Surgical stapling providesa quick and effectivealternative to manualsuturing in certaincircumstances, such asfor skin apposition

Suture materialsand patterns JACQUI NILES AND JOHN WILLIAMS

SUTURES are used either for apposing tissues or for ligation, and a variety of different types of suturematerial is currently available. Suture selection should be based on knowledge of the physical andbiological properties of suture materials, an assessment of the healing rate of a particular tissue and localconditions in the wound. The ideal properties of a suture material have yet to be fulfilled by any singleproduct on the market. The purpose of this article is to outline the properties of the available suturematerials and to give an indication of when and how to use them.

Jacqui Niles qualifiedfrom the RoyalVeterinary College,London, in 1993. Sheis a resident in smallanimal soft tissuesurgery at LiverpoolUniversity and holdsthe RCVS certificate insmall animal surgery.Her special interestsinclude all aspects ofsoft tissue surgery,especially the surgicalmanagement ofportosystemic shuntsand chylothorax.

John Williamsqualified fromCambridge Universityin 1984. He holds thecertificate inveterinary radiology,and an FRCVS, and isa diplomate of theEuropean College ofVeterinary Surgeons.He is currently directorof small animal studiesat Liverpool Universityand is an RCVSSpecialist in SmallAnimal Surgery (SoftTissue). His clinicalinterests lie inportosystemic shunts,and reconstructiveand cardiorespiratorysurgery.

CLASSIFICATION OF SUTURE MATERIALS

Suture materials are broadly clcassified as absorbable ornon-absorbable. They can be further classified as syn-thetic or natural fibre and they may be multifilament ormonofilament, coated or uncoated.

ABSORBABLE SUTURES

All absorbable sutures Lindergco degradation in the tissueand lose their tensile strength within 60 days. They areabsorbed by mieans of the body's defence system and allwill therefore produce so5ic tissuc rcaction. Absorbablesutures are principally designed for use in closintinternal tissue layers or organs which do not require longterm support. There arc some exceptions to this - thenewer synthetic monofilaiment absorbables, such as

polydioxanone (PDS 11) andare designed to provideextended wound support. It isimportant to remember that allabsorbable sutures will losetheir tensile strength beforethey are absorbed.

There has been a trendtowards using absorbablesutures in infected surgicalsites as they will rarely providea nidus for further infection.However, enzymatic process-es may, in fact, increase thedegradation process and makethe suture unreliable.

polyglyconate (Maxon),

Tensile strength

Knot security

Memory

Chatter/tissue drag

Tissue reaction

Natural fibres*Monofilament

Surgical gut PolydioxanonePlain (PDS; Ethicon)Chromic (PDS Il; Ethicon)

SyntheticsMultifilament

Polyglycolic acid(Dexon; Davis & Geck)(Dexon Il; Davis & Geck)

Polyglyconate Polyglactin 910(Maxon; Davis & Geck) (Vicryl; Ethicon)

(Vicryl Rapide; Ethicon)Poliglecaprone 25(Monocryl; Ethicon)

* All are multifilament but fused, so that they are essentiallymonofilament

Surgical gutSurgical gut (catgut) is prepared from the submucosa ofsheep or cattle small intestine. After implantation, gut isabsorbed by a combination of enzymatic degradation andphagocytosis; the rate of absorption is thus affected by

Breaking strength per unit area

Related to surface frictional characteristics

The property to unkink after loops have been formed during thedevelopment of a knot. Suture materials with a high memory(eg, polypropylene) tend to revert to their package shape

Lack of smoothness when sliding down a knot or friction whilepassing through tissue

Tissues respond to the implantation of sutures as they do to otherforeign material. Sutures can evoke an acute or chronic inflammatoryresponse

Capillarity and Tendency to wick, allowing fluid and infection to move along theresistance to infection suture

In Practice * J U N E 1 999

191 :I 41,71 f-Ill

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308

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Catgut Absorption time

Plain untreated

Mild chromicisation

Medium chromicisation

Prolonged chromicisation

10 days14 days21 days40 days

'Memory' of three differentabsorbable suture materials:(top) polyglactin 910(Vicryl) - low memory;(middle) poliglecaprone 25(Monocryl) - higher memorythan polyglactin but stilleasy to handle;(bottom) polydioxanone(PDS II) - high memory,hence knots must be tiedcarefully

vascularity and infection. There is always a mild tosevere inflammatory response to surgical gut and moreso in cats than in dogs. Large diameter gut can act as anidus for infection when placed in contaminated sites.

