Surgical stapling provides a quick and effective alternative to manual suturing in certain circumstances, such as for skin apposition
Suture materials and patterns
JACQUI NILES AND JOHN WILLIAMS
SUTURES are used either for apposing tissues or for ligation, and a variety of different types of suture material is currently available. Suture selection should be based on knowledge of the physical and biological properties of suture materials, an assessment of the healing rate of a particular tissue and local conditions in the wound. The ideal properties of a suture material have yet to be fulfilled by any single product on the market. The purpose of this article is to outline the properties of the available suture materials and to give an indication of when and how to use them. Jacqui Niles qualified from the Royal Veterinary College, London, in 1993. She is a resident in small animal soft tissue surgery at Liverpool University and holds the RCVS certificate in small animal surgery. Her special interests include all aspects of soft tissue surgery, especially the surgical management of portosystemic shunts and chylothorax.
John Williams qualified from Cambridge University in 1984. He holds the certificate in veterinary radiology, and an FRCVS, and is a diplomate of the European College of Veterinary Surgeons. He is currently director of small animal studies at Liverpool University and is an RCVS Specialist in Small Animal Surgery (Soft Tissue). His clinical interests lie in portosystemic shunts, and reconstructive and cardiorespiratory surgery.
CLASSIFICATION OF SUTURE MATERIALS Suture materials are broadly clcassified as absorbable or non-absorbable. They can be further classified as synthetic or natural fibre and they may be multifilament or monofilament, coated or uncoated.
ABSORBABLE SUTURES
191 :I 41,71 f-Ill
Natural fibres*
Monofilament
Surgical gut Plain Chromic
Synthetics Multifilament
Polydioxanone (PDS; Ethicon) (PDS Il; Ethicon)
Polyglycolic acid (Dexon; Davis & Geck) (Dexon Il; Davis & Geck)
Polyglyconate (Maxon; Davis & Geck)
Polyglactin 910 (Vicryl; Ethicon) (Vicryl Rapide; Ethicon)
Poliglecaprone 25 (Monocryl; Ethicon)
All absorbable sutures Lindergco degradation in the tissue * All are multifilament but fused, so that they are essentially and lose their tensile strength within 60 days. They are monofilament absorbed by mieans of the body's defence system and all will therefore produce so5ic tissuc rcaction. Absorbable sutures are principally designed for use in closint Surgical gut internal tissue layers or organs which do not require long Surgical gut (catgut) is prepared from the submucosa of term support. There arc some exceptions to this - the sheep or cattle small intestine. After implantation, gut is newer synthetic monofilaiment absorbables, such as absorbed by a combination of enzymatic degradation and polydioxanone (PDS 11) and polyglyconate (Maxon), phagocytosis; the rate of absorption is thus affected by are designed to provide p I :I :0 Y, Y-IltI extended wound support. It is that all remember important to Breaking strength per unit area Tensile strength absorbable sutures will lose Related to surface frictional characteristics Knot security their tensile strength before they are absorbed. The property to unkink after loops have been formed during the Memory development of a knot. Suture materials with a high memory There has been a trend (eg, polypropylene) tend to revert to their package shape towards using absorbable Lack of smoothness when sliding down a knot or friction while Chatter/tissue drag sutures in infected surgical passing through tissue sites as they will rarely provide Tissues respond to the implantation of sutures as they do to other Tissue reaction a nidus for further infection. foreign material. Sutures can evoke an acute or chronic inflammatory However, enzymatic processresponse es may, in fact, increase the and Tendency to wick, allowing fluid and infection to move along the degradation process and make Capillarity resistance to infection suture the suture unreliable. 308
In Practice * J U N E 1 999
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Catgut
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'Memory' of three different absorbable suture materials:
I
(top) polyglactin 910 (Vicryl) - low memory; (middle) poliglecaprone 25 (Monocryl) - higher memory than polyglactin but still easy to handle; (bottom) polydioxanone (PDS II) - high memory, hence knots must be tied carefully
Absorption time
Plain untreated
10 days
Mild chromicisation
14 days
Medium chromicisation Prolonged chromicisation
40 days
21 days
vascularity and infection. There is always a mild to severe inflammatory response to surgical gut and more so in cats than in dogs. Large diameter gut can act as a nidus 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 nonpredictable fashion. Chromicisation reduces soft tissue reaction to the gut - thus, chromic gut maintains its tensile strength for longer than plain gut. Catgut handles well as a material in moderate gauges but knots which may be secure when dry have a tendency to swell and untie when wet. It is therefore important always to place at least three throws on a knot (see tables on page 316). Catgut also has a tendency to fracture when knots are tied. Polyglycolic acid Polyglycolic acid (PGA; Dexon, Dexon II) is a braided multifilament suture which is absorbed by hydrolysis. Dexon II has a polycaprolate coating which improves its handling characteristics, particularly when wet. Although initially very strong, PGA rapidly loses its strength (ie, 33 per cent loss in seven days and 80 per cent within 14 days), particularly in an alkaline environment. It is completely absorbed within 120 days and associated with a markedly reduced inflammatory response compared with catgut. PGA is well tolerated in both clean and infected wounds. Its disadvantages include its tendency to drag through tissue and, possibly, poorer knot security in comparison with catgut.
