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Wound Management

Phases of Wound Healing 1

Acute Inflammatory Phase

The Normal Extracellular Matrix
phases of wound
This illustration shows the normal extracellular matrix. This is the space between the cells which is rich in hyaluronic acid (proteoglycan), fibronectin and other components that support the surrounding cells.

There are 3 basic phases of wound healing; Acute inflammatory phase, cellular proliferation phase and the remodeling phase.

The first is the acute inflammatory phase, which will help clear foreign materials from the wound. During this phase, a vascular response results in coagulated blood and aggregated platelets forming a clot. Some of these platelets will release chemo-attractants to illicit a cellular response. White blood cells are attracted to the wound to fight infection, remove damaged tissue and start new tissue formation through angiogenesis, the development of new blood vessels, and fibroplasia, the development of connective tissue to fill in the wound. It is important to note here that when the inflammatory phase gets out of control, healing can be compromised later via development of exuberant granulation tissue (an out-growth of fibrous tissue and blood vessels that commonly occurs in lower leg wounds of horses, as seen in the below hind leg wound, and often referred to as "Proud Flesh"). This is why maintaining control of the inflammatory process is important at this stage. It is also important to provide a barrier to help prevent additional bacteria from entering the wound as this will elicit additional inflammatory responses.

equine wound

Cellular Proliferation Phase

The second phase is the cellular proliferation phase that begins 3-5 days after the injury. Macrophages debride the wound and produce cytokines that stimulate fibroplasia, the development of fibrous connective tissue, with individual cells called fibroblasts. The fibroblasts then proliferate new extracellular matrix which is rich in fibronectin and hyaluronan. New capillaries begin to invade the fibrous granulation tissue causing it to appear bright red. In these wounds that are left open to heal, it is necessary for this granulation process to occur. This is what is called second intention healing and this occurs when the wound edges are so far apart they can not be brought together with sutures. With this granulation bed in place, the epithelial cells can migrate inward to restore the epidermis. It is at this point that the presence of a product which can facilitate cell migration is very important.

Remodeling Phase

The last phase of healing is the remodeling phase. If the previous phases have progressed as described, then this phase will close the wound with very minimal scarring. This is done through the action of myofibroblasts which interact with the ECM, cytokines and growth factors, to apply tension on the existing skin surrounding the wound edges to initiate wound contracture. The final phase is the conversion of the remaining granulation tissue to scar tissue.

In review:
As you can see the extracellular matrix which is rich in hyaluronic acid is important in the phases of wound healing.
The prevention or clearing of an infection is key in not prolonging the inflammatory phase of healing thereby resulting in further proliferation of inflammation and granulation tissue formation.
Managing the overall inflammatory phase of healing can also be helpful in accelerating wound healing.

1. Theoret, C. L. Physiology of Wound Management. In: Stashak, T. S. and Theoret, C. L.(eds.) Equine Wound Management 2nd ed, Blackwell Publishing Co. Ames, Iowa, 2008, pp 5-25.

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