Because phagocytosis is important in its absorption,gut tends to lose its tensile strength rapidly and in a non-predictable fashion. Chromicisation reduces soft tissuereaction to the gut - thus, chromic gut maintains its ten-sile strength for longer than plain gut.

Catgut handles well as a material in moderate gaugesbut knots which may be secure when dry have a tenden-cy to swell and untie when wet. It is therefore importantalways to place at least three throws on a knot (see tableson page 316). Catgut also has a tendency to fracturewhen knots are tied.

Polyglycolic acidPolyglycolic acid (PGA; Dexon, Dexon II) is a braidedmultifilament suture which is absorbed by hydrolysis.Dexon II has a polycaprolate coating which improvesits handling characteristics, particularly when wet.Although initially very strong, PGA rapidly loses itsstrength (ie, 33 per cent loss in seven days and 80 percent within 14 days), particularly in an alkaline environ-ment. It is completely absorbed within 120 days andassociated with a markedly reduced inflammatoryresponse compared with catgut. PGA is well tolerated inboth clean and infected wounds. Its disadvantagesinclude its tendency to drag through tissue and, possibly,poorer knot security in comparison with catgut.

Polyglactin 910Polyglactin 910 (Vicryl), a braided suture which is coat-ed to improve its handling and knotting characteristics, ismore resistant to hydrolysis than PGA. Vicryl loses 50per cent of its strength by about two weeks and is totallyabsorbed within 60 to 90 days. Polyglactin sutures arewell tolerated in many different wound conditions, havean excellent size to strength ratio, are relatively easy tohandle, stable in contaminated wounds and elicit mini-mal tissue reaction.

Changes to the manufacturing process produce VicrylRapide, a braided material which provides approximate-ly 66 per cent of the initial tensile strength of coatedVicryl. It loses 50 per cent of its strength by five dayspost-implantation and all tensile strength is lost between10 and 14 days. Absorption by hydrolysis is essentiallycomplete within 42 days. When used in the skin, VicrylRapide typically falls off in seven to 10 days or can bewiped off, thus negating the need for suture removal.

PolydioxanonePolydioxanone (PDS) is a monofilament suture that, likePGA and polyglactin 910, is degraded by hydrolysis, butat a slower rate. It loses 26 per cent of its tensile strengthafter 14 days, 50 per cent after 28 days and 86 per centafter 56 days. Absorption is complete at 182 days after

implantation. PDS is very strong and causes little tissuereaction and less tissue drag than multifilament suturematerials. Improvements have been made in its handlingcharacteristics (PDS II), but care is required when tyingknots because of its high memory.

PolyglyconatePolyglyconate (Maxon) is a monofilament suture materi-al with similar tensile strength to PDS. It also loses itsstrength in a similar fashion: ie, 19 per cent after 14days, 41 per cent after 28 days and 70 per cent after 42days. It is absorbed by macrophages between six andseven months after implantation.

Tissue reaction elicited by a variety ofdifferent absorbable suture materials.Pictures reproduced, with permission, fromEthicon

Polyglactin 910, day 14. There is minimaltissue reaction around the suture

Chromic catgut, day 7. The suture issurrounded by a wide zone of active tissuereaction

Polydioxanone, day 7. The area of tissuereaction is minimal

Chromic catgut, day 28. There is continuedactive cellular tissue reaction

Polydioxanone, day 28. The suture issurrounded by a narrow mature zone oftissue reaction

In Practice * J UNE 1999 3

I311

Poliglecaprone 25Poliglecaprone 25 (Monocryl) is a relatively newmonofilament suture that is prepared from a copolymerof glycolide and E-caprolactone. Dyed and undyedforms are available. Progressive loss of tensile strengthand eventual absorption occurs by means of hydrolysis,with the dyed form losing all its original strength by 21days post-implantation and the undyed form by 28 days.Poliglecaprone elicits a minimal inflammatory reactionin tissues, is easy to handle (having lower memory thanthe other monofilament synthetic absorbables) and hasgood knot security.

