The placement of sutures is the oldest and most common method of wound closure. An ideal suture material would have the following characteristics:
1. A low friction coefficient, so it will not stick to tissue as it is drawn through and not bind to itself as knots are being tied.
2. High pliability, so the suture will not deform tissue when it attempts to straighten itself after being tied.
3. Knot security, so that the ties will not unravel. Sutures with a low friction coefficient will slip more easily and the knots will spontaneously unravel, as opposed to materials with a high friction coefficient.
4. Tensile strength to hold the wound closed.
5. Low tissue reaction to reduce inflammation and the risk of infection.
No suture material possesses all these characteristics; different suture materials are chosen as acceptable compromises for specific types of wounds ( T.a.bIe.,3Z-l). Sutures are generally divided into two general classes based on their rate of degradation:
1. Sutures that undergo rapid degradation in tissues, losing essentially all their tensile strength within 60 days, are considered "absorbable" sutures.
2. Sutures that maintain their tensile strength for longer than 60 days are "nonabsorbable" sutures.
TABLE 37-1 Sutures Commonly Used for ED Wound Repair
This terminology is somewhat misleading, because most absorbable sutures lose half their tensile strength within 4 weeks and some nonabsorbable sutures (e.g., silk and nylon) lose some tensile strength during this 60-day interval. Silk loses approximately half of its tensile strength in 1 year and has no strength at the end of 2 years. Nylon preserves its strength the longest, losing only about 25 percent of its original strength over 2 years.
Sutures are sized according to their diameter. The smallest in general use is designated 6-0 and is used for percutaneous closure on the face and other cosmetically important areas. Suture sizes 5-0 and 4-0 are progressively larger and used on the trunk and extremities. Very thick skin, like that on the scalp and sole of the foot, may require percutaneous closure with size 3-0 sutures.
NONABSORBABLE SUTURES Nonabsorbable sutures can be of either natural or synthetic origin. Natural nonabsorbable sutures include fibers (silk) and metal (stainless steel). Natural materials like silk are easy to handle but incite moderate tissue reaction. Synthetic nonabsorbable fibers include polyamides (nylon), polyesters (Dacron, Dupont), polypropylene, and polybutester. Synthetic suture materials are useful for wound closure because they cause the least tissue reaction. Sutures may be classified according to their physical configuration. Sutures made of one filament are called monofilament sutures (nylon, polypropylene, polybutester, and stainless steel). Knot security with monofilaments is low; therefore at least two square knots (four throws) are required to achieve an adequate hold with 4-0 suture.3 Sutures composed of multiple fibers braided together are called multifilament sutures (silk, nylon, polyester, and stainless steel). Multifilament sutures have greater pliability and increased knot security; they are less likely to unravel than monofilament sutures. 4 The disadvantage of multifilament sutures is that bacteria can migrate down the gaps between the individual filaments into the wound, increasing the likelihood of infection. Nylon and stainless steel are available as both monofilament and multifilament sutures.
ABSORBABLE SUTURES Absorbable sutures are made from either collagen or synthetic polymers. Collagen sutures are derived either from the submucosa of ovine or bovine small intestine (gut suture) or from reconstituted collagen manufactured from bovine tendon collagen (collagen suture). This collagenous tissue is treated in an aldehyde solution, which cross-links and strengthens the suture, making it more resistant to enzymatic degradation. Suture materials treated in this way are called plain gut or plain collagen. If the suture is additionally treated in chromium trioxide, it becomes chromic gut or chromic collagen, which is more highly cross-linked and more resistant to absorption than plain gut or collagen. The shortcomings of collagen and gut sutures include variable strength, unpredictable absorption, and marked inflammation during absorption by proteolytic enzymatic digestion. Gut sutures should be avoided in areas close to surface. Other disadvantages of gut sutures are less tensile and knot strength, a higher infection rate, and more dehiscence than with synthetic sutures. Gut sutures are primarily used to close oral mucosal lacerations, as these wounds heal rapidly and do not require prolonged suture support. Chromium-treated sutures are absorbed less rapidly than plain gut but more rapidly than synthetic sutures. Because of its coating, chromic gut causes less inflammation than plain gut. Chromic gut can also be used in the oral mucosa and for closure of scalp lacerations in children; these sutures typically fall out in 1 to 2 weeks with little or no complication and no need for a return visit for suture removal.
