Wound Healing

April 2012

Bystrzonowski N, Singh M

www.setpras.org

Learning Objectives

• Understand the anatomy of the skin and its functions

• Understand the different types of wound healing

• Understand the different stages of wound healing

• Be aware of factors influencing wound healing

Relevant Anatomy

• Skin

Epidermis

Dermis

Hypodermis(subcutaneous fat)

Hair FollicleDermal Papillae

Sebaceous Gland

Erector Pili

Merocrine Sweat Gland

Relevant Anatomy

• Layers of the Epidermis

• The epidermis is composed of several layers:

– From superficial to deep:

– Stratum Corneum -Acellular keratin layer

– Stratum Lucidum -Dead cells without nuceli

– Stratum Granulsoum -Cell cytoplasm contains keratin granules

– Stratum Spinosum -Cells connected by desmosomes appear “spiny”

– Stratum Germinativum -Basal layer connected to basement membrane

Introduction

• Functions of the skin include:

– Mechanical protection– Sensation– Barrier to infection– Immune surveillance– Thermoregulation– Vitamin D metabolism

Types of Wound Healing

• Types:

– Primary

– Delayed Primary

– Secondary

Types of Wound Healing

• Primary Wound Healing:– Wound is closed directly soon after the injury e.g. suturing an incised

wound

• Advantages:– Faster healing time

– Simplifies wound care/fewer dressing changes

– Vital structures covered

• Disadvantages/Contraindications:– Infected wound

– Old wound

– Too much tension

Types of Wound Healing

• Delayed Primary Wound Healing:– Wound is closed after a few days e.g. allowing infection to clear

from a dehisced wound before proceeding to closing it

• Advantages:– Allows infection to settle prior to closure

• Disadvantages/Contraindications:– Often have worse cosmetic result

Types of Wound Healing

• Secondary Wound Healing:– Also known as secondary intention, wound is left to heal without

approximation e.g. defects too large to suture together

• Advantages:– Useful if wound too large to close

– Contraction of scar over time can produce good results

• Disadvantages/Contraindications:– May have worse cosmetic result

– Larger amount of granulation tissue

– Open wound requires patients to maintain dressings for longer

– Increased risks of infection

Epithelialisation

• Process in which epithelial cells migrate and replicate via mitosis and traverse wound

• Main method in wounds that involve superficial dermis and epidermis

• Wound contracture not common component

• Typically occurs over 48 hours in well opposed wounds

Wound Healing

Stages of Wound Healing

• 1. Haemostasis

o Immediately after injury to the skin, can last for few days

o Small vessels constricto Platelet aggregation triggering clotting cascade

releasing growth factors and cytokineso Fibrin matrix stabilizes the wound and provides a

scaffold

Stages of Wound Healing

• 2. Inflammation

o PMN leucocytes accumulate and transform into MACs

o Mast cells degranulate, releasing histamine and other mediators of vasodilation & cell migration

o Vasoactive substances make small vessels permeable to inflammatory mediators

o Chemotaxis PMN leucocytes digest bacteria, debris and necrotic tissue with enzymes

o Healing of chronic wounds usually becomes arrested at this stage

Stages of Wound Healing

• 3. Proliferation

o Subphases within this phase:o Fibroplasia, matrix deposition, angiogenesis, re-

epithelialization

o Days 5-7 fibroblasts migrate, laying down type I & III collagen

o Tropocollagenprocollagen (triple helix)secreted into extracellular space peptide cleavage collagen fibres

o Angiogenesis – new vasculature formed involving endothelial cells

Stages of Wound Healing

• 3. Proliferation

o Fibroblast growth factor and vascular endothelial growth factor modulate angiogenesis

o Re-epithelialisation – cells spread from periphery of wound within 24 hours

o Cells divide in 48-72 hours resulting in thin epithelial cell layer, bridging the wound

o All above can last up to 4 weeks

Stages of Wound Healing

• 4. Remodelling

o After 3rd week, can last up to yearso Collagen is degraded and depositedo Contraction occurs from proliferation of fibroblasts

(myofibroblasts)o Max tensile strength achieved by 12th week and

resultant scar has only about 75% of original tensile strength1

• Scar maturation may take up to 18 months

Cells of Wound Healing

Platelets

PMNs

Macrophages

Lymphocytes

Fibroblasts

Capillaries

0 2 4 6 8 10 12 14 16Days

Wound Healing

• Factors Affecting Wound Healing2:

• Systemic Factors Local Factors• Congenital

– Ehlers Danlos– Pseudoxanthoma Elasticum– Epidermolysis Bullosa

• Acquried– Nutrition– Drugs: steroids & NSAIDS– Age– Smoking– Endocrine abnormalities

(DM, neuropathy)

• Infection • Radiation• Poor blood supply (fibroblasts

are O2 sensitive)

• Trauma• Denervated tissue (some

evidence)

Tendon Healing

• 1. Inflammation– Inflammatory cells and growth factors

• 2. Proliferation– Fibroblasts secrete collagen, random arrangement,

lacks tensile strength

• 3. Remodelling– Tendon structure becomes organised, early

movement can limit fibrous attachments to tendon sheath

Bone Healing

• 1. Haematoma formation

• 2. Inflammation

– Macrophages and osteoblasts enter haematoma

• 3. Proliferation

– Soft callus – collagen deposition in haematoma

– Hard callus – calcification of cartilaginous callus

• 4. Remodelling

– Restoration of normal structure

Conclusions

• The skin is composed of several layers

• It has many functions such as immune surveillance and Vitamin D metabolism

• Wound healing typically follows set stages:

– Haemostasis– Inflammation– Proliferation– Remodelling

References

• 1. Brown, D, Borschel G. Michigan Manual of Plastic Surgery. Philadelphia: Lippincott, Williams and Wilkins; 2004

• 2. Diegelmann RF, Evans MC. Wound healing: An overview of acute, fibrotic and Delayed healing. Frontiers in Bioscience 2004;9: 283-289