Biomaterials, Suturing, and Hemostasis

Chapter 8

Biomaterials, Suturing, and Hemostasis

Sutures and Suture Selection

Suture plays an important role in wound repair by providing hemostasis and support for healing tissue. Tissues have different requirements for suture support, depending on the type of tissue and anticipated duration of healing. Some tissues need support for only a few days (e.g., muscle, subcutaneous tissue, skin), whereas others require weeks (fascia) or months (tendon) to heal. Individual patient variation further affects suture choice. Healing of wounds may be delayed by infection, obesity, malnutrition, neoplasia, drugs (e.g., steroids), and collagen disorders. In rapidly healing tissue, an ideal suture is one that will lose its tensile strength at a rate similar to that with which the tissue gains strength, and it will be absorbed by the tissue so that no foreign material remains in the wound. Minimally invasive surgical techniques (see Chapter 13) put additional demands on the performance of surgical sutures. Not only must good knot security be maintained, but also the surface lubricant must ensure ease of manipulation, minimal tissue drag, and good biocompatibility with minimal inflammatory responses. Subjective preferences, such as familiarity with the material and availability, need also be taken into consideration when choosing a suture material.

Suture Characteristics

The ideal suture is easy to handle, reacts minimally in tissue, inhibits bacterial growth, holds securely when knotted, resists shrinking in tissue, absorbs with minimal reaction after the tissue has healed, and is noncapillary, nonallergenic, noncarcinogenic, and nonferromagnetic; but such a material does not exist. Therefore, surgeons must choose a suture that most closely approximates the ideal for a given procedure and tissue to be sutured. A wide variety of suture and needle combinations are available.

Suture size

The smallest diameter suture that will adequately secure wounded tissue should be used in order to minimize trauma as the suture is passed through the tissue and to reduce the amount of foreign material left in the wound. There is no advantage to using a suture that is stronger than the tissue to be sutured. The most commonly used standard for suture size is the United States Pharmacopeia (USP), which denotes dimensions from fine to coarse (with diameters in inches) according to a numeric scale, with 12-0 being the smallest and 7 the largest. The USP uses different standards for surgical gut and for other materials (Table 8-1). The smaller the suture size, the less tensile strength it has. Stainless steel wire is sized according to the metric or USP scale or by the Brown and Sharpe (B and S) wire gauge (see Table 8-1).

Knot tensile strength

Knot tensile strength is measured by the force in pounds that the suture strand can withstand before it breaks when knotted (Box 8-1). Sutures should be as strong as the normal tissue through which they are being placed; however, the tensile strength of the suture should not greatly exceed the tensile strength of the tissue.

image Box 8-1

Terminology Used to Describe Suture Characteristics

• Absorbability. Progressive loss of mass and/or volume of suture material; does not correlate with initial tensile strength.

• Breaking strength. Limit of tensile strength at which suture failure occurs.

• Capillarity. Extent to which absorbed fluid is transferred along the suture.

• Elasticity. Measure of the ability of the material to regain its original form and length after deformation.

• Fluid absorption. Ability to take up fluid after immersion.

• Knot-pull tensile strength. Breaking strength of knotted suture material (10% to 40% weaker after deformation by knot placement).

• Knot strength. Amount of force necessary to cause a knot to slip (related to the coefficient of static friction and plasticity of a given material).

• Memory. Inherent capability of suture to return to or maintain its original gross shape (related to elasticity, plasticity, and diameter).

• Plasticity. Measure of the ability to deform without breaking and to maintain a new form after relief of the deforming force.

• Pliability. Ease of handling of suture material; ability to adjust knot tension and to secure knots (related to suture material, filament type, and diameter).

• Straight-pull tensile strength. Linear breaking strength of suture material.

• Suture pullout value. The application of force to a loop of suture located where tissue failure occurs, which measures the strength of a particular tissue; variable depending on anatomic site and histologic composition (fat, 0.2 kg; muscle, 1.27 kg; skin, 1.82 kg; fascia, 3.77 kg).

