Towards a better knot: Using mechanics methods to evaluate three knot-tying techniques in laparo-endoscopic single-site surgery.

INTRODUCTION: Knot tying is difficult but important for laparo-endoscopic single-site surgery (LESS). There are several techniques for LESS knot-tying. However, objective assessment of these skills has not yet been established. The aim of this study was to assess three different knot-tying techniques in LESS using mechanical methods.
MATERIALS AND METHODS: The subject tied 24 knots, eight knots with each of the three techniques in an inanimate box laparoscopic trainer while the movements of their instruments were evaluated using a LESS mechanical evaluation platform. The operations were assessed on the basis of the time, average load of the dominant hand. Then, forces caused the knots to rupture were measured using a material testing system and used to compare the knots's strength.
RESULTS: The intracorporeal one-hand knot-tying technique presented significantly better time and average load scores than the extracorporeal knot-tying technique (P < 0.01), and the intracorporeal side winding technique was more time and average load consuming in comparison to other techniques during the performance of knot-tying (P < 0.01). The intracorporeal one-handed knot-tying knots can tolerate better distraction forces compared with the intracorporeal side winding knot-tying knots and the extracorporeal knot-tying knots (P < 0.05).
CONCLUSIONS: The intracorporeal one-hand knot-tying technique and knots showed better results than the intracorporeal "side winding" technique and the extracorporeal knot-tying technique in terms of the time, average load taken and the force caused the knot to rupture.

INTRODUCTION

Laparo-endoscopic single-site surgery (LESS) was introduced in the 1990s but gained momentum as an advanced laparoscopic surgical approach only a decade later.[1] It has shown advantages over conventional laparoscopic surgery, such as better cosmetic results, less postoperative pain and faster recovery.[2] However, LESS is technically demanding due to the associated technical challenges which made advanced laparoscopic tasks cumbersome, including loss of triangulation, collisions of the instruments, lack of maneuverability and lack of proper exposure.[3]

Knot tying, being a fundamental skill, is considered to be the most difficult laparoscopic skills due to its complexity and intricacy, and it is more difficult for LESS as there are several inherent technical problems mentioned above. Two-handed intracorporeal knot-tying which was routinely performed in standard multiport laparoscopic surgery becomes almost impossible for LESS procedure. Therefore, it is meaningful to find a feasible and better knot-tying skill for the development of LESS. Several methods of creating knots representing by the one-handed knot tying technique,[4] the intracorporeal “side winding” knot-tying technique[5] and the extracorporeal technique with which knot-tying was accomplished “extracorporeally” using a knot-pusher, have been developed and used for LESS. All the methods reported have been considered be able to execute safely, simply and quickly. However, none has used an objective evaluation system to compare these different techniques and evaluate the safety of these knots.

In this study, operation time and average load were measured to compare knot-tying performance with these three techniques using a LESS mechanical platform, and the breaking strength of each of these knots were calculated to evaluate the safety using a material testing system. Based on the objective evaluations, we aim to provide valuable reference for improvement of these LESS knot-tying techniques.

MATERIALS AND METHODS

Materials and Instruments

Laparo-endoscopic single-site surgery mechanical evaluation platform

The platform was set up by a box trainer (Model 200, RUIHONG laboratory equipment Co. Ltd, Shanghai, China), a single incision laparoscopic surgery (SILS) Port™ (Covidien, Mansfield, MA, USA), two load cells and the weighing accessories [Figure 1]. The top of the simulator was modified to introduce the port around which two load cells were layed. The analog signal of load cells will be magnified after adding by the junction box, which will be dealt with by micro controller unit after analog to digital conversion, then will output to PC software by RS232-RS485 module. The weighing systems (Model FN-D3 Stainless Steel Single Point Load Cell, AD750 high precision digital weighing transmitter, RS232-RS485 passive converter, data record analyzer 2.0) were manufactured or provided by ANRUI Automatic Instrument Co. Ltd, Shanghai, China.

