What the knot?

October 17, 2009 3:09 PM

What is special about a square surgical knot? It seems like the regular kind of knot I use to tie my shoes, just using a very specific hand technique. Is there any advantage to this knot tying technique?
posted by Brennus to education (5 comments total)

If you look through this manual put out by a suture manufacturer you will see that there are actually a few different types of knot, including a traditional square knot. To make sure the knot stays tied, they will typically tie several of them together, especially when using monofilament suture. If they need to slip the knot into a tight space they may use a granny knot, and if they need the knot to stay exactly as tight as they have tied it they may use a surgeon's knot instead of a square knot. Other considerations include such things as how much tension they want the tissue under and how strong the knot needs to be. The technique used is important for two reasons. A one hand technique is useful when the other hand is occupied and an instrument tie can be useful when there is little room to work or the suture is short. The other reason for proper technique is to ensure that you are tying the knot you want to (many people do not pay attention to whether they are tying square versus granny knots; indeed, I was using a granny knot in my shoes and wondering why they didn't stay tied better for 40 years until I happened to see an AskMe about shoelaces). Surgeons also need to be able to do these things with either hand. Tying technique is a major part of being a surgeon and I am not alone in basing my opinion of a surgeon's skill in large part on how well he handles suture.
posted by TedW at 3:43 PM on October 17

(First, I'm a scout, not a surgeon. Don't come to me for surgery or sutures. The following is insight I have from non-medical knot tying.)

Your shoe lace knot is a square knot. Or more accurately, a slipped square knot. By tying with the bows, its easy to unknot them. Which is handy for shoes.

As for the value of the knot itself, it's easy to tie, and can be done with one hand free. It has substantial strength and isn't bulky like a ... blood knot. And it resists the right kind of tension. I would expect the main resistance to the knot is being undone, and a square knot reists tension on both lines, unlike some knots that can slide along. This is called "binding". Other knots have more surface area for friction resistance, but that can mean leaving more material with your patient, no?
posted by pwnguin at 3:44 PM on October 17

Before modern surgery, knots were usually the domain of sailors who knew very well the distinction between reef knots and granny knots. Most people tie their shoelaces with granny knots, which is why they come undone.
posted by randomstriker at 3:46 PM on October 17 [2 favorites]

It is just one of the easier to tie and more basic knots. Here is the Ethicon Knot Tying Manual, used by most budding surgeons.
posted by caddis at 6:14 PM on October 17

in my recently completed surgery clerkship, we were told that the special hand technique keeps tension on both ends of the suture while the knot is tied. this keeps the tissue from slipping out of the knot, and as knots are often tied around the ends of blood vessels, tension keeps the vessel from bleeding while the tying is going on.
also, it's really hard to tie knots while wearing gloves (especially bloody, sticky gloves) and i think the special knot makes it easier.
posted by genmonster at 7:18 PM on October 17 [1 favorite]