Multifilament sutures are generally easier to handle and to tie than monofilament sutures, however, all the synthetic materials require a specific knotting technique. With multifilament sutures, the nature of the material and the braided or twisted construction provide a high coefficient of friction and the knots remain as they are laid down. In monofilament sutures, on the other hand, the coefficient of friction is relatively low, resulting in a greater tendency for the knot to loosen after it has been tied. In addition, monofilament synthetic polymeric materials possess the property of memory. Memory is the tendency not to lay flat, but to return to a given shape set by the material's extrusion process or the sutures packaging. The RELAY suture delivery system delivers sutures with minimal package memory due to its unique package design.
Suture knots must be properly placed to be secure. Speed in tying knots may result in less than perfect placement of the strands. In addition to variables inherent in the suture materials, considerable variation can be found between knots ties by different surgeons and even between knots tied by the same individual on different occasions.
General Principles of Knot Tying
Certain general principles govern the tying of all knots and apply to all suture materials.
- The completed knot must be firm, and so tied that slipping is virtually impossible. The simplest knot for the material is the most desirable.
- The knot must be as small as possible to prevent an excessive amount of tissue reaction when absorbable sutures are used, or to minimize foreign body reaction to nonabsorbable sutures. Ends should be cut as short as possible.
- In tying any knot, friction between strands ("sawing") must be avoided as this can weaken the integrity of the suture.
- Care should be taken to avoid damage to the suture material when handling. Avoid the crushing or crimping application of surgical instruments, such as needleholders and forceps, to the strand except when grasping the free end of the suture during an instrument tie.
- Excessive tension applied by the surgeon will cause breaking of the suture and may cut tissue. Practice in avoiding excessive tension leads to successful use of finer gauge materials.
- Sutures used for approximation should not be tied too tightly, because this may contribute to tissue strangulation.
- After the first loop is tied, it is necessary to maintain traction on one end of the strand to avoid loosening of the throw if being tied under nay tension.
- Final tension of final throw should be as nearly horizontal as possible.
- The surgeon should not hesitate to change stance or position in relation to the patient in order to place a knot securely and flat.
- Extra ties do not add to the strength of a properly tied knot. They only contribute to its bulk. With some synthetic materials, knot security requires the standard surgical technique of flat and square ties with the additional throws if indicated by surgical circumstances and the experience of the surgeon.
An important part of good suturing technique is correct method in knot tying. A seesaw motion, or the sawing of one strand down over another until the knot is formed, may materially weaken sutures to the point that they may break when the second throw is made or, even worse, in the postoperative period when the suture is further weakened by increased tension or motion.
If the two ends of the suture are pulled in opposite directions with uniform rate and tension, the knot may be tied more securely. The point is well-illustrated in the knot tying techniques shown in the next section of this manual.
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