Download Anatomy and Physiology of the Skin

Anatomy and
Physiology
Hootan Zandifar M.D.
Anatomy and Physiology of the Skin
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Skin
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More than a simple barrier
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Functions: immune response, regulates temperature, fluids
and electrolyte balance.
Heaviest human organ 3.79kg
 2nd Largest surface area 1.7m2
 Variations in color, thickness, connective tissue
content, and number of adnexal structures.
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Important clinically for wound healing and esthetics
Anatomy and Physiology of the Skin
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Preoperative evaluation of the skin is important.
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Fair skin, light hair, and blue eyes- are at risk for
prolonged redness of postoperative scars
Dark skin, hair, and eyes- are at risk for
hyperpigmented scars that may persist postoperatively
History of keloids and hypertrophic scars are important
Hyperextensibility of joints, lax skin, and Gorlin’s sign,
are increased risk for widen scars.
Common skin conditions: Atopic dermatitis, psoriasis,
and eczema are at increase risk for wound infections.
Anatomy and Physiology of the Skin
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Epidermis–
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keratinizing stratified squamous
epithelium
Turnover 30 days
0.075-0.15mm thick, thin at birth
and increases during puberty and
thins again during the 5th and 6th
decades of life
Four Layers
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Stratum basale (basal cell)
Stratum spinosum (prickle cell)
Stratum granulosum (granular cell)
Stratum corneum (Keratin)
Anatomy and Physiology of the Skin
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Four Cell Types
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Keratinocytes- 80%
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Found throughout the epidermis
Produces Keratin
Source of squamous cell carcinoma
Melanocytes•
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Neural crest origin
located in the basal cell layer
equal number in all races–
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produces melanin which protects nuclei in prickle cell layer
Langerhans’ Cells•
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absent in Vitiligo
Tyrosinekinase absent in Albinism
Contain Birbeck’s granules
antigen presentation
Decrease with UV light exposure
Merkel’s Cells•
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Neural crest origin
function unknown
Merkel’s cell tumors
Anatomy and Physiology of the Skin
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Rete pegs
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Irregular projections of
the epidermis which
interdigitate with
corresponding upward
elevations of the dermis
called dermal papillae.
Important in preventing
shearing of the epidermis
Absent in scars
Decreases with aging
Anatomy and Physiology of the Skin
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Epidermal appendages
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Pilosebaceous Unit
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Sebaceous gland
Hair shaft
Hair follicle
Arrector pili muscle
Sensory organ
The unit has a motor and
sensory component and is
responsible for producing
sebum and hair.
Different components dominate
depending on the location.
The complete pilosebacous unit
is absent on mucous
membranes.
The Pilosebaceous unit aids in
reepithelialization of partial
thickness wounds.
Anatomy and Physiology of the Skin
Dermis
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Thickness varies
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< 1mm eye lids, 1.5mm temple,
2.5mm scalp, >4mm on the back
Increases in thickness from birth
to 4th or 5th decades and is thicker
in males
Two layers
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Papillary dermis•
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thin superficial layer
adnexal structures
Type III collagen
Reticular dermis•
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thicker deep layer
Type I collagen most abundant
Scar formation
Anatomy and Physiology of the Skin
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Dermis
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Collagen
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Synthesized by fibroblast
Provides mechanical strength and extensibility
Configuration changes throughout life.
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Small parallel to skin surface in infancy
Young adult- randomly arranged in papillary dermis and large bundles
of loosely interwoven collagen that are tightly packed
Elderly collagen is more compact due to decrease in ground substance
Continuous state of synthesis and degradation
Decreases by 1% per year during adult life
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Increase in collagenase synthesis from sun exposure
Decrease in collagen production
Anatomy and Physiology of the Skin
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Dermis
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Elastic Tissue
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Synthesized by fibroblast and is made of elastin and a
microfibrillar matrix
Responsible for recoil and elastic properties of skin
Continuous state of synthesis and degradation.
