Wound Healing

1. Wound Healing Tulane University Division of Plastic & Reconstructive Surgery

2. Presentation Overview • Wound Healing • History • Phases • Factors Influencing • Adjuncts to Wound Healing • Fetal • Wound Care • Principles • Dressings • Abnormal Scarring • Exotic Injuries

3. History of Wound Care • Smith papyrus (1700 B.C.) • 7 of 48 case reports dealt with wound healing • Ancient Egypt, Greece, India, and Europe • Gentle wound handling • Foreign body removal • Approximating wound edges • Clean dressings

4. History of Wound Care • 850 - Gunpowder (change in thought process) • Boiling oil, hot cautery, scalding water • Worse outcomes • 1500 - Ambroise Pare • Rediscovered gentle, clean wound handling during the battle of Villaine • 20th Century – Scientific Method

5. Phases of Wound Healing • Tissue Injury and Coagulation • Inflammation • Remove devitalized tissue and prevent infection • Early • Late • Fibroproliferative • Balance between scar formation and tissue regeneration • Fibroblast migration • Collagen synthesis • Angiogenesis • Epithelialization • Maturation/Remodeling • Maximize strength and structural integrity • Contraction • Collagen Remodeling

6. Tissue Injury and Coagulation • Tissue Injury and Coagulation • INJURY (Physical, antigen-antibody reaction, or infection) • Transient (5-10 minute) vasoconstriction • Slows blood flow, aid in hemostasis • Histamine mediated vasodilation and permeability changes • Vessels become lined with leukocytes, platelets and erythrocytes • Leukocyte migration into the wound • Endothelial cells swell and pull away from each other -> allowing serum to enter the wound • Hemostatic factors from platelets, kinins, complement, and prostaglandins send signals to initiate the inflammatory phase • Fibrin, Fibronectin, and plasma help form a clot and stop bleeding

8. Early Inflammation • Complement Cascade Activation • PMN infiltration • 24-48 hours • Stimulated by: • Complement components (C5a) • Formyl-methionyl peptide products from bacteria • Transforming Growth Factor (TGF)-b

9. Early InflammationPMNS • Predominant cell type from 24-48 hours • Phagocytosis and debridement • Removal of PMNS does not alter wound healing

10. Late InflammationMacrophage • Most critical cell type • Predominates after 48-72 hours • Attracted by: • Growth factors (PDGF, TGF-b) • Complement • Clotting components • IgG • Collagen and elastin breakdown products • Leukotriene B4 • Platelet factor IV

11. Late InflammationMacrophage Functions • Phagocytosis • Primary producer of Growth Factors (PDGF, TGF-b) • Recruitment of fibroblasts (proliferative phase) • Proliferation of extracellular matrix by fibroblasts • Proliferation of endothelial cells (angiogenesis) • Proliferation of smooth muscle cells • This leads to the Fibroproliferative phase

12. Late InflammationLymphocyte • Appears at 72 hours • Attracted by: • Interleukins • IgG • Complement products • Role yet to be determined

14. Fibroproliferative • Fibroblasts • Migrate into the wound via ECM • Predominant cell type by day 7 • Collagen synthesis • Begins on days 5-7 • Increases in linear fashion for 2 to 3 weeks • Angiogenesis • Promoted by macrophages (TNF-alpha, FGF, VEGF) • Epithelialization • Mitosis of epithelial cells after 48-72 hours • Modulated by growth factors (EGF, FGF, KGF)

15. FibroproliferativeExtracellular Matrix • Forms a scaffold for cell migration and growth factor sequestration (fibronectin, proteoglycans, collagen, etc.) • Proteoglycans and Glycosaminoglycans • Proteoglycans are proteins covalently linked to Glycosaminoglycans • chondroitin sulfate • heparan sulfate • keratan sulfate • hyaluronic acid (1st to appear) • Proteoglycans • Create a charged and hydrated environment • Facilitates cell mobility • Viscoelastic properties of normal connective tissue