NON-ABSORBABLE SUTURES

Non-absorbable suture materials are not degraded duringthe healing process although they do become encapsulat-ed with fibrous tissue and remain permanently within thetissue unless they are extruded or removed. They aredesigned for use where prolonged mechanical support isrequired until sufficient healing has occurred to maintaintissue apposition.

Non-reactive non-absorbables can be buried withintissues or organs to support slow healing tissues. Theydo not need to be removed as they are generally welltolerated by the body.

SilkSilk is available as a braided multifilament suture mater-ial (Mersilk), which may be coated to decrease its natur-al capillarity. Although classified as a non-absorbable, itslowly loses tensile strength and is absorbed withinapproximately two years of implantation.

Silk is inexpensive and has excellent handling charac-teristics. However, it causes marked tissue reaction and

MonofilamentSynthetics

Nylon 66 and nylon 6(Ethilon; Ethicon)(Dermalon; Davis & Geck)

Polypropylene(Prolene; Ethicon)

Polybutester(Novafil; Davis & Geck)

Stainless steel

Multifilament

Polyester(Mersilene; Ethicon)

Nylon(Surgilon; Davis & Geck)(Supramid; Bayer)

Stainless steel

Poliglecaprone 25(Monocryl) in rapid dispensepackaging

parenchymatous organs, and for cutaneous skin incisionsand skin grafts. The cyanoacrylates have been used most

extensively. Tissue toxicity can be a problem, as can

granuloma formation, wound infections when used in

contaminated sites, delayed healing if the wound edgesare separated, and poor adhesion on excessively moistsurfaces.

In Practice * J U N E 1 999

is inferior to many other suture materials in strength andknot security. Silk should not be used in the liningepithelium of hollow viscera and should be avoided incontaminated wounds.

NylonNylon is available as both a monofilament (Ethilon,Dermalon) and multifilament (Surgilon, Supramid)suture material. It causes minimal tissue reaction and,when used in veterinary work, is regarded as permanent(although it loses 30 per cent of its original tensilestrength by two years as a result of slow hydrolysis).

The main disadvantages of nylon are its poorhandling characteristics and knot security. The braidedforms handle and knot better but suffer from inherentcapillarity. Nylon should not be used within serosa orsynovial cavities because buried sharp ends may causeirritation.

PolyesterPolyester (Mersilene) is a braided multifilament suturematerial available in plain and coated forms. It isextremely strong and offers prolonged support for slowhealing tissues. It has poor knot security and causes themost tissue reaction of any of the synthetic suturematerials.

PolypropylenePolypropylene (Prolene) is a monofilament suture thathas a lower tensile strength than nylon. It retains itsstrength on implantation, is not weakened by tissueenzymes and is the least thrombogenic suture. It is there-fore frequently used in vascular surgery. Its disadvan-tages are its high memory and poor knot holding ability.

PolybutesterPolybutester (Novafil) is a special type of polyestersuture which possesses many of the advantages of bothpolypropylene and polyester. It has good tensile strengthand knot security.

Stainless steelStainless steel is available as a monofilament or multifil-ament suture. It is biologically inert, non-capillary andhas the highest tensile strength of all the suture materi-als. Its main use is in tendon and ligament repair.

The disadvantages of stainless steel include itstendency to cut tissues, its poor handling characteristics(especially in knot tying) and relatively poor ability to

withstand repeated bending without breaking.

