Wound Healing

I.General Considerations Wound healing is a vague term that often confuses and diverts the clinician from focusing on a specific diagnosis.

A. Types of Wound Closure 1. Primary Closure – approximate disrupted tissues by sutures, staples, or tapes. With time there will be a. synthesis b. deposition c. cross-linking of collagen to provide the tissue with strength.

2. Delayed Primary Closure – also called tertiary closure. Wound closure is delayed for several days to prevent wound infection where there is: a. bacterial contamination b. foreign bodies c. extensive tissue trauma * Cleaning of the wound is done daily using NSS

3. Secondary or Spontaneous Closure - wound closes by contraction of the wound edges. Usually takes 4-10 days to close.

B. Mechanism Involved in Wound Healing 1. Epithelialization a. keratinocytes migrate then divide to resurface partial thickness loss of skin or mucosa. b. responsible for coverage c. cells migrate from side to side d. does not originate from the center

Examples: a. partial thickness skin graft donor site b. abrasions c. blisters d. 1 st and 2 nd degree burns

2. Contraction - the process whereby there is spontaneous closure of full thickness skin wounds or constriction of tubular organs such as the CBD or esophagus.

3. Connective Tissue Matrix Deposition - the process whereby fibroblasts are recruited to the site of injury and produce a new connective tissue matrix. The cross-linked collagen provides the strength and integrity to all tissue.

C. Phases of Healing 1. Coagulation – vasoconstriction occurs immediately because of the release of: a. catecholamines b. bradykinin c. serotonin d. histamine

Steps: i. diapedesis ii. hemostatic clot – formed by plateletes iii. fibrin clot formation – formed by fibroblasts - plateletes – 1 st cells to produce essential cytokines which modulates most of the subsequent steps in wound healing

2. Inflammation – migration of leukocytes into the wound. 1 st 24 hours, polymorphonucleocytes followed by macrophages. 3. Fibroplasia – increases wound strength, hence tissue integrity is restored. Within 10 hours after injury, there is increased wound collagen synthesis. Within 5-7 days, collagen has peaked and will decline gradually.

4. Remodeling – inflammatory cells decrease, angiogenesis and fibroplasia end. D.Cytokines –provides communication for cell to cell interaction. Roles include: 1. Regulation of Fibrosis 2. Healing of wounds and skin grafts. 3. Vascularization 4. Bone and Tendon Strengthening 5. Control of Malignancy

E. Extracellular Matrix Metabolism * Collagen – the major component of the cellular matrix of all soft tissues, tendons, bones, and ligaments. 1. Steps in Synthesis a. Transcription – control of mRNA b. Translational – synthesis which occurs on the ribosomes of the rough endoplasmic reticulum.

2. Degradation – breakdown of collagen which is initiated by collagenase secreted by the ff. cells: a. inflammatory cells b. fibroblasts c. epithelial cells - collagenase is activated by other proteases like plasmin

3. Ground Substance – made up of glycosaminoglycan subunits. They function as: a. molecular shock absorbers together with cartilage b. provide for moisture storage c. sequester cytokines - ground substance releases the cytokines following injury signaling the repair process to start

COMPONENTS OF EXTRACELLULAR MATRIX AND FUNCTION ComponentFunction 1.Collagen-strength, support, structure 2.Elastin- allows tissue to expand and contract 3.Fibronectin - mediates cell matrix adhesion 4. Laminin- binds cells to type iv collagen and heparin sulfate 5.Proteoglcans - moisture stores, shock absorption, sequestration of cytokines 6. Hyaluronic acid- provide a fluid environment for cell movement and differentiation; binds to cytokines

F. Wound Contraction – movement of skin edges towards the center - may result in a contracture 1. appears in 2 nd degree burns or skin loss 2. hollow organs will result in stricture

G. Epithilialization – ex. Skin, mucous membranes. Function: 1. prevents fluid loss 2. protection from radiation 3. protection from trauma

a. epidermis act as a barrier b. dermis provides strength c. partial thickness wounds heal by epithelialization d. after epithileal destruction, a blood clot is formed and dries up forming a scab e. the basal layer in the epithilium and deeper hair follicles and sweat glands is where migration is initiated. This process is enhanced by keeping the area moist

H. Nutrition – malnutrition affects wound healing by inhibiting the immune response (opsonization) - lack of vit. C (scurvy) is the most common cause of wound healing deficiency

H. Immunosupression - chemotherapeutic drugs inhibit wound healing II. Specific problems for Wound Healing A. Gastrointestinal Tract 1. Bowel anastomotic strength develops more rapidly than that of the skin.

2. Ulcers are caused by penetration into the basement layer by acid and pepsin. 3. Major complications of intestinal anastomoses are a. leak b. disruption 4. The submucosa provide the major strength in anastmotic closure because it contains the majority of the fibrous connective tissue.

B. Skin 1. Keloids and hypertrophic scars - occur after injury or surgery - caused by an overabundance of collagen 2. Treatment a. Hypertrophic scar – no treatment necssary

b. Keloids i. Triamcinolone ii. Excision – high recurrence rate C. Tendon – composed mainly of type I collagen with significant amounts of proteoglycan. After disruption tendon and sheath have to be sutured.

D. Bone 1. soft callus formation 2. mineralized as cartilage 3. repalced by osteoid or bone – beginning of remodeling E. Chronic Wounds – failure of healing because of an underlying pathology

III. Wound Dressings A. Films – mimics skin B. Hydrocolloids - absorbs fluid - debrides necrotic tissue - protects wounds

C. Hydrogels - creates moist environment D. Foams - debrides, high absorbancy rate E. Impregnates - does not adhere to wound - promotes epithelialization F. Absorptive Powder and Pastes - debrides necrotic tissue G. Calcium Alginate - high absorbancy

IV. Mechanical Closure A. Absorbable 1. Synthetic – polyglycolic acid 2. Plain Cat Gut 3. Chromium Treated Cat Gut B. Non Absorbable 1. Cotton or Silk 2. Nylon 3. Stainless Steel Wire