Suture Material

Vol. 20, No. 2 February 1998

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Refereed Peer Review

FOCAL POINT ★ Suture materials should be chosen with the goal of reducing patient morbidity, not on the basis of personal preference or cost alone.

Selecting Suture Materials for Small Animal Surgery Texas A&M University

Harry W. Boothe, Jr., DVM, MS

KEY FACTS ■ Poliglecaprone 25 has the highest initial tensile strength of absorbable suture materials, and surgical gut has the lowest. ■ Synthetic absorbable monofilament suture materials have advantages over multifilament absorbable materials. ■ Ending knots of a continuous pattern require at least five throws to be secure (polydioxanone requires seven). ■ Excessively tight sutures increase patient morbidity and decrease wound strength. ■ Minimally reactive suture materials, swaged needles, and smaller suture sizes are preferable to more reactive materials, eyed needles, and larger suture sizes.

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ew information about surgical sutures has made it possible for veterinarians to make better-informed decisions about the selection and use of suture material. Also, veterinarians now have a broader range of materials to choose from. Veterinary surgeons should base their choice of suture material on the characteristics of the material and how it interacts with tissue, not just on personal preferences or cost. This article reviews the characteristics of suture materials and provides guidelines for choosing the suture material that will minimize morbidity and maximize wound healing.

CHARACTERISTICS Several physical properties of suture material are important to surgeons (e.g., initial tensile strength, relative knot security, handling characteristics). Important features of the suture–tissue interaction include tissue reactivity, rate of loss of tensile strength, and degradation mechanism. Physical Properties Tensile Strength Most suture materials are stronger fresh from the package than they will be after having been implanted in tissue. Size for size, poliglecaprone 25 has the highest initial tensile strength of absorbable suture materials and surgical (chromic) gut has the lowest (Table I). Stainless steel is the strongest nonabsorbable suture material, whereas silk is the weakest (Table I). Sutures must be strong enough to withstand disruptive forces across a wound until the wound gains sufficient tensile strength. When choosing the type and size of suture material to use in a wound, the surgeon must choose a material whose physical properties closely match the mechanical properties of the tissue being sutured (Figure 1). Mechanical properties of suture materials and their relationship to those of tissue need further characterization for many species. The mechanical properties of polypropylene and nylon (particularly elongation) are similar to those of skin.1 Table II presents guidelines for selecting the proper size of suture material.2 The properties of suture material (including the reliability of knots) improve as

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The Compendium February 1998

TABLE I A Ranking of the Physical Characteristics of Suture Materials Relative Knot Security Suture Material Absorbable Poliglecaprone 25 Polydioxanone Polyglactin 910 Polyglycolic acid Polyglyconate Surgical gut Nonabsorbable Nylon Polyester Polymerized caprolactum Polypropylene Silk Stainless steel

Initial Tensile Strength

Ranking

Effective Strength (%)

Stiffness

1 3 4 5 2 6

5 2 4 3 1 6

— — — 66 — 63

6 4 1 5 3 2

4 2 3 5 6 1

4 6 3 2 5 1

66 51 79 89 57 92

3 5 4 2 6 1

1 = highest, 6 = lowest.

