Author Topic: Not a Giant knot  (Read 631 times)

Isleofgough

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Not a Giant knot
« on: March 26, 2020, 05:56:33 AM »
In Knotting Matters, the knot shown at https://www.newscientist.com/article/mg24532630-400-small-wonder-see-the-microscopic-knotted-beauty-of-a-surgical-stitch/ was referred to as a Giant knot. The image is beautiful, but is actually a common error where a Surgeon's knot with Square finish is inadvertently converted into a noose. It is not secure.
« Last Edit: March 26, 2020, 05:58:05 AM by Isleofgough »

Dan_Lehman

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Re: Not a Giant knot
« Reply #1 on: March 27, 2020, 10:50:19 PM »
Thanks for pointing this out --something I'd
wondered about, but hadn't yet played with
the knot ... to check it.

(There was one one-time IGKT member doctor
who insisted that surgeon knots were never used
by actual surgeons; but I think that there is some
evidence to the contrary of that, though perphaps
it paints the matter in degrees of frequency.)


---dl*
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Isleofgough

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Re: Not a Giant knot
« Reply #2 on: March 29, 2020, 06:02:06 AM »
The Surgeon's knot is commonly used by various surgical specialties as well as by emergency room and family practice physicians. I think it has some limitations when using monofilament suture and tight closures, and I follow Dr. Mayo's advice to tie a Granny, convert that to a noose and secure it with flat Square knots. It is interesting that in Ashley's book of knots, he refers to Dr. Mayo's (founder of the Mayo clinic) use of the Granny knot, but then goes on to explain how he taught surgeons to use the Square knot instead. A Granny knot makes a better noose (about twice as resistant to back slipping in my experiments) but a worse flat knot. That has been born out with recent studies in the physics of knots. Tying all throws flat is frequently not realistic, if there is any tissue tension. Maintaining tension on the two ends of the suture when tying is commonly taught but generally a bad idea. It increases the sawing of the suture through the tissue, increases locking of the knot part way down ("air knots") and often inadvertently converts what should be a flat knot into a noose (if there is slightly more tension on one side - changing that side to a post).

A modification of the Surgeon's knot with the second throw done as a Granny is actually a very good noose. It is called a Nicky knot in surgery, and I've used it several times to bring tissue together.
« Last Edit: March 29, 2020, 06:07:52 AM by Isleofgough »

agent_smith

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Re: Not a Giant knot
« Reply #3 on: March 30, 2020, 02:40:18 AM »
Some questions...

Quote
The Surgeon's knot is commonly used by various surgical specialties as well as by emergency room and family practice physicians.
Why?
I can conjure up lots of reasons in my own mind - but am curious as to the underpinning "why"?
Is it because surgeons are parroting each other or are there solid evidence based reasons?

Quote
A Granny knot makes a better noose (about twice as resistant to back slipping in my experiments) but a worse flat knot.
What is your definition of 'flat'?
And what is your definition of a 'noose'?

Can you define with precision, what the design requirements are for a 'knot structure' to be practicable and efficient for surgical use?
And here the term 'knot structure' encompasses the following:
[ ] fixed eye knot
[ ] end-to-end joining knot
[ ] noose
[ ] slide and grip hitch
etc

Isleofgough

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Re: Not a Giant knot
« Reply #4 on: March 30, 2020, 05:41:44 PM »
The requirements for various surgical knots depend on the use. For example, a typical operation may require one to tie one hundred or more knots. None can fail. In these cases, the important elements are consistency, speed and efficiency, ability to securely appose tissue or ligate blood vessels, and simplicity. In some types of surgery, like arthroscopic procedures, one knot may have critical importance and the most important features may be low profile, ability to resist cyclical loading, perfect apposition without being either too tight or too loose, and ability to be formed by tying through a tubular structure.

There are solid evidence based reasons to use a surgeon's knot over a reef/square knot for skin closures with monofilament suture. The reef knot will not adequately appose the tissue as it loosens during tying. Pulling up on both ends of a suture tears small blood vessels and can saw through tissue, so that is not recommended. For most emergency room suturing, a Surgeon's knot - or the modification on the first throw where both ends are pulled in the same direction to lock it - works fine. It is easy to standardize with hand or instrument tying.

