Special techniques of knot tying are necessary to achieve a secure knot. Insecure knots leading to slippage of a tie may result in catastrophic blood loss or at least revisiting the surgery. The ability to tie a secure knot should be a reflex action based on practice for the proceduralist. The friction between threads of the suture material is also a factor in avoiding slippage of the knot. The monofilament braided synthetics, particularly nylon and polyesters, are more supple and easier to handle so that knots are easier to tie securely.
The traditional secure knot is the reef knot, which is a firm interlocking knot. The basic element is a half-hitch and it forms the basis of the surgeon’s knot. In this knot, one thread is looped around the other and the knot is completed by a mirror image of the first throw. It is achieved by trying the first throw one way and then reversing it. The two free ends of one suture emerge from either above or below the loop created by the other suture (Fig. 1.5). It is basically two loops that pull against each other to interlock. Consider it as ‘left over right’ and then ‘right over left’.
Two views of tying a reef knot (a) and (b)
A granny knot is formed when the reverse of this mirror image throw is formed; that is, the throws go the same way. The free ends emerge one above and one below each loop (Fig. 1.6). It is best to avoid this knot in surgical practice as it tends to slip and is therefore dangerous for precise surgery as the wound will open.
Also known as the square knot, it involves the same pattern as the reef knot, except that there are two throws on each side of the knot instead of one (Fig. 1.7). The ends of the thread should be pulled at 180º to each other.
Two views of tying a surgeon’s knot (a) and (b)
The instrument knot, which is the most common knot, uses the principle of the reef knot. Initially, the thread is wound twice around the needle holder (say in a clockwise direction) to create the double loop of a surgeon’s knot and then firmly tied (Fig. 1.8a). On the reverse side, the thread is wound around the needle holder in the opposite direction (an anti-clockwise spiral), thus creating the double loop of a surgeon’s knot. The knot is finally secured by pulling the ends at 180º to each other (Fig. 1.8b).
Two steps in tying an instrument knot (a) and (b)
Every precaution must be undertaken to avoid the ligature slipping. The first tie should be very tight, and the second slacker than the first. For deep ties on vessels it is best to tie with the hands and keep the ties parallel to the wound. Do not pull upwards on the tie. Leave an adequate cuff of tissue past the tie (see Fig. 1.28).