Материал: surgical knot tying manual covidien

III. scientific basis for the selection of surgical sutures (cont’d)

slightly, machine ground, and polished, yielding a relatively smooth surface that is monofilament-like in appearance. Salthouse and colleagues12 demonstrated that the mechanism by which gut reabsorbs is the result of sequential attacks by lysosomal enzymes. In most locations, this degradation is started by acid

phosphatase, with leucine aminopeptidase playing a more important role later in the absorption period. Collagenase is also thought to contribute to the enzymatic degradation of these collagen sutures.

Natural fiber absorbable sutures have several distinct disadvantages. First, these natural fiber absorbable sutures have a tendency to fray during knot construction. Second, there is considerably more variability in their retention of

tensile strength than is found with the synthetic absorbable sutures. A search for a synthetic substitute for collagen sutures began in the 1960s. Soon procedures were perfected for the synthesis of high molecular weight polyglycolic acid, which led to the development of the polyglycolic acid sutures (Dexon™ II, Dexon™ S).13 These sutures are produced from the homopolymer, polyglycolic acid. Because of the inherent rigidity of this homopolymer, monofilament sutures produced from polyglycolic acid sutures are too stiff for surgical use. This homopolymer

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can be used as a monofilament suture only in the finest size. Consequently, this high molecular weight homo-polymer is extruded into thin filaments and braided.13 The thin filaments of Dexon™ II are coated with Polycaprolate™, a copolymer of glycolide and epsilon-caprolactone, to reduce the coefficient of friction encountered in knot construction. Dexon™ S is an uncoated braided suture. The polyglycolic acid sutures (Dexon™ II, Dexon™ S) degrade in an aqueous environment through hydrolysis of the ester linkage.

Copolymers of glycolide and lactide were then synthesized to produce a Lactomer™ copolymer that is used to produce a new braided absorbable suture (Polysorb™). The glycolide and lactide behaved differently when exposed to tissue hydrolysis. Glycolide provides for high initial tensile strength, but hydrolyses rapidly in tissue.13 Lactide has a slower and controlled rate of hydrolysis, or tensile strength loss, and provides for prolonged tensile strength in tissue.13

The Lactomer™ copolymer consists of glycolide and lactide in a 9:1 ratio.

The handling characteristics of the Polysorb™ sutures were found to be superior to those of the Polyglactin 910™ suture.14 Using comparable knot construction and

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III. scientific basis for the selection of surgical sutures (cont’d)

suture sizes, the knot breaking strength for Polysorb™ sutures was significantly greater than that encountered by Polyglactin 910™ sutures. In addition, the mean maximum knot rundown force encountered with the Polysorb™ sutures was significantly lower than that noted with the Polyglactin 910™ sutures, facilitating knot construction.

The surfaces of the Polysorb™ sutures have been coated to decrease their coefficient of friction.14 The new Polysorb™ suture is coated with an absorbable mixture of caprolactone/glycolide copolymer and calcium steraroyl lactylate. At 14 days post-implantation, nearly 80% of the USP (United States Pharmacopoeia) tensile strength of these braided sutures remains. Approximately 30% of their USP tensile strength is retained at 21 days. Absorption is essentially complete between days 56 and 70.

We recently studied the determinants of suture extrusion following subcuticular closure by synthetic braided absorbable sutures in dermal skin wounds.15 Miniature swine were used to develop a model for studying suture extrusion. Standard, full-thickness skin incisions were made on each leg and the abdomen.

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The wounds were closed with size 4/0 Polysorb™ or Coated Vicryl™ (Ethicon, Inc., Somerville, NJ) sutures. Each incision was closed with five interrupted, subcuticular, vertical loops secured with a surgeon’s knot. The loops were secured with 3-throw knots in one pig, 4-throw knots in the second pig, and 5-throw knots in the third pig. The swine model reproduced the human clinical experience and suture extrusion, wound dehiscence, stitch abscess, and granuloma formation were all observed. The cumulative incidence of suture extrusion over 5 weeks ranged from 10 to 33%. Coated Vicryl™ sutures had a higher mean cumulative incidence of suture extrusion than that of Polysorb™ sutures (31% vs. 19%). With Polysorb™ sutures, the 5-throw surgeon’s knots had a higher cumulative incidence of suture extrusion than the 3-throw or 4- throw surgeon’s knot square, 30% vs. 17% and 10%, respectively. This swine model offers an opportunity to study the parameters that influence suture extrusion. Because the volume of suture material in the wound is obviously a critical determinant of suture extrusion, it is imperative that the surgeon construct a knot that fails by breakage, rather than by slippage with the least number of throws. Because both braided absorbable suture materials are constructed with a secure surgical knot that fails only by breakage rather than slippage with a 3-throw surgeon’s knot square (2 =1 = 1), the

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III. scientific basis for the selection of surgical sutures (cont’d)

construction of additional throws with these sutures does not enhance the suture holding capacity, but plays a key factor in precipitating suture extrusion. Finally, it is important to emphasize that the surgeon must always construct symmetrical surgical knots for dermal subcuticular skin closure in which the constructed knot is always positioned perpendicular to the linear wound incision. Asymmetrical knot construction for dermal wound closure becomes an obvious invitation for suture extrusion.

A monofilament absorbable suture (Maxon™) has been developed using trimethylene carbonate.16 Glycolide trimethylene carbonate is a linear copolymer made by reacting trimethylene carbonate and glycolide with diethylene glycol

as an initiator and stannous chloride dihydrate as the catalyst. The strength of the monofilament synthetic absorbable suture, glycolide trimethylene carbonate (Maxon™), is maintained in vivo much longer than that of the braided synthetic absorbable suture. This monofilament suture retained approximately 50% of its breaking strength after implantation for 28 days, and still retained 25% of its original strength at 42 days. In contrast, braided absorbable sutures retained only 1% to 5% of their strength at 28 days. Absorption of the trimethylene carbonate

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