Mastering the use of needles, sutures, and instruments, as well as the technique of knot tying, is the technical foundation of the surgeon’s craft. A bewildering array of needles and sutures are available. Some offer distinct advantages in specific situations, while others are simply competitive equivalents. This chapter describes the variety of available needles and sutures, guidelines for their selection and use, and principles and techniques of surgical knot tying.

Characteristics of surgical needles include their attachment to the suture, the shape of the tip, the suture lever in tissue, and the curve of the needle. Surgical needles consist of three structural parts: the point or tip, the body, and the swage or eye. Their specific design depends on their intended surgical use and each variation has merits and disadvantages.

Swage

Three types of eye are commonly used in surgery: swaged, controlled release or “pop-off,” and open. With a swaged needle, the suture is placed inside the hollowed end of the needle and crimped in place by the manufacturer. This anchors the suture to the needle, and the suture must be cut to free the needle. Because of this security, a swaged needle is ideal for a running suture line and thus is often selected for obstetric applications. The swaged end is flattened to permit a secure grasp by the needle driver. Therefore, during suturing, the swage is ideally grasped rather than the rounder needle body to avoid lateral needle rotation. The diameter of the swaged needle end is larger than that of the rest of the needle and determines the size of the suture tract through tissue (Bennett, 1988).

Controlled-release needles differ from a swaged-on needle in that they allow the surgeon to release or “pop off” the needle with a sharp tug of the needle holder. This saves the time required to cut the suture with scissors. This design is used for interrupted sutures or for vascular pedicle ligation.

Last, the open-eyed needle is fashioned similar to a sewing needle, and suture must be threaded through the eye before use. Open-eyed needles offer the ability to pair a great variety of suture types and needles. Disadvantages include the time needed to thread the eye and its easy unthreading during suturing. Open-eyed needles are rarely used in obstetric surgery.

Body

In cross section, the needle body may be round or ovoid and is tapered gradually to the point. Ovoid needles may be flattened on top and bottom with rounded sides, or flattened on all four sides, producing a square or rectangular body. Some needle bodies also are ribbed longitudinally on the inner curvature to allow them to be securely grasped by the needle holder. For most obstetric surgery, the needle body is round and smooth.

The length of the needle body may be either straight or curved. Most curved needles have either a ½ or ⅜ circle configuration, although a ⅝-circle needle is sometimes used in vaginal surgery (Fig. 1-1). The ⅜-circle needle is most commonly used in obstetrics. However, the ½- or ⅝-circle design aids maneuvering in small places.

Point

Needles are most commonly classified according to the cross section of their point (Fig. 1-2). Needle points may be tapered, cutting, reverse cutting, or blunt. As shown, cutting needles have three sharp edges and are more likely to pull through tissue than are tapered points. Tapered points are used for softer tissues such as uterus, vagina, and fascia (Fig. 1-3). The blunt point is used for very friable tissues, or occasionally for cannulating, and does not easily penetrate gloves.

Conventional-cutting needles have the cutting edge directed toward the wound edge. In contrast, the reverse-cutting needle has its flat surface toward the wound (see Fig. 1-2). For this reason, conventional-cutting needles have a greater tendency to pull through the edge when tightened. Although most commonly available cutting needles are of the reverse-cutting design, conventional-cutting needles may be useful for very fine skin suturing.

Needlestick injuries are a frequent concern during suturing. DeGirolamo and colleagues (2013) reviewed several methods to reduce the incidence of sharp surgical injuries and concluded that many maneuvers with sharp instruments can be replaced with less dangerous techniques. For example, there is moderate-quality evidence that double gloving reduces perforations (Mischke, 2014). Mornar and Perlow (2008) also have shown that blunt needles are suitable and likely decrease the incidence of needlestick injuries during episiotomy repair.

Technique

Curved needles are designed to be grasped and driven through tissue with a needle holder, also called a needle driver. The placement of the needle in the holder is dependent on the tissue to be sutured. In cases in which a thick tissue segment is traversed or in which little resistance is expected, the needle may be grasped ⅔ or ¾ of the distance from point to eye (Fig. 1-4). One example is hysterotomy incision closure. If tougher tissue is anticipated, then the needle is more appropriately grasped in the middle or even slightly more toward the point. This aids needle passage yet helps avoid bending deformation of the needle. One example is sutures placed through the pubic periosteum.

