Advanced Knotting Techniques (Examples from Surgical Practice)

Abstract

In this chapter, the topology of recently used knots is described regarding conventional and laparoscopic surgery. Morphological and technical similarities and differences of the most common knots are discussed, while also considering their transformability. Knots are introduced and made by hand and by instruments, while further demonstrating laparoscopic and microsurgical knotting techniques.

1. Introduction

Knots are widely used by many professions varying from decorating to life-saving knots and even theoretical ones. Topologists, mathematicians, engineering, sailing and shipping, mountain climbers, and of course surgeons cannot operate without adopting their field’s specific knotting techniques. For example, a conventional tied knot (open-loop knot) is not equivalent to the mathematical concept of a knot (closed-loop knot). However, the proper way of tying a functional knot is not so easy to acquire. Therefore, it is essential to clarify the best methodology for this very basic, but also very diversified element of primordial surgical techniques.

A few thoughts as an introduction to the world of knots:

1. A tied knot can easily be converted into a mathematical knot by joining the threads’ ends to a closed loop [1]. This transformation can be performed on even an 18-crossing-tied knot. But from the perspective of a mathematical knot, it can hardly be transformed to a conventional tied version from about a 6 or 7 crossing extension (Figure 1).

2. There is an enormous difference between mathematical and surgical knots as all tied knots have to count with the laws of Physics such as surface geometry of the thread and consequent torsion, the used material’s attributes, friction, elasticity, and producing methodology. Therefore, interprofessional insight is needed to minimalize the possible source of mistakes.

3. There is a constant common and individual need to improve tying skills in every field of use—especially in the surgical practice and during the so-called learning curve. Thus, limitations and expectations of the different knotting techniques must be well-defined and spread in an accessible form.

4. All professions—especially surgeons—have to set and apply their own standards and nomenclature of their tied knots, which should be clarified during interprofessional communication.

5. Surgeons not only own special tying techniques, but also have specific, sometimes historical names of its knots and knot combinations.

6. We should note that ambient isotopic knots may have a different functioning role in the practice. Mathematically equivalent knots are not necessarily equivalent as conventional tied knots during its practical use.

7. In some cases, only the practitioner’s experience can predict the outcomes and question the theoretic borders of the function of a knot.

Figure 1.

Convert a tied knot to a mathematical knot.

2. Detailed explanation

Ad 1: The fact, that composite knots are built up from prime knots, lets us reach a deeper understanding of the structure and the function of knots. This simplified perspective is an essential cornerstone of proper knotting. Furthermore, this simplicity gives space to an easier demonstration of the commonly used 18-crossing knots, that would be more difficult to present with conventional formulas.

Ad 2: Only a small fraction of the theoretically existing knots can be used in practical applications. We can examine a knot’s creating circumstances and conditions, and investigate its final functions and limitations as well.

Knots can be made for countless reasons from poorly functional decorative knots through the climbing knots to surgical knots that have serious practical importance. The most common function of a knot besides decoration is to fix objects and get them stick together. Fixable things can have different characteristics such as shape, flexibility, rigidity, and capability of resistance. Fixation is usually provided by the loop of a cord or a thread secured by knots. The knot-tying procedure can be performed under tension or not under tension, where the previously fastened knot suffers the burden later. Selecting the proper knotting technique depends on the circumstances of the tying process and the properties of the participating objects. Untyability is also a crucial point of view during the selection of the appropriate type of the knot—like the untying property is surely needed in case of sailing and is unacceptable during surgical procedures.

The most frequent knot application (referring to surgery):

1. Strangulation of a tubular object or organ (e.g., closure of a sac or an open vessel): the first knot of the loop strangulates while the following ones strengthen the participant while the whole tying process is performed under tension.

2. Skin stitches, for example, vertical mattress stitch: adjustment of the wound edges in the same plane tight and under tension.

3. Bowline knot: previously blinded knot (not under tension) for postponed application and strain. In surgical practice, we decisively use under-tension knotting techniques for holding and fixing the living elastic tissues together. Thus, the loop-fixing knots must be safe and hard or impossible to untie. Our proper tying techniques are discussed in a later section.

Ad 3: Numerous ways exist to describe mathematical knots. The most common methods are planar diagrams, Gauss codes, Morse link presentation, braid representation, etc. However, it can be trying to find parallelism between these methods regarding the similarly made knots or the more complex composite knots. It is also difficult to prepare a tied knot based on mathematical nomenclature. Surgical knots are mostly made of numerous simple prime knots following each other in a well-defined order. Therefore, it was easy to create a specific nomenclature which is representative and provides a proper description of the composite knots’ appearance. This gives us a simple way to compare the bearing capacity and the nature of different knots.

3. Special notation and abbreviations in surgical knotting

3.1 The base “half knot”

The root of surgical knotting is the single twisted half knot. Mathematically, the half knot is a disjunct trefoil (AB 3.1) knot. The notation of this half knot is “1,” or H1. (Other general notation for that term is “overhand knot”) (Figure 2).

