Suture Selection and Knot Tying Demonstration
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Knot tying is a fundamental skill in the surgical field, essential for securing sutures, ligating vessels, and creating secure anastomoses. The art of knot tying requires precision, dexterity, and a thorough understanding of suture materials and techniques. This text aims to provide a comprehensive overview of surgical knot tying, drawing from the presented video.
Surgical sutures serve a crucial role in wound management by approximating tissues, allowing the healing process to occur effectively. Sutures can be categorized based on their structure (braided or monofilament), absorbability (non-absorbable or absorbable), and origin (natural or synthetic).1,2 Braided sutures, composed of multiple strands woven together, are often easier to tie and hold knots better, making them suitable for ligating vessels. Monofilament sutures, with their smooth surface, minimize tissue drag and are preferred for vascular anastomoses. Natural sutures like surgical gut and silk were traditionally used but have largely been replaced by synthetic sutures due to better biocompatibility and predictable degradation rates. Common synthetic absorbable sutures include poliglecaprone (Monocryl), polyglactin (Vicryl), and polydioxanone (PDS). Non-absorbable synthetics include nylon, polypropylene (Prolene), and polyester (Ethibond). Non-absorbable sutures, such as silk (braided) or nylon, are used in tissues requiring prolonged healing, while absorbable sutures, like Vicryl (braided) or Monocryl (monofilament), are used for rapidly healing tissues like intestinal mucosa.
Some sutures have coatings to improve handling and knot security. For example, Vicryl Plus has a polyglactin/calcium stearate coating, while Prolene is coated with polydioxanone to improve smoothness.
Mass absorption and strength retention for various suture materials can be seen in Table 1.
Table 1. Tensile strengths and mass absorption rates of different widespread suture materials.8
| Suture Thread Material | Strength Retention | Mass Absorption |
| Fast-Absorbing Surgical Gut | 5–7 days | 21–42 days |
| Surgical Gut | 7–10 days | 70 days |
| Chromic Gut | 21–28 days | 90 days |
| Fast-Absorbing Polyglactin 910 (Vicryl Rapide) | 50% at 5 days | 42 days |
| Polyglactin 910 (Vicryl) | 50% at 21 days | 56–70 days |
| Polyglactin 910 Monofilament (Vicryl) | 40% at 21 days | 56–70 days |
| Polyester (Velosorb) | 45% at 5 days | 50–60 days |
| Polyglyconate (Maxon) | 59% at 28 days | 180 days |
| Polyglytone 6211 (Caprosyn) | 50-60% at 5 days | 56 days |
| Polydioxanone (PDS) | 4-0 : 35% at 42 days | 183–238 days |
| Polydioxanone Barbed (PDO) | 67% at 14 days | 180 days |
| Poliglecaprone 25 (Monocryl) Undyed | 50–60% at 7 days | 91–119 days |
| Poliglecaprone 25 (Monocryl) Dyed | 60–70% at 7 days | 91–119 days |
| Polyglactone 72 (Monoderm) Undyed + Dyed | 62% at 7 days | 90–120 days |
Sutures are sized using a numerical system, with larger numbers indicating thicker sutures (e.g., 0, 1, 2). However, when followed by a zero (e.g., 2-0, 3-0), the numbers indicate smaller suture diameters, with more zeroes signifying a finer suture.
The square knot (two overhand knots in succession with opposite orientations) is the most common surgical knot. Other knots used include the surgeon's knot (one extra throw on the first part of the square knot to prevent slipping) and the slip knot.3–5
The two-handed knot tying technique involves creating a square knot, consisting of two throws in opposite directions. This method can be performed right-handed or left-handed and requires equal tension on both strands to ensure a flat, secure knot. Practicing with gloves and colored suture materials aids in visualizing the knot formation.
The one-handed knot tying technique is useful in situations where one hand is required for retraction or instrument manipulation. In this method, one hand serves as the post, holding the suture taut, while the other hand performs the knot tying motions. The process involves creating a cross with the suture, pinching and rotating the hand to form the first throw, followed by the "karate chop" motion and stealing the suture from the adjacent finger to create the second throw.6,7
The presented video offers a comprehensive and detailed explanation of surgical knot tying techniques, emphasizing the importance of proper suture material selection, sizing, and knot tying methods. The clear visual demonstrations and step-by-step instructions make it an invaluable resource for surgical trainees and practicing surgeons alike. By mastering these fundamental skills, surgeons can achieve secure wound closure and healing, and ultimately enhance patient outcomes.
Citations
- Chittoria RK, Reddy BP. Suture materials – recent advances. Cosmoderma. 2023;3. doi:10.25259/csdm_176_2023.
- Dennis C, Sethu S, Nayak S, Mohan L, Morsi Y, Manivasagam G. Suture materials - current and emerging trends. J Biomed Mater Res A. 2016;104(6). doi:10.1002/jbm.a.35683.
- Dinsmore RC. Understanding surgical knot security: a proposal to standardize the literature. J Am Coll Surg. 1995;180(6).