Thin and run perpendicular to the skin surface in the papillary
dermis.
Thicker and run parallel to the skin surface in the reticular
dermis.
Sun-damaged causes thickening and clumping of elastic fibers
in the papillary dermis
Anatomy and Physiology of the Skin
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Dermis
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Ground Substance
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Connective tissue and cellular components are embedded in ground
substance.
Synthesized by fibroblasts, mast cells, and smooth-muscle cells
Composed primarily of fibronectin, glycosaminoglycans, hyaluronic
acid, chondroitin-sulfate, and dermatan sulfate.
Important in maintaining skin hydration and tensile elasticity of
compressed skin. Decreases with age.
Dehydration of skin due to the displacement of ground substance is
responsible for biological creep of skin. Creep plays a role in
immediate intraoperatie tissue expansion
Hypertrophic scars and keloids contain an excessive amount of
ground substance and why pressure helps to reduces their size.
Anatomy and Physiology of the Skin
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Dermis
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Cellular components
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Fibroblast–
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most abundant cell located mainly in the papillary dermis.
Produces collagen, elastin, and ground substance
Behaves as a contractile cell during wound contraction
Number decrease with age
Mast cells
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Are found perivascularly and in the papillary dermis
May produce ground substance
Abundant in scars and histamine production and release is
responsible for puritus in hypertrophic scars and keloids
Anatomy and Physiology of the Skin
Skin
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Nerve supply
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Allows the skin to accurately interpret and adapt to continuous
sensory input from the environment.
Sensory nerves relay pain, temperature, pressure, and
proprioception
Merkel cell complexes located in the epidermis respond to
touch.
Meissner’s corpuscles located in the papillary dermis mediate
fine touch sensation.
Pacinian corpuscles located in the deep subcutaneous tissue
mediate deep pressure and vibration.
Efferent nerves in the dermis innervate blood vessels and
adnexal structures.
Anatomy and Physiology of the Skin
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Skin
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Vascular supply
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Rich source of blood to the head
and neck via the internal and
external carotid arteries.
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Two vascular plexuses
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Low infection rate.
Superficial plexus- located in the
superficial papillary dermis.
Provides nutrition to the epidermis
via diffusion.
Deep plexus- located in the
superior aspect of the reticular
dermis. It is supplied from
subcutaneous perforators and
provide nutrition to the skin
appendages and supply the
superficial plexus
Venous and lymphatic drainage
follow the vascular plexuses
Relaxed Skin Tension Lines (RSTLs)
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RSTLs
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perpendicular to the
underlying facial
musculature
Exception: central eyelids
In the neck perpendicular
to areas of flexion
Place incisions along
RSTLs
Relaxed Skin Tension Lines
Lines of Maximum Extensibility
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Lines of Maximum
Extensibility (LMEs) are
perpendicular to RSTLs
Facial Subunits
Physiology of Wound Healing
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3 overlapping phases:
Inflammatory (reactive) phase
 Proliferative (regeneration)
phase
 Remodeling
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Inflammatory Phase (Injury-Day 4)
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Hemostasis
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Brief initial vasoconstriction
Platelet activation and aggregation
Coagulation and complement pathways
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Platelet degranulation
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Fibrin clot initiates inflammatory phase
Vessel dilation and inc. permeability
Release of chemoattractants for
inflammatory cells
Influx of WBC’s
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Initially PMN’s
Shift to macrophages (day 2)
Inflammatory Phase
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Macrophages
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Phagocytosis
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Clears wound of bacteria and
debris
Secrete growth factors
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Attract endothelial cells,
fibroblasts, and keratinocytes for
repair
Mediators Involved in Wound Healing
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Eicosanoids
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Prostaglandins
Prostacyclins
Thromboxanes
Leukotrienes
Lipoxins
Cytokines
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Chemokines
Lymphokines
Monokines
Interleukins
Interferons
TNF
GM-CSF
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Nitric Oxide (NO)
Growth Factors
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PDGF
EGF
FGF
TGF
Proliferative Phase (Day 4-14)
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Principle Steps
Epithelialization
 Angiogenesis
 Granulation tissue formation
 Collagen deposition
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Epithelialization
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EGF, TGF-α, KGF
