Wound Healing/Keloids Flashcards
What are the layers of the epidermis and dermis?
Epidermis (superficial to deep):
1. stratum corneum
2. stratum lucidum
3. stratum granulosum
4. stratum spinosum
5. stratum basalis
Dermis—contains adnexal structures and vasculature Papillary dermis—superficial, contains vascular tissue Reticular dermis—deep, contains denser tissue
What are the steps involved in wound healing?
- Inflammation: 1 to 2 days.
- Proliferation: 3 to 30 days (depends on bacterial load). 3. Remodeling/differentiation: up to 1 year.
What are the cell types primarily responsible for each of these stages?
- Inflammation: PMNs, macrophages.
- Proliferation: macrophages, fibroblasts.
- Remodeling: myofibroblasts (wound contraction), epithelial cells (reepithelialization).
What are the steps involved in epithelialization across a wound?
Mobilization, migration, mitosis, and differentiation of epithelial cells. The loss and reestablishment of contact inhibition initiate and terminate the process.
In a healthy individual, how long does it take for a surgical incision to reepithelialize after closure?
After a surgical incision is closed, it takes approximately 24 hours for the wound to reepithelialize. After this point, it is not necessary to keep the surgical area dry with an occlusive dressing
What is the key cell involved in wound remodeling?
Macrophage. The macrophage is probably the most critical cell in wound healing in general—it initiates the
growth factor cascade that results in fibroblast proliferation and thus collagen production.
Which cells are responsible for wound contracture?
Myofibroblasts—fibroblasts that contain myofibrils permitting contractile activity similar to muscle.
What provides tensile strength to a healing wound?
Collagen.
Which cells produce collagen in the healing wound, and when does production peak?
Fibroblasts produce collagen; maximal net collagen production occurs at about 1 to 2 weeks.
When is a scar fully matured, and how much tensile strength does it achieve?
Wounds have gained approximately 50% of their final strength by 6 weeks and a scar fully matures in 1 year, at which point it has gained approximately 80% to 90% of its initial tensile strength. The most rapid increase in tensile strength occurs between 10 and 30 days, secondary to collagen cross-linking.
What defines a chronic wound?
Wounds that fail to close in 3 months are classified as “chronic wounds.”
How does the metalloproteinase level in chronic wounds compare to that in acute wounds?
In chronic wounds, the metalloproteinase level is increased as compared to that of an acute wound resulting in
increased extracellular matrix degradation.
What are the different types of collagen?
There are many types of collagen (more than 10). Critical to wound healing are:
Type I: most common; in skin, bone, and tendon/ligament. Type II: hyaline cartilage.
Type III: vessel walls; intestine; skin.
Type IV: basement membrane.
Type V: fetal and placental tissue.
What is the ratio of type I to type III collagen in normal skin and scars?
- Normal skin: 4:1 (ie, predominantly type I collagen).
- Immature scar: 2:1.
- Hypertrophic scar: 2:1.
- Keloid: 3:1 (varies).
- Fetal skin: predominantly type III collagen.
Which conditions adversely affect key steps in collagen synthesis?
- Vitamin C deficiency (scurvy): inhibits hydroxylation of proline and lysine (required for collagen cross-linking).
- Colchicine: inhibits secretion of tropocollagen from the cell.
- Copper deficiency and penicillamine: prevent lysine oxidation (which is necessary for intra- and intermolecular bonding).
Which cytokines are produced by macrophages?
IL-1, IL-6, IL-8, IL-10, TNFa, IFNg.
What isomers mediate the profibrotic phenotype of TGF-b?
TGF-b has three isomers. TGF-b1 and TGF-b2 are profibrotic. TGF-b3 is antifibrotic.
Various fibrotic diseases (such as keloids) might result from aberrant ratios of TGF-b isomers (ie, increased TGF-b1 and TGF-b2 and decreased TGF-b3).
What are the biologic effects of FGF?
Fibroblast and epithelial proliferation.
Collagen production.
Potent angiogenic factor.
What is the role of FGF in wound healing?
FGF-1 and FGF-2 (acidic and basic FGF) are the major proteins in this family and drive rapid proliferation of r fibroblasts, epithelial cells, and endothelial cells.
FGF-7 (keratinocyte growth factor) is a major epidermal growth factor and is involved in dermal–epidermal r signaling.
The sequence of events in wound healing is largely mediated by orchestration of intra- and extracellular regulation of FGF proteins in a defined pattern.
