Dr. Eric Monnet provides a comprehensive review of the newest suture materials available to practitioners and their applications for wound closure.
Many different types of suture materials are available to the veterinary surgeon. Suture materials should be chosen on knowledge of physical and biological properties of the suture materials, assessment of local conditions in the particular wound, and the healing rate of different tissues. However, suture selection has too often been governed by training, experience, economical reasons and personal preferences rather than by scientific facts. Even with more suturing products now available, there is not a suture material that will be suitable for every condition.
Suture material should maintain tensile strength until its purpose is accomplished. It should be easy to use, have good knot security and should not induce an adverse reaction, such as an allergic reaction, severe inflammation or neoplasia. Even with the development of new materials, the ideal suture does not exist. Therefore, the choice of the suture materials needs to be determined by the characteristics of the suture material, the tissue and the environment.
Suture materials have been classified according to their behavior in tissue (nonabsorbable or absorbable), their structure (monofilament or braided), and their origin (synthetic, organic or metallic). Nonabsorbable suture materials retain their tensile strength more than 60 days while absorbable rapidly lose their tensile strength within 60 days.
Synthetic absorbable suture materials are degraded by hydrolysis, which is very predictable, while organic suture material such as catgut is degraded by phagocytosis. Phagocytosis is influenced by the number of neutrophils and macrophages present in the wound while hydrolysis is not.
Tissue reaction is an important factor to consider when choosing a suture. Tissue reaction is a function of the nature of the implant (organic material versus synthetic monofilament), the tissue into which the suture is placed (intestine or bladder versus muscle facia), the amount of foreign material (size of the suture), technique of implantation (tightness of the suture), and the length of time until absorption. The amount of foreign material left and the surface area exposed are important factors for the tissue reaction. Therefore, the smallest suture material that will hold the tissue sutured together should be used. For sutures of similar sizes, braided sutures will trigger a more severe inflammatory reaction than monofilament sutures because their surface area exposed to tissue is more important.
The rate of reduction of tensile strength has to be taken into consideration in the choice of a suture during a surgery and it has to match with the rate of healing of the tissue. It is more desirable and logical to choose a suture that matches the rate of healing because of its composition instead of using a suture that has larger diameter but does not match the rate of healing. Veterinary surgeons tend to choose sutures that are inappropriately of a large suture size. A large diameter suture does not influence the rate of degradation of a suture and does not compensate for a fast rate of degradation of the suture material. More likely, a larger than needed diameter suture has a higher tensile strength initially. If the rate of degradation is too fast, it will lose its tensile strength or be completely absorbed too early. Therefore, the risk of dehiscence is increased. A large suture material induces a more important inflammatory reaction, increases morbidity and gives a false sense of security.
Most of the monofilament nonabsorbable sutures are inert suture materials while braided sutures like silk or polyester are encapsulated by fibrous tissue. This reaction can result in an extrusion of the suture if placed in the subcutaneous tissue. It will also induce an inflammatory reaction that will increase the risk of self-mutilation by increasing the awareness of the wound to the patient.
Monofilament suture materials do not have a capillary effect like braided suture materials, which make them very valuable for intestinal surgery or surgery in a contaminated environment. It has been shown that monofilament sutures are better tolerated in infected tissue than braided suture materials. Braided absorbable or nonabsorbable sutures created a nidus for chronic local infection as indicated by the elevated number of neutrophils present in the wounds. Polyglycolic acid triggered the most severe inflammatory reaction in the early phase of healing in an infected wound, but the tissue reaction became minimal in the absorption stage.
The knot security of monofilament suture is poor when compared to braided sutures. Therefore, more throws have to be placed for each knot to have good knot security. However, the addition of throws reduces the tensile strength by 30 to 40 percent, and increases the amount of foreign material left in the tissue. The augmentation of foreign material will induce a more severe inflammatory reaction, which can increase the morbidity. This is more critical when the suture has been placed in the subcutaneous tissue.
Table 1: Characteristics of absorbable suture. Tensile strength is reported in percent from original tensile strength at 7, 14, and 28 days after implantation.
