The aim of suturing is to hold tissues together with the least interference with their blood supply. Apply the technique most suitable for the tissue, but use the smallest size and, for economy, the fewest types of sutures.
There are three basic knots: square, surgeon’s, and double throw ( Fig. 2.1 ).
Square knot (see Fig. 2.1A ) . The simple square knot holds in polyglactin and polyglycolic acid sutures if they are uncoated (Dexon). If coated sutures (Vicryl and Dexon S) are used, an additional throw is needed (see Fig. 2.1B ). Care must be taken to lay each throw square to the last.
The surgeon’s knot (see Fig. 2.1C ) allows the suture to hold the tissue without slipping after placement of the first throw but is no more secure than the square knot, requiring, except with Dexon, additional throws.
The double-throw knot (see Fig. 2.1D ), essentially a double surgeon’s knot, has the greatest knot-holding ability for all suture materials. Only polydioxanone (PDS) and nylon (Ethilon, Dermalon) require an extra throw. Polyglyconate (Maxon) was found to be the best for knot-holding capacity and breaking force. To be absolutely safe, tie synthetic absorbable sutures (SASs) with three knots. Monofilament nonabsorbable sutures (NASs) may require six or even seven extra throws, all placed flat.
Tie a suture while holding it near its free end; the suture may thus be used twice, saving suture material and time. Instrument ties are somewhat slower to make but use appreciably less suture material.
Individual surgeons have their own preferences for sutures, but two important variables must be considered: the persistence of strength and the degree of tissue reactivity. The initial strength is proportional to size, but the rate of loss of strength is a function of the suture material. The rate of absorption also depends on the suture material, but it is not directly related to the rate of loss of strength. In general, the strength of the suture is lost much more rapidly before it has been absorbed. A suture must maintain sufficient strength to ensure adequate apposition of tissue until the wound can withstand stress without mechanical support. Decrease in the strength of a suture during healing should be no more than proportional to the gain in wound strength. Relative absorption of suture material in the subcutaneous tissues: catgut—1 month; polyglactin (Vicryl)—2–3 months; polyglycolic acid (Dexon plus)—4 months; PDS—6 months; polyglyconate (Maxon)—7 months. Bladder regains 70% of tensile strength in 2 weeks, fascia 50% in 2 months, and skin 30% in 3 weeks.
Reactivity of the tissue to the foreign body depends on the size and type of suture material and the type of reaction it invokes. The larger the size, the greater the reaction:
|Most Reactive||→||Catgut |
|→||Synthetic absorbable |
Absorbable and nonabsorbable sutures have different effects. Plain catgut (PCG) and chromic catgut (CCG) sutures, being absorbed by proteolytic enzymes, have quite a variable absorption time and incite the most reaction in the tissue. In addition, they vary in tensile strength, which is generally lower than that of synthetic sutures. SASs, in contrast, are removed by hydrolysis and have moderate tissue reactivity and predictable absorption times. Those made from polyglycolic acid (Dexon, Vicryl) retain 20% of their strength at 14 days, and those made from PDS retain 50% of their strength at 4 weeks, but neither is absorbed for several months. In infected urine, catgut sutures retain the most strength. NAS as monofilaments stimulate the least reaction in the tissues and have the least attraction for bacteria; when braided, they handle better and tie more securely. They are unsuitable in the presence of bacteria or urine. Silk and cotton rapidly lose their strength after the second month but probably are useful in the outer layer of an intestinal anastomosis and in the mesentery. Nylon is a polyamide, Dacron is a polyester, and polyethylene and polypropylene are polyolefins; of these, nylon loses its strength first.
A recent addition to the suture armamentarium are the barbed suture varieties. A bidirectional barbed suture made by Quill Medical Inc. was approved by the Food and Drug Administration (FDA) in 2004, and a unidirectional barbed suture made by Covidien (V-Loc) was approved in 2009. These sutures are manufactured with tiny barbs etched onto a monofilament suture and spaced approximately 1 mm along the entire length of the suture. Sutures are monofilament and come in a variety of absorbable and nonabsorbable materials, and come in a variety of needles for specific uses. Once the suture is passed through tissue, the barbs provide anchoring and prevent backward slipping of the previously thrown sutures. With each individual barb to tissue connection contributing to the overall strength of the closure, less tension is placed on the knot(s) holding together a traditional closure. Their ease of use also includes a decreased need for slack management as an assistant instrument is not needed to follow and maintain tension on the closure. These sutures have gained popularity among surgeons, especially within the fields of laparoscopy and robotics where knot-tying has increasing difficulty and surgical exposure is more limited. Two common uses include the renorrhaphy closure in partial nephrectomy and the vesicourethral anastomosis in radical prostatectomy.
