Sutures and Grafts in Pelvic Reconstructive Surgery
Marjorie Jean-Michel
Willy G. Davila
INTRODUCTION
Surgeons require tools to accomplish their art. Despite our recent attempts at standardization of surgical techniques, reconstructive surgery is still an art. Besides surgical instruments, sutures, grafts, and other implants are required to complete a surgical procedure. Grafts have recently been widely promoted for use in vaginal surgery with only limited supportive evidence. Surgeons should familiarize themselves with the various available suture and graft types, as well as their indications and biologic behavior, in order to optimize surgical outcomes.
SUTURES
The surgeon’s most indispensable tool is the suture. It is meant to augment the patient’s own ability to re-establish normal anatomy. Sutures are available in many varieties and are categorized as permanent or absorbable, natural or synthetic, braided or nonbraided, and coated or uncoated. Suture selection depends greatly upon the tissue involved, the anticipated duration of wound closure, the healing environment, and the surgeon’s preference.
The ideal suture may have the following characteristics (1):
Easy to manipulate
Does not readily tear tissue
Has enduring tensile strength
Maintains knots securely
Is nonallergenic
Resists infection
Changes in a predictable fashion over time
The unfortunate reality is that the ideal suture does not exist. In fact, sutures may carry several of the different properties, but not all of them. When selecting a suture, the surgeon must determine which properties can and cannot be compromised in that particular setting. Table 32.1 summarizes the various suture materials (1).
Absorbable Sutures
Natural Materials
Plain catgut is not derived from feline tissue, but from the jejunum and ileum of sheep. It is shaped into longitudinal strips and treated with formaldehyde, which confers resistance to enzymatic degradation. These strips are joined, desiccated, cut, and sterilized with cobalt 60 irradiation. This foreign body elicits a pronounced tissue response and is rapidly metabolized by immune cell proteases. Tensile strength is maintained for approximately 5 days only, and the suture is completely absorbed after 14 days.
Catgut treated with chromium salts gives rise to the chromic suture, a new and stronger material. Its tensile strength is 4-fold greater than plain catgut. It is enzymatically lysed fairly quickly, maintaining its tensile strength for 14 to 21 days. After 14 days, 34% of its original strength is retained. It is used on serosa, viscera, and the vagina, as these tissues heal within this period of time.
Synthetic Materials
Polyfilaments are thin filaments braided into various sutures. Polyglycolic acid (DexonTM) is a copolymer of glycolic acid (hydroacetic acid) that is transformed into a linear chain polymer. It is then converted into long filaments that are braided into different sizes. Polyglactin (Vicryl) is a copolymer of lactic acid and glycolic acid that is also braided. Unlike catgut, both are slowly hydrolyzed, resulting in less inflammation. Absorption occurs in a predictable
fashion: it begins in 10 to 15 days and is completed in 28 to 70 days. By 21 days, 40% to 50% of its original tensile strength is maintained. These synthetic materials are more difficult to handle and more prone to knot slippage than natural materials. Coated forms of these sutures, such as Dexon-Plus and Coated Vicryl, were constructed to minimize these shortcomings. Dexon-S is composed of thinner filaments intertwined into a structure that is easier to handle, but with less knot security.
fashion: it begins in 10 to 15 days and is completed in 28 to 70 days. By 21 days, 40% to 50% of its original tensile strength is maintained. These synthetic materials are more difficult to handle and more prone to knot slippage than natural materials. Coated forms of these sutures, such as Dexon-Plus and Coated Vicryl, were constructed to minimize these shortcomings. Dexon-S is composed of thinner filaments intertwined into a structure that is easier to handle, but with less knot security.
