instrument before tension is applied to the two ends in order to not get stuck in the box lock. The most tension is applied on the needle end in order to not pull the loop end longer. If so, the tag will lengthen, which makes the remainder of the knot more challenging. (G). The right instrument is wrapping the suture material in a counter‐clockwise direction. (H). Tension is applied to both ends, and the right instrument path crosses over the left at this time. (I). The third and final single throw is wrapped in clockwise fashion. (J). Tension is applied, without crossing of instruments.
Figure 2.19 Clockwise and counter‐clockwise wrapping of suture. (A). Clockwise wrapping around the left instrument. (B). Counterclockwise wrapping around the right instrument.
Figure 2.20 Knot tying with horizontal C‐loops, as described by Szabo [14]. (A). A suture bite has been taken from right to left. The left instrument is used as a “pulley” to gently pull the suture through, forming a horizontal C‐shaped loop. (B). A horizontal C‐loop has been formed on the left side, and the left instrument is placed on top of the C‐loop close to the needle. (C). The right‐hand instrument has wrapped the suture twice around the shaft of the left instrument in a counter‐clockwise fashion. The two instruments move together to pick up the short loop end with the left instrument. (D). Tension is applied, with care taken to not pull hard on the short end and thus lengthen the tag. The tag should remain 2–3 cm throughout. (E). The left instrument picks up the needle and forms a reversed horizontal C‐shaped loop, and the right instrument is placed on top of the loop close to the needle end. (F). The suture is wrapped around the right instrument once in clockwise direction, the wraps are moved over the needle driver. (G). tension is applied to the suture bilaterally. Note that crossing of instrument paths is not occurring with this technique. (H). The third and final throw is applied similar to the first, but only a single throw is required, in counter‐clockwise direction. (I). Tension is applied.
Figure 2.21 (A). Extracorporeal suturing requires suture material to enter and exit the cavity through the same cannula. (B). A slip knot is tied extracorporeally. (C). A knot pusher is used to cinch the knot. (D). A slip‐knot is stronger than a double throw and can overcome more tension than an intracorporeally tied knot.
Figure 2.22 Extracorporeal knot tying requires the use of a knot pusher. (A). These can be of open type, as depicted here, ore closed‐and thus threaded onto the suture. (B). By advancing the knot pusher while applying tension on the suture end, the knot is cinched.
Complex slip knots do not accept any tension placed on the loop end while being cinched, and it is more practical to cinch them into the abdomen along the post end of the suture, with a short loop end, and the remainder of the throws are placed with intracorporeal technique.
Slip Knots
The simplest of slip knots is a regular single throw advanced and cinched down with the knot pusher, but this does not withstand any tension on the suture line. A great number of more complex knots have been described for the latter purpose, and the veterinary literature has evaluated the performance of a number of these, including the 4S modified Roeder (4SMR), modified Roeder, and Weston and Brooks knots [17]. The 4SMR knot was significantly stronger than the other knots. Weston and many other slip‐knots require added throws for security. The 4SMR and Weston knots have also been compared in smaller suture size, 3‐0 polyglactin and polydioxanone (PDS). The 4SMR, a complex knot without need for added throws, performed comparable to a Weston with three additional square throws in 3‐0 PDS but tended to slip with the braided polyglactin, which was counter‐intuitive. The Weston knot performed well in both braided and monofilament suture, with the added 3 throws [18]. In our experience, the 4SMR knot is very sensitive to errors; with any air in the knot it becomes prone to slippage. We therefore prefer the use of a modified Roeder knot (Figure 2.23), similar to that described by Ragle [19].
This knot is in our opinion easier to tie and with less risk for air in the knot, than the 4SMR. When we used it tied with 2‐0 polyglactin 910 for ovary pedicle ligation in 16 dogs, it was secure without added throws (data to be published). However, the surgeon needs to ensure the knot is correctly tied and avoids air knots. We use this knot also for hand tied ligature loops, again in polyglactin 910, which greatly reduces the cost compared to commercially available loops.
The Weston knot has been advocated as the knot of choice [20] for ease of tying. However, it requires three added throws for security. The Weston knot tumbles and locks when tension is applied to the (short) loop end and therefore needs to be cinched without any tension on the loop end. Most often the added throws are made with intracorporeal technique, which may be a disadvantage to this knot if intracorporeal space is limited.
The modified Roeder as discussed above is these authors' preferred slip knot in clinical MIS. In our experience, it is less complex, with less risk of air knots, than the 4SMR. We have used it without complications for ovarian pedicle ligation in live dogs, without the need for added throws.
Figure 2.23 Modified Roeder knot. This is similar to a previously described knot [19], but with an added, 4th, throw. (A) The loop end crosses posterior to the post end and a single throw is formed. The loop end is wrapped four times around in a clock‐wise fashion. (B) The loopend forms a half‐hitch around itself by moving posterior and then anterior from under the last wrap. (C) The loop end is moved from anterior to posterior immediately adjacent to the first single throw. (D) The knot is complete when there are no air‐gaps present.