(there are two throws in a square knot) needed to tie a diameter increases.3 However, larger-diameter sutures secure knot depends on the suture material and the sucause greater tissue reaction.3 The size of material choture pattern5 (Table III). To make a secure knot in an sen usually represents a compromise between maximal 3 interrupted suture pattern takes at least three throws mechanical support and minimal tissue reactivity. when polyglactin 910, polyglycolic acid, surgical gut, or Sometimes, the need for mechanical support (e.g., polypropylene suture material is used but at least four for body-wall closure or tension sutures) is more critical throws when polydioxanone or nylon is used. When than the need to minimize tissue reaction. When one is starting a continuous pattern using polydioxanone, surclosing a body wall with a continuous pattern of gical gut, or nylon, the surgeon should add one throw polypropylene suture, a suture diameter one size larger more than would be needed for an interrupted pattern. than that usually selected is recommended.4 In other The ending knots of a consituations (e.g., closure of tinuous pattern tend to be visceral wounds or subcutathe least secure and require neous tissue), the need to at least five throws—or more minimize tissue reaction if polyglactin 910, nylon, or predominates. polydioxanone is used 5 Because larger-diameter (Table III). suture materials provide For some suture materials more-secure knots, a veterithat were developed recently narian may be tempted to (e.g., poliglecaprone 25 and use excessively large suture polyglyconate) or that have materials routinely. Howevbeen used frequently in veter, veterinarians should reerinary patients (e.g., polysist this temptation because the larger materials cause ex- Figure 1—Relationship between loss of tensile strength by se- merized caprolactum and lected absorbable sutures and gain in strength of various tis- stainless steel), the number cessive tissue reaction. sues as a result of healing (From Bucknall TE, Ellis H: of throws necessary to create Wound Healing for Surgeons. London, Baillière Tindall, 1984, secure knots has not been Knot Security pp 77, 81. Modified with permission.) evaluated. The knot security The number of throws MECHANICAL SUPPORT ■ TISSUE REACTION ■ ENDING KNOTS

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of many suture materials has been evaluated qualitatively. 6,7 All sutures lose strength when knotted; many lose at least a third of their initial tensile strength7 (Table I). Relative knot security expresses knot-holding capacity as a percentage of initial tensile strength (Table I). The effective strength of the suture material depends on both the initial tensile strength and the relative knot security (see Effective Strength of Suture Materials).

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TABLE II Guide for Selecting Suture Size for Small Animal Surgerya Tissue or Use Skin Subcutaneous tissue Muscle Fascia Viscera Ligation of small vessels Ligation of large vessels Tension sutures

Recommended Size 4-0 to 2-0 4-0 to 3-0 3-0 to 2-0 3-0 to 0 5-0 to 3-0 4-0 to 3-0 2-0 to 1 2-0 to 1

aData from Grier RL: Surgical sutures—Part II: Indications for different suture materials and comparable costs. Iowa State Univ Vet 34:89–92, 1972.

tures.8 Silk is so easy to handle that suture materials with excellent pliability are described as “handling like silk.” Poliglecaprone 25, a recently marketed absorbable suture material, has the least stiffness (greatest pliability) of the absorbable sutures9 (Table I). Although handling characteristics may be the decisive factor in the choice of suture material for some surgical procedures, a suture material should never be chosen solely on the basis of its handling characteristics.

Handling Characteristics The handling characteristics of suture materials are an important consideration. Stiffer (i.e., less pliable) suture materials are more difficult to handle.8 When using a stiff suture material, the surgeon must take particular care to ensure that the knots are secure. In general, monofilament sutures are stiffer than multifilament sutures of the same composition, Also, largerdiameter sutures are stiffer than smaller-diameter su-

Suture–Tissue Interaction Suture materials influence patient morbidity primarily through their interaction with tissue. Many factors affect this interaction, including the amount (diameter and length) of suture material in the wound as well as the placement technique. The impact of sutures on the wound is an important consideration in the selection of a suture material. Although much is known about the influence of sutures as foreign material in wounds, little is known about their effect TABLE III on the wound microenvironment. 10 TisNumber of Throws Needed to Create a Secure Knota sue–suture interactions are complex, involvContinuous Pattern ing humoral and cellular factors.11 Interrupted Sutures alter the healing process in conSuture Material Pattern Start End taminated or infected wounds. The presence of any suture in tissue increases the tisAbsorbable sue’s susceptibility to infection. Thus, the Poliglecaprone 25 — — — veterinarian should avoid placing suture in Polydioxanone 4 5 7 a contaminated wound unless it is essential Polyglactin 910 3 3 6 for positioning tissue.12 Polyglycolic acid 3 3 5 Both the physical construction (monofilPolyglyconate — — — ament versus multifilament) and the chemiSurgical gut 3 4 5 cal composition of the suture material affect Nonabsorbable whether a contaminated wound will beNylon 4 5 6 come infected.13–15 Monofilament sutures Polyester — — — withstand contamination better than multiPolymerized caprolactum — — — filament sutures. The number of sutures in Polypropylene 3 3 5 the wound also influences whether a conSilk — — — taminated wound will become infected. SuStainless steel — N/Ab N/Ab ture size and length should be minimized in a For many suture materials, the number of throws needed to create a secure any wound but particularly in a contamiknot has not been established. nated wound. bNot applicable: Stainless steel should not be used in a continuous suture Because of their monofilament construcpattern. tion, polydioxanone, polyglyconate, and RELATIVE KNOT SECURITY ■ PLIABILITY ■ CONTAMINATED WOUNDS

