Tissue Healing Phases and Injuries

Phases of Tissue Healing

• Tissue healing is a multi-stage process encompassing several key phases.
• The stages of soft tissue healing are bleeding, inflammation, proliferation, and remodelling.
• Knowledge of these phases is vital, not only for the current course, but for future career development.

Initiation of Tissue Healing

• Acute inflammation can stem from acute trauma, mechanical irritation, thermal insult, or chemical insult.
• The extent of primary injury is determined by the acute trauma and may increase with aggravating activity. Further damage may occur following initial injury, leading to secondary injury, which can often be decreased.

Primary and Secondary Injury

• Primary injury is the initial tissue damage from the acute trauma. This is not typically reducible.
• Secondary injury results from subsequent management, particularly hypoxic damage and subsequent cell death.
• Tissue healing involves replacement of damaged tissue with healthy tissue.

Tissue Repair Phases and Timescale

• Tissue repair phases include bleeding, followed by inflammation, proliferation, and remodelling.
• Bleeding occurs over hours.
• Inflammation is a reaction occurring over days.
• Proliferation takes place over weeks.
• Remodelling is measured in months.

Bleeding

• Bleeding, also known as hemostasis, is a relatively short-lived process, usually lasting 4–6 hours.
• The duration of bleeding varies based on the affected tissue's vascularity.
• This initial phase involves vasoconstriction of blood vessels, followed by platelet aggregation and clot formation.

Inflammation

• Inflammation is a natural response to tissue damage.

• Characteristic signs are heat, redness, swelling, pain, and loss of function.

• Essential for tissue removal of damaged and dead cells.

• Also prepares the body for repair.

• Inflammation can be acute or chronic.

• Chemicals like histamine and prostaglandins promote vasodilation.

• Increased permeability in capillaries allows fluid to leak into the tissue causing swelling.

• Involves recruitment of phagocytes to remove cellular debris.

• Chemical stimuli such as lactic acid promotes cellular proliferation.

Vascular Events

• Vasodilation and increased vascular permeability lead to inflammatory response.
• Vasodilation is a brief vasoconstriction, mediated by chemicals like histamine and prostaglandins.
• Increased vascular permeability, mediated by histamine and serotonin, leads to the leaking of fluid into tissues, causing swelling (edema).

Cellular Events

• Phagocytes (e.g., neutrophils) migrate to the site of injury and remove dead/dying cells, fibrin, and other debris.
• This process is facilitated by chemicals, including lactic acid from phagocytosis.

Chronic Inflammation

• Chronic inflammation is a prolonged inflammatory response.
• Can be caused by ongoing irritation such as infections, inappropriate immune responses, poor circulation, or autoimmune conditions.
• It leads to the body attempting to produce fibrous material to aid in the repair process.

Proliferation

• Also called regeneration phase.
• Involves the formation of fibroblasts and angiogenesis.
• Fibroblasts produce collagen, essential for tissue repair.
• Angiogenesis creates new blood vessels, delivering oxygen and nutrients.
• Timescale from 48 hours to 3-6 weeks.

Fibroblast Formation

• Fibroblasts manufacture and maintain collagen in connective tissues.
• The resulting collagen assists repair of damaged tissue.
• Macrophage Growth Factors are instrumental in fibroblast migration to the area of injury.

Angiogenesis

• Formation of new blood vessels.
• Essential for delivering oxygen and nutrients for the repair process.
• Provides nourishment for the metabolic processes required in repair.

Remodelling

• Refinement of collagen and extracellular matrix.
• Progressive strengthening and realignment of collagen.
• Occurs over the timescale of weeks to months.
• Stress, like exercise, is crucial in optimizing the remodeling process, directing collagen alignment appropriately based on the tissue's stresses.

Injured and Healthy Tendon Tissue

• Images comparing structural characteristics of healthy and injured tendon tissue.

Collagen Strength

• A graph illustrating the gradual increase in tensile strength of collagen over time. Crucial for healing tissues.
• Represents the progression of healing from inflammation, through proliferation and into the remodeling phase.

Proliferation and Remodelling

• Images displaying the stages of healing over time from injury, demonstrating how the collagen progressively strengthens.

Factors that Affect Healing

• Age, smoking, prolonged steroid/NSAID use, temperature, poor blood supply (ischemia), and excessive movement/mechanical stress are negative influences affecting healing.

Injury Management and Healing

• Treatment methods should stimulate, not alter intrinsic events in healing phases.
• Medical interventions should be carefully chosen depending on the tissue and stage of repair.

Summary

• Tissue repair has four main phases: bleeding/hemostatis, inflammation, proliferation, and remodelling.
• Inappropriate treatment can hinder the healing process.