CHAPTER 01: GENERAL PRINCIPLES: Healing and grafts - under construction!

Question 1

Describe the stages of wound healing

Answer 1

Wound healing involves several overlapping stages

1. Haemostasis - immediate
   - vasoconstriction, platelet plug and fibrin clot formation
   - clotting cascade activated
2. Inflammation - injury to 3 days
   - mast cells degranulate and release histamine
   - PDGF, TGFb and cytokines released by platelets attract:
   o Neutrophils - produce inflammatory mediators and cytokines (peak at 24hrs)
   o Monocytes - become macrophages (peak 2-3 days)
   o Macrophages - produce cytokines and growth factors PDGF & TGFb, remove debris, stimulate collagen production and attract fibroblasts
   o Lymphocytes - unknown significance, possibly fibroblast recruitment and activation
3. Proliferation - 3rd day to 3wks
   - Fibroblasts – attracted by PDGF and TGFb (are D3, peak D7)
   - Collagen synthesis - Type III mainly
   - Angiogenesis - induced by VEGF
   - Re-epithelialisation
4. Remodeling - 6mths to 1yr
   - Type III collagen replaced by type I until a ratio I:III of 3:1 reached as in normal tissue
   - Wound tensile strength increases as disorganised collagen becomes lamellar along tension lines and cross-links
   - Vascularity decreases
   - Fibroblasts mature into myofibroblasts and cause wound contraction by forming cell-cell contacts
   - Peak tensile strength reached at 60 days (80% pre-injury level)

Question 2

How do you classify factors that affect wound healing?

Answer 2

Systemic factors

• Acquired
• Congenital

Local

Question 3

What are the SYSTEMIC factors that affect wound healing?

Answer 3

Systemic conditions - congenital
(see below)

Systemic conditions - acquired NEEPAS

• Nutrition
• Environmental
• Endocrine
• Pharmacological
• Age
• Smoking

Local IIRBCTNM

• Infection
• Iatrogenic
• Radiotherapy
• Blood supply
• Chemotherapy
• Trauma
• Neuropathy
• Mechanical stress

Question 4

What are the PATIENT factors affecting wound healing?

Answer 4

Patient factors
Age
Nutrition
Systemic illness
Diabetes - (infection, vascular disease and reduced oxygenation, neuropathy)
Drugs - steroids, NSAIDS, chemo
Genetic - Ehler-Danlos, cutis laxa, EB, progeria

Wound factors

• Infection
• Oedema
• Denervation
• Radiation

Question 5

What are the congenital systemic factors affecting wound healing?

Answer 5

Ehlers-Danlos (cutis hyperelastica)

• heterogenous collection of connective tissue disorders
• results from collagen synthesis, cross-linking or structural defects
• characterised by fragile hyperelastic skin, joint hypermobility, aortic aneurysm

Pseudoxanthoma elasticum

• increased collagen degradation
• AR
• angina, aneurysms, retinal detachment, angioid streaks

Cutis Laxa

• defective elastic tissues (non-functioning elastase inhibitor)
• coarse drooping skin, aneurysm, pneumothorax, emphysema, congenital cardiac disease, hernias
• no problems with wound healing

Epidermolysis bullosa

• skin v susceptible to mechanical stress
• Nikolsky sign - blistering with minor trauma
• severe form - extensive fibrosis, adduction contracture of thumbs, volar contactures of palms and digits, pseudosyndactyly

Progeria

Question 6

What are the acquired systemic factors of wound healing? NEEPAS

Answer 6

Nutrition

• Vit A
• Vit C: essential cofactor for collagen synthesis
• Vit E: membrane stabiliser, deficiency inhibits healing
• Zinc: enzymes co-factor, accelerates healing
• Albumin: indicator of nutritional status
• Methionine: essential amino acid for inflammation

Environmental
- Temperature - ↑ healing > 30° C , ↓tensile strength

Question 7

What are the local factors affecting wound healing? Part 1

Answer 7

1. Infection
   - Wounds over 100,000 organisms/g tissue are considered infected
   - ↓ tissue PO2 , ↑ collagenase, prolongs inflammation
   - reduced leucocyte chemotaxis
   - Impaired angiogenesis and epithelialisation
   - Bacterial toxins and metabolites impair epithelialisation
2. Iatrogenic
   Manipulation - rough handling and over-diathermy, tension.
3. Radiation
   - Stasis and occlusion of small vessels.
   - Causes endothelial cell, capillary and arteriole damage.
   - Lymphatics damaged, oedema and ↑ risk of infection.
4. Chemotherapy
   - ↓ fibroblast proliferation and wound contraction.
   - Chemo best left until 10-14 days post op.