Table 2.1 summarizes the characteristics of several sutures. In general, polyglycolic acid sutures are preferable to PCG or CCG for urologic surgery, except in cases of infected urine and for the skin. Because of expense, use as few different sizes and kinds of sutures as possible in a given case. Even though suture selection is a matter for the individual surgeon, certain practical guidelines can be considered.
|Polyglycolic acid||Coated||Dexon plus|
|Plain gut||Plain gut||Plain gut|
|Chromic gut||Chromic gut||Chromic gut|
|Barbed Locking Sutures|
|Absorbable and Non-Absorbable Monofilament Polymers|
Regardless of what suture is used, the immediate strength of the wound is only 40%–70% of the intact structure. With NASs, reduced strength persists at least for the 2 months or so that it takes for the wound to heal completely. For an absorbable suture, the initial strength is the same as that of a nonabsorbable one if an equivalent size is used, but in 1 or 2 weeks the strength declines appreciably. However, by that time, the wound itself has gained enough strength that it balances the diminished strength of the sutures. Thus the wound is most vulnerable to separation during the second week. For this reason, NASs are often used for closure of wounds subjected to stress, such as those of abdominal and flank incisions.
For contaminated wounds, the process of absorbing the sutures stimulates macrophage activity with resultant low tissue oxygen tension. This activity also reduces endothelial migration and capillary formation, thus providing a suitable environment for anaerobic bacterial growth. Polyglycolic acid sutures foster the least inflammatory response of absorbable sutures, and the degradation products themselves may be antibacterial. Conversely, NASs, especially monofilaments, produce the least reaction, but once infected they may stay infected because they remain in the wound. Polypropylene is the best choice in contaminated wounds, much better than silk or cotton. For a debilitated patient, in whom poor healing is expected, use either an NAS or an absorbable suture that retains its strength the longest (i.e., PDS). Retention sutures of heavy nonabsorbable material (polypropylene or wire) may be needed in a debilitated patient, especially if the wound is contaminated. Bolsters cut from a red rubber catheter reduce damage to the skin.
The subcutaneous tissue layer is the site of most wound infections because of the weak defense mechanisms in the fatty areolar tissue. Do not use sutures here unless necessary, and then use the finest minimally reactive absorbable suture of polyglycolic acid. Avoid PCG or CCG.
Waterproof tape is best if it is not subjected to too much tension. Staples, if not too tight, are the next best choice because they do not penetrate the wound, but they cost more and require subsequent removal. A subcuticular stitch of monofilament nonabsorbable material leaves a better wound but must be removed. Polyglycolic acid sutures subcuticularly can remain until resorbed, at the same time producing little reaction. This material is not suitable when placed through the skin as interrupted sutures because absorption depends on hydrolysis, and so it persists on the dry surface.
Urothelium covers the suture line within 5 days. Ureteral and vesical wounds gain strength more rapidly than those in the body wall; normal strength is reached in 21 days. The type of suture material is not as critical here, but absorbable sutures cause less reaction than nonabsorbable ones in the long term. Although more subject to encrustation, absorbable sutures are usually gone before stones can form. Polyglycolic acid sutures are less reactive than CCG sutures, and they have a more predictable rate of absorption. Although polyglycolic acid sutures are not completely absorbed before 28 days, they are usually the better choice, with one exception. In the presence of Proteus infection, resorption is much too rapid and catgut should be used.
Use interrupted NAS, reaching through the muscularis well into the submucosa. If a hemostatic layer is desired, place a running absorbable suture in the mucosa-submucosa. CCG is suitable for sutures penetrating the lumen; otherwise, use SAS. Controlled-release needles speed the process of suturing. In general, place continuous sutures if the tissue is of good quality and interrupted sutures if tissue quality is poor.
Monofilament synthetic NASs are strongest and least reactive.
Size and Type
The size and type of suture and the appropriate needle for various structures are listed in Table 2.2 .