Skin functions Protective barrier, against: Trauma Radiation Temperature changes Infection

Cont… Thermoregulation, through: Vasoconstriction & Vasodilatation Insensible fluid loss control

Skin anatomy Skin varies in thickness depending on: Anatomic location: – thickest in the palm & sole of the feet – thinnest in the eyelids & postauricular region. Sex / male thicker than female. Age / children have thin skin

Skin layers 1. Epidermis Stratified squamous epithelium / Keratinocytes. No blood vessels Nutrients from dermis by diffusion through basement membrane.

Cont… 2. Dermis: Papillary dermis – Thinner – Loose connective tissue, containing: Capillaries Elastic fibers Reticular fibers Some collagen

Cont… Reticular dermis: – Thicker layer – Dense connective tissue, containing: Larger blood vessels Closely interlaced elastic fibers Coarse, branching collagen fibers arranged in layers parallel to the surface. Fibroblasts Mast cells Nerve endings Lymphatics Some epidermal appendages

Epithelial cell source Epithelial cells re-epithelialize when the overlying epithelium is removed or destroyed by: – Partial thickness burn – Abrasions – STSG harvesting.

Cont… Source, intradermal structures (epithelial appendages): – Sebaceous glands – Sweat glands – Apocrine glands – Hair follicles

What’s skin graft? Is transplantation of the skin from one part to another part (removed from its blood supply).

Types According to the origin: – Autograft / from the same individual – Allograft / from different individual (of the same species) – Xenograft / from different species (gene pig)

Cont… According to the dermal thickness: – STSG (epidermis + variable thickness dermis) Thin (0.005 – inches) Intermediate (0.012 – 0.018) Thick (0.018 – 0.030) Could be; – Meshed – Sheet FTSG (epidermis + entire dermis) Contains adnexal structures (sweat glands, sebaceous glands, hair follicles & capillaries).

THICK GRAFTS ???!!! ADVANTAGES: – The thicker the dermal component, the more the characteristics of normal skin are maintained following grafting, because: Greater collagen content Larger no. of dermal vascular plexuses Larger no. of epithelial appendages DISADVANTAGES : – More favorable conditions for survival – greater amount of tissue requiring – revascularization.

CHOICE BETWEEN FULL- AND SPLIT-THICKNESS SG. Depends on the wound’s : – Condition – Location – Size – Aesthetic concerns

FULL THICKNESS SKIN GRAFTS Advantages Ideal for the face / where local flap is inaccessible or not indicated. Retain more characteristics of normal skin, including; – Color – Texture – Thickness Less secondary contraction In children grow with the individual Greater sensory return (greater availability of neurilemaal sheet)

Cont… Disadvantages More primary contractures More hair follicles transferred More precarious survival (well vascularized bed) Limited range of applications, for; – Small wounds – Uncontaminated wounds – Well – vascularized wounds PRIMARY CONTRACTURE: immediate recoil of a freshly harvested graft due to the ELASTIN in the dermis (the more dermis the graft has, the more primary contracture).

FTSG DONOR SITES Closed : Primarily STSG / from another site.

FTSG Procedure Planning ( measuring, pattern made, donor site infiltration “LA +/- Epinephrine”) Harvesting  scalpel Donor site closed primarily. Graft placed.

STSG ADVANTAGES: Less ideal conditions for survival, broader range of application. Less hair follicles transferred Used to resurface : – Large wounds – Line cavities – Mucosal defects – Flap donor sites – Muscle flap Donor site heals by epidermal appendages cells immigration & proliferation.