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poliglecaprone 25 are the preferred absorbable suture materials for use in contaminated wounds. Polypropylene and monofilament nylon are the superior nonabsorbable suture materials for a contaminated wound.13

The Compendium February 1998

and tissue reactivity by a factor of approximately 1.5. The effective strength of a suture material depends How tightly the suture on both the initial tensile strength and the relative should be tied depends knot security. The materials listed here are in deon the intended use. Ligatures are tied tightly scending order according to effective strength: to strangulate vessels. 1. Stainless steel 7. Nylon Sutures to approximate wounds should be tied 2. Polymerized caprolactum 8. Polyglactin 910 Tissue Reactivity just tightly enough to 3. Polypropylene 9. Polyglycolic acid Tissue reactivity is unprovide tissue contact 4. Polyglyconate 10. Polyester desirable, particularly without strangulation. 5. Poliglecaprone 25 11. Silk when the sutures are Excessively tight suture 6. Polydioxanone 12. Surgical gut placed near the body surlines increase patient morface. Increased tissue reacbidity and reduce shorttivity probably leads to increased morbidity (e.g., an and long-term strength in fascial wounds.17 intensified or prolonged inflammatory phase of wound Tensile Strength Loss healing or enhanced patient awareness of the wound Although many nonabsorbable suture materials lose and subsequent self-mutilation). Sutures of natural oristrength over time in tissue, such loss of tensile strength gin tend to be more reactive than those of synthetic is usually clinically insignificant. However, absorbable origin. materials lose strength dramatically as they are abSurgical gut stimulates the greatest tissue reactions; sorbed. silk, polymerized caprolactum, and polyester are the When choosing an absorbable material, the veterinarmost reactive nonabsorbable suture materials (Table ian should select one that loses strength at a rate that is IV). Although some surgeons like to use surgical gut appropriate for the healing characteristics of the tissue when strong adhesions are desired at the surgical site being sutured. Materials that lose tensile strength rapid(e.g., perineal herniorrhaphy), surgical gut did not enhance adhesion formation in dogs.16 Tissue reactivity is minimized by use of TABLE IV inert monofilament materials.11 Sutures that Characteristics of Suture–Tissue Interaction stimulate minimal tissue reactivity (e.g., Rate of Tensile polypropylene, nylon, stainless steel, polyTissue Reactivity Strength Loss Degradation dioxanone, polyglyconate, polyglactin 910, Suture Material (Rank) (Rank) Pattern polyglycolic acid, or poliglecaprone 25) are preferable to more-reactive sutures (e.g., Absorbable surgical gut, silk, polymerized caprolactum, Poliglecaprone 25 2 2 Hydrolysis or polyester). Because of excessive reactivity, Polydioxanone 6 6 Hydrolysis surgical gut has largely been replaced by Polyglactin 910 4 4 Hydrolysis synthetic absorbable sutures. Polyglycolic acid 3 3 Hydrolysis Inflammatory reactions to sutures are Polyglyconate 5 5 Hydrolysis most pronounced near knots.3 Knots have Surgical gut 1 1 Foreign body the highest density of foreign material, and Nonabsorbable they cause the greatest mechanical trauma Nylon 5 2 Hydrolysis in tissue.3 Knot size or volume (which dePolyester 3 N/A NA pends on suture size and number of throws) Polymerized caprolactum 2 N/A NA affects tissue reactivity. Suture size has the Polypropylene 6 N/A NA major influence on knot volume and tissue Silk 1 1 Foreign body reactivity. An increase of two suture sizes reStainless steel 4 N/A NA sults in more than a four- to sixfold increase 1 = highest (i.e., most tissue reaction or fastest loss of tensile strength); 6 = lowin knot volume and more than a two- to est (i.e., least tissue reaction or slowest loss of tensile strength); N/A = not ap3 threefold increase in tissue reactivity. Addplicable. ing two extra throws increases knot volume