16. Collagen • Principle building block of connective tissue • 1/3 of total body protein content • 3 polypeptide chains that wrap around each other to form a collagen unit (tropocollagen) • Filaments ->Fibrils -> Fibers

17. Collagen Types • Type 1 • Bones, skin, and tendons • 90% of total body collagen • Found in all connective tissues except hyaline cartilage and basement membranes • Type 2 • Hyaline cartilage, cartilage-like tissues, and eye tissue

18. Collagen Types • Type 3 • Skin, arteries, uterus, abdominal wall, fetal tissue • Association with Type I collagen in varying ratios (remodeling phase) • Type 4 • Basement membranes only • Type 5 • Basement membranes, cornea • Skin • Type 1 : Type 3 ratio is 4:1 • Hypertrophic scars/immature scars ratio maybe as high as 2:1

19. Collagen Metabolism • Dynamic equilibrium • Synthesis (Fibrosis) vs. Degradation (collagenases) • Collagenase activity • Stimulated: PTH, Adrenal corticosteroids, colchicine • Inhibited: Alpha 2-macroglobulin, cysteine, progesterone • Healing wound • 3-5 weeks equilibrium is reached between synthesis and degradation (no net change in quantity)

20. Angiogenesis • Formation of new blood vessels throughout inflammatory and proliferative phase of wound healing • Initiated by platelets • TGF-b and PDGF • PMN • Macrophages • TNF-alpha, FGF, VEGF

21. Angiogenesis • Endothelial Cell • Forms new blood vessels • VEGF(predominant chemotactic stimulator) • Move along the ECM created by fibroblast

22. Epithelialization • Repithelialization begins within hours of injury • Stimulated by • Loss of contact-inhibition • Growth factors • EGF (mitogenesis and chemotaxis) • KGF, FGF (proliferation) • Dissolution of hemidesmosomal links between epidermis and basement membrane allows lateral movement of epidermal cells • Expression of integrin receptors on epidermal cells allows interaction with ECM

23. Epithelialization • Epithelium advances across wound with leading edge cells becoming phagocytic • Collagenase (MMP) • Degrades ECM proteins and collagen • Enables migration between dermis and fibrin eschar • Mitosis of epithelial cells 48-72 hours after injury behind leading edge

25. Maturation/Remodeling • Longest phase: 3 weeks – 1 year • Least understood phase • Wound Contraction and Collagen Remodeling • Wound Contraction • Myofibroblast • Fibroblasts with intracellular actin microfilaments • Uncertain if fibroblasts differentiate into, or if a separate type of cell

26. Maturation/Remodeling • Collagen Remodeling • Type 3 Collagen degraded and replaced with Type 1 • Collagen degradation achieved by Matrix Metalloproteinase (MMP) activity (fibroblasts, PMNs, macrophages) • Collagen reorientation • Larger bundles • Increased intermolecular crosslinks

27. Tensile Strength • Collagen is the main contributing factor • Load capacity per unit area • (Breaking capacity- force required to break a wound regardless of its dimensions) • Rate of tensile strength increases in wounds vary greatly amongst species, tissues and individuals • All wounds begin to gain strength during the first 14-21 days (~20% strength), variable then after • Strength PEAKs @ 60 days • NEVER reaches pre-injury levels • Most optimal conditions  may reach up to 80%

28. Predominant Cell Types

29. Special Characteristics of Fetal Wound Healing • Lack of inflammation • Absence of FGF and TGF-b • Regenerative process with minimal or no scar formation • Collagen deposition is more organized and rapid • Type 3 Collagen (No Type 1) • High in hyaluronic acid • Area of ongoing research

30. Factors That Influence Wound Healing • Oxygen • Fibroblasts are oxygen-sensitive • Collagen synthesis cannot occur unless the PO2 >40mmHg • Deficiency is the most common cause for wound infection and breakdown • Hematocrit • Mild to moderate anemia does not appear to have a negative influence wound healing (given sufficient oxygenation) • >50% decrease in HCT • some studies report a significant decrease in wound tensile strength • while other studies find no change