Cont… Disadvantages; More fragile Can not withstand subsequent radiation therapy More secondary contracture Do not grow with the individual Smoother & shiner than normal skin Abnormal pigmentation tendency (pale/ white/ hyperpigmented) Donor site more painful than the recipient site SECONDARY CONTRACTURE: contraction of a healed scar due to MYOFIBROBLAST activity (the thinner the STSG, the greater the secondary contracture). STSG is more functional than cosmetic

Skin graft survival (TAKE) Depends on the graft’s ability to; – Receive nutrients & vascular ingrowth from the bed (in 3 phases, 4 theories) – Close contact & immobilization (skin graft adherence, in 2 phases)

Skin graft revascularization Phases; Serum imbibition; – Lasts 24 – 48 hr – Fibrin layer forms (adhere the graft to the bed. – Nutrient absorption into the graft (from the bed by capillary action). Inosculation; – Recipient & donor end capillaries aligned. Kissing capillaries; – Graft revascularized through kissing capillaries.

Graft revascularization theories Neovascularization (invade graft) Communication (between graft & bed vessels) Neovascularization + communication Graft vasculature made up primarily from its Original vessels before transfer.

How to optimize TAKE? Well vascular bed, seldom take in exposed; – Bone without periosteum (despite orbit or temporal bone) – Cartilage without perichondrium – Tendon without paratenon Close contact (between graft & bed); – Hematomas – Seromas These 2 immobilize & compromise graft take.

Skin graft adherence phases First phase: – Begins with placement of the graft on the bed. – Graft adhered by fibrin deposition. – Lasts 72 hr. Second phase: – Growth of fibrous tissue & vessels into the graft.

Cont… Sheet graft – Definition/ Is a continuous, uninterrupted graft. Advantages/ – Superior aesthetic result Disadvantages/ – Not allowing blood or serum to drain.

Cont… Meshed graft – Definition/ Is a sheet graft after multiple mechanical incisions. Advantages/ – Allowing immediate graft expansion. – Cover larger area per cm2 – Allows blood & serum drainage. Disadvantages/ – Pebbled appearance (aesthetically not acceptable).

What will happen if a wound heals without skin graft? Granulating wounds heal secondarily demonstrate the greatest degree of contraction & are most prone to hypertrophic scarring.

EPITHELIAL APPENDAGES IN THE SKIN GRAFT Their no. depends on the dermal thickness. Graft sweats / depend on: – Sweat glands no. transferred – Sympathetic reinnervation of these glands from the recipient site. Skin graft reinnervated from: – Nerve fiber ingrowth from the recipient site. – From the periphry.

Donor site Epidermis – Regenerate from epidermal appendages cells immigration, left in the dermis. Dermis – Never regenerates. STSG – Original donor site can be used for subsequent harvest – (dependant on donor dermis thickness). Healing – By re-epithelialization from epidermal appendages within nearly 7 days according to its thickness. – Enhanced by moist dressing & protection from; Mechanical trauma Desiccation

Donor site selection Consider – Color – Texture – Thickness – Vascularity – Donor site morbidity Sites – Any where – Face: Supracalvicular area Upper eyelid (small amount, very thin) – Common sites (for STSG): Thigh Buttocks Abdominal wall

SG postoperative care Graft failure, causes; – Hematoma – Serroma Raising the graft, prevent revascularization. Infection ( > 105 organism per gram of tissue) Minimized by careful bed preparation & early graft inspection after applying to a contaminated bed. Infection at the graft donor site can converts partial thickness dermal loss into complete thickness dermal loss. Mobilization Interrupt revascularization, prevented by tie-over bolster dressing on the face & trunk, splinting on the extremities.

Biologic dressing Definition/ – Temporary wound coverage, eg. Large burns, necrotizing facsiitis. Advantage/ – Protect the recipient bed from desiccation & further trauma until definitive closure. Biologic skin substitutes/ – Human allograft (take, rejected after 10 days, unless the recipient immunosuppressed as in large burns, rejection take longer). – Amnion – Xenograft (pig skin), rejected before becoming vascularized (take). Synthetic skin substitutes/ – Silicone – Polymers – Composed membranes

Human epidermis (in vitro) Human epidermis cultured in vitro to yield sheet of cultured epithelium that will provide coverage, albeit fragile (due to lack of epidermis), for Large wounds.