Curved needles are never grasped with the hand. In a review of surgical glove perforation in obstetrics, Serrano and associates (1991) described a 13-percent rate of glove perforation. Most punctures occurred in the nondominant hand and suggested perforation due to grasping the needle. Such technique increases the risk of infection transmission to both patient and physician (Dalgleish, 1988). Longer, straight needles of the Keith type are sometimes used manually without a needle holder for mattress-type skin closures. These, too, are also likely to cause injury.

Some form of suture has been used for centuries either to approximate tissue or to ligate vessels. Wound suturing was described as early as 3500 BC in an Egyptian papyrus, and it was used by Galen, physician to the gladiators, to stop their bleeding (Snyder, 1976; Stone, 1988). Joseph Lister (1869), who pioneered the concept of antisepsis, made a major advance in suture material. His chromatization of gut suture in 1876 resulted in significant prolongation of suture tensile strength. In Lister’s day, the violin was often referred to as a “kit.” The most common source of gut material for suture was violin strings fashioned from sheep or ox intestines. Thus the term “kitgut” was introduced, and this later was modified to “catgut” (Stone, 1988).

Table 1-1 describes various characteristics of suture material. The ideal suture would cost little, tie easily and securely, possess superb tensile strength, stretch to accommodate wound edema, exhibit recoil to return to its initial length, and have no adverse effect on wound healing or infection rates (Yag-Howard, 2014). Unfortunately, no suture meets all of these requirements. Thus, compromises are made when selecting suture material, and both advantages and disadvantages are weighed.

Characteristics

Physical Characteristics

Several terms describe the physical characteristics of suture material. First of these, physical configuration refers to mono- or multifilamentous construction. Multifilamentous material ties more easily but has an increased tendency to harbor bacteria in its braiding (Balgobin, 2016; Bennett, 1988).

Capillarity refers to the ability of fluid to track along the suture. Namely, if one suture end is exposed to liquid, the ease with which fluid wicks to the opposite dry end defines its capillarity. In general, multifilament sutures have greater capillarity (Geiger, 2005). Fluid absorption ability is the capacity of suture to absorb fluid when immersed. Both of these characteristics increase the tendency to absorb and retain bacteria. For example, braided nylon, a material with high fluid-absorption capability and capillarity, absorbs three times as many bacteria as the corresponding monofilament suture (Bucknall, 1983).

Suture diameter is measured in tenths of a millimeter and is commonly expressed according to United States Pharmacopeia (USP) standards (Table 1-2). With USP nomenclature, a midpoint diameter size is designated as 0, and as suture diameter increases above this, arabic numbers are assigned. For example, no. 1 catgut is thicker than 0-gauge catgut. In contrast, as suture diameter decreases from this designated midpoint, 0s are added. By convention, an arabic number followed by a 0 also may be used to reflect the total number of 0s. For example, 3-0 suture may also be represented as 000. Therefore, 3-0 suture is greater in diameter than 4-0 (0000) suture. That said, specific tensile strength and diameter affect USP terminology, and thus, 4-0 catgut has a slightly larger diameter than 4-0 nylon.

Tensile strength is defined as the amount of weight necessary to break a suture divided by its cross-sectional area. In this respect, the breaking load will be quadrupled by a doubling of suture diameter. A knotted suture has roughly a third the strength of an unknotted suture, but the strength depends to some degree on the type of knot used, as discussed subsequently (Rodeheaver, 1981; Tera, 1977). Table 1-3 lists relative tensile strengths of various knotted and unknotted suture materials. Note the dramatic decline in strength of knotted versus unknotted suture for all except metallic sutures. Figure 1-5 depicts the relationship between suture diameter and tensile strength. Figure 1-6 depicts tensile strength over time following suture placement. The tensile strength also is affected by surgical technique. For example, a stray knot in a Prolene suture decreases tensile strength by 17 percent. Grasping a suture with forceps or needle holder lowers suture strength in a dose-dependent fashion (Abidin, 1989; Stamp, 1988).