implantation. PDS is very strong and causes little tissue reaction and less tissue drag than multifilament suture materials. Improvements have been made in its handling characteristics (PDS II), but care is required when tying knots because of its high memory. Polyglyconate Polyglyconate (Maxon) is a monofilament suture material with similar tensile strength to PDS. It also loses its strength in a similar fashion: ie, 19 per cent after 14 days, 41 per cent after 28 days and 70 per cent after 42 days. It is absorbed by macrophages between six and seven months after implantation.
Tissue reaction elicited by a variety of different absorbable suture materials. Pictures reproduced, with permission, from Ethicon
Polyglactin 910 Polyglactin 910, day 14. There is minimal Polyglactin 910 (Vicryl), a braided suture which is coat- tissue reaction around the suture ed to improve its handling and knotting characteristics, is more resistant to hydrolysis than PGA. Vicryl loses 50 per cent of its strength by about two weeks and is totally absorbed within 60 to 90 days. Polyglactin sutures are well tolerated in many different wound conditions, have an excellent size to strength ratio, are relatively easy to handle, stable in contaminated wounds and elicit minimal tissue reaction. Changes to the manufacturing process produce Vicryl Rapide, a braided material which provides approximateChromic catgut, day 7. The suture is ly 66 per cent of the initial tensile strength of coated surrounded by a wide zone of active tissue Vicryl. It loses 50 per cent of its strength by five days reaction post-implantation and all tensile strength is lost between 10 and 14 days. Absorption by hydrolysis is essentially complete within 42 days. When used in the skin, Vicryl Rapide typically falls off in seven to 10 days or can be wiped off, thus negating the need for suture removal.
Polydioxanone Polydioxanone (PDS) is a monofilament suture that, like PGA and polyglactin 910, is degraded by hydrolysis, but at a slower rate. It loses 26 per cent of its tensile strength after 14 days, 50 per cent after 28 days and 86 per cent after 56 days. Absorption is complete at 182 days after In Practice * J UNE 1999
Polydioxanone, day 7. The area of tissue
reaction is minimal
Chromic catgut, day 28. There is continued active cellular tissue reaction
I
Polydioxanone, day 28. The suture is surrounded by a narrow mature zone of tissue reaction 3311
is inferior to many other suture materials in strength and knot security. Silk should not be used in the lining epithelium of hollow viscera and should be avoided in contaminated wounds.
Poliglecaprone 25 (Monocryl) in rapid dispense packaging
Poliglecaprone 25 Poliglecaprone 25 (Monocryl) is a relatively new monofilament suture that is prepared from a copolymer of glycolide and E-caprolactone. Dyed and undyed forms are available. Progressive loss of tensile strength and eventual absorption occurs by means of hydrolysis, with the dyed form losing all its original strength by 21 days post-implantation and the undyed form by 28 days. Poliglecaprone elicits a minimal inflammatory reaction in tissues, is easy to handle (having lower memory than the other monofilament synthetic absorbables) and has good knot security.