Question 8

What are the local factors affecting wound healing? Part 2

Answer 8

5. Blood supply
   - ↓ tissue perfusion = ↓ wound oxygenation
   - Fibroblast function ↓ in hypoxic tissue ↓ O2 delivery = ↓ collagen formation, ↓ extracellular matrix, ↓Angiogenesis, ↓ epithelialisation
6. Trauma
   - Disrupts the neo-epidermis
7. Neural Supply
   - Wound in denervated tissue heal slowly. (pressure sores, DM)
   - ↑ collagenase activity
8. Mechanical Stress
   - Affects quality, aggregation and orientation of collagen fibres
   - ↑Tension = blanching → necrosis and rupture → stretching

Question 9

How does epithelialisation occur?

Answer 9

1. Mobilisation.
2. Migration.
3. Mitosis (Proliferation).
4. Cellular differentiation.

Question 10

What occurs during mobilisation?

Answer 10

• Marginal epithelial cells elongate, flatten and form pseudopodia.
• Cells detach from neighbour and basement membrane.

Question 11

What occurs during migration?

Answer 11

• decreased contact inhibition promotes cell migration.
• meanwhile marginal epi cells proliferate to replace them.
• when cells meet opposite migrating epi cells, contact inhibition is reinstituted and migration ceases.

Question 12

What occurs during mitosis?

Answer 12

Epithelial cells

• proliferate.
• secrete proteins to form new BM.
• desmosomes and hemdesmosomes re-establish themselves and anchor the cells to BM and each other.
• becomes new stratum germinativum.

Question 13

What occurs during cellular differentiation?

Answer 13

• normal structure of stratified squamous epithelium is re-established.

Question 14

How do skin grafts take?

Answer 14

Full thickness vs split thickness

• contraction (physiological),
• contracture (pathological).

Stages of skin graft take

1. Adherence (fibrin) (48hrs)
2. serum imbibition (first 2-4 days)
   - surrounding fluid absorbed, SG swells
3. Revascularisation (4-5 days)
   - inosculation: vessels in graft and bed kiss
   - revascularisation: new vessels in bed grow into graft vessels
   - neovascularisation: new vessels grow into graft
4. Remodelling

Question 15

Why do skin grafts fail?

Answer 15

HIS SHIT!!
Haematoma
Infection (if >100,000 organisms / gram, less if Group A B-haemolytic Strep, as streptokinase and hyaluronidase prevent adhesion)
Seroma
SHear
Inappropriate bed (bare cartilage, bone, tendon)
Technical error

Question 16

What do you know about fetal wound healing?

Answer 16

Foetus’ first 6 months - heals by regeneration, not repair, therefore no scarring.

• Reduced inflammation.
• Reduced platelet aggregation and degranulation.
• Reduced angiogenesis.
• More rapid epithelialisation.
• No myofibroblasts, no wound contraction.
• Type III > I collagen, more organised.
• Wound contains more water and hyaluronic acid.
• More TGF-B3 than 1&2
• Tenascin (cytotactin)

Question 17

Microvascular anastomosis healing

Answer 17

Necrosis between sutures, 
Neo-intimal hyperplasia, 
Loss of media,
Remodelling,
Endothelial migration.

Question 18

What are the layers of skin?

Answer 18

Epidermis - Colin Likes Grilled Spicy Beef 
Stratum 
- corneum 
- lucidum 
- granulosum 
- spinosum 
- basale (germinativum)

Dermis

• papillary
• reticular

Question 19

What are the functions of skin?

Answer 19

control of fluid loss 
thermoregulation 
barrier against micro-organisms 
sensation 
immunology and 
metabolism (e.g. vit D)