Wound Healing

Ramon Garza III

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Questions tend to revolve around physiology of how wounds heal, that is, secondary intention, myofibroblasts, and which cells are involved in wound healing.
The strength layer of bowel/skin is also commonly tested. One should also be familiar with which organs lack certain tissue layers such as the esophagus with no serosa and where the posterior rectus sheath starts/stops.

Name the 3 phases of wound healing:

Inflammation (1–6 days), proliferation (3 days–3 weeks), maturation (3 weeks–1 year)

Name several factors that can inhibit wound healing:

Diabetes, infection, ischemia, malnutrition, radiation, steroids, neoplasia, anemia

What are the optimal nutrition parameters?

Albumin >3 g/dL and prealbumin >16 mg/dL

What is primary wound closure (primary intention)?

Immediate closure of a wound with suture or staples

Most important factor in healing closed wounds by primary intention:

Tensile strength

What is the most important layer to close for strength in skin lacerations?

Dermis

How long does it take a surgical incision become "water tight"?

24 to 48 hours

What is secondary wound closure?

Leaving a wound open and allowing it to heal by granulation, contraction, and epithelialization over time

Most important factor in the healing of open wounds by secondary intention:

Epithelial integrity

What causes contraction in wounds healing by secondary intention?

Myofibroblasts

What is delayed primary closure?

Closing a wound several days (3–5 days) after incision

Rate of regeneration of a peripheral nerve:

1 mm/d or 1 in./mo

Rate of epithelialization:

1 to 2 mm/d

The strongest layer of the bowel:

Submucosa

The time period that a small bowel anastomosis is at its weakest:

3 to 5 days

Name the 2 major events in the process of epithelialization:

Migration and mitosis

Name the process by which keratinocytes pile up on top of each other at the leading edge of a migration and tumble forward over the top of the heap:

Epiboly

What cell is the most essential for wound healing?

Macrophage

This cell is responsible for the movement and contraction of wound edges:

Myofibroblast

Name the order of arrival of the different cells involved in wound healing:

Platelets (not a true cell)
Neutrophils (predominant cell type from day 0–2)
Macrophages (predominant cell type from day 3–4)
Fibroblasts (predominant cell type from day 5 and so on)
Lymphocytes

Platelet factor 4, β-thrombomodulin, PDGF, and TGF-β are contained in this type of platelet granule:

α granule

Adenosine, serotonin, and calcium are contained in this type of platelet granule:

Dense granule

Name the predominant cell during days 0 to 2 of wound healing:

Neutrophils

Name the predominant cell during days 3 to 4 of wound healing:

Macrophages

Name the predominant cell present after day 5 of wound healing?

Fibroblasts

When does the maturation phase usually begin?

~3 weeks after the injury

What is the maximal tensile strength that a wound can reach?

80% of original tissue strength

Time period for maximum collagen accumulation in a wound:

2 to 3 weeks (mostly type III, then gets converted to type I with maturation)

FIGURE 9-1.

The cellular, biochemical, and mechanical phases of wound healing. (Reproduced from Brunicardi FC, Anderson DK, Billiar TR, et al. Schwartz's Principles of Surgery. 9th ed. http://www.accessmedicine.com. Copyright © The McGraw-Hill Companies, Inc. All rights reserved.)

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Time period for a wound to reach its maximal tensile strength:

8 weeks

True or false: Denervation negatively affects epithelialization and wound contraction:

False; denervation has no effect on epithelialization/wound contraction

The number of organisms/cm² required to retard wound healing:

100,000 organisms/g (10⁵ organisms/g)

What is the generally recommended period of time to wait for scar maturation before considering scar revision?

12 to 18 months

What can be given to combat the inhibitory effects of steroids on wound healing and epithelialization? Dose?

Vitamin A; 25,000 IU daily

Necessary cofactor for hydroxylation and cross-linking of proline and lysine in collagen synthesis:

Vitamin C (deficiency causes scurvy)

Type of scar that extends beyond the boundaries of the original wound:

Keloid

Type of scar that remains confined to the boundaries of the original wound and contains an overabundance of collagen:

Hypertrophic scar

The most common type of collagen is:

Type I collagen

Type of collagen predominantly synthesized in the first 48 hours of a healing wound:

Type III collagen

Type of collagen located in skin, bone, tendon, and is the primary collagen found in a healed wound:

Type I collagen

Type of collagen found in hyaline cartilage:

Type II collagen

Type of collagen in arteries, dermis, and increased in wound healing:

Type III collagen

Type of collagen that is predominant in the basement membrane:

Type IV collagen (type IV found on floor)

Type of collagen found in the cornea:

Type V collagen

Stage the pressure sore: nonblanchable erythema of intact skin:

Stage I (can be seen after 30 minutes, resolves after 1–2 hours)

Stage the pressure sore: partial-thickness skin loss involving epidermis/dermis:

Stage II (can present as blister, forms after 2–6 hours, erythema lasts >24 hours)

Stage the pressure sore: full-thickness skin loss with involvement of underlying subcutaneous tissue:

Stage III (does not extend through fascia)

Stage the pressure sore: full-thickness skin loss with tissue necrosis or extensive destruction of underlying structures (muscle/bone):

Stage IV

Areas at greatest risk for pressure sores:

Ischium 28%, Trochanter 19%, Sacrum 17%, Heel 9%, Occiput of scalp

Rules of operative management for pressure sores (name 4):

Debride all devitalized tissue
Excise entire bursa (can use methylene blue to identify entire bursa)
Identify and remodel bony prominences
Reliable tissue coverage with appropriate flap without burning bridges for future reconstruction

Name the amino acid that is found in every 3 residues in collagen:

Proline

Name the necessary cofactors for the hydroxylation of proline:

Vitamin C, oxygen, iron, and α-ketoglutarate

What enzyme is the rate-limiting step in collagen synthesis?

Propylhydroxylase

Albumin level that puts a patient at risk for poor wound healing:

<3.0 g/dL

Time period to wait for chemotherapy to have no effect on wound healing:

14 days

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