• Tensile strength. Measure of the ability of a material or tissue to resist deformation and breakage.

• Wound breaking strength. Limit of tensile strength of a healing wound at which separation of the wound edges occurs.

From Lai SY, Becker DG: Sutures and needles, e-medicine, Topic 38, 2004.

Specific Suturing Materials

Suture materials may be classified according to their behavior in tissue (absorbable or nonabsorbable), their structure (monofilament or multifilament), or their origin (synthetic, organic, or metallic) (Fig. 8-1 and Table 8-2). Two major mechanisms of absorption result in the degradation of absorbable sutures. Sutures of organic origin, such as surgical gut, are gradually digested by tissue enzymes and phagocytized, whereas sutures manufactured from synthetic polymers are principally broken down by hydrolysis. Nonabsorbable sutures are ultimately encapsulated or walled off by fibrous tissue.

Monofilament sutures are made of a single strand of material and therefore have less tissue drag than multifilament sutures and do not have interstices that may harbor bacteria or fluid. Care should be used in handling monofilament suture because nicking or damaging the material with forceps or needle holders may weaken the suture and predispose it to breakage. Multifilament sutures consist of several strands of suture that are twisted or braided together. Multifilament sutures generally are more pliable and flexible than monofilament sutures. They may be coated to reduce tissue drag and enhance handling characteristics (see previous discussion).

Absorbable Suture Materials

Absorbable suture materials (e.g., surgical gut, polyglycolic acid [Dexon, Covidien, Mansfield, Mass.], polyglactin 910 [Vicryl, Ethicon, Somerville, N.J.], polydioxanone [PDS II, Ethicon, Somerville, N.J.], polyglyconate [Maxon, Covidien, Mansfield Mass.], poliglecaprone 25 [Monocryl, Ethicon, Somerville, N.J.], glycomer 631 [Biosyn, Covidien, Mansfield, Mass.]) lose most of their tensile strength within 60 days and eventually disappear from the tissue implantation site because they have been phagocytized or hydrolyzed (see Figure 8-1 and Table 8-2). The time to loss of strength and for complete absorption varies among suture materials.

Organic absorbable materials

Catgut (surgical gut) is the most common nonsynthetic absorbable suture material. Although once very popular, its use has decreased substantially in veterinary medicine with the advent of strong, monofilament synthetic absorbable suture materials (discussed later). The word catgut is derived from the term kitgut or kitstring (the string used on a kit, or fiddle). Misinterpretation of the word kit as referring to a young cat led to the use of the term catgut. Surgical gut is in fact made from the submucosa of sheep intestine or the serosa of bovine intestine and is approximately 90% collagen. It is broken down by phagocytosis and, in contrast with other suture materials, elicits a notable inflammatory reaction. Plain surgical gut loses strength rapidly after tissue implantation. “Tanning” (cross-linking of collagen fibers), which occurs by exposure to chrome or aldehyde, slows absorption. Surgical gut is available as plain, medium chromic, or chromic; increased tanning generally implies prolonged strength and reduced tissue reaction. Surgical gut is rapidly removed from infected sites or areas where it is exposed to digestive enzymes and is quickly degraded in catabolic patients. The knots may loosen when wet.

Synthetic absorbable materials

Synthetic absorbable materials (see Table 8-2) generally are broken down by hydrolysis and cause minimal tissue reaction. The time to loss of strength and to absorption is fairly constant even in different tissue. Infection or exposure to digestive enzymes does not significantly influence the rate of absorption of most synthetic absorbable sutures. Polyglactin 910 and polyglycolic acid are more rapidly hydrolyzed in alkaline environments, but they are relatively stable in contaminated wounds. Polyglycolic acid, polyglactin 910, and poliglecaprone 25 may be rapidly degraded in infected urine; polydioxanone, polyglyconate, and glycomer 631 are acceptable for use in sterile bladders and those infected with E. coli. However, any suture that is degraded via hydrolysis may be at risk for accelerated degradation when the bladder is infected with Proteus spp. (see also p. 755), as all common monofilament absorbable sutures have been shown to degrade within 7 days in P. mirabilis–inoculated urine.

