It is a braided suture with excellent handling properties and knot security. Silk loses a significant amount of its tensile strength after extended implantation but is considered nonabsorbable because the material remains in the tissues for a significant amount of time. There is a 30% loss of tensile strength at 14 days and 50% loss at 1 year. Time for complete absorption is greater than 2 years. Silk leads to significant reaction in tissues, and the presence of silk suture can reduce the number of bacteria needed to induce an infection from 106 to 103 (Fossum 2002).
Nylon
Nylon is a synthetic nonabsorbable suture that is available as a monofilament or braided suture (Ratner et al. 1994; Fossum 2002; Roush 2003; Tan et al. 2003). Nylon maintains a high level of elasticity, but undergoes little to no plastic deformation prior to breakage and monofilament nylon is relatively stiff. Overall, it has moderate handling characteristics and knot security with minimal tissue response. Multifilament nylon has improved handling characteristics, but increased capillarity. Although it is nonabsorbable, monofilament nylon loses 30% of its tensile strength after two years and braided nylon loses 75–100% of its tensile strength at 6 months.
Polypropylene
Polypropylene is a synthetic monofilament nonabsorbable suture material composed of stereoisomers of polypropylene (Tan et al. 2003). It has the greatest strength of the synthetic nonabsorbable sutures and has no appreciable loss of tensile strength after implantation (Tan et al. 2003); however, evaluation of polypropylene sutures over 2 and 5 year periods show some fragmentation (Postlethwait 1970, 1979). Polypropylene has a very smooth surface and has minimal tissue drag, but this property can also lead to slippage and poor knot security (Ratner et al. 1994). Other disadvantages are the handling properties and memory.
Stainless Steel
Stainless steel is an alloy of chromium, nickel, and molybdenum and is available as a monofilament or braided suture (Fossum 2002; Tan et al. 2003). It is biologically inert and has the greatest strength of all suture materials. Stainless steel sutures are extremely stiff and tend to cut through tissues or cause necrosis when there is tissue movement over buried knots.
Barbed and Antibacterial‐Coated Suture
Barbed sutures have been used for a variety of human surgical procedures. The suture barbs are arranged in order to prevent pull out and eliminate the need for a knot at the end of the suture line. There are a few studies in the veterinary literature regarding barbed sutures, but their use is not widespread.
Triclosan is a broad spectrum antibacterial agent that has been added to many suture materials. Triclosan‐coated sutures inhibit growth of common skin flora and some methicillin‐resistant strains of Staphylococcus in vitro. Triclosan‐coated sutures are available for use in veterinary surgery; however, their efficacy in reducing surgical site infections is unclear and current studies have varying results (Rothenburger et al. 2002; Storch et al. 2004; Etter et al. 2013). Triclosan‐coated sutures were studied in ball pythons and no difference was seen in inflammatory response or surgical site infections (McFadden et al. 2011).
In addition to triclosan, chlorhexidine‐coated sutures are also available. Chlorhexidine diacetate is a biguanide antiseptic that exhibits a broad range of antimicrobial activity intended to inhibit the growth of Gram‐negative and Gram‐positive bacteria. Studies assessing the effectiveness of chlorhexidine are limited (Onesti et al. 2018), and at the time of this chapter preparation, no veterinary specific studies have been published.
Tissue Healing
In addition to understanding specific characteristics of available suture materials, it is important to understand tissue healing. Although tissues heal through the same basic phases of wound healing, there are significant differences in the healing times. This affects the amount of time the sutures are required to support the tissue during the healing process. Table 2.1 summarizes tissue healing times and suture absorption profiles.
Compared with other tissues, the bladder heals very quickly and regains normal tensile strength in 14–21 days (Cornell 2012). When choosing a suture material to use for bladder repair, Monocryl, Biosyn, Dexon, or Vicryl may be recommended based on the amount of time these suture materials retain sufficient tensile strength, thus allowing the bladder tissue to heal. Longer‐lasting absorbable sutures such as Maxon or PDS are probably not appropriate for bladder surgery unless delayed healing is anticipated. Nonabsorbable sutures may promote calculus formation. Conversely, sutures that are absorbed very rapidly (e.g. Caprosyn, Vicryl Rapide) probably do not retain sufficient tensile strength long enough and may increase the risk of dehiscence.
The gastrointestinal tract also heals at a relatively rapid rate, with the strength of the repair site approximating the original tissue strength in 10–17 days for the small intestine and up to 30 days for the large intestine (Durdey and Bucknall 1984; Hedlund 2002). The maturation phase in gastrointestinal tract healing occurs between 10 and 180 days after surgery. Polydioxanone, Monocryl, Biosyn, or Maxon provide sufficient tissue support for the gastrointestinal tract to allow for adequate healing.
Healing time for fascia is longer than for the gastrointestinal tract or urinary tract; therefore, fascia requires prolonged tissue support. Twenty days after surgery, the body wall has only regained 20% of its original tensile strength (Cornell 2012). Because fascia has a slower healing time, suture materials that will provide longer support of the tissues (e.g. PDS, Maxon) are recommended. Tissues such as tendons can take six weeks to a year to completely heal and require long‐term support with orthopedic implants or external coaptation in addition to sutures (Montgomery and Fitch 2003). When repairing tissues that take an extended period of time to heal, longer‐lasting sutures such as PDS or Maxon, or nonabsorbable sutures like Prolene or nylon should be used.
In many cases, tissue‐healing times were determined using animal models to assess healing in mammalian tissues. Studies have shown differences in healing times between mammalian species (Cornell 2012), and these will vary significantly from reptile or amphibian tissues. The healing times presented here are to demonstrate the relationship between loss of tensile strength, time to complete absorption, and tissue healing. Veterinarians must consider the specifics of the species and tissues they are operating on to determine the best suture choice.
Table 2.1 Percentage of retained tensile strength following implantation and number of days required for complete absorption for commonly available suture materials.
| Suture material | 7 d | 14 d | 21 d | 28 d | 42 d | Complete absorption (d) |
|---|---|---|---|---|---|---|
| Chromic gut | 0 | 60–90 | ||||
| Polydioxanone (PDS) | 70 | 50 | 25 | 180–210 | ||
| Polyglyconate (Maxon) | 80 | 75 |