31. Factors That Influence Wound Healing • Smoking • Multifactorial in limiting wound healing • Nicotine • Vasoconstrictive -> decreases proliferation of erythrocytes, macrophages, and fibroblasts • CO • Decreases the oxygen carrying capacity of Hgb • Hydrogen Cyanide • Inhibits oxidative enzymes • Increases blood viscosity, decrease collagen deposition and prostacyclin formation • A single cigarette may cause cutaneous vasoconstriction for up to 90 minutes

32. Factors That Influence Wound Healing • Mechanical Stress • Affects the quantity, aggregation, and orientation of collagen fibers • Abnormal tension -> blanching, necrosis, dermal rupture, and permanent stretching • Subcutaneous expansion produces stronger more organized scars • Hydration • Well hydrated wounds epithelialize faster • Environmental Temperature • Healing is accelerated at temperatures of 30 C • Tensile strength decrease by 20% in 12C environment

33. Factors That Influence Wound Healing • Denervation • No direct effect on epithialization or contraction • Loss of sensation and high collagenase activities in skin -> prone to ulcerations • Foreign Bodies (including necrotic tissue) • Delay healing and prolong the inflammatory phase • Nutrition • Delays increases in tensile strength • Prolonged inflammatory phase and impaired fibroplasia • Edema • May compromise tissue perfusion

34. Factors That Influence Wound Healing • Lathyrogens • Inhibit the cross linking of collagen bundles • Ex. D-penacillamine • Oxygen Derived Free Radicals • Degrade Hyaluronic acid and collagen • Destroy cell and organelle membranes • Interfere with enzymatic functions • Age • Tensile strength and wound closure rates decrease with age

35. Factors That Influence Wound Healing • Infection • Prolongs inflammatory phase, impairs epithiliazation and angiogenesis • Increased collagenolytic activity -> decreased wound strength and contracture • Bacterial counts > 105, b-hemolytic strep • Chemotherapy • Decreases fibroblast production and wound contraction • If started 10-14 days after injury, no significant long term problems, but short term decreased tensile strength • Radiation • Stasis and occlusion of small blood vessels • Decreased tensile strength and collagen deposition • Systemic Diseases • DM • Glycosylated RBCs  Stiffened RBCs & Increased blood viscosity • Glycosylated WBCs  impaired immune function • Renal Dz

36. Factors That Influence Wound Healing • Steroids • Inhibit wound macrophages • Interfere with fibrogenesis, angiogenesis, and wound contraction • Vitamin A and Anabolic steroids can reverse the effects • Vitamin A • Stimulates collagen deposition and increase wound breaking strength • Topical Vitamin A has been found to accelerate wound reepithealization

37. Factors That Influence Wound Healing • Vitamin C • Essential cofactor in the synthesis of collagen • Deficiency is associated with immune dysfunction and failed wound healing (Scurvy) • Immature fibroblasts and extracellular material • Decreased Alkaline phosphatase • Defective capillary formation -> local hemorrhages • High concentrations do not accelerate healing

38. Factors That Influence Wound Healing • Vitamin E • Large doses inhibit wound healing • Decreased tensile strength • Less collagen accumulation • HOWEVER • Antioxidant that neutralizes lipid peroxidation caused by radiation  Decreasing levels of free radicals and peroxidases increases the breaking strength of wounds exposed to preoperative radiation

39. Factors That Influence Wound Healing • Zinc • Deficiency: • Impairs epithelial and fibroblast proliferation • Decreases B and T cell activity • Only accelerates healing when there is a preexisting deficiency

40. Factors That Influence Wound Healing • NSAIDs • Decrease collagen synthesis an average of 45% (ordinary therapeutic doses) • Dose-dependent effect mediated through prostaglandins

41. Factors That Influence Wound Healing • Fibrin-based tissue adhesives • Increase breaking strength, energy absorption, and elasticity in healing wounds