OTHER OPTIONS FOR TISSUE APPOSITION/LGATION

Tissue adhesivesTissue adhesives have been used experimentally andclinically in the management of comeal lacerations, inthe control of haemorrhage from the cut surface of

*iI]0wl il-4*1 AFViNatural fibres*

Silk(Mersilk; Ethicon)

Linen

* All are multifilament

312

Skin stapler being used toclose a wound on the distallimb of a dog

Use of skin staples toallow rapid closure of alarge wound on the trunkof a dog

Surgical staplingStapling provides a quick and effective alternative tomanual suturing in certain circumstances (eg, for gastro-intestinal anastomosis, skin apposition and pulmonary,cardiovascular and hepatic resections). Many staplinginstruments place a staggered double row of stainlesssteel staples, each staple having a 'B' configuration.Skin staples, however, are rectangular-shaped and placedin a single row.

The advantages of surgical stapling include improvedefficiency, consistency of application and haemostaticsecurity, and ease of use in areas of difficult accessi-bility. Care should be taken to ensure that the amountof tissue to be stapled is not excessive. The stapled areashould be carefully inspected to check that there hasbeen no mechanical failure of the stapling device.

Ligating clipsLigating clips can be used for a variety of surgicalprocedures, including neutering, splenectomy andintestinal resection. They are quick and easy to apply,and are particularly useful in areas of limited accessi-bility. They are, however, limited to use on vessels

that are less than 11 mm in diameter.Both metallic and absorbable clips are available.

Metallic clips (tantalum, stainless steel and titanium) arewidely used, V-shaped and produce minimal reaction intissues. Absorbable clips (polyglactin 910 and PDS)have an integral locking mechanism to prevent reopen-ing; this adds to the bulk of the clip.

SUTURE SELECTION

Suture selection involves the choice of both the appro-priate type (see table below) and size of suture material.Use of too large a suture results in excessive foreignmaterial in the wound and needlessly alters the architec-ture of the sutured tissue.

Sutures are usually gauged using the metric systemwhich measures suture diameter in multiples of 0 1 mm(ie, 3 metric = 0 3 mm diameter). The older USPsystem also still persists, in which sutures are graded inincreasing diameter from the finest 0000000000 (usuallywritten '10-0') up to 0, then 1, 2, 3 on up to a maximumof 7.

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Skin Monofilament - nylon or polypropylene. Avoidsutures that are capillary or reactive

Subcutis Synthetic absorbables

Fascia

Muscle

Synthetic non-absorbables

Synthetic absorbables or non-absorbables

Hollow viscus Synthetic absorbables. Avoid multifilamentnon-absorbables

Tendon Nylon or stainless steel. Polydioxanone andpolyglyconate may also be effective

Blood vessel Polypropylene

NerveLigating clip applicator

In Practice * J U N E 1 9 9 9

Nylon or polypropylene

313

A ide y of swaged-on ( s edles are availablefor th sure materials derid Thi mnai;n advantagesarett:litum-a is. casdhnring the suturethreuhtets,adtea ovnett s,ec uro-ee with a new, sarned. If an eyed nee

iSC D.sased, the,.sut.re,should nee Xe knte or. tied to theES:

: this il rult otetauma.

KNOTS

The surgical suture has three components:* The loop - the suture material within thligated tissue;* The knot - composed of a number of throvthe wrapping of two strands of suture arounde The ears - the cut ends of the suture,against the loop untying due to knot slippage

The basic surgical knot is a square knotwo throws in which the ear and the loopthe same side of the knot (see below). Ithand tied or instrument tied. (When tying, itto avoid creating a granny knot whichOccasionally, when suturing elastic tissue oitension, the two free strands of the suturaround each other twice before the knotproduce the so-called 'surgeon's knot'. Thethis in such situations is that it reduces thfirst throw unwrapping before a second thr4The disadvantage of the surgeon's knot is tiand uneven and may damage monofilament

Though knots should be snug, they shoulso that the suture loop is shortened, as this

