Selection of suture materials

Suture material of inadequate strength may result in wound breakdown, while suture material with high memory can lead to knots coming undone unless the surgeon is aware of this and adds additional throws to the knot to counteract this property. Excessively large diameter suture material results in a weaker knot, leading to knot insecurity and also more foreign material at the surgical site.

The smallest diameter suture material that will adequately hold the healing tissue should be used. In cats, size 1.5–3 metric gauge (M) will be suitable for most general use. For either very delicate work or areas where a higher tensile strength is required, sutures outside this size range may be needed. Size conversion for suture materials is shown in Table 10-1.

Multifilament suture material is usually stronger than monofilament and has better knot security due to the higher friction co-efficient. Conversely, multifilament material, particularly if dry, can cause drag which can damage delicate tissue and inadvertently cause the surgeon to tug on the material, which can cause iatrogenic injury and suture pullout. Multifilament suture material also has a greater surface area for bacterial penetration and contains crevices which can harbor bacteria. These characteristics are reduced when the multifilament or braided suture is coated.

Natural materials like silk, cotton, ovine intestinal submucosa, or bovine serosa (catgut) can cause inflammatory reactions within the tissues and their absorption, by phagocytosis, may be variable depending on implant site and patient status. Synthetic materials are usually chemical polymers absorbed by hydrolysis, and thus they often have a more predictable rate of absorption independent of these factors (Table 10-2).

Modifications to several of the generic suture materials include the introduction of rapidly absorbable sutures (the ‘Rapide’ range) and sutures with improved resistance to bacterial penetration (the ‘Plus’ range). The ‘Plus’ range sutures, which include polyglactin 910, polydioxanone and poliglecaprone, are coated with triclosan, which is an inhibitor of bacterial fatty acid synthesis with demonstrable antibacterial activity. The use of triclosan-coated sutures in humans has been associated with a decreased infection rate.¹

Suture placement and patterns

Careful attention to proper suturing technique and use of the appropriate suture patterns for wound closure is important in ensuring optimal closure and incisional healing. Careless handling of the suture or the use of damaged instruments can weaken the suture and make it more prone to breakage. Eversion of skin edges or excessively tight skin sutures can encourage self-trauma by the patient, increasing the risk of suture line infection or premature suture removal by the cat. Excess tension on sutures in wound closure can lead to ‘cutting out’ of sutures or to ischemia of tissue adjacent to the sutures. In areas of tension, the surgeon should consider other techniques such as the use of subcutaneous walking sutures, undermining of the skin, tension-relieving sutures, and then surgical procedures, including relaxing incisions, plasty procedures, or skin flaps (see Chapter 19).

Placing an adequate number of throws is important to minimize the risk of the sutures undoing. Although some manufacturers give guidelines, strict recommendations are not made for individual suture materials, as this is dependent on many factors such as tightness of each throw, length of the cut end(s) or ears and the tissue tension. The knot security of individual suture materials is influenced by the memory, plasticity and pliability of the suture material. Braided material generally has good knot security but this is also influenced by suture coating: some braided material is coated to decrease tissue drag and bacterial penetration but this will tend to decrease knot security. General recommendations for simple interrupted suture placement would be to place four throws, ensuring that the throws are tightened after the third (or second if suturing skin) and subsequent throw. For simple continuous patterns the recommendation is for five to six throws at the start of the suture line with one or two additional throws at the end of the suture pattern, as the suture material becomes damaged during use and the end knots are generally less secure.

Suture patterns commonly used in feline general surgery are shown in Figures 10-1 and 10-2. There are several different suture materials on the market (Table 10-3) with a variety of different properties, indications and contraindications. The materials available in practice will vary according to surgeon preference and procedures commonly performed. The indications and contraindications for the different suture materials are listed in Tables 10-4 and 10-5.

Catgut

Catgut is made of collagen obtained from bovine intestines. It is naturally degraded by the body’s own proteolytic enzymes. It can cause a significant foreign body reaction when implanted in tissues. Absorption is unpredictable, occurring faster in patients with cancer, anemia, and malnutrition or when used in gastric surgery, an infected wound, or highly vascularized tissue.² It is also absorbed faster when used in the mouth and in other mucous membranes, e.g., vagina, due to the presence of microorganisms. In one study of 12 cats where suture material was implanted into the oral cavity it completely disappeared between days 3 and 7.³

Chromic catgut suture is a variant treated with chromic acid salts. This treatment produces roughly twice the suture-holding time of plain catgut, but greater tissue inflammation occurs. Full tensile strength is extended to 18–21 days. Fast catgut suture is heat-treated to give even more rapid absorption in the body.