NON-ABSORBABLE SUTURES Non-absorbable suture materials are not degraded during the healing process although they do become encapsulated with fibrous tissue and remain permanently within the tissue unless they are extruded or removed. They are designed for use where prolonged mechanical support is required until sufficient healing has occurred to maintain tissue apposition. Non-reactive non-absorbables can be buried within tissues or organs to support slow healing tissues. They do not need to be removed as they are generally well tolerated by the body. Silk Silk is available as a braided multifilament suture material (Mersilk), which may be coated to decrease its natural capillarity. Although classified as a non-absorbable, it slowly loses tensile strength and is absorbed within approximately two years of implantation. Silk is inexpensive and has excellent handling characteristics. However, it causes marked tissue reaction and
Nylon Nylon 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 tensile strength by two years as a result of slow hydrolysis). The main disadvantages of nylon are its poor handling characteristics and knot security. The braided forms handle and knot better but suffer from inherent capillarity. Nylon should not be used within serosa or synovial cavities because buried sharp ends may cause
irritation. Polyester Polyester (Mersilene) is a braided multifilament suture material available in plain and coated forms. It is extremely strong and offers prolonged support for slow healing tissues. It has poor knot security and causes the most tissue reaction of any of the synthetic suture materials.
Polypropylene Polypropylene (Prolene) is a monofilament suture that has a lower tensile strength than nylon. It retains its strength on implantation, is not weakened by tissue enzymes and is the least thrombogenic suture. It is therefore frequently used in vascular surgery. Its disadvantages are its high memory and poor knot holding ability.
Polybutester Polybutester (Novafil) is a special type of polyester suture which possesses many of the advantages of both polypropylene and polyester. It has good tensile strength and knot security. Stainless steel Stainless steel is available as a monofilament or multifilament suture. It is biologically inert, non-capillary and has the highest tensile strength of all the suture materials. Its main use is in tendon and ligament repair. The disadvantages of stainless steel include its tendency to cut tissues, its poor handling characteristics (especially in knot tying) and relatively poor ability to withstand repeated bending without breaking. OTHER
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AFVi Synthetics
Natural fibres* Silk (Mersilk; Ethicon)
Monofilament
Multifilament
Nylon 66 and nylon 6 (Ethilon; Ethicon) (Dermalon; Davis & Geck)
Polyester (Mersilene; Ethicon)
Linen
Polypropylene (Prolene; Ethicon)
Polybutester (Novafil; Davis & Geck) Stainless steel *
OPTIONS FOR TISSUE APPOSITION/
LGATION
All are multifilament
Nylon (Surgilon; Davis & Geck) (Supramid; Bayer) Stainless steel
Tissue adhesives Tissue adhesives have been used experimentally and clinically in the management of comeal lacerations, in the control of haemorrhage from the cut surface of parenchymatous organs, and for cutaneous skin incisions and 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 edges are separated, and poor adhesion on excessively moist
surfaces. 312
In Practice * J U N E 1 999
Skin stapler being used to close a wound on the distal limb of a dog
Use of skin staples to allow rapid closure of a large wound on the trunk of a dog
Surgical stapling Stapling provides a quick and effective alternative to manual suturing in certain circumstances (eg, for gastrointestinal anastomosis, skin apposition and pulmonary, cardiovascular and hepatic resections). Many stapling instruments place a staggered double row of stainless steel staples, each staple having a 'B' configuration. Skin staples, however, are rectangular-shaped and placed in a single row. The advantages of surgical stapling include improved efficiency, consistency of application and haemostatic security, and ease of use in areas of difficult accessibility. Care should be taken to ensure that the amount of tissue to be stapled is not excessive. The stapled area should be carefully inspected to check that there has been no mechanical failure of the stapling device. Ligating clips Ligating clips can be used for a variety of surgical procedures, including neutering, splenectomy and intestinal resection. They are quick and easy to apply, and are particularly useful in areas of limited accessibility. 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) are widely used, V-shaped and produce minimal reaction in tissues. Absorbable clips (polyglactin 910 and PDS) have an integral locking mechanism to prevent reopening; this adds to the bulk of the clip.
SUTURE SELECTION Suture selection involves the choice of both the appropriate type (see table below) and size of suture material. Use of too large a suture results in excessive foreign material in the wound and needlessly alters the architecture of the sutured tissue. Sutures are usually gauged using the metric system which measures suture diameter in multiples of 0 1 mm (ie, 3 metric = 0 3 mm diameter). The older USP system also still persists, in which sutures are graded in increasing diameter from the finest 0000000000 (usually written '10-0') up to 0, then 1, 2, 3 on up to a maximum of 7.
