SKIN & ITS APPLIED ANATOMY

Snehal Kharche

Contents INTRODUCTIONBASIC STRUCTURE OF SKINBASIC LESION OF SKINSURGERY OF SKIN

◦ BIOMECHANICAL PROPERTIES OF SKIN◦ SKIN LINES◦ COSMETIC UNIT OF FACE◦ PRINCIPAL OF INCISION AND SUTURING OF FACE◦ WOUND DRESSING◦ SCAR AND SCAR REVISION (OVERVIEW)◦ ADVANCES IN SKIN SURGERY

IntroductionSkin is the largest organ of the

body which forms 8% of total body mass

Covers entire external surface of body

Is continuous around body orifices

Basic structure of skin• Skin may be viewed as a double-

layered sheath, cushioned by underlying subcutaneous fat,

the layers are

Epidermis Dermis

EpidermisEpidermis is a continually

renewing, keratinizing, stratified, squamous epithelium

Layers of epidermis Stratum basale Stratum spinosum Malpighian

layer Stratum granulosum Stratum corneum

The cells present in skin are keratinocytes(80%), melanocytes, langerhans cells & merkel cells

Dermal-epidermal junctionFirmly attaches epidermis to

dermisMechanical support to epidermisActs as a semi-penetrable

membrane

Epidermal appendages

Epidermal AppendagesHair follicle: is main component of pilosebaceous

unit which is composed of sebaceous gland, arrector pili muscle & sensory end organ

Sebaceous gland: it is unilocular or multilocular st. which connects hair follicle by a sebaceous duct

Eccrine sweat glands: reticular dermis, duct opens directly on skin, innervated by cholinergic nerve fibres

Apocrine sweat gland: adregenic innervation, duct connects to hair follicle above sebaceous duct

DermisConnective tissue between

epidermis & dermisIt is divided into papillary &

reticular dermisIt is composed primarily of

collagen, elastin & ground substance

Regional skin variationGlabrous skin(non hairy skin)Non glabrous skin(hair bearing skin)

Vascular supply of skin

It originates from three main sources Direct cutaneous: main arterial trunk Musculocutaneous: arise from

intramuscular vasculature, pass through surface of muscle, pierce deep fascia to reach skin

Fasciocutaneous: perforating branches from vessels deep to deep fascia, pass along intermuscular septa, fan out at level of deep fascia

Plexi Subpapillary Reticular dermal Deep dermal

Basic lesions of skinMacules (1 - 2cm, different color, flat)Patches (large macule)Papule (elevated, less than 1 cm)Nodule (dome shaped, more than 1 cm)Wheals (round pale red)Vesicle (contains fluid, less than 0.5cm)Bullae (more than 0.5cm)Erosion (break in epidermis)Pustules (raised, purulent)Fissures (cracks in skin)

Burns woundBurns cause damage in no. of diff.

ways, but most common affected organ is skin

Assessing size (for treatment plan & morbidity) Pt. Whole hand is 1% TBSA and is

useful guide for small burns Rule of nine(wallace’s) UL-9%, LL-

18%, Torso-18% each side, H&N-9%, GR-1% only for initial approx.

Browder chart for large burns

Wallace chart(rule of nine)

BROWDER CHART

Classification of burnsSuperficial partial thickness

(papillary)

Deep partial thickness (reticular)

Full thickness (whole dermis)

Biomechanical properties of skinNonlinearity:1. Flat section- considerable extension with

little force2. Intermediate section- rapid transition3. Terminal section- little or no extension

despite increased forces Anisotropy:

variation in skin tension atdiff. sites of bodydirectional considerations for skin movement

Viscoelasticity:At high stresses skin shows viscoelastic

properties, two time-dependent properties of skin are

Creep: (permanent stretching)increase in length of skin compared to original length when placed under const. stress

Stress relaxation: decrease in stress when skin is held under tension at a const. strain as relaxation occurs as tissue creeps

Skin linesRelaxed Skin tension lines

(RSTL) correspond to the directional pull when skin is relaxed do not always correspond to wrinkle lines result from orientation of

collagen fibre of skin used for incision making Lines of maximum extensibility

Wrinkle line – caused by contraction of underlying muscle, perpendicular to their axis of shortening

Kraissl’s line – exaggerated wrinkles lines

Langers line- lie at right angle to RSTL

Aesthetic regions of faceCovered by skin having common

characteristicsPrinciple aesthetic regions of face

are Forehead Cheek (five subunits) Eyes & eyebrow Nose (nine subunits) Lips & chin

Esthetic units of nose

Principals of incision Incisions placed on exposed surface

of face must follow some basic principles so the scar is inconspicuous Avoid imp. Neurovascular structures Use as long incision as necessary Place incision perpendicular to surface of

nonhair-hair bearing skin Place incisions in line of minimal tension Seek for other favorable sites for incision

placement

Commonly used skin incision

Suturing

Optimizing outcome of sutured woundShould be at even level to prevent “step off

deformity”Prior to placement of top stitch all tension

should be off the wound edgesTo reduce wound tension buried absorbable

suture should be usedEverted wound edges for thinner and flatter

scar In cosmetic areas fine caliber suture or

subcuticular suture are used

Post operative careSuture left for long promotes infec.Remove suture at appropriate time to

prevent “Rail Road” scarRecommended suture removal time Eyelid – 2 to 4 days Face – 4 to 6 days Neck and scalp – 5 to 7 days Extremities – 10 to 14 days

Wound dressing Functions: Maintain a moist wound healing environment Absorb exudate Provide a barrier against bacteria Reduce edema Eliminate dead space Protect against further injury from trauma,

pressure and sheer

Scar and scar revisionThe trace of healed wound sore, or burn.