- Zhang W, Wu X. How to convert a square knot or surgeon’s knot into a sliding knot and an assessment of their sliding and re-locking properties? Surgeon. 2020;18(6). doi:10.1016/j.surge.2019.11.004.
- Jha PK, Barabas AG, Sharma H. Surgical technique the ambidextrous surgeon’s knot: an alternate way to tie the surgeon’s knot. Can J Surg. 2007;50(6).
- Edlich RF. Surgical knot tying manual. Covidien. Published online 2005.
- Dimick JB, Upchurch Jr GR, Alam HB, Pawlik TM, Hawn MT, Sosa JA. Mulholland and Greenfield’s Surgery: Scientific Principles and Practice.; 2021.
- Yag-Howard C. Sutures, needles, and tissue adhesives: a review for dermatologic surgery. Dermatol Surg. 2014;40 Suppl 9:S3-S15. doi:10.1097/01.DSS.0000452738.23278.2d.
Cite this article
Rothman D. Suture selection and knot tying demonstration. J Med Insight. 2024;2024(478). doi:10.24296/jomi/478.
Procedure Outline
Transcription
CHAPTER 1
Hi, everyone. My name is Deanna Rothman. I'm a General Surgery Resident at Massachusetts General Hospital, and welcome to our knot tying session. So before we practice our knot tying, let's learn a little bit about the sutures that you'll often encounter in the operating room.
So there are three main ways that we categorize our sutures. First is their structure. They can be braided or monofilament. Braided sutures are made of several strands woven together, oftentimes are a little bit easier to tie, and can hold better knots. Monofilament, on the other hand, is a smooth suture, and so therefore it causes less tension and less traction on the suture that you're actually tying with the tissue. We use braided sutures, as you can imagine, when ligating vessels, for example, 'cause you really don't want that knot to move. On the other hand, we use monofilament for sewing anastomotic vessels together. So you can imagine you don't want any drag on those tissues as you're sewing. Another way to categorize sutures is based on their absorbability. So we have non-absorbable and absorbable sutures. Absorbable sutures usually are reincorporated into the body pretty quickly, while non-absorbable sutures stay there forever. So usually, we use non-absorbable sutures for tissues that have more tension and require a longer time to heal. For example, we use non-absorbable sutures on the fascia. Absorbable sutures, on the other hand, we use on tissues that repair quickly, such as the intestinal mucosa. You can have both braided non-absorbable, braided absorbable, or any combination of these. For example, a non-absorbable braided suture is Silk; an absorbable braided suture, on the other hand, is Vicryl; a non-absorbable monofilament is polypropylene; and an absorbable monofilament is Monocryl. There's one last category we can use to categorize these sutures, and that is based on their structure. So some sutures are natural and some are synthetic. Synthetic sutures, as their name implies, are made out of synthetic materials. So for example, PDS is a synthetic suture made out of polyester. Natural sutures are made out of natural materials that are found in the environment.
So the sutures we use in the operating room also come in different sizes, so let's talk about the specific way that we size our sutures. So let's start with 0. Sutures start at size 0 and then can go upwards in size. 1, 2, 3. Basically, the larger the number, the larger the suture size or the diameter of the suture itself. However, you'll often hear us in the operating room, saying, "We want a 2-0 suture, or a 3-0, or a 4-0." And while it sounds like the numbers are getting bigger, it actually means a smaller suture. So let's talk about why. As you go down in suture size, you actually start adding zeroes. So when you hear a 2-0 suture, it actually means two zeroes. 3-0 suture is three zeroes and so forth. So as you hear 2-0 or anything with 0 following it, you're actually getting smaller. Whereas if you only hear 1, 2, 3, or 0, you're getting larger. And that way, you can tell the different sizes of your sutures as you use them.
CHAPTER 2
So we're gonna start with the two-handed knot tie. As you're practicing your two-handed knot tie, I recommend using gloves 'cause that's what you'll be using in the operating room, so it's good to practice using them as well. And we'll also be using a shoestring. This helps you visualize your knots really clearly. It also really helps to have a shoestring that's two colors. So for example, this one is pink and white, and this will help you visualize your square knots. So in surgery, we use square knots, which basically involve one loop going one way and the other one going in the reverse to stop it from going anywhere. You'll see soon exactly what that looks like.