Morphologic changes in
keratinocytes at wound edge
seen within hours of injury
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Marginal basal cells migrate
Angiogenesis
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TNF-α
Migration of capillaries
into wound bed
Granulation
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PDGF and EGF
Fibroblasts migration
 Collagen and ECM replaces initial fibrinplatelet matrix
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Dense population of blood vessels,
macrophages, and fibroblasts within
an ECM
“Beefy red” appearance
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Secondary to new capillary network
Contraction
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Surrounding skin pulled in toward
open wound
Degree varies
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Greatest in trunk
Least in extremities
Intermediate in head and neck
Mechanism
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Myofibroblasts – contain smooth
muscle
Remodeling Phase (Day 8 – 1 Year)
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Collagen deposition & organization
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Maximum collagen deposition by 21 days
Never as organized as uninjured skin
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Thicker fibers and more x-linking Fibroblasts become
myofibroblasts
Matrix metalloproteinases (MMPs)
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Modulate deposition and organization of ECM
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Scar remodeling and contraction
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Wound Strength
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1 week: 3%
3 weeks: 30%
>3 months: 80%
Scar remodeling continues for up to 12 months
Wound healing
Hypertrophic Scars vs. Keloids
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Hypertrophic Scars
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Within wound margins
Onset early after injury
Regress with time
More responsive to
excision
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Keloids
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Extend beyond wound
margins
Delayed onset
Grow and recur
Gross Appearance
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Raised
Rubbery
Firm
Histology of Keloids
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Excessive collagen
Irregular bundles
Basics of wound
closure
Hootan Zandifar M.D.
Prior to Closure
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A,B,Cs, ATLS
Hemostasis
Thorough irrigation of the wound
Removal of foreign bodies to avoid future
infection or tattooing.
Injection of local anesthetic usually with
epinepherine for vasoconstriction.
Local Anesthetics
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Esters (deactivated locally in tissues)
Cocaine (only for topical not for injection)
 Procaine (Novocaine)
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Amides (deactivated in the liver)
Xylocaine (Lidocaine)
 Bupivicaine (Marcaine)
 Prilocaine
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Local Anesthetics
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Cocaine (max dose 4 mg/kg)
Procaine (max dose 7 mg/kg not to exceed 350600 mg)
Local Anesthetics
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Lidocaine (max dose 4.5 mg/kg without
epinepherine and 7 mg/kg with epinepherine)
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3 formulations
0.5 % has 5 mg/cc
 1.0 % has 10 mg/cc
 2.0 % has 20 mg/cc
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Bupivicaine (max dose 3 mg/kg)
Prilocaine (max dose 7 mg/kg)
Local Anesthetics
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Toxicity
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First level
CNS excitation (agitation, muscle twitching, hypertension,
emesis, sweating)
 Benzodiazepine to prevent seizures, Oxygen, possible need for
intubation
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Second level
CNS depression (somnulence, coma, bradycardia, hypotension,
cardiovascular depression leading to shock and cardiorespiratory arrest)
 ABCs, ACLS, Pressors
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Prilocain can cause meth-hemoglobinemia like
poisoning that is treated with methylene blue
Local Anesthetics
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Epinepherine (max dose of 10 mcg/kg)
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Formulations
1:100,000 has 10 mcg/cc
 1:200,000 has 5 mcg/cc
 1:1,000 has 1,000 mcg/cc
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Toxicity – Sympathetic activation (tachycardia,
hypertension, diaphoresis…)
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Treat with beta blockers
Tissue handling
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Be gentle—hooks, non-crushing forceps
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DEBRIDEMENT: don’t be afraid to debride
Re-cutting the wound: bevel the edges
 Allows for skin eversion
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Closures
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Eversion of wound edges
Make incisions perpendicular to the skin (unless
in hair bearing areas)
Good technique: twist your wrist, insert needle
at correct angles (90 Degrees to the skin)
Cleaning the wound: dilute H2O2, dilute
betadyne solutions, saline
Techniques
Techniques
Wrong method
Correct method
Needle point Geometry
Taper-Point
•Suited to soft tissue
•Dilates rather than cuts
Reverse
cutting
•Very sharp
•Ideal for skin
•Cuts rather than dilates
Conventional
Cutting
•Very sharp
•Cuts rather than dilates
•Creates weakness allowing suture tearout
Taper-cutting
•Ideal in tough or calcified tissues
•Mainly used in Cardiac & Vascular
procedures.