42. Adjuncts to Wound Healing • Hydrotherapy • Whirlpool • Pulsed Lavage • Stimulates formation of granulation tissue • Clean non draining wounds with healthy granulation tissue should NEVER be subjected to hydrotherapy • Water agitation damages fragile cells • Electrostimulation • Imitates the natural electrical current that occurs when skin is injured • Increases migration of neutrophils and macrophages • Promotes fibroblasts • Increased collagen production and tensile strength

43. Adjuncts to Wound Healing • Ultrasound Therapy • Electrical energy converted to sound waves • Thermal component -> improves scar outcome • Nonthermal component -> cavitation • In animal models • Changes in cell membrane permeability, increase cellular recruitment, collagen synthesis, tensile strength, angiogenesis, wound contraction, fibrinolysis, and stimulates fibroblast and macrophage production • Clinically results are equivocal • LED (Light-emitting diode) • Produces light at multiple wave lengths • Larger area than lasers • Studied by NASA in weightless environments (space station, submarines) • Improved wound healing alone or in combination with hyperbaric oxygen

44. Adjuncts to Wound Healing • Hyperbaric Oxygen • Increases levels of O2 and NO to the wound • Benefit: Amputations, osteoradionecrosis, surgical flaps, skin grafts • None to minimal benefit with necrotizing soft-tissue infections • Wounds require adequate perfusion • Many off-label uses (Benefit? Financial?) • Acne, Migraines, Lupus, Stroke, MS, and many more • Medicare Coverage • 14 Covered Areas (next slide) • ~1/3 of claims are for problems not covered

45. Medicare Coverage of HBO • (1)  Acute carbon monoxide intoxication • (2)  Decompression illness • (3)  Gas embolism • (4)  Gas gangrene • (5)  Acute traumatic peripheral ischemia • (6)  Crush injuries • (7)  Progressive necrotizing infections • (8)  Acute peripheral arterial insufficiency • (9)  Preparation and preservation of compromised skin grafts • (10)  Chronic refractory osteomyelitis • (11)  Osteoradionecrosis (ORN) • (12)  Soft tissue radionecrosis (STRN) • (13)  Cyanide poisoning • (14)  Actinomycosis

46. Adjuncts to Wound Healing • Lasers “Biostimulation” • Excites physiologic processes and increases cellular activity in wounded skin • Accelerates healing of hypoxic and infected wounds when combined with hyperbaric oxygen • Low energy -> promote epithelialization • Different wave-lengths (multiple treatments) • VAC • Bioengineered Matrices

47. Adjuncts to Wound Healing

48. Wound Care General Principles • Cleaning and Irrigation • Need at least 7psi to flush bacteria out of a wound • High pressure can damage wounds and should be reserved only for heavily contaminated wounds • Debridement • Most critical step to produce a wound that will heal rapidly without infection • Non-selective: WTD, DTD, WTW,Hydrogen Peroxide, etc. • Useful in wounds with heavy contamination • When starts to granulate, start selective • Selective: sharp, enzymatic, autolytic, or biologic

49. Selective Debridement • Enzymatic • Naturally occurring enzymes that selectively digest devitalized tissue • Collagenase (Santyl), Papain-Urea (Accuzyme), etc. • Autolytic • Uses the body’s own enzymes and moisture to breakdown necrotic tissue • 7-10 days under semi occlusive and occlusive dressings • Ineffective in malnourished patients • Biologic • Maggots • Calcium salts and bactericidal peptides • Separate necrotic from living tissue making surgical debridement easier

50. Wound Care General Principles • Fundamentals of Surgical Wound Closure • Incision should follow tension lines and natural folds in the skin • Gentle tissue handling • Complete hemostasis • Eliminate tension • Fine sutures and early removal • Evert wound edges • Allow scars to mature before repeat intervention (2 weeks to 2 months scar appearance is the worst) • Scar appearance depends more on type of injury than method of closure • Technical factors of suture placement and removal are more critical than type of suture used • Immobilization of wounds to prevent disruptions and excessive scarring (Adhesive strips after suture removal)