Effective Strength of Suture Materials

KNOT SIZE ■ KNOT VOLUME ■ SUTURE TIGHTNESS

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Small Animal

ly (e.g., surgical gut and less steel is minimally reacpoliglecaprone 25) should tive and has excellent knot be reserved for use in wounds security; but it is stiff and that regain tensile strength subject to breaking when quickly (Figure 1). Absorused in a continuous patbable suture materials that tern. Polypropylene with lose tensile strength more fluorescent pigment has slowly (e.g., polydioxanone properties similar to those of and polyglyconate) are appolypropylene, and it is easy propriate to use in body to visualize in ambient or walls because fascia heals black light.22 Subcutaneous tissue should slowly. be closed with small amounts The site of implantation may affect the behavior of Figure 2—Stainless steel has excellent knot security, produces of small-diameter, minimalsutures. Urine weakens minimal tissue reaction, and is appropriate for an interrupted ly reactive absorbable material. Synthetic absorbable polyglactin 910 and poly- pattern to close skin. materials, particularly polyglycolic acid.18 Surgical gut loses tensile strength quicker where there is increased glyconate or polydioxanone, seem most appropriate for inflammation or proteolytic enzymes. 19 In general, subcutaneous tissue. monofilament absorbable sutures tend to maintain tenViscera sile strength longer than do multifilament absorbable Visceral wounds heal relatively quickly, usually atsutures. Surgical gut loses tensile strength quicker, taining full tensile strength by 21 days after surgery whereas polydioxanone loses strength slower than other (Figure 1). Because of its rapid healing, the gastroinabsorbable suture materials20,21 (Table IV). The tissue response to sutures depends on the testinal tract is well suited to the use of absorbable suamount of suture placed in the wound and the techture materials. Synthetic absorbable sutures, especially nique of suture placement. Multifilament sutures have polydioxanone and polyglyconate, are recommended greater surface area than monofilament sutures have, so because of their minimal reactivity. Relatively small-dimultifilament sutures tend to stimulate more tissue reameter sutures (3-0 to 5-0) and swaged needles are recsponse.19 The suture pattern affects the amount of suommended for gastrointestinal surgery. ture implanted in a wound. Continuous patterns usualClosure of various canine viscera has been evaluated ly have fewer knots than do interrupted patterns and recently. Sutures recommended for closing the urinary probably result in less suture material in the wound. bladder include polydioxanone and polyglyconate—in The technique of suture placement also affects tissue part because they maintain tensile strength when in response. Excessively traumatic tissue handling, use of contact with urine.18 Contact with urine may cause premature absorption of polyglactin 910 and polyglycolic eyed (nonswaged) needles, and excessively tight sutures acid. Although sutures used to close urinary bladder inall enhance tissue reaction. cisions do not usually come into contact with urine, SUTURE FOR SPECIFIC TISSUE the use of monofilament synthetic absorbable suture Skin and Subcutaneous Tissue materials (e.g., polydioxanone or polyglyconate) to Recent information can help the veterinary surgeon close a cystotomy incision seems appropriate. Tracheal select an appropriate suture material for a specific tisclosure with polydioxanone resulted in minimal tissue sue. Veterinarians frequently use polymerized caprolacreaction.23 In general, suture material used to close visceral incisions should be absorbable and minimally retum, polypropylene, nylon, stainless steel (Figure 2), or active. polypropylene with fluorescent pigment to close skin. Polymerized caprolactum, which is a coated multifilaBody Wall ment, has good handling and knotting characteristics Body walls require prolonged suture support because but stimulates the greatest reaction in skin.22 Polypropylene is minimally reactive and has excellent knot securifascia heals relatively slowly.17 Although the abdominal walls of many small animals have been closed successty; like nylon, it has mechanical properties similar to fully with surgical gut, synthetic absorbable materials those of skin. Monofilament nylon is also minimally re(particularly polydioxanone or polyglyconate) are preactive; but it has lower knot security than does stainless ferred because of their prolonged maintenance of tensteel, polypropylene, or polymerized caprolactum. StainURINE ■ NONSWAGED NEEDLES ■ TISSUE HANDLING