Synthetic substitutes commonly used instead of gut sutures are produced from polyglycolic acid (Dexon, Sherwood Davis & Geck) or polyglactin 910 (Vicryl, Ethicon, Inc.). These braided sutures lose half their strength in tissues approximately 2 weeks after implantation, with absorption essentially complete by 2 months. Two other synthetic absorbable monofilament sutures, polyglyconate (Maxon, Sherwood Davis & Geck) and polydioxanone (PDSII, Ethicon, Inc.), retain their tensile strength longer. The chemical degradation of all these synthetic absorbable sutures is by hydrolysis of their ester bonds and opposed to the proteolytic inflammatory reaction required to degrade gut sutures. Absorbable suture materials are useful when working just below skin surface and in special circumstances when later suture removal is awkward (in children and inaccessible sites). Synthetic braided polymers are less reactive and more resistant to infection from contaminating bacteria than plain or chromic catgut. Polyglycolic acid has excellent knot security and will hold tight with a single square knot (two throws). The main drawback is that its high friction coefficient makes it "bind and snag" when wet. Major uses of polyglycolic acid are for single deep (dermal) closures or superficial fascial closure as well as ligature of small bleeding vessels. Dexon Plus (Sherwood Davis & Geck) is coated with polaxamer 188, which reduces friction and drag through tissues; it is easier to handle but more throws (four to six) are required to prevent knot slippage than with plain polyglycolic acid. Polyglactin 910 (Vicryl, Ethicon, Inc.) mentioned above, is used for deep closures. It has less knot security, similar dry tensile strength, and longer in vivo strength as compared with polyglycolic acid.
INFECTION All sutures compromise local tissue defenses and increase the potential for infection for the following reasons:
1. The trauma of inserting a needle is sufficient to incite an inflammatory response.
2. Sutures that are tied too tightly impair blood flow and cause tissue necrosis of the wound edges.
3. Sutures that penetrate the intact skin provide an avenue for wound contamination through the perisutural cuff ( Fig:.37zl).
FIG. 37-1. A. Epithelial cells migrate along the suture track, forming a perisutural cuff. B. If percutaneous sutures are not removed before 8 days, needle puncture scars develop.
4. The quantity of suture and the chemical reactivity of the material increase the susceptibility to infection.
Sutures made of natural fiber potentate infection more than other nonabsorbable sutures and should be avoided in contaminated wounds. The incidence of infection from monofilament sutures is less than that from multifilament sutures made of comparable materials. Therefore synthetic monofilament sutures should be used for wounds at risk for infection.
NEEDLES The ideal surgical needle should guide the suture through the tissue and provide for meticulous approximation of the wound edges with the least damage.5 All surgical needles are produced from stainless steel alloys, which have excellent resistance to corrosion. High nickel maraging adds resistance to bending and breakage compared with plain stainless steel surgical needles. Every surgical needle has three basic components: swage, body, and point.
The swage is the point of attachment of the suture to the needle. The swaging process provides a smooth junction between the needle and suture as opposed to the rough junction of a thread being attached to the needle by insertion through an eye. Almost all sutures used today have laser-drilled swages down the center of the needle for about 2 mm for the attachment of sutures. Channel needles have a channel cut into one side of the needle for about 6-mm for attachment of the suture. The needle is attached to the suture by uniformly compressing the walls of the swage against the suture. In most uses, this attachment strength is so great that separation of the needle from the suture is most easily accomplished by cutting the suture. A swage requiring lower uniform forces to detach its suture, sometimes called pop-off or control release, is also available. The control release was originally developed for abdominal wound closure, bolus dressings for skin grafts, and hysterectomies in which large numbers of interrupted sutures are used; eliminating the need to cut the suture considerably reduces the length of the operation. For ED wound closure, where a single length of suture is used for multiple loops, the control-release attachment is rarely used.
Both laser-drilled and channel swaged needles are more susceptible to bending and breakage by the needle-holder jaws when grasped over the swage than the body of the needle. To prevent this, the needle should be grasped with the needle holder on the body of the needle, not over the swage. Conversely, suturing is easier when as much of the needle as possible is available for passage through the tissue in one stroke, therefore the needle holder should be close to the swage end but not over it. Since laser-drilled swages are shorter than channel swages, the needle can be grasped with more available for passage through the tissue ( Fig 37-2).
