Tissue Healing Phases
Effective treatment, management and rehabilitation of soft tissue injuries necessitate knowledge and understanding of phases of tissue healing. Wound healing refers to the body's replacement of destroyed tissue with living tissue. All connective tissue injuries, regardless of their severity, must undergo the same healing process (1,2,3). A consensus exists, consisting of 4 mutually exclusive overlapping, interlinked phases (Fig.1); Bleeding, Inflammation, Proliferation, and Remodeling (4,5). It is generally accepted that treatment and rehabilitation should be based on sound scientific principles underlying tissue healing (6).
Inflammation Phase - Acute
Following injury, damaged blood vessels bleed causing hypoxia, the injured tissue contains dead cells and extravasated blood (1). This triggers a natural but essential inflammatory reaction, involving a vascular and cellular response with fluid exudate, resulting in oedema and phagocytic activity (5). Acute inflammation results from vasodilatation and vasopermeability of the blood vessels, initiated and controlled by a wide array of chemical mediators released by the damaged tissues (7). Clinically, acute inflammation manifests as swelling, erythema, increased temperature, pain, leading to loss of function (2). The physical characteristics of acute inflammation were first formulated by Celsus in (30 BC – 38 AD) using Latin; rubor, calor, tumor and dolor (8). Typically, the inflammatory phase (Lag phase) lasts between 4-6 days, and prepares the wound for the proliferation phase (9).
Adapted from: Watson, (2006). Tissue repair: the current state of art. Figure 1. The basic response to tissue injury
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Figure 2. Hypothetical model of tissue tensile strength during healing Adapted from: Hunter (1998). Specific soft tissue mobilisation etc.
Proliferation Phase - Subacute
The proliferative phase is essentially the generation of repair material which involves the production of scar tissue (type III collagen), which commences after 2-3 days, reaching a peak at 2-3 weeks post-injury. There are two fundamental processes involved; fibroplasia (formation of collagen) and angiogenesis (formation of new local blood vessels) (5).
Although a short period of immobilisation following injury is necessary (2,4), early controlled mobilisation is essential for decreased healing time, increased vascular ingrowth, quicker regeneration of scar tissue (10,11,12) and stronger mobile tissue (6). Prolonged immobilisation leads to deleterious tissue effects such as; random deposition of collagen, excessive cross-link formation and atrophy. Consequently this leads to functional implications such as losses in range of movement and tensile strength (13).
During early and intermediate subacute healing, new tissue is fragile and easily interrupted, consequently, mobilisation too early or too intensively may re-rupture the injured tissue (2). Exercise loading and intensity should remain within the tensile capability of the healing tissue (Figure 2). Careful tensioning of the healing tissue during the proliferation phase increases collagen synthesis, thus, potentially speeds up the healing process (9).
Approximately 2-3 weeks post-injury, collagen maturation and remodeling initiate (2,4). With maturity, the collagen remodels becoming more obviously oriented in line with local stresses (5). A portion of the type III collagen is reabsorbed and is replaced by type I collagen with greater tensile strength Remodeling continues for months, even years. The tensile strength of the tissue improves due to formation of intra and extra molecular cross linkages between the collagen fibers (9).
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