What are the detrimental effects of corticosteroids on wound healing?
Corticosteroids inhibit macrophages, resulting in poor fibroblast stimulation and wound contraction.
What strategy can overcome the effects of steroids?
Vitamin A (25,000 IU by mouth daily for 3 to 5 days, alternatively 200,000 IU topically three times a day).
How long should you wait before revising a scar?
One year to allow scar remodeling to complete.
What factors impair wound healing?
- Foreign bodies.
- Infection.
- Radiated tissue—decreases blood supply.
- Inadequate blood supply—any cause.
- Local trauma.
- Systemic factors (steroid use, obesity, edema, smoking, comorbidities, malnutrition).
What are the escalating strategies that can be used to close a defect (the “reconstructive ladder”)?
secondary intent
primary intent
skin graft
local tissue rearrangement
transposition flap
free tissue transfer
How do the following tissues differ in healing?
Bone, Tendon, Nerve, Liver.
Bone: Following fracture, bony healing is accomplished via osteoinduction and osteoconduction. Osteoinduction refers to precursor cells in the bony tissue becoming osteoblasts, and osteoconduction refers to these osteoblasts entering the fracture site. A bony callus forms, which is remodeled by osteoclasts and osteoblasts into lamellar bone (endocohondral ossification).
Tendons heal by intrinsic (minimal inflammation with epitenon cells producing collagen) and extrinsic (inflammation, proliferation, remodeling) healing. Extrinsic healing produces adhesions and is increased with immobilization.
Peripheral nerves heal by a combination of degeneration and regeneration. The degenerative process is called Wallerian degeneration and occurs distal to the site of nerve injury.
Hepatic tissue undergoes regeneration.
What adult tissues are able to heal without scarring?
Bone and liver are the only adult tissues that are able to heal without scar formation. Chronic damage can cause
hepatic scarring (cirrhosis).
What is the Fitzpatrick classification of skin types?
Based on density of melanin pigment:
Type I: White or freckled skin (always burns, never tans). Type II: White skin (usually burns, sometimes tans). Type III: White to olive skin (equally burns and tans). Type IV: Brown skin (tans easily, rarely burns).
Type V: Dark brown skin (always tans, very rarely burns). Type VI: Black skin (deeply tans, never burns).
How are operative wounds classified?
Class I: Clean—atraumatic, uninfected, no entry into GI/GU/respiratory tract.
Class II: Clean-contaminated—entry into GI/GU/respiratory tract.
Class III: Contaminated—traumatic wounds or gross spillage of enteric contents.
Class IV: Dirty—drainage of abscess or soft tissue infection.
How are nerve injuries classified?
There are two accepted classification systems for nerve injuries, Seddon and Sunderland. Seddon
1. Neuropraxia—transient block of conduction, rapid recovery expected.
2. Axonotmesis—axonal damage within the nerve, Wallerian degeneration occurs, prolonged recovery expected.
3. Neurotmesis—nerve is transected, Wallerian degeneration occurs, surgical repair needed.
Sunderland
1. First degree—demyelinate nerve, rapid recovery expected (neuropraxia).
2. Second degree—axons disrupted, but sheath intact (axonotmesis), undergoes Wallerian degeneration, slow recovery expected.
3. Third degree—some endoneurial sheaths disrupted, incomplete recovery.
4. Fourth degree—loss of perineurium, little to no recovery, requires operative intervention.
5. Fifth degree—nerve is completely transected, no recovery without operative intervention.
6. Sixth degree—combination injury, including areas with first- to fifth-degree damage.
What organisms are associated with bite wounds?
Cat and dog bites are associated with Pasteurella multocida as well as Staphylococcus and Streptococcus species.
Human bites are associated with Eikenella corrodens as well as Staphylococcus and Streptococcus species and Bacteroides.
Bite wounds are typically treated with Augmentin for prophylaxis.
What is the staging of pressure ulcers?
Stage 1: Skin intact; non-blanching erythema.
Stage 2: Partial-thickness skin loss, abrasions, and blisters included (so into epidermis or dermis). Stage 3: Full-thickness skin loss with extension into subcutaneous tissue/muscle.
Stage 4: Full-thickness skin loss with extension into bone, joint, tendon.
How long does it take for pressure ulcers to arise?
Early (stage I, nonblanching erythema) pressure ulcer formation can occur within 30 minutes of unrelieved pressure. Partial-thickness skin loss (stage II) can be seen in as little as 2 to 6 hours.