TABLE 32.1 Types of Suture | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Monofilaments are single-stranded synthetic sutures, including PDS (polydioxanone) and Maxon (polyglyconate). Tensile strength, inflammatory reaction, and knot security are similar to those of polyfilaments. The level of inflammation, however, is less marked. The lack of interstices confers an increased resistance to bacterial infection. By postoperative day 28, Maxon retains 40% its original tensile strength, while PDS retains 50% of its original tensile strength. This feature is desired in patients with delayed wound healing, as in immunosuppressed individuals. In fact, Maxon and PDS are favored sutures in vaginal and pelvic surgery. Their monofilamentous composition
serves as both an advantage and a disadvantage. They are more difficult to handle and make knot tying more challenging. Aggressive suture handling with instruments can readily damage and weaken the suture, resulting in compromised wound healing.
serves as both an advantage and a disadvantage. They are more difficult to handle and make knot tying more challenging. Aggressive suture handling with instruments can readily damage and weaken the suture, resulting in compromised wound healing.
Nonabsorbable Sutures
Natural Materials
Cotton is a naturally occurring absorbable suture that is no longer popular. It handles well but is comparatively weaker than silk. Similarly, it causes significant inflammation.
Surgical silk is also considered nonabsorbable, although it retains 50% of its tensile strength after 1 year, with minimal loss after 2 years. It is easily handled and offers good knot security secondary to its low memory. It elicits a significant immune response, which deters its use by many surgeons.
Synthetic Materials
Nylon is composed of synthetic fiber polymers. It can be manufactured as monofilaments, or twisted into polyfilament constructs. Unlike natural products, it produces less inflammation, making it a favorable option in skin closure. Twenty percent of its original tensile strength is lost by hydrolysis after the first year. It remains unchanged thereafter. Nylon is easy to handle but is more prone to knot unraveling and slipping. Good surgical technique is critical.
Polypropylene is a monofilamentous synthetic polymer of propylene [poly (1-methylethylene)]. Its structural makeup does not allow for easy handling or knot security, as it is quite stiff and has very high memory. It has low tensile strength compared to other nonabsorbable synthetic materials. Polypropylene has the advantage of low tissue reactivity and very slow absorption, which makes it useful in anchoring permanent materials, such as grafts, or in areas of slow wound healing.
Polyester sutures (Ethibond) are multifilament materials that exist in several forms. They can be noncoated or coated, with various agents: silicone, polybutilate, or polytetrafluoroethylene (PTFE or Teflon). The uncoated versions offer improved knot security, while the coated versions are easier to handle. Specifically, silicone coating improves suture manageability, at the expense of increased knot slippage and inflammation. Polybutilate coating causes less inflammation and is easy to handle, while PTFE coating simply facilitates handling. The common disadvantage of all these braided materials is they must be completely excised from tissue if infected.
Gore-Tex is a nonabsorbable suture composed of expanded PTFE, an inert compound. It therefore elicits minimal inflammatory reaction. PTFE is “expanded” to produce a material that is porous, with an air volume of approximately 50%. It was originally designed for cardiovascular anastomotic procedures. Its low immune response results in decreased adhesion formation. By the same token, infiltration of leukocytes and fibroblasts may be hindered, resulting in less tissue ingrowth. This feature is not necessarily favorable in its larger mesh form and may be associated with a heightened susceptibility to infection. As a consequence, its use in pelvic reconstructive surgery is becoming less common.
The metal suture material available is stainless steel wire, created from a metal alloy. It provides the best tensile strength and knot security of any of the suture materials previously mentioned. It produces less of an immune response than the other nonabsorbable materials. In exchange, it is very difficult to handle and deforms quite easily. An attempt to overcome this feature has been made by twisting the material into multistrands. This new, thicker construct must be managed with great care, as it can unintentionally penetrate gloves quite readily.
Suture Sizes
Sutures exist not only in different types, but also in different diameters. The standard classification system of suture sizes was introduced by the United States Pharmacopeia in 1937. This metric value designates numerical whole values for large sizes and multiple zeroes for smaller sizes. For example, 2-0 (or 00) is larger than 3-0 (000), which is larger than 4-0 (0000).