So for two-handed knot ties, you can do it right-handed or left-handed. I'm going to start with a right-handed knot tie. So initially, you wanna start with your strings as if you're holding the reins of a horse. So the string's gonna go over your pointer fingers and into your palms. When you're doing the right-handed knot tie, the white string is gonna stay in your right palm, and you're gonna bring the pink string over into your palm and over your pointer finger. You're then gonna pinch your pointer finger and thumb and bring it through that loop that you made between the two strings. You are gonna pinch the pink string, bring it through that loop again, and cinch down that first throw of the knot. As you can see, I do have to rotate my hands pretty well to make sure that that knot is nice and flat. Now, that's only half of the square knot. So the other half now, we're gonna hold our strings around our thumbs. So we were initially holding it like a horse rein, and now we're moving to our thumbs. So it's this kind of motion. So once again, holding the string in my right palm, I'm gonna bring the pink string to my palm over my thumb. And this time, the loop is between my thumb and my pointer finger. I'm gonna pinch my pointer finger and thumb, bring it through that loop again, pinch the pink string, bring it back through the loop, and slide that knot down. And that is a complete two-handed knot tie. As you can see, it's a nice square knot. You have one string going one direction and the other string going the other direction, forming a square knot. Another thing that I see people doing that's a common mistake is they don't apply equal tension to the string as it's going down, and I'll show you what I mean by that. So if you do the first throw of your two-handed tie and you don't rotate your arms all the way, and you instead were to pull upwards or not make sure the knot goes down flat, you instead form this kind of loop. And then if you were to do your second throw and do the same thing, you, once again, form another loop. And this actually forms a slip knot, which can slip, like its name, which is not what you want ideally in surgery. Instead, with your square knots, it's important to make sure that you're putting equal tension on both sides of the string and making sure that it goes down flat to prevent that from happening. So as I showed you the first time, you'll want to rotate your arms, really get that knot down flat, and then do it again. And there you go, a nice, flat square knot.
It's important to know how to do both left-handed and right-handed two-handed knot ties. So to show you just briefly how the left-handed knot tie works. Very similarly to the right-handed, we're gonna start with our hands, as if we're holding the reins of a horse. Except this time, the white string is gonna go into the palm of your left hand, forming that loop. You are gonna pinch your pointer finger in your thumb, bring it through the loop, and this time you're gonna pinch the white string, bring it through, and then cinch it down. Once again, rotating your hands, making sure to get equal tension to get that nice, flat knot. We're gonna bring it back. We already did our pointer fingers, so now, we're going to our thumbs. We're gonna bring all the white string into our palm over our thumb, forming the loop, pinching our pointer finger and thumb, bring it back through the loop, pinching that white string, bring it through the loop, and cinching down that knot, so you get a nice square knot. I would recommend practicing both left-handed and right-handed 'cause they're helpful in different situations, so it's good to practice both.
CHAPTER 3
So now we're gonna do the one-handed knot tie. Just like with your two-handed knot tie, it's helpful to practice with gloves and with a shoestring, so you can really clearly visualize your knots. It's helpful to get very comfortable with the two-handed tie first before moving on to the one-handed tie. But it is good to also learn the one-handed tie because it's helpful in different situations. So for your one-handed tie, you're gonna have one hand that's gonna be your post. So it's just gonna be holding the string. And the other hand is gonna be doing all the work of making the knots, which is why it's called the one-handed knot tie.
I'm gonna start by demonstrating the right-handed one-handed knot tie. So in this situation, my left hand is going to be my post, and my right hand will be making the knots. So to start out, we're gonna have our string going into our palms. Just like before, we're gonna hold it tightly in our right hand and form a nice taut string over our pointer finger and our thumb like this. We're then gonna form a cross with the pink string, like this, and pinch your pointer finger and your thumb over the pink string. Your pointer finger is then gonna go over your thumb and steal the string on top of the thumb. And this time, you're gonna rotate your palm through, let go of that string, bringing that string through that loop, and forming your first throw. So to show you once again what that looks like... You're gonna have your string taut between your pointer finger and your thumb. You're gonna form a cross with the pink string. Pinch your pointer finger in your thumb. Your pointer finger is gonna steal from your thumb. Bring that string through that loop. Let go of the string and then form that first knot. So that's your first throw of your square knot. As you know, square knots have two throws. So the second throw is commonly called the karate chop. You're still gonna have your left hand as your post, and I still have my string tautly in my other hand. But this time, instead of using my forefinger and thumb, I'm gonna take my last three digits, so my middle finger, ring finger, and pinky finger, and chop towards myself like this. So you're gonna take the string, karate chop, bring it towards you. You're then gonna form that cross between the pink string and the white string between your middle finger and your pointer finger. This time, instead of your pointer finger stealing the string, your middle finger is gonna steal that string from over your pointer finger like this, and then bring that string through the loop, forming that second throw. So to show you what that looks like one more time... You're gonna karate chop the string towards yourself, form that cross between your middle finger and your pointer finger, steal the string from your pointer finger, and bring it through the loop by rotating your palm down to form that second throw. And there you have a nice square knot.
So as I mentioned, this could also be done with your left hand. So in a left-handed one-handed knot tie, my right hand is going to be my post and my left hand's going to be the one making the knots. Just like last time, I'm gonna hold the string very tautly in my left hand. Once again, you're gonna form the taut string between your pointer finger and your thumb and form a cross with the white string. You are gonna pinch your pointer finger and thumb, slide your pointer finger over your thumb to steal the string, and then rotate your palm to bring that string through the loop. That's your first throw. And for your second throw, you can do the karate chop, bring it towards yourself, form that cross between your middle finger and your pointer finger, steal the string from your pointer finger, bring it through the loop, and that's your second throw. And there, you can see another nice square knot. And that is your one-handed knot tie. Just like with your two-handed, it's good to practice both left and right-handed single-handed knot tie.