Wound Closure
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Basic suturing techniques:
Simple sutures
 Mattress sutures
 Subcuticular sutures
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Goal: “approximate, not strangulate”
Simple Sutures
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Simple interrupted stitch
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Single stitches,
individually knotted (keep
all knots on one side of
wound)
Used for uncomplicated
laceration repair and
wound closure
Mattress Sutures
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Horizontal mattress stitch
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Provides added strength in
fascial closure; also used in
calloused skin (e.g. palms and
soles)
Two-step stitch:
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Simple stitch made
Needle reversed and 2nd
simple stitch made adjacent to
first (same size bite as first
stitch)
Mattress Sutures
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Vertical mattress stitch
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Affords precise approximation
of skin edges with eversion
Two-step stitch:
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Simple stitch made – “far, far”
relative to wound edge (large
bite)
Needle reversed and 2nd
simple stitch made inside first
– “near, near” (small bite)
Subcuticular Sutures
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Usually a running stitch,
but can be interrupted
Intradermal horizontal
bites
Allow suture to remain
for a longer period of
time without
development of
crosshatch scarring
Suturing
Rule of halves
Suturing
Rule of halves
Closures
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Absorbable
Fast Absorbing gut
 Chromic Gut
 Vicryl
 PDS
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Non-absorbable
Nylon
 Prolene
 Silk
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Absorbable vs. Non-Absorbable
Closures
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Smaller sutures on face: 5-0 or 6-0
Prolene vs. Nylon
 COLOR MATTERS (hairline, ear crevices,
eyebrows)
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Neck: 5-0 sutures
Scalp: staples
Leave tails to remove non-absorbable
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“If you had to take them out”
Deeper stitches
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Deeper stitches: are used for support to remove
tension and close dead space
With tension removal  less scarring
 Last longer: ABSORBABLE
 Vicryl
 PDS
 Chromic
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“Burying the knot”: buried interupted
“Difficult” closures
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Lips: align the vermillion: key stitch
Eyelid: if thru and thur:
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Ears: exposed cartilage / auricular hematomas
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Align the grey line
Repair perichondrium, Close cutaneous layers
Avulsion injuries: reattach if little pedicle versus pocket
principle
Nose: Exposed cartilage
Through and Through lacerations. Close the
inside first.
Secondary Intention
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Concave surfaces
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Lateral forehead
Glabella
Medial Canthal Subunit
Depressed area of ear
Supraalar hollow of nose
Soft tissue triangles
Philtrum
Perinasal melolabial
Fair healing
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Nasal sidewall subunit
Lateral canthal subunit
Animal Bites
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Most infections are mixed bacteria of aerobic
and anerobic.
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Need wide spectrum antibiotics
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Many organisms produce beta-lactamase
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Augmentin oral drug of choice. Unasyn or Zosyn
for IV treatment.
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Copious irrigation of the wound is a must.
Human Bites
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Mixed aerobic and anerobic
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Can treat with Augmentin or Clindamycin
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Debate to close or not to close human bites because
of risk of infection.
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Irrigate 48 hours of IV antibiotics delayed closure vs.
secondary intention vs. primary closure after
irrigation with oral antibiotic use.
Tetanus
Thank You.