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Skin
Monofilament - nylon or polypropylene. Avoid sutures that are capillary or reactive
Subcutis
Synthetic absorbables
Fascia
Synthetic non-absorbables
Muscle
Synthetic absorbables or non-absorbables
Hollow viscus
Synthetic absorbables. Avoid multifilament non-absorbables
Tendon
Nylon or stainless steel. Polydioxanone and polyglyconate may also be effective
Blood vessel
Polypropylene
Nerve
Nylon or polypropylene
Ligating clip applicator
In Practice * J U N E 1 9 9 9
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KNOTS The surgical suture has three components: * The loop - the suture material within the apposed or ligated tissue; * The knot - composed of a number of throvws (a throw is the wrapping of two strands of suture around each other); e The ears - the cut ends of the suture, which guard against the loop untying due to knot slippagee. The basic surgical knot is a square knoxt, formed by two throws in which the ear and the loop come out on the same side of the knot (see below). It can be either hand tied or instrument tied. (When tying, itt is important to avoid creating a granny knot which is weaker.) Occasionally, when suturing elastic tissue oir tissue under tension, the two free strands of the suture are passed around each other twice before the knot is closed, to produce the so-called 'surgeon's knot'. The advantage of this in such situations is that it reduces th e risk of the first throw unwrapping before a second thr4ow is placed. The disadvantage of the surgeon's knot is tiiat it is bulky and uneven and may damage monofilament materials. Though knots should be snug, they shoulld not be tied so that the suture loop is shortened, as this may compro-
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mise vascular supply, enhance infection and delay healing. It may also be uncomfortable for the patient and lead to self-trauma. There will almost invariably be a degree of inflammation and oedema and this should be allowed for by the suture loop; the suture should lie flat on the tissue but, if lifted, there should be a gap between the suture loop and the tissue. The aim when suturing soft tissues is to achieve gentle apposition of the wound edges. Once tied, knots should be placed on one side of the incision so as to minimise interference with healing. Knot security The knot is the weakest part of the suture. Knot failure can lead to a variety of surgical disasters, such as evisceration or exsanguination. If overloaded, sutures may break or unravel at the knot. The breaking strength of a suture loop is equal to the sum of the breaking strength of the straight strand and the knotted strand. To overcome the risk of suture breakdown, it is important to place enough sutures of slightly greater strength than the holding power of the tissue. If only two throws are used the majority of knots will slip - this is a particular problem with monofilament materials, such as polypropylene, which have a high memory as there is a tendency for knots to unravel. The minimum number of throws required for a snug knot is shown in the table below. If continuous suture patterns are used (eg, simple continuous or Ford interlocking), it is essential that the knots are tied with extra throws for additional security (see bottom table).
Granny knot
Square knot
Number of throws
Surgeon's knot
(above) Surgical knots. (below left) Basic surgical or square knot. (below right) Surgeon's knot, consisting of a double throw initially, followed by a single throw
Chromic gut Polyglactin 910
3
Polyglycolic acid Polypropylene Poliglecaprone 25 Polydioxanone Monofilament nylon
3
3
3 4 4
4
Start
316
Finish
Chromic gut Polyglactin 910
4
5
3
Polyglycolic acid Polypropylene Polydioxanone Monofilament nylon
3
6 5
3
5
5
7
6
In Practice * J UNE 1 999
CHOICE OF SUTURE PATTERN Skin Like many other tissues, skin heals most rapidly when repaired with appositional patterns which allow epidermis to heal directly across to epidermis. Hence patterns such as simple interrupted, continuous intradermal (subcuticular), simple continuous and Ford interlocking are appropriate, while everting or inverting patterns delay repair. The aim shouldl he to gently appose the skin edges. with no overlapping or gaping of the wound edges. In the case of simple interrupted sutures, the individual sutures should be placed squarely across the wound. at least 5 mm t'rom the wound edge and at anl interval 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.
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Gastrointestinal tract Despite a tendency in the past to use inverting suture patterns (eg. Cushing. Lembert. Halsted or Connell) for the repair of gastrointestinal structures, a more rational approach achieves appositional reconstruction of the intestinal wall using simple interrupted or simple continuous patterns. In the intestine, the suture-retaining layer of the wall has been shown to be the submucosa and a suture pattern which includes this layer should be used. Synthetic absorbables are most frequently selected for this purpose because of their comparatively long retention of tensile strength and reduced tissue response. Repair- of the oesophagus should also be based on appositional patterns which include the submucosa, although a second layer through the outer adventitia or muscle may be used. In the past, two-layer invertinT patterns weere used for repair of the bladder, but recent studies have shown that single or double layer appositional sutures provide equal resistance to bursting of the viscus and may allow more rapid healing. Laparotomy incisions Suture patterns selected for the repair- of laparotomies should make use of the suture-retaining layer, which is the tough linea alba oI the external rectus fascia away fi-om the midline. Closure of the peritoneum or rectus and oblique muscle layers is unnecessar-y and may contribute to ischaemia in these layers and, possibly. increase the risk of abdominal adhesions. Synthetic absorbables are preferred to natural absorbables and retain sufficient tensile strength for per-miianent materials (monofilament nylon or polypropylene) not to offer any significant advantage here.