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sile strength (Figure 1). As surgeons to select the type an alternative, synthetic and size of suture material nonabsorbable materials and the suture pattern that (e.g., polypropylene, monois appropriate for each filament nylon, or monofilwound and that will maxiament stainless steel) can be mize the patient’s wellused. Stainless-steel fascial being. The goal is to prostaples have compared favide secure wound closure vorably with a simple conwhile minimizing morbiditinuous pattern of polyty. For example, the surgeon propylene suture material in may have to use a smallerclosing the body wall of diameter material (which is dogs.24 Removing such staharder to handle and proples at a subsequent laparo- Figure 3—Relatively large purchases (8 mm) should be taken vides a somewhat less-secure tomy may be more difficult in the external fascial sheath during closure of the body wall. closure) in order to reduce than removing sutures. Synthetic absorbable or nonabsorbable suture materials are the likelihood that a conBody walls should be closed recommended. taminated wound will bewith sutures that are tied come infected. just tightly enough to appose the wound edges. Tissue The type and size of suture material chosen should purchases should be approximately 8 mm wide—larger be appropriate for the task. It is important to place suthan those used in other tissues25 (Figure 3). tures of the appropriate composition, size, and tightness. In general, it is better to use a material that causes SOURCES OF SUTURE MATERIAL minimal tissue reaction. Surgeons should avoid using The packaging of suture materials affects cost and excessively large sutures and should try to minimize tisease of use. Bulk sources (e.g., suture cassette) are less sue trauma during suture placement. expensive than prepackaged suture. Although bulk sources are cheaper, they have disadvantages. First, they require the use of eyed needles, which produce more About the Author tissue trauma and are less efficient to use than swaged Dr. Boothe is affiliated with the Department of Small needles.26 A member of the surgical team must thread Animal Medicine and Surgery, College of Veterinary the needle, and the needle can separate from the suture Medicine, Texas A&M University, College Station, Texas. during use. Second, bulk sources of suture probably He is a Diplomate of the American College of Veterinary carry a greater risk of contamination than does preSurgeons. packaged suture. Third, only selected suture materials are available in bulk sources (e.g., surgical gut, polymerized caprolactum, stainless steel, and polypropylene REFERENCES with fluorescent pigment). The risk of contamination 1. Chu CC: Mechanical properties of suture materials: An imrelates primarily to the steps necessary to retrieve the portant characterization. Ann Surg 193:365–371, 1981. suture from the cassette and to the prolonged shelf life 2. Grier RL: Surgical sutures—Part II: Indications for different of the suture. suture materials and comparable costs. Iowa State Univ Vet 34:89–92, 1972. Despite their lower cost, bulk sources of suture 3. van Rijssel EJC, Brand R, Admiraal C, et al: Tissue reaction should be used sparingly in veterinary surgery. Use of a and surgical knots: The effect of suture size, knot configurabulk-source nonabsorbable suture for skin closure tion, and knot volume. Obstet Gynecol 74:64–68, 1989. seems acceptable if the suture is placed with eyed nee4. Crowe DT Jr: Closure of abdominal incisions using a condles that are sharp and of the appropriate size. Use of tinuous polypropylene suture: Clinical experience in 550 bulk-source surgical gut seems to carry an increased risk dogs and cats. Vet Surg 7:74–77, 1978. 5. Rosin E, Robinson GM: Knot security of suture materials. of greater morbidity because of both its reactivity and Vet Surg 18:269–273, 1989. the potential for contamination.

