Wound Closure
Sutures, staples, and
adhesives
Some material taken from http://www.vetmed.auburn.edu/~hendera/guide/guide1.htm#outline
Historical Background – Sutures
• Sutures
– Use of textiles goes back
at least 4000 years
– Linen (earliest)
– Other
• Fe wire, Au, Ag, dried gut,
horse hair, strips of hide,
bark fibers, silk, and
tendon
– Up until 1930, catgut and
silk
• Stainless wire and
polymers (nylon, polyester,
polypropylene) during and
after WW II
• 1970s Dexron® (polyglycolic
acid) and Vicryl® (polyglactic
acid) resorbable
• Controlled degradation
The “Ideal” Suture Material
• Universal applicability – only difference in diameter
• Limp – easy to handle, no kinks, coiling, twisting, or
levitating
• Biocompatible
• Inert
• Strong
• Frictionless surface to glide through tissue
• High friction for secure knotting
• Sterlizable without composition changes
• Complete absorption, no residue, after healing is
complete – no matter how long it takes
Suture Classification
Physical/Mechanical
Size (diameter)
Number of Filaments
Tensile strength and
elongation
Elastic modulus
Bending stiffness
Stress relaxation and creep
Capillarity
Swelling
Coefficient of friction
Handling
Pliability
Packaging
memory
Knot tie-down
Knot slippage
Tissue drag
Biocompatibility
Biodegradation
Inflammatory
reaction
Propensity toward
wound
infection,
thrombi
formation,
carcinogenicity,
and allergy
Tensile breaking
strength and mass
loss
Biocompatibility of
degradation
properties
Absorbability
• Lose 50% of breaking strength within 60 days of
implanting
• Monofilament, braided, or twisted
• Natural or synthetic
– Natural – enzymatic attack
– Synthetic – hydrolysis
• More stable mechanism
• Rapidity commonly rated as percentage of
breaking strength – breaking strength rate (BSR)
– Can be modified in synthetic sutures
BSRs for Some Absorbable Sutures
Natural Fiber
Monofilament
Synthetic Fiber
BSR
Poly(glycolide-co-εcaprolactone)
(Monocryl)*
7
Poly(p-diaxonone)
(PDS II)*
35
Poly(glycolide cotrimethylene
carbonate)
(Maxon)+
Polyglactin 910 (Vicryl)*
Polyglactin 910 (Vicryl
Rapide)*
Polyglycolic acid
(Dexon)+
Braided
Twisted
Plain Surgical Gut
Light Surgical Gut
Medium Surgical Gut
Heavy Surgical Gut
BSR = Approximate days after placement when 50% of breaking strength remains.
*Ethicon Inc., +Davis & Geck Inc.
35
15
5
12
1
4
8
11
Nonabsorbable
• Retain majority of breaking strength for
more than 60 days
• Three classes
– Class I – silk, monofilament, and sheathed
– Class II – cotton and linen
– Class III – metallics
• Classes I and III most common as Class II
are prone to contamination and infection
Common Nonabsorbable Sutures
Monofilament
Polypropylene (Prolene* & Surgilene+)
Nylon (Ethilon* & Dermalon+)
Braided
Polyester (Mersilene*)
Silk
Nylon (Surgilon* & Nurolon+)
Braided & Coated
Polyester & Polybuterate (Ethibond*)
Polyester & Silicone (Tichron+)
Polyester & Teflon (Tevdek#)
Silk & Beeswax
Multifilament Sheathed
Multistrand Nylon & Polyethylene Sheath (Supramid$)
*Ethicon Inc., +Davis & Geck Inc., #Deknatel Inc., $S. Jackson Inc.
Suture Sizes – Two Systems
• United States
Pharmacopœia (USP)
– Complex relationship
between diameter,
tensile strength, and
knot security
– Precise criteria vary with
suture class, natural or
synthetic, and
absorbability
– Whole numbers from 5
to 12-0
– Allows comparison
among different types
• European
– Diameter in mm
– Differences in tensile
strength of materials
make comparisons
difficult
• Sutures function best
when their strength and
tissue strength are
similar.
Suture Sizes/Use
Examples of Suture Sizes for Use in Pet Animals
10-0 - 8-0
7-0 - 5-0
Microvascular
Corneal
Ophthalmic
Neural
Vascular
4-0 - 3-0
Skin & Subcutis
Bowel
Bladder
2-0 - 0
Abdominal Fascia
Stomach
Hernia
1-2
Rib Retention
Cutaneous Stents
Increase or decrease abdominal fascia and retention sutures appropriately based on weight & suture pattern
Tensile Strength of Sutures
• Dependent upon
– Material
– Size/diameter
– Condition
•
•
•
•
Wet
Dry
Knotted
Absorption of bodily fluids
– Hydrophobic
– Hydrophilic
• “Abuse”
• Heat history – “re-autoclaving”
Knot Strength vs. Tensile
Strength
• Strength of a knotted suture generally
significantly less than strength of a straight
yarn (~ 50%)
• Knotting induces stresses in the suture
due to bending and twisting
• As knotted suture pulled compressive
stress develops increasing residual stress
and lowering overall strength values
Sizes and Breaking Strengths of Dry 2-0 and 3-0 Sutures
Straight Pull
Dia. inches
3-0
2-0
No. 3-0
lbs.