Figure 2.

H1 knot transformation.

The half knot can also be formed by more than one throws. If it is formed by two throws, the notation is “2,” or H2. This knot is a disjunct cinquefoil knot (AB 5.1) (or “double overhand knot”) (Figure 3).

Figure 3.

H2 knot transformation.

Three, or more throws in a half knot is uncommon (“3” or H3, and above). These simple or “opened” prime knots are the basics of the practical used composite knots.

In these knots, both threads enter to the crossing point from the same direction, bending and twisting through an imaginary line, and leave it to a continuous direction.

3.2 The base half hitch

In the surgical notation, there are equivalent pairs of these knots, which are invariants (ambient isotopy), but have different initial shapes, and characteristics.

This ambient isotopic pair of the half knot is the half hitch, or otherwise called the sliding knot. The notation of this knot is “S.” In this case, one part of the thread is active and the other is passive. The passive thread is nearly straight while the active thread ends it is turn around the passive one. Therefore, the active end leaves the knot toward the opposite direction than the entering (Figure 4).

Figure 4.

S1 knot, H1 to S1 transformation.

If the active end turns around more than one time, the notation is “2S,” or S2, or above (Figure 5).

Figure 5.

S2 knot, H2S2 transformation.

3.3 Linking knots

From the combination of these basic knots, sequential practical knots (composite knots) are derived.

3.4 Combining half knots

There are two possibilities to combine half knots (“1, H1”). Using a symmetric knot means that the threads are entering to the linking loop from the same side (both under or above), while in the case of the asymmetric knot, the ends are entering from the opposite direction (one from above and one from under). The notation of symmetrically linking half knots is “=” or “s” (e.g., 1 = 1 or H1H1s). The notation of asymmetrical knots is “×” or “a” (e.g., 1 × 1 or H1H1a). The 1 = 1 (H1H1s) is called the square knot (reef knot, surgical knot {not surgeon’s knot}), which is a knot consisting of two trefoils with opposite chirality’s. The 1 × 1 (H1H1a) is the granny’s knot, which is the knot consisting of two trefoils with the same chirality (Figure 6).

Figure 6.

Flat knots.

Based on that, it is easy to present the classic surgeon’s knot which is described by the formula of 2 = 1 (H2H1s). Generally used safe knots in surgery is 1 = 1 = 1 = 1 = 1 (H1H1sH1sH1sH1s), or 2 = 2(=1 = 1) (H2H2s{H1sH1s}) (Figure 7).

Figure 7.

Some types of flat knots.

3.5 Combining half hitches: sliding

To form and combine half hitches, the first key step is to identify the relation between the passive and the entering active end. The passive thread is the one which lays under or above the entering active end (depending on the type). If the direction of the entering thread at the crosspoint changes from half hitch to half hitch, the knot sequence is symmetric. If it keeps crossing from the same direction, the knot combination is asymmetric. The notation of the symmetric combination is “×” or “s” (e.g., S × S or SSs). The notation of the asymmetric sequence is “=” or “a” (e.g., S=S, SSa or can be left: SS(a) or SS) (Figures 8 and 9).

Figure 8.

Basic sliding knots.

Figure 9.

Some examples of sliding knots.

3.6 Combining half hitches—blocking

When half hitches are combined, there is another important possibility to define function If the passive thread remains untouched after the tying process, it could suffer continuous sliding. But fortunately, it can be blocked if we perform a change on the passive thread. The notation of the half hitches’ blocking sequence is “//” or “b” (e.g., S//S or SSb). Therefore if “//” or “b” is missing, the knot is a continuous sliding knot. We also have to mark the symmetricity in the case of blocking knots. In case of symmetry we use the plan blocking sign “//” or “b” (clarified sign is: SSsb, e.g., S//S, SSb or SSsb). In case of an asymmetric blocking combination, the notation is “//×”, “ab” or “(a)b” (e.g., S//×S, SS(a)b or SSab) (Figures 10 and 11).

Figure 10.

Basic blocking knots.

Figure 11.

More blocking knots.

Ad 4. Knot conversion. Most important thing is to be aware of the properties of the used knots for the exact task. We also have to know which knots are equivalent and 22 how to convert them if necessary [2]. For example, in a place which is hard to access, we should prefer sliding knots and then transform it to a blocking knot. The next table presents the equivalency of the different knots.

The 1 = 1 (H1H1s) knot can be transformed to an S × S (SSs) or an S//S (SSb) knot.

The 1 × 1 (H1H1a) knot can be transformed to an S=S (SS(a)) or an S//×S (SSab) knot (Figure 12).

Figure 12.

Knot conversation.

This notation leaves the symmetricity index unchanged throughout the conversions (H1H1s > SSs > SSsb, or H1H1a > SSa > SSab). It can be distractable, that the more frequently used abstract notation is changing during knot conversions (1 = 1 > S × S > S//S), ill. (1 × 1 > S=S > S//×S) and it is not a mistake but a habitual use.