Monofilament absorbable materials

Polydioxanone and polyglyconate are classic monofilament sutures that retain their tensile strength longer than multifilament sutures with complete absorption occurring in 6 months. Poliglecaprone 25 and glycomer 631 are relatively new monofilament rapidly absorbable synthetic materials that are pliable, lack stiffness, and have good handling characteristics. These sutures have good initial tensile strength that deteriorates in 2 to 3 weeks following implantation and are completely absorbed by 120 days. Polyglytone 6211 (Caprosyn, Covidien, Mansfield, Mass.) is the newest rapidly absorbable monofilament suture. It is a synthetic polyester of glycolide, caprolactone, trimethylene carbonate, and lactide. Absorption of this material is essentially complete in 56 days, which is thought to lead to fewer wound complications and tissue reactions. This suture retains up to 30% knot strength at 10 days postimplantation and has excellent handling characteristics; however, its rapid absorption also limits its application.

Multifilament absorbable materials

Polyglycolic acid is braided from filaments extracted from glycolic acid and is available in both coated and uncoated forms. Polyglactin 910 is a multifilament suture made of a copolymer of lactide and glycolide with polyglactin 370. It is coated with calcium stearate and its rate of loss of tensile strength is similar to that of polyglycolic acid. Polysorb (Covidien, Mansfield, Mass.) is a new synthetic absorbable suture material composed of a glycolide/lactide co-polymer. Polysorb has good initial tensile strength and is completely absorbed by 60 days (see Table 8-2). Vicryl Rapide (Ethicon, Somerville, N.J.) is a relatively new, rapidly absorbed, synthetic braided suture that has an initial strength that is comparable to nylon and gut. However, the tensile strength declines to 50% in 5 to 6 days, and it is completely absorbed in 42 days. This suture is indicated for superficial closure of mucosa, gingival closure, and periocular skin closure. Vicryl Plus (Ethicon, Somerville, N.J.) is a new suture that was designed to reduce bacterial colonization on the suture. It has been coated with an antibacterial agent, triclosan.

Nonabsorbable Suture Materials

Synthetic nonabsorbable materials

Synthetic nonabsorbable suture materials (see Table 8-2) are marketed as braided multifilament threads (e.g., polyester or coated caprolactam) or monofilament threads (e.g., polypropylene, polyamide, or polybutester). These sutures are typically strong and induce minimal tissue reaction. Nonabsorbable suture materials with an inner core and an outer sheath (e.g., Supramid [S. Jackson, Alexandria, Va.) should not be buried in tissue because they may predispose to infection and fistulation. The outer sheath frequently is broken, which allows bacteria to reside underneath it.

Surgical Needles

A variety of needle shapes and sizes are available; selection of a needle depends on the type of tissue to be sutured (e.g., penetrability, density, elasticity, and thickness), the topography of the wound (e.g., deep or narrow), and the characteristics of the needle (i.e., type of eye, length, and diameter). Needle strength, ductility, and sharpness are important factors in determining the handling characteristics and use of a needle. The amount of angular deformation a needle can withstand before becoming permanently deformed is called surgical yield. Ductility is the needle’s resistance to breaking under a specified amount of bending. The sharpness of a needle is related to the angle of the point (see below) and the taper ratio of the needle. The sharpest needles have a long, thin, tapered point with smooth cutting edges. Most surgical needles are made from stainless steel wire because it is strong, corrosion free, and does not harbor bacteria.

The three basic components of a needle are the attachment end (i.e., swaged or eyed end), the body, and the point (Fig. 8-2, A). Eyed needles must be threaded, and because a double strand of suture is pulled through the tissue, a larger hole is created than when swaged suture material is used. Eyed needles may be closed (i.e., round, oblong, or square) or French (i.e., with a slit from the inside of the eye to the end of the needle for ease of threading) (Fig. 8-2, B). Eyed needles are threaded from the inside curvature. The use of eyed needles in veterinary practice has decreased substantially in recent years. With swaged sutures, the needle and suture form a continuous unit, which minimizes tissue trauma and increases ease of use.

