Wound Healing

1
Wound Healing
2

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

3

• 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.

4

• 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

5

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

6

• 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

7

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

8

• 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.

9

• 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.

10

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

11

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

12

• 2. Inflammation migration of leukocytes into
  the wound. 1st 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.

13

• 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

14

• 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.

15

• 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

16

• 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

17

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

18

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

19

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

20

• 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

21

• 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

22

• 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.

23

• 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.

24

• 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

25

• 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.

26

• 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

27

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

28

• 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

29

• 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