Healing of Injury

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Healing of Injury

Healing of an injury consists of a number of overlapping phases that are generally recognised and can generally be applied to most tissues. Inflammation is a protective response that permits the body to rid itself of injurious agents, damaged cells and to repair tissues.

Basic normal steps of inflammation and repair:
Injury (eg trauma, infection)  acute inflammatory response (vasoconstriction  vasodilatation  formation of clot  phagocytosis)  proliferative and remodelling response (epithelisation  collagen production  contracture of wound  neovascularisation)  maturation phase (balance between collagen synthesis and lysis  collagen fibre orientation)  healed injury

The acute inflammatory response:
• occurs 0 to 72 hours after injury – begins after any disruption of the normal physiology of the tissues
• injury  cell necrosis; small capillary rupture  haemorrhage into tissues; capillaries then vasoconstrict after 5 – 10 minutes  then vasodilate  leakage of fluid
• platelets adhere to site of damage in capillaries
• fibrin and other clotting factors  block damaged capillaires and lymphatics (this ‘mesh’ blocks further drainage from injury site)
• classic signs of inflammation – pain, redness, swelling and heat
• chemical mediators are released – histamine (vasodilaion), serotonin ( increases capillary membrane permeability), heparin ( prevents occlusion of blood flow in capillaries), neutophil chemotactic factor ( attracts neutraophils), kinins ( increases capillary permeability), prostaglandins ( vasodilate and increased capillary permeability), leukotrienes ( attracts neutrophils), complement ( facilitate all aspects of acute inflammation)

Matrix and cellular proliferation phase:
• occurs 72 hours to 6+ weeks post initial injury – new tissue growth occurs
• macrophages predominate
• proliferation of capillaries and fibroblasts  synthesise collagen (initially type III) and proteoglycan matrix
• new vascular tissue (neovascularisation) occur by budding from capillaries (under control of growth factors)

Remodelling and maturation phase:
• occurs about 6 weeks to several months
• myofibroblasts interact with collagen  contraction of collagen  reorientate in direction of loading/stress
• decrease in capillaries
• Type I collagen fibres produced (stronger than type III)

Chronic inflammation:
• acute inflammatory response usually resolves in 3 – 10 days, if not  chronic inflammation
• chronic inflammation due to:
• infection
• granulomatous (eg tuberculosis)
• autoimmune inflammatory response (eg rheumatoid arthritis)
• constant irritation with mechanical stress

Time required for healing :
Generally:
Muscles – 6 weeks
Tendons and ligaments – 12 weeks
Bone and joints – 6 – 12 weeks

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