A fault or blemish remaining as a trace of some former condition or resulting from some particular cause

Ideal scar: Imperceptible Not cause distortion of adjacent structure Lie in aesthetic borders or in RSTL Flat and in level with surrounding tissues Same color and texture as surrounding skin

Adverse scar: Wrong direction Poor alignment Stretched scar Contracted scar Pigment alteration Contour deformity (trapdooring) Tattooing Stitch mark (after 7 days) Hypertrophic scar Keloid scar

Hypertrophic scar- Not familial- Not race related- Female = Male- Children- Remains with wound- Subsides with time- Flexor surface- Tension related

Keloid scar- May be familial- Black > White- Female > Male- 10 – 30 yrs- Outgrows wound- Rarely subsides- Sternum , shoulder- Unknown

Scar revisionReconstructive ladder

Timing of scar revisionScar should be mature

Collagen remodeling and reorientation takes upto 18 months

If scar is grossly deforming revision is recommended 2-3mnths- dermal scar serves as wound base

Techniques for scar revision Non surgical methods Massage (1month post operative) Silicone gel (topical application) Intralesional steroids Lasers Vitamin E Vitamin A Herbal extract (allium cepa) Make up (camouflage)

Surgical Methods

Scar excision Scar irregularization• Z-plasty• W-plasty• Geometric broken line

Scar excisionMost common excisional tech. is elliptical

excisionReserved for scars that are parallel to RSTL,

less than 2cm in length or short straight wide depressed or raised scars

Fusiform shaped incisions made parallel to RSTL

Angle<30 degree to prevent skin rebundancy & l:w ratio – 3:1

Scar irregularizationZ- plasty:• Classic z-plasty is 60 degree transposed flap

• Used for scar not along RSTL

• It alters the direction of scar to be parallel with RSTL

• Two points in Z- plasty are critical (a) Angle size (tissue lengthening ) (b) Length of common diagonal (scar)

• In larger scar multiple z-plasty is done

W- plasty:

• Based on principle that irregular line is less visible than straight line

• Used for scar not along RSTL

• Zigzag incision on one side and its mirror image on opposite side

Geometric broken line:

• used for longer scar

• outline is made on one side using geometric designs (circles, triangles)

• undermine and suture

V-Y & Y-V advancement flap: V-Y adv. Flap is unique in that V shaped flap

is not stretched or pulled into recipient site It is particularly useful when a structure or

region requires lengthening or release from contracted scar

Y-V advancement is similar to V-Y flap except that V shaped flap is stretched or pulled

The maximum wound closure tension is at apex of flap

DermabrasionSuperficial injury to papillary dermisDeposition of new organized collagenImproves surface irregularities &

pigmentation

TechniqueSkin preparation (1 month prior) (optional) - 4 % Hydroquinone (depigmentation) - retinoic acid & tertinoin Entire scar & adjacent skin is dermabraded

Abrasion is carried to the level of upper to midreticular dermis

End point of abrasion is appearance of pinpoint bleeding – indicates invasion of dermal papillae

ArmamentariumElectric powered rotary Hand piece

Diamond Fraise & Files (round, wheel)

Derma abrasion is carried out at 10,000 to 15,000 rpm

Advances in skin surgery

LASERS – Light amplification by stimulated emission of radiation

- Principles :A quantum of electromagnetic energy called photon can stimulate an EXCITED atom to emit another photon with same energy and wavelength

- Key word is EXCITED atom, as resting atom will simply absorb the photon

Parts of a Laser system A gas, solid or liquid medium that can be

excited to emit laser light Mirror, reflects light back and forth,

increases intensity A source of energy to excite medium Delivery system (fibro-optic cable)

Type of Laser Continuous laser Pulsed Laser

Chromophores – medium that absorb light Three primary chromophores in skin: (a) Water (b) Hemoglobin (blue, green) (c) Melanin (Broad spectrum) The laser light absorbed by the tissue is

converted into HEAT Time required by the tissue to loose half its

heat to surrounding tissue is thermal

relaxation time (TRT)

SELECTIVE PHOTOTHERMOLYSIS - When pulse duration is shorter than

TRT of target – localized heating

CO2 laser and Er:YAG laser for skin resurfacing (wrinkle , scar)

Argon laser for vascular lesion

Skin graftsTwo main forms

Split-thickness (Thiersch graft) Full-thickness (Wolfe graft)

- Composite graft – Contains skin plus other structure eg. cartilage

SPLIT-THICKNESS (STSG)

DONOR SITE-large area -heals spontaneously-site reusable

RECEPIENT SITE-contracts more-easily abraded -poor color match-inferior cosmetics-reliable ‘take’-inelastic-over large areas

FULL-THICKNESS (FTSG)

DONOR SITE-smaller area-site must be closed-site scars

RECEPIENT SITE-contracts less-abrasion resistant-good color-good cosmetics-less reliable ‘take’-normal texture, elastic-used over face