SUMMARY New suture materials have become available to veterinarians, and there is new information on how sutures affect morbidity. These developments enable veterinary

6. Trimbos JB, Niggebrugge A, Trimbos R, van Rijssel EJC: Knotting abilities of a new absorbable monofilament suture: Poliglecaprone 25 (Monocryl®). Eur J Surg 161:319–322, 1995. 7. Holmlund DEW: Knot properties of surgical suture materials. Acta Chir Scand 140:355–362, 1974.

BULK SUTURE ■ SWAGED NEEDLES ■ SUTURE SIZE

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8. Chu CC, Kizil Z: Quantitative evaluation of stiffness of commercial suture materials. Surg Gynecol Obstet 168: 233–238, 1989. 9. Bezwada RS, Jamiolkowski DD, Lee I-Y, et al: Monocryl® suture, a new ultra-pliable absorbable monofilament suture. Biomaterials 16:1141–1148, 1995. 10. Uff CR, Scott AD, Pockley AG, Phillips RKS: Influence of soluble suture factors on in vitro macrophage function. Biomaterials 16:355–360, 1995. 11. Metz SA, Chegini N, Masterson BJ: In vivo and in vitro degradation of monofilament absorbable sutures, PDS® and Maxon®. Biomaterials 11:41–45, 1990. 12. Edlich RF, Rodeheaver G, Thacker JC, Edgerton MT: Technical factors in wound management, in Hunt TK, Dunphy JE (eds): Fundamentals of Wound Management. New York, Appleton-Century-Crofts, 1979, pp 427–438. 13. Edlich RF, Panek PH, Rodeheaver GT, et al: Physical and chemical configuration of sutures in the development of surgical infection. Ann Surg 177:679–687, 1973. 14. Katz S, Izhar M, Mirelman D: Bacterial adherence to surgical sutures: A possible factor in suture induced infection. Ann Surg 194:35–41, 1981. 15. Sharp WV, Belden TA, King PH, Teague PC: Suture resistance to infection. Surgery 91:61–63, 1982. 16. Rochat MC, Lin J, Pope ER, et al: Comparison of the degree of abdominal adhesion formation associated with chromic catgut and polypropylene suture materials. Am J Vet Res 57:943–947, 1996. 17. Stone IK, von Fraunhofer JA, Masterson BJ: The biomechanical effects of tight suture closure upon fascia. Surg Gynecol Obstet 163:448–452, 1986.

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18. Schiller TD, Stone EA, Gupta BS: In vitro loss of tensile strength and elasticity of five absorbable suture materials in sterile and infected canine urine. Vet Surg 22:208–212, 1993. 19. Bellenger CR: Sutures. Part I. The purpose of sutures and available suture materials. Compend Contin Educ Pract Vet 4(6):507–515, 1982. 20. Bourne RB, Bitar H, Andreae PR, et al: In-vivo comparison of four absorbable sutures: Vicryl, Dexon Plus, Maxon and PDS. Can J Surg 31:43–45, 1988. 21. Lober CW, Fenske NA: Suture materials for closing the skin and subcutaneous tissues. Aesthetic Plast Surg 10:245–247, 1986. 22. Beardsley SL, Smeak DD, Weisbrode SE: Histologic evaluation of tissue reactivity and absorption in response to a new synthetic fluorescent pigmented polypropylene suture material in rats. Am J Vet Res 56:1248–1252, 1995. 23. Fingland RB, Layton CI, Kennedy GA, Galland JC: A comparison of simple continuous versus simple interrupted suture patterns for tracheal anastomosis after large-segment tracheal resection in dogs. Vet Surg 24:320–330, 1995. 24. Kirpensteijn J, Fingland RB, Boyer JE Jr, et al: Comparison of stainless steel fascial staples and polypropylene suture material for closure of the linea alba in dogs. Vet Surg 22: 464–472, 1993. 25. Bellenger CR: Abdominal wall, in Slatter D (ed): Textbook of Small Animal Surgery, ed 2. Philadelphia, WB Saunders Co, 1993, pp 399–406. 26. Trier WC: Considerations in the choice of surgical needles. Surg Gynecol Obstet 149:84–94, 1979.