Needles
The suture unit is completed by its attachment to a sterile, stainless steel needle. The needle is composed of a distal point, a middle body, and a proximal swage. The point is designed to penetrate the tissue with little resistance. It exists as a cutting point, which facilitates entry into dense tissues; a taper point, which enters by way of stretching, thus minimizing tissue shearing and injury; and a blunt point, which does not cut tissue but dissects it. The body is the anchoring structure upon which the needle driver is placed. It, too, varies in conformation. The body of the needle can be straight and easily controlled by the hand for skin closure, such as the Keith needle; curved for use in smaller spaces; and compound curved, which has two different
angulations (80 degrees proximally and 45 degrees distally), and is primarily used in microvascular and ophthalmic surgery. The shape of the curved needle ranges in fractions of an inch, from 1/4, 3/8, 1/2, 5/8. The greater the curvature, the more wrist rotation required to deliver the needle through tissue. The swage, which directly attaches to the suture, can be shaped as an eyelet or flattened onto the suture itself. Each of these features affects the degree of tissue trauma made upon entry and the durability of the suture being introduced. (See Lai SY, Becker DG. Suture and needles. 2004. http://www.emedicine.com.)
angulations (80 degrees proximally and 45 degrees distally), and is primarily used in microvascular and ophthalmic surgery. The shape of the curved needle ranges in fractions of an inch, from 1/4, 3/8, 1/2, 5/8. The greater the curvature, the more wrist rotation required to deliver the needle through tissue. The swage, which directly attaches to the suture, can be shaped as an eyelet or flattened onto the suture itself. Each of these features affects the degree of tissue trauma made upon entry and the durability of the suture being introduced. (See Lai SY, Becker DG. Suture and needles. 2004. http://www.emedicine.com.)
Clinical Applications
The choice of a particular suture for a surgical purpose is based traditionally on previous experience and more recently on scientific rationale. As such, catgut suture is rarely used in reconstructive surgery, although it may be used for tubal ligations and abdominal hysterectomies. Most hysterectomies are performed utilizing polyglactin sutures, which may also be used for anterior and posterior colporrhaphies and closure of the vaginal epithelium. These sutures are typically in place for 4 to 6 weeks, allowing for significant healing time of the vaginal epithelium as well as connective tissue and fascia.
Fascial defect repairs as well as suspensory procedures are typically performed utilizing synthetic, nonabsorbable, or delayed absorbable sutures. As such, polypropylene sutures are commonly used for paravaginal repairs, Burch colposuspensions, and abdominal sacrocolpopexies. The principal benefit of a synthetic monofilament suture such as polypropylene is that there is minimal tissue reaction, such that if the sutures are placed through the vaginal epithelium inadvertently, no significant inflammatory response occurs and the suture typically becomes buried spontaneously. This is in comparison to multifilament sutures such as Gore-Tex, which have been used for Burch colposuspensions and sacrocolpopexies, and are associated with some, albeit low, risk of suture infection and/or rejection. Multifilament sutures such as polyester (Ethibond) and silk are utilized in situations where permanent suspension or attachment is necessary. However, their multifilament nature may lead to a significant reaction and possibly infection, resulting in the formation of granulation tissue and the need to remove the suture. This has led to a decreased use of both of these suture materials.
As such, most pelvic surgeons’ preferences are limited to the use of polyglactin (i.e., Vicryl), polydioxanone (i.e., PDS), and polypropylene (i.e., Prolene) sutures. Development of healing abnormalities due to reactions to sutures and grafts has lead to reduced experimentation with suture materials and adherence to traditional suture materials of known reactivity.
GRAFTS
The use of artificial implanted materials to enhance tissue repair has long been a hallmark of general surgery. Based on previous data collected from hernia medicine, the use of grafts in pelvic reconstructive surgery has increased over the past 10 years. Today, abdominal herniorrhaphies are usually performed with graft augmentation, resulting in improved outcomes; the recurrence risk of abdominal incisional hernias has been shown to be reduced by half (2). Intuitively, grafts have also been used to enhance treatment of vaginal prolapse, often considered “hernias of the vagina.” This makes sense, due to the relatively high recurrence rate of prolapse surgeries. The popularization of fascial defects and tears as a primary etiology for the development of genital prolapse has lead to increased graft utilization to augment fascial strength in an attempt to promote repair longevity and permanence.
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