Small Animal Laparoscopy and Thoracoscopy. Группа авторов

Materials for Minimally Invasive Suturing

      Conventional Sutures

      Conventional suture materials are routinely used in MIS, especially for interrupted sutures or ligatures. Braided synthetic absorbable sutures are often favored over monofilament synthetic absorbable sutures for intracorporeal suturing. The primary reason for this preference is the ease of handling that follows from the decreased memory of braided versus monofilament sutures. Furthermore, braided sutures are more resistant to instrument-induced damage during the knotting process. As knots are formed, there is significant interstrand friction, commonly known as chatter. This friction can induce significant damage to suture materials, particularly monofilaments. Braided materials are less vulnerable to this damage because their strength is distributed over many fibers similar to the cables of a suspension bridge. Braided materials are not without their downside, however. They have considerably more tissue drag than monofilament sutures, and they can harbor and potentiate bacterial infections. To minimize these effects, suture manufacturers have devised two solutions. First, application of coating agents, such as caprolactone and calcium stearate, fills in the gaps in the interstices of the braid and decreases friction during tissue passage. Second, some manufacturers use antimicrobial coatings on their materials to preemptively address suture-potentiated infections.

Figure 2.5 Double‐ligated cystic duct (A) and right ovarian pedicle (B) using 2 strands of 2‐0 polyglactin 910, with one double throw and two single throws. Use of a short suture strand, 15 cm or less, facilitates knot tying. Thus, using two separate strands may be more effective than to attempt two sutures with one longer strand. Laparoscopic knots tend to be weaker than openly tied, so the surgeon needs to take care to apply even and adequately high tension on the knots.

Knot security is a function of suture interstrand friction. Braided suture materials in general have a higher coefficient of friction than monofilament sutures. As such, braided sutures can form secure knots with fewer throws than monofilament sutures. However, knot security varies greatly between materials and sizes [7]. We have found one double throw (“Surgeon's throw”) and two single throws on 2‐0 polyglactin 910 to be safe for suture ligated ovarian pedicles and cholecystectomy (Figure 2.5), with two ligations per pedicle/bile duct. However, if the suture is not used for ligation but instead approximating tissues under tension, it is likely advisable to add one or two throws. Intracorporally tied knots tend to be weaker than knots tied by conventional open surgery [8]. This is true also for robotically tied knots [9]. Inappropriately tied knots can severely impact knot security. If tension is applied unequally or inadequately during tying, the knot may have gaps between throws, i.e. an air knot. Air knots further contribute to lack of knot security [10]. Therefore, the surgeon interested in using laparoscopic knot tying need to perfect his or her technique and take care to adequately tighten each throw when tying intracorporeal knots.

      Suture Needles

Conventional 1/2 and 3/8 suture needles are commonly used in MIS. Specialized half‐curved (“ski”) needles can be advantageous when operative space is limited. The J needle may be beneficial when closing port incisions. Straight needles can be used in special circumstances, but limited access precludes their general usage (Figure 2.6).

      It is helpful to use needles that are flattened along their bodies to allow stable grasping with an endoscopic needle holder. Taper or tapercut points are best. Reverse cutting needles may be used, but one must be conscious of the cutting edge on the convex surface. Inadvertent cutting of vascular structures is possible because of poor visualization of the back side of the reverse cutting needle. Usage of cutting needles should be avoided because the sharp concave edge cuts through tissue during needle passage. This can lead to suture “pull‐through” as well as increased hemorrhage.

      Suture needles used in MIS should be strong enough to resist the increased forces placed on them during intracorporeal suturing. Suture needles are made of stainless steel alloys containing chromium and nickel. Chromium confers corrosion resistance, and nickel imparts strength to the needle. With the optimal component ratios, suture needles demonstrate the ability to deform without fracture, a property known as ductility [6]. Major suture manufacturers commonly produce standard and premium grade suture needles as part of their suture line. There is a premium to be paid for higher quality suture needles, which can be custom manufactured in combination with any suture material. Proprietary coatings are applied to suture needles to facilitate their tissue passage.

Figure 2.6 Numerous needle configurations can be used for intracorporeal suturing. In general, whereas shorter needle arcs allow easier needle retrieval, longer needle arcs facilitate working where access is limited.

Figure 2.7 Barbed suture has greatly facilitated intracorporeal continuous suturing in veterinary medicine.

      Barbed Suture

Two of the most difficult aspects of intracorporeal suturing are square knot formation and to maintain suture tension during continuous pattern suturing. The incorporation of barbed suture technology into MIS has made a significant impact in alleviating these difficulties (Figure 2.7). Barbed suture are knotless but also carries the advantage of multiple fixation points and tension distribution over the entire incision. The latter feature greatly enhances the strength of the repair [11]. In fact, even when cut at several sites, barbed suture can maintain the integrity of a closure [12]. Barbed suture technology has increased the number of clinical applications of intracorporeal suturing in small animal MIS (Figure 2.8).

Figure 2.8 A number of clinical applications have been facilitated by barbed suture. (A) cystopexy, (B) colopexy, (C) gastropexy, (D) peritoneal‐pericardial diaphragmatic herniorraphy.

Several barbed sutures (Quill™, V‐loc™, and Stratafix™ spiral; Table 2.1) are all produced by cutting into a parent strand of smooth suture. This is readily apparent when closely observing the suture strand (Figure 2.9). This manufacturing technique reduces the strength of the suture. Therefore, it is important that the surgeon understands the tensile strength of the particular suture used. Relative strength compared to the parent strand is presented in Table 2.1. To date, the most commonly used barbed suture in veterinary medicine