Ad 5. knotting, dynamic knotting technics. To use the most suitable knot for a task, not only the awareness of the knot’s conformation, but also the tying method is crucial. A knot can have two basic functional use during practical application. On one hand, we can bind knot for postponed application and strain it later (e.g., some mountain climbing knots). On the other hand, the knot can be tied under tension, when even the initial form of the knot suffers strain that will expand by the end of the process. This ulterior case demands a more complex approach. The attachable living tissue elements are usually elastic, slippery and even moving. All these properties facilitate the untiement of the knot and the consequent release of the tissue. Only the knot itself can maintain the attaching effect, and therefore the knot sequence should be built up with a constant holding technique.

Tense-holding methods are:

1. the first half knot should be tied tense and then the following knots should be made with the constant pulling of the thread ends.

2. we can perform a sliding knot that will be either transformed into a blocking knot or stressed among the active and the passive thread.

3. while making the first half knot, we can perform more than one throws and therefore there will be a bigger frictional resistance between the threads that can hold the half knot together tightly.

4. the first half knot can be grabbed by assisting tool until we place the next half knot on the top of it.

Ad a) a knot can be made by hands or with instruments (apodactilic knotting technique) [3, 4]. Suggested video: https://www.youtube.com/watch?v=SL3lF17ocuE. Hand-knotting techniques have their own science and notation (one-handed, two-handed tying technique, instrument-tied technique, etc.). We have to note, that only the two-handed knotting technique is suitable for knotting under tension from all possibilities (Figures 13–15).

Figure 13.

One-hand tie technique—alternating hands.

Figure 14.

Two-hand tie technique—first H1 half knot.

Figure 15.

Two-hand technique—second symmetric H1 knot pair.

Ad b) (continuous) sliding knots were previously discussed that can assure continuous tension. Here we present some sliding knots usually employed in Orthopedics [5]. These knots receive a really great burden, therefore these should hold especially tight (Figure 16).

Figure 16.

Sliding (arthroscopic) knots.

Ad c) multiple throws applied in case of the first half knot are setting a larger joining surfaces. The modeling of this is a very complex task and depends on elasticity, the thread’s composition (mono- or multifilament) and frictional resistance. These attributes of the knots are widely investigated by numerous research groups [6]. In surgical practice, mostly the double-throwed first half knot is used and enough, more throws are barely used.

Ad d) the first half knot can be grabbed and fixed by surgical forceps and released right just before the tightening of the second half knot.

4. Knot security

The tying technics are to ensure the security of the knots. When talking about the security of a surgical knot we distinguish loop security and knot security.

The loop security means that during the knotting the distance between the tied tissues at the first loop is not increasing, therefore the diameter of the loop is not growing and therefore the loop will not get loose. The knot security means that the knot ensures a safe closure, thus the knot sequence does not or only due to a really strong force can a) untie, b) slide, c) break. In research regarding knot testing usually the knot security defined and investigated as it is more standardized. By contrast, the loop security only provides some additional information and is investigated as an acceptance interval measured in mm.

The secure knots (Table 1) [7].

	Secure
+	H1s		Sb							Sb
+	H1s		S							Sb
+	H1s		H1s						S	Sb
+	H1s	H1a	H1s	H1a	H2s	H2a	H2s	H2a	S
	H1		H2		H2		H3		S

Basis

Unsafe

Unsafe

Safe

Safe

Table 1.

Composite knot securing.

A challenge is rising when we need to tie a knot where there is not enough space for our hands (or the hand-knotting is too rough). For example, knotting in deep cavity or knotting with minimally invasive techniques (laparoscopy, arthroscopy, thoracoscopy, and microsurgery). In such cases, instrumental knotting techniques are used. This method has two fundamental subgroups: extracorporal- and intracorporal-knotting techniques. During extracorporal knotting, we make the knot at the free space (extracorporally) and then insert it into the badly accessible final spot with an instrument. Usually during extracorporal knotting we tie a sequenced sliding knot, then add additional fixing knots, prepared as blocking knots that are also pushed down as SSb knots. These knots can be made even through a 5 mm wide laparoscopic working tunnel (port). Two tools are used during intracorporal knotting.

4.1 Instrumental knotting techniques

See Figure 17.

Figure 17.

Instrumental knotting.

5. Conclusions

There are several nomenclatures for the composite knots made of the combination of simple prime knots. It is suggested to use the detailed nomenclature which includes not only the type of the knots (H, S) but also the number of throws (e.g., H1, H2, H3, S1, S2, etc.). In the case of composite knots, it is suggested to use the symmetricity/asymmetricity markings which can constantly be used even in case of conversions. Instead of the “=“↔ “×”, identical ↔ non-identical nomenclature, the “s” (symmetrical), and the “a” (asymmetrical) index are suggested. There is great potential in the partnership of topology as it can provide a deeper understanding through the investigation of the dynamic behavior of knots—and that field has to be further studied.