Process of Wound Healing
Process of wound healing involves a complex series of interactions between different cell types, cytokine mediators, and the extracellular matrix.
The phases of normal wound healing include haemostasis, inflammation, proliferation, and remodelling. Each phase of wound healing is distinct, although the wound healing process is continuous, with each phase overlapping the next.
Before the advent of modern veterinary practice, many soft tissue injuries healed with time.
The difference that the modern veterinary practice has made is that the more severe injuries that would have killed the animal are now manageable; the deformity and infection that often accompanies natural unaided tissue healing can be avoided or minimized.
The Four phases of wound healing are–
Haemostasis phase of wound healing
Tissue injury initiates a response that first clears the wound of devitalized tissue and foreign material, setting the stage for subsequent tissue healing and regeneration.
The initial vascular response involves a brief and transient period of vasoconstriction and hemostasis.
A 5-10 minutes period of intense vasoconstriction is followed by active vasodilatation accompanied by an increase in capillary permeability.
Platelets aggregated within a fibrin clot secrete a variety of growth factors and cytokines that set the stage for an orderly series of events leading to tissue repair.
Inflammatory phase of wound healing
The second phase of wound healing is the inflammatory phase lasts for 1-3 days in uninfected wounds.
Classic signs (Five cardinal signs of inflammation) of Inflammatory phase of wound healing are the following-
- Redness (rubor)
- Swelling (tumor)
- Pain (dolor)
- Heat (calor)
- Loss of function (function laesa)
The inflammatory response increases vascular permeability, resulting in migration of neutrophils and monocytes into the surrounding tissue. The neutrophils engulf debris and microorganisms, providing the first line of defense against infection. Neutrophil migration ceases after the first few days post-injury if the wound is not contaminated. If this acute inflammatory phase persists, due to wound hypoxia, infection, nutritional deficiencies, medication use, or other factors related to the patient’s immune response, it can interfere with the late inflammatory phase.
In the late inflammatory phase, monocytes converted in the tissue to macrophages, which digest and kill bacterial pathogens, scavenge tissue debris and destroy remaining neutrophils. Macrophages begin the transition from wound inflammation to wound repair by secreting a variety of chemotactic and growth factors that stimulate cell migration, proliferation, and formation of the tissue matrix.
Proliferative phase of wound healing
The subsequent proliferative phase is dominated by the formation of granulation tissue and epithelialization.
Proliferative phase of wound healing duration is dependent on the size of the wound.
Chemotactic and growth factors released from platelets and macrophages stimulate the migration and activation of wound fibroblasts that produce a variety of substances essential to wound repair, including glycosaminoglycans (mainly hyaluronic acid, chondroitin-4-sulfate, dermatan sulfate, and heparan sulfate) and collagen. These form an amorphous, gel-like connective tissue matrix necessary for cell migration.
New capillary growth must accompany the advancing fibroblasts into the wound to provide metabolic needs.
Collagen synthesis and cross-linkage is responsible for vascular integrity and strength of new capillary beds.
Improper cross-linkage of collagen fibers has been responsible for nonspecific post-operative bleeding in patients with normal coagulation parameters.
Early in the proliferation phase fibroblast activity is limited to cellular replication and migration.
Around the third day after wounding the growing mass of fibroblast cells begin to synthesize and secrete measurable amounts of collagen. Collagen levels rise continually for approximately three weeks.
The amount of collagen secreted during this period determines the tensile strength of the wound.
Wound remodelling phase of wound healing
The final phase of wound healing is remodelling, it develops 3 weeks following injury and continues up to two years, achieving 40-70 percent of the strength of undamaged tissue at four weeks.
This phase is characterized by re-organization of new collagen fibers, forming a more organised lattice structure that progressively continues to increase wound tensile strength.
The strength of scar tissue formed in this phase is less than the surrounding normal tissue.
Old type wound Healing Process
Old type wound Healing Process says that wound heals by three types of intensions-
- First Intention wound healing (Primary union)
- Second Intention Healing (Healing by granulation)
- Third Intention Healing (Healing by Secondary suture)
First Intention wound healing (Primary union)
- Healing completed in about 5 to 14 days
- Scar formed is very little
- Sufficient tensile strength in14 days
- Surgical wound heal by this type
Second Intention Healing (Healing by granulation)
- Healing by replacement of tissue
- Extensive loss of tissue
- Wound edges are widely separated
- Granulation tissue consisting of budding capillaries and fibroblasts fills the gap. It is highly vascular, velvety, soft, moist and pink in colour
- Healing takes 14 to 20 days
Third Intention Healing (Healing by Secondary suture)
- Granulation tissue of an extensive wound united by sutures at a latter date
- Granulation tissue does not have any nerve supply
- Granulation tissue is resistant to infection