Phases of wound healing

There are three classic phases of wound healing: inflammation, fibroplasia, and maturation (Fig. 7-3).1

Inflammatory Phase

The inflammatory phase occurs during days 0-4 after injury. The initial changes are vascular including a vasoconstriction phase leading to reduced blood flow to aid hemostasis. Vasoconstriction is followed by a period of vasodilation with a simultaneous increase in endothelial cell permeability secondary to histamine. Hemostatic factors, such as kinin components and prostaglandins, initiate local inflammation. Fibronectin, a major component of granulation tissue, attracts neutrophil granulocytes, fibroblasts, mono-cytes, and endothelial cells culminating in a dynamic cellular milieu and local substances at the injury site. The precise role of each type of inflammatory cell remains unclear. Both polymorphonuclear (PMN) granulocytes and mononuclear leucocytes (MONO) migrate into the wound in numbers

Figure 7-2 Chronic wound of the sternum with granulation tissue.

directly proportional to the concentration of local factors. Studies have demonstrated that monocytes must be present during the inflammatory phase to trigger fibroblast production and subsequent migration into the wound.

Proliferative (Fibroblastic) Phase

During the proliferative phase of wound healing, fibroblasts move into the wound bed along a framework of fibrin fibers. Fibroblasts produce several essential substances, including glycosaminoglycans such as hyaluronic acid, chondroitin-4 sulfate, dermatan sulfate, and heparin sulfate which are all hydrated into ground substance. Fibroblasts also produce tropocollagen, a precursor of collagen. Collagen is responsible for the increasing tensile strength of the wound. The proliferative phase lasts from day 4 to approximately 2-4 weeks (Fig. 7-4).

Figure 7-3 Schematic of three classic phases of wound healing: inflammatory phase, proliferative phase, and remodeling phase.

Vasoconstriction

Vasoconstriction

Injury

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