The most desirable knot is the simplest one that can be made with the suture being used. The knot must be as small as possible in order to avoid an excessive tissue reaction when an absorbable suture is used, or in order to minimize the foreign body reaction when a nonabsorbable suture suture is used.
The type of knot employed depends on the suture used, the depth and location of the incision, and the amount of stress likely to be placed on the wound postoperatively.
The coefficient of friction, which affects the tendency of the knot to loosen after it has been tied, is relatively high in multifilament sutures and low in monofilaments. Therefore, all monofilament synthetic sutures require specific knotting techniques. The greatest variable affecting knot security is the human factor.
- The two ends of the suture should be pulled in opposite directions with uniform rate and tension.
- Squashing or trapping of the suture by surgical instruments such as the needle-holder or tweezers has to be avoided.
- The surgeon should not have to hesitate when changing position relative to the patient in order to make a plain and safe knot.
- The finished knot must be firm and tense enough that it cannot slide. The use of additional knots does not help to increase the resistance of a well-tied and square knot; it just contributes to raising its caliber/gauge.
Types of knot
- A slip knot consists of two single overhand knots, but both are made and tied in the same direction.
- A square knot consists of two single overhand knots, each completed in opposite directions. It is easy to tie but may loosen when a synthetic or monofilament suture is used.
- A surgeon knot is a modified square knot with two overhand knots, each completed in opposite directions. It is the most commonly used.
Forceps are used to delicately hold, not pierce or crush, the tissue to be sutured and for suture tying.
A needle-holder is equally good for holding the needle or tying knots and must be of an appropiate size for the needle selected.
The needle body and needle-holder tips should be designed to give stability when the needle is grasped and passing through tissues. Guidelines for use of a needle-holder by the assistant are:
- Grasp the needle in an area about one-third to one-half the distance from the swaged area to the point.
- The needle and needle-holder should be managed as an entity.
- Do not hold the needle very hard because the clamps of the needle-holder can twist or damage the needle.
- Check always the alignment of the clamps of the needle-holder to make sure it does not turn, twist or distort.
- Pass the needle-holder to the surgeon in a way such that he or she does not have to readjust before taking the suture to the tissue.
- Make sure that the needle points towards the direction it is going to be used and it does not tangle up with the suture thread.
- Offer always a needle-holder, never hemostatic tweezers, to pull the needle and take it out from the tissue. Any kind of tweezers could damage the needle. Avoid touching the suture with the needle-holder
A variety of scissors are available. Those with gently curved blades, lightly rounded at the tips and spring-handled are preferred.