Phases of healing
Early
Intermediate
Late
Terminal
Early wound healing events
Hemostasis
Platelet aggregation
Intrinsic and extrinsic coagulation cascade
Thrombin, fibrin
Vasoconstriction
Inflammation
Vasodilatation
Increase in vascular permeability
Chemotaxis
Cellular response
Intermediate wound healing events
Mesenchymal cell chemotaxis and proliferation
Angiogenesis
Epithelisation
2-4 days after injury
Mediated by cytokines
Fibroblasts- migration and proliferation
Smooth muscle
Angiogenesis- reconstruction of vasculature
Stimulate: High lactate, acidic Ph, low O2 tension
Endothelial cell migration and proliferation
Epithelisation
Partial thickness- Cells derived from wound edges and epithelial appendages.
Incisional wound: cellular migration over less then 1 mm. Wound sealed in 24-48h.
Cellular detachment
Migration
Proliferartion
differentiation
Late wound healing events
Collagen synthesis
3 helical polypeptide chains
Lysine and proline hydroxylation
Required for cross-linking
Wound contraction
Centripetal movement of the wound edges toward the center. ( 0.6-0.7 mm/day)
Begins at 4-5 days
Maximal contraction 12-15 days
Trivial component in closed incisional wounds, significant for closure of open wounds
Rate- depends on tissue
Circular wounds- slower closure but avoid stenosis
Mechanism- cell mediated processes, not requiring collagen synthesis
Myofibroblasts- fibroblasts with myofilaments in cytoplasm
Appear in wound day 3-21
Located in periphery- pull wound edges together.
Contractures- contraction across joint surface
Terminal wound healing events
Remodeling- turnover of collagen. Type 3 replaced by type 1
Day 21- net accumulation of wound collagen becomes stable
Wound bursting strength- 15% of normal.
Week 3-6- greatest rate of increase
6 weeks- 80-90% of eventual strength.
6 months maximum strength ( 90% ). Process continues for 12 months
Cytokines and growth factors
Primary mediators in wound healing.
Endo, para, auto, intracrine function
EGF
FGF
PDGF
TGF
Which of the following is primarily responsible for tensile strength in a healing wound 4 days after injury?
Collagen
Elastin
Fibrin
Fibronectin
Hyaluronic acid
Which of the following is primarily responsible for tensile strength in a healing wound 6 weeks after injury?
Myofibroblasts
Fibrin
Fibronectin
Collagen
Collagen cross linking
Infection
foreign body/ necrotic tissue, hematomas
local/ systemic factors
type of surgery
Hypoxia and smoking
O2 delivery necessary for cellular respiration and hydroxylation of proline and lysine
Smoking- vasoconstriction, atherosclerosis, carboxyhemoglobin.
Radiation
Collagen synthesized to abnormal degree- fibrosis
Fibrosis of vessels- (media)-occlusion
Thinned epidermis, pigmentation
Limited access of inflammatory cells and cytokines- impaired healing
Damage to fibrocytes and keratinocytes.
Systemic factors
Malnutrition
Limited AA supply for collagen synthesis
Consumption of proteins d/t CHD and fat deficiency.
Vit C deficiency- diminished hydroxylation of lysine and proline,
Vit D- impaired bone healing
Zinc- inhibition in cellular proliferation and defficient granulation tissur formation
Normal healing is accelerated by which of the following?
VitC
VitA
Zinc
Increased local oxygen tension
Scarlet red
Cancer
Cachexia, anorexia
Altered host metabolism.
Protein catabolism
Abnormal inflammatory cell response
Old Age
Diabetes
Impaired healing ( decreased chemotaxis and phagocyte function )
Risk of infection
Hypertrophic scars and kelloids
Excessive healing processes- increase in net collagen synthesis raised thickened scar
Keloid- Extension beyond wound margin, familial, may develop up to 1 year, rarely subside
Hypertrophic scar- Confined to wound margin, light skinned, early after injury, may subside, cause contractures
Tx- excision, steroid injection, pressure garments, radiation tx
Types of wound closure
Primary closure
Approximation of acutely disrupted tissue with sutures, staples or tape
Secondary wound closure
Open wound margins approximate by biologic contraction
If a patient requires reoperation 1 month after a midline abdominal incision which of the following promotes the most rapid gain in strength of the new incision
Separate transverse incision
Midline scar is excised with a 1 cm margin
Midline incision reopended without scar excision
Rate of strength ganed is not effected by incision technique