Simple interrupted sutures of polyglactin 910 (Vicryl) being used following resection of a urethral prolapse
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Skin closure on a cat's limb using a combination of simple interrupted sutures and tension-relieving sutures 318
Ford interlocking suture pattern for rapid appositional closure of a laparotomy wound
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In Practice * JUNE 1999
Suture patterns * INTERRUPTED. Each suture has a separate knot. Sutures are easily inserted and removed and tension may be readily adjusted. Failure of one suture is inconsequential
Appositional sutures (a-f)
* CONTINUOUS. These patterns comprise a row of sutures with a knot present only at each end. They are quick to insert and provide even tension along the incision with a minimum amount of suture placed in the tissue. They are an acceptable alternative to simple interrupted sutures, especially for long wounds (eg, closure of a midline laparotomy incision). Suture breakage, however, may lead to disruption of the entire line of closure
(a) Simple interrupted
* MATTRESS. These are tension patterns, allowing faster closure than a simple pattern, but tend to interfere with healing due to incorporation of tissue on each side of the wound and potential vascular compromise - Horizontal mattress patterns cause eversion of the wound edges. Sutures may be difficult to remove due to burying in the skin - Vertical mattress patterns involve the placement of sutures at a distance from the wound margin. These sutures have less tendency to reduce circulation at the wound edges than horizontal mattress sutures, and can be used together with simple interrupted sutures for skin apposition
(b) Gambee
(e) Continuous intradermal or subcuticular
* APPOSITIONAL. Sutures bring wound edges together
Tension sutures (g-k)
* INVERTING. Sutures turn wound edges inwards
S EVERTING. Sutures turn wound edges outwards * PURSE STRING. Sutures are used to close a circular defect or reduce the size of an orifice
(g) Vertical mattress
(h) Horizontal mattress
(j) Far-far-near-near
(i) Continuous horizontal mattress
(k) Far-near-near-far
Inverting sutures (I-o)
(I) Lembert Can be used in interrupted or continuous patterns
In Practice C JUNE 1999
(m) Haisted
(n) Cushing Penetrates the submucosa but not the lumen. Provides less inversion than Lembert
A variation of Lembert
(o) Connell Similar to Cushing except penetrates bowel lumen
319
Contaminated and infected wounds The overriding concern when dealing with contaminated or infected wounds is the risk of bacterial adherence within the suture material. Braided or multifilament materials are notoriously prone to the persistence of bacteria within the interstices of the fibres, where they are resistant to removal by the macrophages. In the presence of contamination or established sepsis, the surgeon is therefore wise to choose either a monofilament material, which is more resistant to bacterial adherence, or an absorbable material, which will be removed from the wound together with any associated bacteria. It should be noted, however, that other factors may influence the persistence of bacteria in a suture material; in particular, the size of the knot and amount of suture material required when using monofilament materials may be responsible for the formation of sinuses. Closure of the linea alba with a simple continuous suture of polydioxanone (PDS 11)
SUTURE REMOVAL
The choice of a simple or continuous pattern for laparotomy repair is still somewhat controversial, with concern about the risk of dehiscence swaying some surgeons' choice towards an interrupted pattern. Nevertheless, with modern synthetic absorbable materials and an adequate number of throws at each end of the suture (a minimum of six for monofilament materials), a simple continuous pattern is perfectly safe. Furthermore, significantly less suture material is left in the wound and the tissue response is minimised.
Sutures are generally removed after seven to 10 days, even though at this time the skin bursting strength is only 10 to 20 per cent of normal. Such early suture removal minimises the inflammatory and infectious processes which are encouraged by sutures. There are rarely any problems with wound dehiscence as most of the stresses are taken up by the underlying fascia. If tension appears to be a problem, it may be better to leave the sutures in place for 14 to 21 days. Where tension sutures have been interspersed between appositional sutures, they are usually removed after three to five days.
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