FIG. 37-2. A. The laser-drilled swage is only 1.5 mm long and the needle holder can grip close to the end of the needle, leaving more length available for passage through tissue on the initial movement. B. The channel swage is 6 mm long and the needle holder must grip further along the needle, leaving less needle available for passage through tissue on the initial movement.
The body of the needle is the portion that is grasped by the needle holder. The security with which needle-holder jaws grasp the needle is influenced primarily by the presence of teeth in the needle-holder jaws and the ratchet setting of the needle-holder handle and less so by the cross-sectional shape of the needle body.
The overall biomechanical performance of the surgical needle and holder combination is determined by (1) needle sharpness, (2) needle resistance to bending, (3) needle ductility, and (4) needle-holder clamping moment. Sharpness measures the force needed to pass a needle through a membrane that simulates the density of human tissue, and needle resistance to bending is measured by recording the force required to bend the needle 90°. But the more critical measurement to the emergency physician is the force required to deform the needle irreversibly—the yield moment. Ductility is a measure of the needle's resistance to complete breakage. The needle-holder clamping moment is a measure of the force exerted by the needle-holder jaws on a curved surgical needle.
The body of a suture needle can be defined according to (1) the cross-sectional shape and (2) the geometric configuration. The cross-sectional shape will determine the resistance of the needle to bending as well as the security with which the needle-holder jaws grasp the needle. The cross-sectional shapes in common use are round, triangular, trapezoidal, rectangular with rounded sides, and side-flattened. Rectangular cross sections are created by flattening the inner and outer surfaces of the circular wire during the manufacturing process. Needle holders are able to hold the body more securely when it has flat surfaces parallel to the grasping face of the jaws. With rectangular and trapezoidal shapes, the needle-holding security against twisting and rotation is greater than with any other cross-sectional configuration. Unfortunately, flattening the inner surface reduces resistance to bending, partially reducing the benefit of enhanced needle holding security. For suturing of tough tissues, side-flattened needle bodies are preferred because they exhibit greater resistance to bending than any other cross-sectional shape.
The geometry of the suture needle can be described by its radius, curvature, diameter, length, and chord length. The radius of the needle is the distance from the center of the circle to the body of the needle if the curvature of the needle is continued to make a full circle. The curvature at the needle is measured in degrees of the l 5
subtended arc and may vary from 90° (4) to 225° (s) (Fig 37-3). Needles with a curvature of 135° are ideal to approximate divided edges of thin planar structures that are readily accessible (e.g., skin), requiring a limited arc of wrist rotation to pass the needle. It is difficult to use the 135° needle in deeper tissues (e.g., muscle, fascia) because the limited arc of the wrist rotation involved in passing this needle is usually not sufficient to expose the needle point, which will remain buried in the tissue. The 180° needle is ideally suited for use in deeper tissues because a limited arc of wrist rotation will successfully pass the entire needle through the tissue, allowing adequate exposure of the needle point for easy retrieval of the needle. Curved needles are ideally suited for closure of thin layers, such as epidermis and fascia. The compound curved needle is most often used to alter the 135° needle; the straight point readily facilitates initial entrance through the tissue and controls the depth, while the tight curvature beyond the point permits accurate exiting at a selected level. This design offers a mechanical advantage over the standard needle with one radius of curvature. The compound needle is useful for closure of the dermis.
Needle diameter is the width of the original circular wire utilized in the manufacturing process for the production of the needle. Cord length is the linear distance measured from the central point of the needle swage to the point of the needle. Needle length is the length of the needle measured at the center of the wire's cross section.
The point of the needle extends from the tip of the needle to the maximum cross section of the body. A variety of needle-point configurations have been designed to penetrate specific types of tissue.
The simplest configuration is the taperpoint, where the needle tapers to a sharp tip ( Fig 3.Z.-.4). The taperpoint spreads the tissue without cutting and is used for soft tissue that does not resist needle penetration, such as vessels, fascia, and muscle. The taperpoint makes the smallest hole in tissue and does not cut small incisions at the periphery of the hole.
FIG. 37-4. Taperpoint surgical needle. Top left. Front view of point. The geometry of this needle tapers to a point and has no cutting edges. Side view. The point of this needle has a narrow taperpoint geometry. Bottom right. The body of the needle has a side-flattened cross-sectional configuration.