Knotted Pull
No. 2-0
psi.
lbs.
No. 3-0
psi.
lbs.
No. 2-0
psi.
lbs.
psi.
Surgical
Gut
Dexon
Vicryl
PDS II
Maxon
0.0125
0.0100
0.100
-
0.0160
0.0127
0.0130
0.0130
0.0153
6.7
6.1
-
54600
77800
-
9.8
9.6
11.5
14.8
48000
75900
80000
80000
3.8
3.9
5.0
-
30900
49700
-
5.7
6.4
7.9
10.8
28000
50300
50000
58000
Silk
Cotton
Polypro
pylene
Nylon
Polyeste
r
0.104
0.0103
0.0097
0.0131
0.0128
0.0123
0.0131
0.0131
5.3
4.0
8.5
62400
48000
115000
8.2
5.5
7.6
9
14.5
60900
40200
63000
67000
107600
3.4
2.7
3.8
4.3
3.7
40000
32400
50100
4.8
3.5
5.5
6.5
6.8
35600
27200
46000
48000
50400
Coating Materials
• Facilitate handling
– Ease of passing through tissue
– Ease in sliding knots down
– But can result in poor knot security
• Nonabsorbable coatings
–
–
–
–
Beeswax
Silicone
Paraffin wax
Poly(tetrafluoroethylene)
• Absorbable
– Must be absorbable like the suture
• Water soluble
• Water insoluble – break down by hydrolysis
Problems Associated with Surgical
Sutures
• Time-consuming nature of secure knot
tying
• Need for knot security under all conditions
with all sutures
• Risk of suture breakage during surgery
• Loss of control due to needle slippage or
rotation within the needle holder
• Postsurgical slippage of the knotted suture
• Early or pathologically induced
degradation of absorbable suture
Ligating Clips
• Essentially “clips” to
replace sutures when
occluding (closing)
the lumen (central
canal) of a vessel or
tubular organ
– Blood vessels
– Gynecological &
urological (GU)
procedures
• Metallic or polymeric
• Requirements
– Nontoxic and
biocompatible
– Absence of allergic
and immunogenic
effects
– Tolerated by wide
range of tissue types
– High strength and low
solubility
– Finite longevity
– Secure
Metallic Clips
•
First – Cushing neurosurgery clip,
1910
– Ag wire formed in the shape of
a “U” and closed around blood
vessel
– Tantulum (1940)
• Tubule ligation
– Others
• Co-Cr
• Titanium
• Stainless Steel
• “Memory metal” – Ni-Ti
alloy
•
•
Desirable properties in metallic
clips
– High strength
– Malleability & ductility – can
make fine wire
– Capacity for work-hardening
– Corrosion resistance
Some problems
– Allergic reaction
– Radio-opaque – can cause
problems with CT, X-ray, and
MRI examinations
Polymeric Clips
• Absorbable and nonabsorbable
• Viscoelastic
– Creep
– Stress-relaxation
Surgical Stapling
• Introduced in the late
1970s
• Used widely in human
and veterinary
medicine
–
–
–
–
–
Gynecological
Cardiovascular
Gastrointestinal
Esophageal
Pulmonary
• Staples originally
stainless but now Ti
and polymeric used
– Polymeric – 2 parts
• “U”-shaped fastener
• Figure “8” retainer
Surgical Staples
Staple
Staple Gun
Staple Remover
Staples & Clips vs. Sutures
•
•
•
•
•
Speed
Convenience
Reduced infection rate
Lower cost
If done properly, no cosmetic difference
Tissue
Adhesives
Before Curing
After Curing
• Sterilizable
• Easy in preparation
• Viscous liquid or liquid
possible for spray
• Nontoxic
• Rapidly curable under
wet physiological
conditions (pH 7.3, 37°C,
1 atm)
• Reasonable cost
• Strongly bondable to
tissues
• Biostable union until
wound healing
• Tough and pliable
• Resorbable after wound
healing
• Nontoxic
• Nonobstructive to wound
healing or promoting
wound healing
Natural Tissue – Fibrin Glue
• First reported in 1940
• Mimics blood clot – major component fibrin
network
• Excellent tissue adhesive but insufficient in
amount for larger wounds
• Nontoxic if human protein sources are
used to obtain fibrin
Synthetic Systems:
Poly-Alkyl-2-Cyanoacrylates
• Discovered in 1951
• “Crazy Glue”
• H2C=C―CO2―R
CN
• R = alkyl group
– CH3 (methyl)
– H3CCH2 (ethyl)
• Release small amount of
formaldehyde when
curing
– amount lessens with
length of alkyl chain
Characteristics of Currently Available Adhesive
Systems
Fibrin Glue
Cyanoacrylate
Handling
Excellent
Poor
Set time
Medium
Short
Poor
Good
Pliability
Excellent
Poor
Toxicity
Low
Medium
Resorbability
Good
Poor
Cell infiltration
Excellent
Poor
Tissue bonding
Other Experimental Systems
• Gelatin-based adhesives
– Mimic coagulation but without fibrin
• Polyurethane (-HNOCO-) based
adhesives
– Capped with isocyanate to rapidly gel upon
exposure to water
– More flexible than current cyanoacrylate
adhesives
• Collagen-based adhesives