Knot strength refers to the force needed to cause a given type of knot to slip, either partially or fully. It is dependent on the coefficient of friction of the material and its stretch capability (Bennett, 1988).

Elasticity refers to the tendency of the suture to return to its original shape after stretching. With high elasticity, a suture will be easily stretched by tissue swelling and will not cut into or through the tissue. Plasticity refers to the proneness of suture to retain its new shape after stretching. A highly plastic suture will retain its larger form even after tissue swelling subsides and thus may become loose.

In addition to elasticity, the tendency of suture material to cut through tissue is also directly related to tensile strength, inversely related to suture diameters, and dependent on tissue type. Of tissues, suture is least likely to cut through fascia, and in descending order, through muscle, peritoneum, and fat (Bennett, 1988; Tera, 1976). Moreover, the force required for suture to tear various tissue types changes during healing. From week 1 to week 2 following surgery, the likelihood that suture will cut through tissue is less than in the immediate postoperative period (Aberg, 1976).

Memory refers to the propensity of a material to return to its original shape after being deformed, for example, after being tied (Bennett, 1988). Suture with a high memory attempts to return to its original shape, and thus does not hold a knot well. Nylon is an example of a suture with a high degree of memory.

Handling Characteristics

Pliability is a subjective term related to how easily suture can be bent. Relatively pliable sutures such as silk are easier to handle than stiffer, monofilament nylon sutures. The coefficient of friction of a suture can be viewed as a measurement of “slipperiness” (Bennett, 1988). The inherent coefficient of friction of a given suture material may be altered by the application of special coatings. Sutures with high coefficients of friction are more difficult to pull through tissue. Materials with low coefficients of friction—for example, monofilament nylon or coated polyglactin—are easier to set by a slipknot, but may more easily come undone. For example, a simple square surgeon knot with uncoated polyglycolic acid (Dexon) approaches maximum knot security, but the same knot tied with coated polyglactin 910 (Vicryl) is insecure (Trimbos, 1984).

Tissue Reaction

All suture material is foreign to the body and will elicit a tissue reaction directly proportionate to the amount of suture material present (Bennett, 1988). In this respect, the fewer sutures used, the better. Furthermore, the diameter of suture used under many circumstances is more closely linked to adhesion formation than the inherent reactivity of the material itself (Stone, 1988).

Three sequential histologic stages reflect the normal reaction of tissue to suture material (Madsen, 1953; Postlethwait, 1975). Stage I lasts from days 1 to 4 and consists of a leukocytic infiltrate of polymorphonuclear leukocytes, lymphocytes, and monocytes. During Stage II, from days 4 to 7, macrophages and fibroblasts arrive. Stage III begins after day 7 and consists primarily of a chronic inflammatory response and the appearance of additional fibrous tissue. Following this, findings diverge according to suture quality. With nonabsorbable suture, a fibrous capsule forms by day 28. With absorbable suture, a continued inflammatory response results in eventual complete suture absorption.

Table 1-4 ranks suture material according to tissue reactivity. Within this ranking, multifilamentous suture elicits greater tissue reaction than monofilamentous material and increases the risk of infection to a greater degree (Alexander, 1967; Sharp, 1982). Risk of infection is also heightened with braided suture material. Braiding can harbor bacteria in its interstices, where they are less susceptible to the cidal actions of leukocytes. Knots similarly provide interstices favorable to bacterial growth, which suggests that the number of knots placed should be minimized (Moy, 1992; Osterberg, 1983).

Specific Suture Types

Properties of absorbable and nonabsorbable sutures are detailed in Table 1-5 and Table 1-6. The terms absorbable and nonabsorbable are relative. Plain catgut, for example, which is an absorbable suture, may persist in tissue for many years (Postlethwait, 1975). And, with the exception of polyester (Dacron), polypropylene (Prolene), and stainless steel, all “nonabsorbable” sutures eventually degrade or are absorbed (Edlich, 1974; Nilsson, 1982). For these reasons, by convention, sutures that retain significant tensile strength beyond 60 days are commonly classified as “nonabsorbable” (Bennett, 1988; Moy, 1992).