Monofilament synthetic absorbable suture materials offer excellent glide characteristics and cause minimal tissue trauma as a result of their smooth monofilament structure and gradual bioabsorption. Monofilament suture materials such polyglyconate and polydioxanone have the tendency to be stiff and have memory, which makes them difficult to handle. Combined with the fact that more throws are required for a good knot security, monofilament suture materials are not ideal for subcutaneous and intradermal sutures. New monofilament suture materials such as Glycomer 631 and Polyglecaprone 25 might be valuable suture to consider for subcutaneous tissue closure since their flexibility and knot security are better than older monofilament absorbable suture materials.
Absorbable suture materials differ by their rate of loss of tensile strength and rate of absorption (see Table 1). Monofilament absorbable sutures are used more commonly than braided sutures because they maintain tensile strength longer in a wide variety of tissues and environments. Lactomer seems to have the highest out-of-the-package tensile strength among braided sutures.
Monofilament absorb-able is strongly recommended for any surgery of the gastrointestinal system, urinary system, and respiratory tract. Glycomer 631 and Poliglecaprone 25 have been used without significant augmentation of complications in a wide variety of gastrointestinal surgeries in human patients. Enterotomy or enterectomy can be completed with a 4-0 monofilament suture. Gastrotomies are closed with 3-0 monofilament absorbable sutures. Cystotomy is closed with a simple continuous suture pattern with a 4-0 monofilament absorbable suture. Since the suture is absorbed in less than 60 days the suture can be placed full thickness and be exposed to urine. The risk of creating a nidus for urinary stone formation is limited. During in-vitro testing with sterile and infected urine, monofilament suture materials seem to retain a higher tensile strength than braided suture materials. Monofilament absorbable suture materials seem to trigger less inflammation than braided suture when used in the oral cavity of cats.
Braided absorbable suture materials have been commonly used to close subcutaneous tissue. Since they require less throws than monofilament to have good knot security, less suture material is left in the subcutaneous tissue. It is easier to bury the knot at each end of the simple continuous suture line since braided sutures are less stiff than monofilament sutures. However, Glycomer 631, Poliglecaprone 25 and Polydioxanone were found to have extremely low tissue reaction values in rat skin. Glycomer 631, Poliglecaprone 25 and Polydioxanone were deemed particularly suitable for use as intracuticular sutures. Absorption times in rat skin were less than three months for Poliglecaprone 25, between three and six months for Glycomer 631 and six months for polydioxanone.
Nonabsorbable suture materials are available as monofilament or braided sutures. Most of the recent nonabsorbable suture materials available for veterinary surgery are monofilament (Table 2). Polybutester and polypropilene are commonly used to close linea alba in dogs. The closure of the linea alba with a monofilament nonabsorbable suture can be safely performed with a continuous suture pattern which can save time in surgery. Polybutester is a monofilament nonabsorbable suture that has unique stress-strain properties that are potentially beneficial for abdominal wound closure. In a study in rats, Polybutester was superior to nylon and polyglycolic acid for the closure of the linea alba because the abdominal volume at the moment of wound dehiscence correlated with the extensibility of the suture material used for closure. A braided nonabsorbable suture materials is not recommended to close the linea alba. It triggers an important inflammatory reaction, which is not desirable near the body surface. Tissue reactivity increased the morbidity because it induces a prolonged inflammatory reaction that can enhance patient awareness of the wound and subsequent self-mutilation.
Table 2: Characteristics of nonabsorbable sutures
Closure of skin can be safely accomplished with nylon, polypropylene or stainless steel. Polypropylene is minimally reactive and has excellent knot security. Its mechanical properties are very similar to those of skin. Polybutester is more likely the least reactive suture for skin closure.
New suture materials are available to veterinarians. These developments enable surgeons to select the type of suture and size of suture material that is appropriate for each wound to close. Selection of the appropriate suture minimizes morbidity and maximizes well-being of each patient. Reduction of soft tissue trauma at the time of placement of suture reduces the amount of tissue reaction and improves the healing process.