Square knot

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mise vascular supply, enhance infection and delay heal-ing. It may also be uncomfortable for the patient andlead to self-trauma. There will almost invariably be a

e apposed or degree of inflammation and oedema and this should beallowed for by the suture loop; the suture should lie flat

ws (a throw is on the tissue but, if lifted, there should be a gap betweeneach other); the suture loop and the tissue. The aim when suturingwhich guard soft tissues is to achieve gentle apposition of the wounde. edges. Once tied, knots should be placed on one side ofxt, formed by the incision so as to minimise interference with healing.come out oncan be either Knot securityt is important The knot is the weakest part of the suture. Knot failureis weaker.) can lead to a variety of surgical disasters, such as evis-

r tissue under ceration or exsanguination.e are passed If overloaded, sutures may break or unravel at theis closed, to knot. The breaking strength of a suture loop is equal toadvantage of the sum of the breaking strength of the straight strand ande risk of the the knotted strand. To overcome the risk of suture break-ow is placed. down, it is important to place enough sutures of slightlyiat it is bulky greater strength than the holding power of the tissue.materials. If only two throws are used the majority of knots willld not be tied slip - this is a particular problem with monofilamentmay compro- materials, such as polypropylene, which have a high

memory as there is a tendency for knots to unravel. Theminimum number of throws required for a snug knot isshown in the table below. If continuous suture patternsare used (eg, simple continuous or Ford interlocking), itis essential that the knots are tied with extra throws foradditional security (see bottom table).

Granny knot

Surgeon's knot

(above) Surgical knots. (below left) Basic surgical or square knot. (below right) Surgeon'sknot, consisting of a double throw initially, followed by a single throw

Number of throws

Chromic gut 3

Polyglactin 910 3

Polyglycolic acid 3

Polypropylene 3

Poliglecaprone 25 4

Polydioxanone 4

Monofilament nylon 4

Start Finish

Chromic gut

Polyglactin 910

Polyglycolic acid

Polypropylene

Polydioxanone

Monofilament nylon

In Practice * J UNE 1 999

4

3

3

3

5

5

6

5

5

7

6

316

CHOICE OF SUTURE PATTERN

SkinLike many other tissues, skin heals most rapidly whenrepaired with appositional patterns which allow epider-mis to heal directly across to epidermis. Hence patternssuch as simple interrupted, continuous intradermal (sub-cuticular), simple continuous and Ford interlocking areappropriate, while everting or inverting patterns delayrepair. The aim shouldl he to gently appose the skinedges. with no overlapping or gaping of the woundedges. In the case of simple interrupted sutures, the indi-vidual sutures should be placed squarely across thewound. at least 5 mm t'rom the wound edge and at anlinterval of 5 mm to produce maximum wound strength;sutures placed closer- thani this only add to the amount ot'foreign material present in the tissues.

Gastrointestinal tractDespite a tendency in the past to use inverting suturepatterns (eg. Cushing. Lembert. Halsted or Connell) forthe repair of gastrointestinal structures, a more rationalapproach achieves appositional reconstruction of theintestinal wall using simple interrupted or simple contin-uous patterns. In the intestine, the suture-retaining layerof the wall has been shown to be the submucosa and asuture pattern which includes this layer should be used.Synthetic absorbables are most frequently selected forthis purpose because of their comparatively long reten-tion of tensile strength and reduced tissue response.Repair- of the oesophagus should also be based on appo-sitional patterns which include the submucosa, althougha second layer through the outer adventitia or musclemay be used. In the past, two-layer invertinT patternsweere used for repair of the bladder, but recent studieshave shown that single or double layer appositionalsutures provide equal resistance to bursting of the viscusand may allow more rapid healing.

Laparotomy incisionsSuture patterns selected for the repair- of laparotomiesshould make use of the suture-retaining layer, which isthe tough linea alba oI the external rectus fascia awayfi-om the midline. Closure of the peritoneum or rectusand oblique muscle layers is unnecessar-y and maycontribute to ischaemia in these layers and, possibly.increase the risk of abdominal adhesions. Syntheticabsorbables are preferred to natural absorbables andretain sufficient tensile strength for per-miianent materials(monofilament nylon or polypropylene) not to offer anysignificant advantage here.