For suturing cutaneous wounds in the ED, needles with cutting edges are useful to penetrate the relatively tough skin. Cutting-edge needles have at least two opposing edges that are designed to separate tough tissue. Usually, a third cutting edge is added, and the position of this third cutting edge categorizes the needle as either a conventional cutting-edge needle or a reverse cutting-edge needle.
A conventional cutting-edge needle has the third edge located on the inner or concave surface, which produces two effects during suturing: (1) cutting action directed toward the center of the wound and (2) pressure that directs the needle point toward the skin as it passes through tissue (surface-seeking) ( Fig 37-5). The central cutting action has a tendency to divide tissues that ultimately will be encircled by the suture. As the needle passes through the skin, it produces a triangular defect, the apex of which is directed toward the incision. If it is positioned in this apex, the suture may cut through when tied.
FIG. 37-5. Conventional cutting edge surgical needle. Top left. Front view of point. The point of the needle has three cutting edges, with its apical cutting edge on the inside, concave surface of the needle. Side view. Its apical cutting edge is positioned on the inside, concave surface of the needle. Bottom right. The body of the needle has a side-flattened cross-sectional configuration.
In contrast, the reverse cutting-edge needle has the third cutting edge located on the outer, convex curvature of the needle ( Fig..37:6). This configuration has the flat surface of the needle closest to the edges of the incision or wound and directs the point of the needle toward the depth of the wound (depth-seeking). The skin hole left by the reverse cutting-edge needle leaves a flattened wall of tissue for the suture to be tied against, which should resist suture cut-through.
FIG. 37-6. Reverse cutting edge surgical needle. Top left. Front view of point. The point of the needle has three cutting edges, with its apical cutting edge on the outer, convex surface of the needle. Side view. Its apical cutting edge is located on the outer, convex side of the needle. Bottom right. The body of the needle has a side-flattened cross-sectional configuration.
Sharpness of cutting needles can be enhanced by narrowing the point configuration, reducing the angles of the cutting edges, and coating the point with silicone. For conventional and reverse cutting-edge needles, the shape of the needle point is triangular, with two lateral cutting edges and a cutting edge at the apex. The bevel-edge needle has opposing concave surfaces rather than the straight planar surfaces encountered in the standard cutting-edge needles ( Fig 37-7). The angles of the cutting edges at the apex and sides of the bevel cutting edges are 45° and 52.5°, respectively, rather than the 60° for the standard cutting-edge needles, which enhances the sharpness. Coating the cutting-edge surfaces with silicone increases their initial sharpness in tissues and maintains the sharpness after repeated passage (durability).
FIG. 37-7. Bevel conventional cutting edge surgical needle. Top left. Front view of point. The opposing sides of the point of the needle have a concave geometry that reduces the angle of its cutting edges. Side view. The sides of the point of this bevel conventional cutting edge needle are beveled to reduce the angle of its cutting edges. Bottom right. The body of the needle has a side-flattened cross-sectional configuration.
Tapercut needles combine the unique features of taperpoint and cutting-edge needles ( Fig 37.-8). The cutting edges of the tapercut needle extend only a very short distance from the needle tip and blend into a round taper body. This needle provides smooth passage through oral mucous membrane, yet its round shaft without cutting edges will not cut through the deeper tissues.
FIG. 37-8. Tapercut surgical needle. Top left. Front view of point. This tapercut needle has a short reverse cutting edge that blends into a taperpoint geometry. Side view. The reverse cutting edges are confined to a small portion of the tip of this needle. Bottom right. The body of the needle has a side-flattened cross-sectional configuration.
Surgical sutures currently in use have a needle-to-suture diameter ratio of approximately 2:1; the hole left by the needle will not be completely filled by the suture and the unfilled space at each suture hole may invite infection to pass through. To resolve this problem, two new sutures attached to taperpoint needles have been developed. A polytetrafluoroethylene monofilament suture can be produced with a porous microstructure that is approximately 50 percent air by volume. This porous nature allows it to be swaged to a needle that closely approximates its suture diameter; a needle-to-suture ratio of 1:1. Alternatively a monofilament polypropylene suture can be made with a tapered end that is significantly smaller than that of the remainder of the suture, and swaged to a needle with a needle-to-suture diameter ratio approaching 1:1.
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