The needle body comes in a variety of shapes (Fig. 8-2, C); the tissue type and depth and the size of the wound determine the appropriate needle shape. Straight (Keith) needles generally are used in accessible places where the needle can be manipulated directly with the fingers (e.g., placement of purse-string sutures in the anus). Curved needles are manipulated with needle holders. The depth and diameter of a wound are important when selecting the most appropriate curved needle. One-fourth (image) circle needles are primarily used in ophthalmic procedures. Three-eighths (image) and one-half (image) circle needles are the most commonly used surgical needles in veterinary medicine. Three-eighths circle needles are more easily manipulated than one-half circle needles because they require less pronation and supination of the wrist. However, because of the larger arc of manipulation required, they are awkward to use in deep or inaccessible locations. A one-half circle or five-eighths (image) circle needle, despite requiring more pronation and supination of the wrist, is easier to use in confined locations.

The needle point (i.e., cutting, taper, reverse cutting, or side cutting) (Fig. 8-2, D) affects the sharpness of a needle and the type of tissue in which the needle can be used. Cutting needles generally have two or three opposing cutting edges and are designed for use in tissues that are difficult to penetrate, such as skin. With conventional cutting needles, the third cutting edge is on the inside (i.e., concave) curvature of the needle. The location of the inside cutting edge may promote more “cut out” of tissue because it cuts toward the edges of the wound or incision. Reverse cutting needles have a third cutting edge on the outer (i.e., convex) curvature of the needle; this makes them stronger than similarly sized conventional cutting needles and reduces the amount of tissue cut out. Side cutting needles (i.e., spatula needles) are flat on the top and bottom and are generally used for ophthalmic procedures. Taper needles (i.e., round needles) have a sharp tip that pierces and spreads tissues without cutting them. They generally are used in easily penetrated tissues, such as the intestine, subcutaneous tissue, or fascia. Taper-cut needles, which are a combination of a reverse cutting edge tip and a taperpoint body, generally are used for suturing dense, tough fibrous tissue, such as a tendon, and for some cardiovascular procedures, such as vascular grafts. Bluntpoint needles have a rounded, blunt point that can dissect through friable tissue without cutting. They occasionally are used for suturing soft, parenchymal organs, such as the liver or kidney.

Suture Selection for Different Tissue Types

Considerations for suture selection include the length of time the suture will be required to help strengthen the wound or tissue, the risk of infection, the effect of the suture material on wound healing, and the dimension and strength of the suture required.

Abdominal closure

The rectus fascia may be closed with either an interrupted or a continuous suture pattern; however, most surgeons routinely close the rectus fascia with a simple continuous suture pattern. When using an interrupted pattern, numerous suture materials are adequate; however, suture that is rapidly removed (e.g., surgical gut) should be avoided in catabolic (i.e., hypoalbuminemic and malnourished) patients. When a continuous suture pattern is used, a strong nonabsorbable or standard absorbable monofilament suture with good knot security should be used (e.g., polypropylene, polybutester, polydioxanone, polyglyconate). One size larger suture than would normally be used is preferred for a continuous suture pattern. The knots should be tied carefully, and three or four square knots (six or eight throws) should be placed. Standard absorbable suture (e.g., polydioxanone or polyglyconate) may be preferable to prevent large amounts of foreign material from remaining permanently in the incision.

Muscle and tendon

Muscle has poor holding power and is difficult to suture. Absorbable or nonabsorbable suture material may be used. Sutures placed parallel to the muscle fibers are likely to pull out, so consideration should be given to the type of suture pattern chosen (see p. 75). Suture material used for tendon repair should be strong, nonabsorbable, and minimally reactive. Suturing with a taper or taper-cut needle generally is less traumatic to these tissues. The largest suture that will pass without trauma through the tendon should be used.

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Sep 11, 2016 | Posted by in SMALL ANIMAL | Comments Off on Biomaterials, Suturing, and Hemostasis

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