Simple interrupted suturesof polyglactin 910 (Vicryl)being used followingresection of a urethralprolapse

N-

Skin closure on a cat's limb using a combination of simpleinterrupted sutures and tension-relieving sutures

Ford interlocking suturepattern for rapidappositional closure ofa laparotomy wound

In Practice * JUNE 1999

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Suture patterns* INTERRUPTED. Each suture has a separate knot.Sutures are easily inserted and removed and tensionmay be readily adjusted. Failure of one suture isinconsequential

* CONTINUOUS. These patterns comprise a row ofsutures with a knot present only at each end. Theyare quick to insert and provide even tension alongthe incision with a minimum amount of sutureplaced in the tissue. They are an acceptable alterna-tive to simple interrupted sutures, especially forlong wounds (eg, closure of a midline laparotomyincision). Suture breakage, however, may lead todisruption of the entire line of closure

* MATTRESS. These are tension patterns, allowingfaster closure than a simple pattern, but tend tointerfere with healing due to incorporation of tissueon each side of the wound and potential vascularcompromise- Horizontal mattress patterns cause eversion of thewound edges. Sutures may be difficult to remove dueto burying in the skin- Vertical mattress patterns involve the placement ofsutures at a distance from the wound margin. Thesesutures have less tendency to reduce circulation atthe wound edges than horizontal mattress sutures,and can be used together with simple interruptedsutures for skin apposition

* APPOSITIONAL. Sutures bring wound edges together

* INVERTING. Sutures turn wound edges inwards

S EVERTING. Sutures turn wound edges outwards

* PURSE STRING. Sutures are used to close a circulardefect or reduce the size of an orifice

Appositional sutures (a-f)

(a) Simple interrupted (b) Gambee

(e) Continuousintradermalor subcuticular

Tension sutures (g-k)

(g) Vertical mattress

(h) Horizontal mattress (i) Continuoushorizontal mattress

(j) Far-far-near-near (k) Far-near-near-far

Inverting sutures (I-o)

(I) Lembert (m) HaistedCan be used in interrupted A variation of Lembertor continuous patterns

In Practice C JUNE 1999

(n) CushingPenetrates the submucosabut not the lumen.Provides less inversion thanLembert

(o) ConnellSimilar to Cushing except penetratesbowel lumen

319

Closure of the linea alba with a simple continuous suture ofpolydioxanone (PDS 11)

The choice of a simple or continuous pattern forlaparotomy repair is still somewhat controversial, withconcern about the risk of dehiscence swaying somesurgeons' choice towards an interrupted pattern.Nevertheless, with modern synthetic absorbable materi-als and an adequate number of throws at each end of thesuture (a minimum of six for monofilament materials), asimple continuous pattern is perfectly safe. Furthermore,significantly less suture material is left in the wound andthe tissue response is minimised.

Contaminated and infected woundsThe overriding concern when dealing with contaminatedor infected wounds is the risk of bacterial adherencewithin the suture material. Braided or multifilamentmaterials are notoriously prone to the persistence ofbacteria within the interstices of the fibres, where theyare resistant to removal by the macrophages. In the pres-ence of contamination or established sepsis, the surgeonis therefore wise to choose either a monofilament materi-al, which is more resistant to bacterial adherence, or anabsorbable material, which will be removed from thewound together with any associated bacteria. It shouldbe noted, however, that other factors may influence thepersistence of bacteria in a suture material; in particular,the size of the knot and amount of suture materialrequired when using monofilament materials may beresponsible for the formation of sinuses.

SUTURE REMOVAL

Sutures are generally removed after seven to 10 days,even though at this time the skin bursting strength isonly 10 to 20 per cent of normal. Such early sutureremoval minimises the inflammatory and infectiousprocesses which are encouraged by sutures. There arerarely any problems with wound dehiscence as most ofthe stresses are taken up by the underlying fascia. Iftension appears to be a problem, it may be better to leavethe sutures in place for 14 to 21 days. Where tensionsutures have been interspersed between appositionalsutures, they are usually removed after three to five days.

In Practice * JUNE 1999

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