on the wound

Delayed primary wound closure

Delayed primary closure is a compromise between primary repair and allowing an acute wound to heal secondarily. This option may be considered for a wound with characteristics that require secondary closure(e.g., a wound over 6 hours old) even though primary closure is preferable.

Initially treat the wound with wet-to-dry dressing changes for a few (2–3) days with the hope of being able to suture the wound closed within 3–4 days. The dressings should clean the wound, the tissue swelling caused by the trauma may subside, and all bleeding may be fully controlled.

In conclusion

Primary wound closure is done, if injury healed within 6 hours and if it is clean wound. This is to prevent infection. But this method is good for faster recovery of healing.

Delayed primary wound closure, after 2-3 days of wet-to-dry dressing to remove the debris and control the oedema or bleeding. If no sign of infection, primary closure is done on day 3 or 4.