Wound Healing

Question 1

Why is the panniculus muscle a critically important landmark when performing reconstructive cutaneous surgery?

Answer 1

failure to identify and preserve it will lead to loss of blood supply and wound dehiscence

Question 2

What blood supply do dogs and cats have that humans don’t?

Answer 2

direct cutaneous arteries that run parallel to the skin and terminate as the deep, middle, and superficial plexuses

Question 3

Why is the subdermal plexus so important?

Answer 3

provides the major blood supply to the skin and is therefore of most importance with regards to cutaneous surgery; must be preserved when undermining or dissecting skin

Question 4

What are the 5 stages of wound healing?

Answer 4

1. Coagultion: <5 minutes
2. Inflammatory stage: 0-24 hrs
3. Debridement stage: 2-5 days
4. Proliferative or repair stage: 5-21 days
5. Maturation stage: 21 days - 2 years

Question 5

What happens in the coagulation phase?

Answer 5

• primary coagulation: damaged endothelium exposes neg charged collagen to platelets and vWF, forming the platelet plug
  
  • occurs in < 5 minutes in healthy dog/cat
• secondary coagulation: clotting factors form fibrin meshwork
  
  • intrinsic (12, 11, 9, 8)
  • extrinsic (3, 7)
  • common (10, 5, 2 ,1)

Question 6

What happens during the inflammatory stage?

Answer 6

• 0-48 hours
• incr vascular permeability, extravasation of cellular/non-cellular blood components to form stable fibrous plug
• marked by infiltration of neutrophils (incr #s for first 24-48hrs) and macrophages (predominate 2-5d after injury)

Question 7

Why are macrophages critical for uncomplicated wound healing?

Answer 7

they not only degrade and remove organic material, but also modify the extracellular milieu and synthesize fibronectin, which is important for wound repair

Question 8

What occurs during the debridement stage?

Answer 8

• 2-5 days
• removal of necrotic tissue and elimination of infection
• carried out by neutrophils and macrophages
• involves: pressure lavage, sharp dissection of necrotic tissue, adherent bandages
• end is characterized by influx of fibroblasts (max # at 7-10d), speeding up formation of granulation tissue and collagen deposition
• period of minimal wound strength - lag phase

Question 9

What is the phase where the veterinarian has the largest impact on wound healing?

Answer 9

debridement stage

Question 10

Why is the debridement stage referred to as the lag phase of wound healing?

Answer 10

because the majority of wound strength is provided by the suture material and pattern used to close the defect

Question 11

What occurs during the proliferative stage?

Answer 11

• 5-21 days
• influx of fibroblasts and rapid accumulation of type-1 collagen and angiogenesis > formulation of granulation tissue
• wound gets tensile strength from type-1 collagen accumulation (14-21d) - log phase
• epithelialization - epithelial cells migrate across wound defect until like cells tough each other (contact inhibition)

Question 12

What does it mean for a wound to heal by second intention?

Answer 12

• closure occurs by contraction (5-7d after injury) of wound via specialized myofibroblasts (1mm/day)
• this continues until skin edges meet and halts the process

Question 13

What occurs during the maturation stage?

Answer 13

• 21 days - 2 years
• period of collagen remodeling, reorientation, and cross-linking
• second lag phase of wound healing - relatively minimal increases in tensile strength are accomplished
• collagen fibers reorient in linear fashion parallel to lines of mm and gravitational tension

Question 14

What are some intrinsic factors influencing wound healing?

Answer 14

• hypoproteinemia - decr fibrous tissue deposition
• anemia and blood loss - limit tissue O2 delivery
• malnutritition - same as hypoproteinemia
• uremia - reduces rate/quality of collagen deposition; down-regulates epithelization
• diabetes mellitus - relative periph tissue ischemia
• hyperadrenocorticism - delayed wound healing
• infection - prolongs debridement stage
• antibiotics

Question 15

What are extrinsic factors that affect wound healing?

Answer 15

• Type of injury
• Foreign material
• irradiation
• antiseptics

Question 16

What are the differences between crushing, shearing, and laceration injuries?

Answer 16

Crushing injuries cause severe vascular injury and devitalization and appropriate debridement is critical

Lacerations are precise injuries with little collateral tissue destruction - much less susceptible to infection and significant tissue debridement isn’t typically necessary

Question 17

T or F: you should almost always close a bite wound upon presentation

Answer 17

False; closure almost always contraindicated and should be avoided

Question 18

What are the effects of tissue irradation?

Answer 18

increased susceptibility to infection (leukocyte death), sloughing of epithelium (loss of germinal epithelium), and failure of proliferation (fibroblast death)

Question 19

Why is the use of antiseptics for lavage and wound treatment contraindicated in most cases?

Answer 19

they are lethal to fibroblasts and leukocytes and they inhibit epithelialization and granulation tissue formation

Question 20

What is the difference between the 3 different classes of wounds (duration classification)?

Answer 20

• Class 1: clean lacerations of 0-6 h duration w/ minimal contamination (most amenable to primary closure)
• Class 2: 6-12 h duration w/ significant contamination (avoid primary closure)
• Class 3: >12 h duration w/ gross contamination (avoid primary closure)

Question 21

What is the difference between clean, clean-contaminated, contaminated, and dirty wounds?

Answer 21

• Clean: surgical procedures not entering resp or GI tracts, UTI, no contamination or break in sterile technique (e.g. castration, spay); infxn rate - 5%
• Clean-contaminated: sx of the GI (no gross contamination of peritoneal cavity) or resp tracts, or minor break in aseptic technique; infxn rate - 10%
• Contaminated: acute inflammation (no pus/infxn) or gross dumping of ingesta from SI/LI into peritoneal cavity; infx rate - 30%
• Dirty: wound with devitalized tissue, organic material and/or pus representing active infection or chronicity

Question 22

What are two things you should pay close attention to when evaluating a patient’s wound?

Answer 22

vascularity and neurologic function; if these are absent, healing and return to function may not ever occur and amputation of tissues may be necessary

Question 23

What are appropriate indications for drain use in wound healing?

Answer 23

abscess, pocketing, vast dead space

Question 24

Define primary closure

Answer 24

surgical closure of wounds within the golden period (<6 h); typically indicated for clean/sharp wounds e.g. lacerations

• allows wound healing to proceed with a significant reduction in time for all phases of healing

Question 25

Define delayed primary closure

Answer 25

surgical closure of a wound after the golden period but before the appearance of granulation tissue; for recent traumatic wounds like dogs bites or HBC, decreases likelihood of infection

• reduction in the time necessary for wound contraction and re-epithelialization

Question 26

Define late secondary closure

Answer 26

• closure of a wound by surgical intervention following the proliferation phase (after granulation tissue is present)
• generally used for wounds that are more contaminated and have greater soft tissue damage
• lower risk of infection than primary/delayed primary closure, but typically results in less mobile skin and greater tension on the suture line

Question 27

What is second-intention healing?

Answer 27

leaving the wound open to heal without any surgical intervention; depends entirely on neovascularization and matrix remodeling to restore tissue bulk, wound contraction to re-establish normal tissue tension/to reduce scar size