Knot Construction

Sutures are secured by tying the free ends into a series of square knots, often beginning with the surgeon's knot, where the initial double throw offers better knot security with less slipping of the suture material as the wound is pulled together during tying. The initial double throw is followed by subsequent single throws to create the series of square knots. The square knot is used because it is the strongest knot that can be tied while still keeping the knot small. Knot tying can be accomplished by either instrument or hand tying technique. The instrument tie is useful for both deep and superficial closures. Because the needle holder does not have to be moved on and off the hand, the instrument tie is also faster than hand tying for placing a series of percutaneous sutures during wound closure.

Formation of each throw is accomplished in three steps. The first step is the formation of a suture loop. In the second step, the free suture end is passed through the suture loop to create a throw. The final step is to advance the throw to the wound surface as tension is applied to the suture ends in opposite directions. The initial throw should approximate the wound edges as it is advanced down to the wound surface. Once this throw contacts the wound, the physician will have a preview of the ultimate apposition of the wound edges. Additional throws are placed in succession, reversing the direction of the suture ends as tension is applied. The knot should be constructed by carefully snuggling each throw tightly against the preceding one. The rate of applying tension to each throw should be relatively slow. Ideally, the knotted suture should reapproximate the wound edges without strangulating the tissue encircled by the suture loop.

With the instrument tie, knots can be tied rapidly in the following steps:

1. The suture is placed through the tissue leaving a short free end, usually 2 cm.

2. The initial throw is started by looping the portion of suture attached to the needle around the instrument in a counterclockwise manner.

3. A complete loop is then formed around the tip of the needle holder with the long end directed away from the wound ( Fig 3Z-13).

FIG. 37-13. Formation of the first suture loop. The fixed suture end held by the left hand is wrapped counter-clockwise over and around the needle holder jaws to form the first suture loop. (If the suture is wrapped twice around the needle holder jaws, the first, double-wrap throw of the surgeon's knot square will be formed. A double-wrap, first throw displays a greater resistance to slippage than a single-wrap throw, accounting for its frequent use in instrument ties in wounds subjected to strong, static skin tensions.)

4. The needle holder then grasps the free end of the suture and pulls it through the suture loop while the left hand slides the loop off the needle holder down and around the free end of the suture.

5. Tension is applied to both the fixed and free ends in opposite directions to form half of the square knot.

6. The second throw is created by passing the suture around the needle holder tip in a clockwise direction, opposite that of the first throw. Z. The loop created again has the long end directed away from the wound.

8. The free end is grasped and pulled through the suture loop.

9. The suture loop is slipped off the needle holder to form the second half of the square knot, this time with tension applied in a direction opposite the first throw. 10. Additional square knots are placed down over the first knot. For monofilament and multifilament nylon sutures of 2-0 to 4-0 size, two square knots (four throws)

placed snugly against each other are adequate for knot security. Finer sutures, 5-0 and 6-0, should have three square knots (six throws).

The direction of the suture loops will determine the type of knot created. When successive throws are in opposite directions, a square-type is created. In contrast, a granny-type knot will result when the suture loops are in the same direction for two successive throws.

The major disadvantage of an instrument tie is that it is difficult to apply continuous tension to the suture ends and maintain wound edge coaptation during the process of tying. Consequently, widening of the suture loop and separation of wound edges due to slippage is frequently encountered in wounds subjected to strong tensions. Instrument ties are ideally suited for closing a wound that is subjected to weak tensions. Instrument ties can be accomplished more rapidly and accurately than hand ties while conserving considerably more suture; the parsimonious physician can complete 10 interrupted suture loops from one length of suture measuring 18 in. (46 cm), a feat that would be impossible if the knots were tied by hand. Instrument ties are invaluable in special situations where hand ties are impractical or impossible, such as body recesses or cavities (e.g., the mouth); there, instruments can form knots where hands could never gain access.

Failure of the knotted suture loop may be the result of either knot slippage or breakage, suture cutting through tissue, or mechanical crushing of the suture by surgical instruments. All knots slip to some degree, regardless of the type of suture material, and the cut ends of the knot must provide the additional material to compensate. If the amount of knot slippage exceeds the length of the cut ends, the throws of the knot become untied. In general, leaving the free ends approximately 3 mm in length will accommodate most knot slippage. To facilitate removal in some locations (e.g., scalp or eyebrow), it may be useful to leave longer suture ends so that they can be easily located and grasped with forceps. Dermal sutures are, however, an exception to this rule. Because the ends of dermal suture knots may protrude through the wound, it is best to cut the dermal suture ends close to the knot. It must be emphasized that knot security is enhanced by additional throws and not by longer ends.

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