You would know better than I the proper definition of a noose, but basically they are knots where one side acts as a post. To distribute tension on a wound closure, suturing is often done with a running suture, and the knots at the ends are more resistant to breakage if they are tied as a noose rather than flat. I'm not sure what you are asking about defining "flat" but it is a common expression in surgery. Knots tied flat have proper knot conformation (like a typical reef knot) and suture tension is equal at each end. They also are properly dressed, with the knot lying at the level of the tissue and without looseness in the conformation.
« Last Edit: March 30, 2020, 05:43:22 PM by Isleofgough »

Dan_Lehman

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Re: Not a Giant knot
« Reply #5 on: March 30, 2020, 09:03:04 PM »
...I follow Dr. Mayo's advice to tie a Granny,
convert that to a noose and secure it with flat Square knots.
...  A Granny knot makes a better noose (about twice as resistant
to back slipping in my experiments) but a worse flat knot.
A granny capsized yields 2 half-hitches vs. a square's cow.
But if one is backing it up with square knots, wouldn't the
slippage of the base knot be irrelevant --prevented by
the back-up knots?

Quote
That has been born out with recent studies in the physics of knots.
Are you referring to the 03 January 2020 article?
(I'm still puzzled over some of what I can understand
of it all --NOT the math/physics-, and question those
results that run counter to what has been held (and
seen) for rope.  (And the name "bowline" for a sheet bend!)
There is also one if not more cases of a calculated value
for identical knots (mirrors) coming out unequal!?
--and for the like but not identical loadings of the
asymmetric (hence merely "like") butterfly being equal (!).

Quote
A modification of the Surgeon's knot with the second throw done as a Granny
 is actually a very good noose. It is called a Nicky knot in surgery,...
Do you mean something similar to the adjustable bend's
hitch component knots?
https://daveroot.neocities.org/knots/Knots_Bends.html


--dl*
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Isleofgough

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Re: Not a Giant knot
« Reply #6 on: March 30, 2020, 10:13:02 PM »
As you correctly point out, a capsized Granny yields two Half Hitches in a Clove Hitch formation whereas a capsized Square yields two Half Hitches in a Cow Hitch formation. Reversing chirality between the two Half Hitches with a Cow Hitch means frictional forces are additive (or even less if the loop pushes the two half hitches apart), whereas the frictional force is exponential if chirality is not reversed. Apart from the theory from the Capstan equation, I tested it with various monofilament sutures using a spring tensiometer, and indeed a capsized Granny is significantly more resistant to back slipping.

The slippage after the Square knots are added would also, as you say, be irrelevant. But it is during the formation of the knot that back slippage is an issue, assuming the final knot is secure. As an example, pretend your thigh is a big blood vessel. Tie a Square knot around your thigh with fishing line. I would guess that knot might be (somewhat) secure but it will be loose. You can incorrectly try to prevent this by pulling up hard on both ends when you are tying the Square knot. Assuming there are side branches of blood vessels off your thigh, there is a good chance you will tear them by pulling up on the suture.  If you are dealing with an elderly patient or a transplant patient, the tissue may be like wet toilet paper. You can tie a knot around it, but you wouldn't want to pull up at all.

The January 2020 article from MIT does indicate that reversed chirality for flat knots is a good thing. A Square knots is better than a Granny. This also fits experimental studies. I am trying on this forum to use the terms that are considered correct in this community, so I am referring to what a surgeon would call a slip knot as a noose. Rather than saying the direction is reversed, I am using the term chirality - which the study from MIT did not specifically use. Mirror image knots should not have a different calculated value for security, so I am assuming that the differences were just insignificant experimental measurements.

The Nicky knot is similar to the Taut Line Hitch, so it is an adjustable bend. It is often used to start a continuous suture, but has the downside of possibly strangulating the tissue which is encircled. To prevent that, often a half hitch off opposite post is added (a specific example of this in orthopedic surgery is called a Revo knot).

Surgical knots are often tied incorrectly, unfortunately. To give some wonderful examples from Anne Weston's scanning electron microscopy photos, see:
https://www.sciencephoto.com/media/1041235/view and
https://www.sciencephoto.com/media/270551/view and
https://www.sciencephoto.com/media/206933/view .

All the images are beautifully done, but all are of surgical errors. I would guess you could identify the mistakes without being a surgeon.
« Last Edit: March 31, 2020, 01:32:25 AM by Isleofgough »