Catgut is banned in Europe and Japan because of concern over bovine spongiform encephalopathy (BSE), although the herds from which gut is harvested are certified BSE-free. Catgut has largely been replaced by synthetic absorbable polymers such as polyglactin, polyglytone and poliglecaprone.

Poliglecaprone 25

Poliglecaprone 25 is a monofilament absorbable suture material made of glycolide and epsilon caprolactone copolymer (PGCL). It is pliable, with low tissue drag giving it smooth tissue passage. Knot security is not reliable, hence the ears should not be cut too short and additional throws placed if used for a continuous pattern. It loses its strength relatively quickly, with the tensile strength capability reduced to about 60% within a week, 20–30% at two weeks and all strength is lost within three weeks. It undergoes reliable absorbtion by hydrolysis.

It was used in a prospective study for all ligatures and closure of the linea alba in routine ovariohysterectomies in 24 cats.⁴ Dehiscence did not occur in any of the cats; however, the author has seen dehiscence of the linea alba after celiotomy closure and would recommend alternative suture material such as polydioxanone or glycomer 631 be used in this situation. Poliglecaprone is commonly used for subcutaneous and subdermal tissue closure. Careful technique ensuring an adequate number of throws, good knot security and sufficient purchase of tissue with each bite should be taken when placing in areas of high tension. It causes a relatively short-lived inflammatory response.

Polyglactin 910

Polylactin 910 is an absorbable, braided suture material made of polyglycolic acid. The suture holds its tensile strength for three to four weeks in tissue, retaining 75% of strength after two weeks, 50% after three weeks and 25% after four weeks and it is completely absorbed by hydrolysis within 70 days. The suture material, being braided, has some tissue drag, particularly if it dries out, but it has good knot security and is good for ligation. The sutures are coated with a copolymer of calcium stearate to allow less drag and better water repellency. The suture material can also be treated to enable more rapid breakdown for its use in rapidly healing tissues such as mucous membranes.

Polyglycolic acid

Polyglycolic acid (PGA) suture is classified as a synthetic, absorbable, braided multifilament. It is coated with N-laurin and l-lysine, which render the thread extremely smooth, soft, and safe for knotting. It is also coated with magnesium stearate and finally sterilized with ethylene oxide gas. It is naturally degraded in the body by hydrolysis and has approximately 60% strength left at 14 days; absorption is completed between 60 and 90 days. It has the advantages of high initial tensile strength, smooth passage through tissue, easy handling, excellent knotting ability, and secure knot tying (better when wet). It is commonly used for subcutaneous sutures, intradermal closure, abdominal and thoracic surgeries. Elderly, anemic and malnourished patients may absorb the suture more quickly. Absorption is faster in urine, and so it is not recommended for urinary tract surgery.⁵

Polydioxanone

Polydioxanone (PDS) or poly-p-dioxanone is a slowly absorbable monofilament suture composed of the polyester, poly (p-dioxanone). This is a monofilament with greater strength than monofilament nylon and polypropylene, and with less tissue drag than the multifilament materials. It has good strength retention, with only 20% loss over two weeks and 60% loss after eight weeks. It can sometimes be difficult to handle due to its memory and tendency to coil or ‘pig-tail’. Knot security can be relatively poor, and seven throws are advisable at the end of a continuous suture line. Complete absorption occurs by hydrolysis and takes around 200 days.

Polydioxanone was still intact at day 28 in the oral cavity of cats, and it is recommended for procedures in which longer healing time is anticipated³ such as hernia repair or pexy procedures.

Despite the less than ideal knot security, the strength and predictable rate of absorption make this an ideal suture material for closure of the linea alba and it has become a very popular material for this use.

Polyglyconates

These suture materials are polymers of glyconates (Monosyn: Braun) or combinations such as glycolic acid and trimethylene carbonate (Maxon: USS/DG). The tensile strength and absorption is dependent on the composition. Maxon can be used for linea alba closure; Monosyn has quicker absorption and loses 50% of its tensile strength by two weeks so would be more suitable for subcuticular closure.

Glycomer 631

This monofilament is a copolymer of glycolide, dioxanone, and trimethylene carbonate. It is advertised as the strongest monofilament suture material available, second only to steel. A quarter of the strength is gone by day 14, and only 40% remains at three weeks. Full absorption takes 90 to 110 days. It has fair handling characteristics with low tissue drag and slightly better knot security than polydioxanone, which is a comparable though longer-lasting monofilament. It has slightly less memory compared to polydioxanone. This material is promoted as suitable for abdominal closure and soft tissue repair requiring a strong but absorbable material.