PRINCIPLES OF SKIN COVER - GRAFTS AND FLAPS

Characteristics

• Largest organ of the human body- surface area 1.5-2.0 sq.m,  2-3mm thick
• 15% of body weight
• Epidermis- Corneum, Lucidum, Granulosum, Spinosum, Basale,
• Dermis- papillary and reticular, made of collagen, 

Functions of skin

• Protective layer - Langhan’s cells of adaptive immune system
• Sensation
• Heat regulation
• Control evaporation
• Aesthetics 
• Makes vitamins D

When is skin required?

• Loss of large area of skin
• Large wound 
• Post burn raw area
• Release of contracture

Reconstructive Ladder

Graft and Flap

• Graft is free tissue without its vascular supply- skin, bone, tendon, nerve, vessels, muscle, fascia, mucosa
• Flap is tissue with its original blood supply
• Areas where we cannot put graft will need a flap-Flaps for bone devoid of periosteum, cartilage devoid of perichondrium, tendon devoid of paratenon

Grafting 

• Skin graft is essentially dead with no circulation. Under favourable conditions obtain new blood supply from recepient wound or defect. This is known as graft take
• Infection, pressure, hematoma or shear forces can result in graft failure
• Meshing – increase surface area and prevention of collections
• Immobilisation with Sutures / plaster slab
• Prevention of hematoma / seroma
• Dressing of recipient wound
• Donor site management

Process of graft take

1. Imbibition

2. Inosculation

3. Vascularization

Conditions affecting graft take

• Malnutrition- hypoproteinemia, vitamin deficiency
• Presence of hypertension, diabetes
• Compromised immune status
• Collagen vascular disease
• Constant pressure on the area

When to graft?

• Wound flat and red / can see the imprint of gauge piece
• No unhealthy granulation tissue or necrotic tissue
• Margins are healing and spreading
• Not much bleeding on touch
• dressing peels  with difficulty
• Bacterial count less than 105 
• No evidence of beta hemolytic streptococci

Types of skin graft:

Partial thickness- thin intermediate thick

Full thickness

Composite graft- More than one tissue type required to perform reconstruction

Split thickness skin grafting (Thiersch graft)

• Donor site heals spontaneously as part of dermis is left behind
• Contracture may occur
• Sensation function of hair sebaceous gland not present
• Donor area is dressed and dressing is removed after 10 days and after 5 days in recepient area

Skin graft harvesting

Instruments  -  Humby’s knife

Donor sites:

Thigh , legs, arm, forearm, body

Taking split skin graft with a Humby’s knife holder

Differences

Split thickness Skin graft:

• Epidermis and part of dermis
• Donor sites heal spontaneously 
• Extensive defects
• Graft take – good
• More contraction later
• Less stable
• Less colour and texture matching

Full thickness graft:

• Epidermis and whole dermis
• Donor site needs to be closed – direct or SSG
• Small defects
• Graft take – less readily- needs optimal condition
• Secondary contraction less
• More stable
• Good colour and texture matching

Full thickness skin grafting (Wolfe’s graft)

• Harvested with surgical blade
• Accurately fitted to the defect and sutured
• Donor sites – postauricular, upper eyelid, supraclavicular, flexural, abdomen
• Donor site closure
• Recipient site – dressing / immobilisation
• Whole thickness of skin is excised
• Defatting is done to improve graft take
• Blood supply must be restablished
• Where cosmesis is important (face) or flexibility is important (over joint)

Flaps

• Flap is tissue with its original blood supply

Classification:

1. Based on blood supply – 

• Random pattern (dermal and subdermal plexus)

Rotation flap / transposition flap / advancement flap

• Axial pattern (named vessel) e.g. groin flap (lat. Circumflex artery)

Peninsular flap / island / free flap

Free tissue transfer

• Most technically demanding
• Single stage wound closure
• Wide variety of flaps- tailored to coverage needs
• More acceptable aesthetic outcome

2. Classification based on tissue type
1. Cutaneous flap
2.Faciocutaneous flap
3.Muscle flap
4.Musculocutaneous flap
5.Osteocuaneous flap

3. Specialized flaps
1. Fascial flap
2. Vascularized bone flap
3. Functional muscle flap