14: Wound Healing

Question 1

Which 4 components are necessary for hydroxylation and subsequent cross-linking of proline residues in collagen?

Answer 1

1. Alpha-ketoglutarate
2. Vitamin C
3. Oxygen
4. Iron

[Collagen has proline every 3rd amino acid. Proline cross-linking improves wound tensile strength.]

Question 2

What is the difference between collagen deposition in keloid scars vs hypertrophic scars?

Answer 2

Keloid scar: Collagen goes beyond the original scar

Hypertrophic scar: Collagen stays within the confines of the original scar

[Hypertrophic scars are more common in dark skinned individuals and more frequently occur on flexor surfaces of the upper torso. Hypertrophic scars often occur in burns or wounds that take a long time to heal.]

Question 3

Where are the following types of collagen typcially found?

• Type I
• Type II
• Type III
• Type IV
• Type V

Answer 3

• Type I: Skin, bone, tendons, healed wounds (days 3-4 and beyond)
• Type II: Cartilage
• Type III: Healing wounds (days 1-2), blood vessels, skin
• Type IV: Basement membranes
• Type V: Cornea

[Type III collagen is replaced by type I collagen in healing wounds by 3 weeks.]

Question 4

At what time point does a healing wound reach maximal strength and what percent of original strength does it attain?

Answer 4

• Maximal strength at 8 weeks
• Maximal strength is 80% of original strength

[Maximum collagen accumulation occurs by 2-3 weeks, but while the amount of collagen remains constant after that, continued cross-linking improves strength. Collagen cross-linking is inhibited by d-penicillamine.]

Question 5

How long should one wait before revising a scar?

Answer 5

1 year to allow maturation

[Scar may improve with age. Infants heal with little or no scarring.]

Question 6

What are the predominant cells in a wound for the below time frames?

• 0-2 days
• 3-4 days
• Day 5 and beyond

Answer 6

• 0-2 days: PMNs
• 3-4 days: Macrophages
• Day 5 and beyond: Fibroblasts

[Reopening a wound results in quicker healing the 2nd time as healing cells are already present there.]

Question 7

What is the correct order of arrival to a wound for the below cells?

• Fibroblasts
• Lymphocytes
• Macrophages
• Platelets
• PMNs

Answer 7

1. Platelets
2. PMNs
3. Macrophages
4. Lymphocytes
5. Fibroblasts

[Macrophages are essential for wound healing as they release growth factors, cytokines, etc.]

Question 8

What is the pace of peripheral nerve regeneration?

Answer 8

1mm/day

Question 9

What are 6 conditions associated with abnormal wound healing?

Answer 9

1. Osteogenesis imperfecta: Type I collagen defect
2. Ehlers-Danlos syndrome: 10 types identified, all collagen disorders
3. Marfan’s syndrome: Fibrillin defect (connective tissue protein)
4. Epidermolysis bullosa: Excessive fibroblasts (treatment is phenytoin)
5. Scurvy: Vitamin C deficiency
6. Pyoderma gangrenosum

Question 10

For the following stages of wound healing, what is the timing, which cells are involved, and what process is taking place?

• Inflammation
• Proliferation
• Remodeling

Answer 10

• Inflammation: Day 1 through day 10. PMNs, macrophages. Epithelialization
• Proliferation: Day 5 through 3 weeks. Fibroblasts. Collagen deposition (replacement of ype III collagen with type I collagen), neovascularization, granulation tissue formation
• Remodeling: Week 3 through 1 year. Fibroblasts. Decreased vascularity, collagen cross-linking, net amount of collagen does not change with remodeling (although significant production and degradation occurs)

Question 11

What is the strength layer of the bowel and what is the weakest time point for a small bowel anastomosis?

Answer 11

• Strength layer of the bowel is the submucosa
• Weakest time point for a small bowel anastomosis is days 3-5

Question 12

What is the inheritance pattern of keloid scarring and what is the treatment?

Answer 12

• Autosomal dominant
• Treatment is intra-lesional steroid injection, silicone, pressure garments, XRT

[Keloids are more common in dark skinned individuals.]

Question 13

What is the treatment for a hypertrophic scar?

Answer 13

Steroid injection, silicone, pressure garments

[Similar to treatment of keloid scars.]

Question 14

Which vitamin can counteract the effects of steroids on wound healing?

Answer 14

Vitamin A (25,000 IU daily)

Question 15

Chemotherapy has no effect on wound healing after what time point?

Answer 15

14 days

[Chemotherapy impairs wound healing in first 14 days.]