Figure 1

The laparo-endoscopic single-site surgery mechanical evaluation platform

Instron 5543 material testing system

The system is an electromechanical material testing system and integrated software for digital test control and data collection. Capable of uniaxial tests up to 1kN force with a travel speed range from 0.05 to 1000 mm/min. Variety of compatible load cells from 5N to 1kN allows for accurate measurements.

Instruments

The conventional laparoscopic grasper and knot-pusher were manufactured by the YIDA Medical Device Co. Ltd (Hangzhou, Zhejiang province, China). The SILS™ Kits was purchased from Covidien, Inc. (Mansfield, MA, USA). The suture used was silk braided nonabsorbable suture (4 metric, Ethicon, Minhang, Shanghai, China). The knot-tying operation board on which the jig fixed was homemade. All knots were tied in the central of the jigs [Figure 2].

Figure 2

The knot-tying operation board

Laparo-Endoscopic Single-Site Surgery Knot-Tying Techniques

The extracorporeal knot-tying technique

The knot was tied with following steps: introducing a long length of suture via a port, passing it around the structure to be ligated, exteriorizing the suture and fashioning a knot, which is then slid down using a knot-pusher. The procedure is repeated until another knot has been made.

The intracorporeal “side winding” knot-tying technique

In the first step, the Roticulator Endograsp is opened in the knotting area, and the suture was wound around. Then, the reef knot is converted into a knot by applying distracting forces on the suture material at the two opposite points. The procedure is repeated until another knot has been made [Figure 3a].

Figure 3

(a) The intracorporeal “side winding” knot-tying technique. (b) The intracorporeal one-handed knot-tying technique

The intracorporeal one-handed knot-tying technique

The knot was tied with following steps: Encircling the tissue; formation of an “o” with over wrapping; formation of the first half knot; completion of the first half knot; formation of the second “o” by wrapping; formation and completion of the second half knot [Figure 3b].

Subject and Study Design

All the performances were carried out by an experienced surgeon who has performed more than 200 LESS surgery, and he is right-handed and hence the right hand is the dominant hand.

All the knots were tied on the operating board. To compare objectively, all knots were single winded and tied, and then the same process was repeated. Timing started when the suture was holding by instrument and (or) hand. Knots were tied 8 times with each technique of which the sequence was decided by corresponding order created by a random number table. Both ends of the 24 knots tied around the stick were cut to same length [Figure 4]. These knots were then placed into the Instron 5543 materials testing machine [Figure 5]. An extension rate of 30 mm/min was used, and the maximum capacity of the load cell was 50N. The force was applied until the suture loosed. The maximum force (in Newtons) achieved prior to breakage was recorded and logged into the database.

Figure 4

Both ends of the 24 knots were cut to same length (the shorter end was 1 cm)

Figure 5

The materials testing machine with knot placed

Statistical Analysis

When performing the knot tying with each technique using the LESS mechanical platform, a power-of time curve was recorded by the analyzer. The measured outcomes included operation time and workload. Load is a measure of the amount of work that the system performs. The average load represents the average system load over a period. In our study, the given interval of recording data is same, so the average load is the mean value of all the loads and can be worked out by the data of an Excel table which was exported from the analyzer. In another test, for each knot, the force caused the knot to rupture (in Newtons) was recorded by the material testing system.

Possible differences in the operation time, average load and the force caused the knot to rupture were investigated using one-way analysis of variance or its nonparametric form (Kruskal–Wallis test) where appropriate. All statistical analyses were conducted by using Statistical Package for the Social Sciences (SPSS) statistical software (version 15.0; SPSS, Inc., Chicago, IL, USA). Statistical significance was set, and P < 0.05.

RESULTS

Results of comparisons of knot-tying with different techniques were showed in Table 1. There were significant differences of operation time and average load in all groups compared with each other (P < 0.01). The longest time and largest average load were seen with the intracorporeal “side winding” knot-tying technique (90.48 ± 17.21s, 4.23 ± 0.66N). The differences between the extracorporeal knot-tying technique and the intracorporeal one-handed knot-tying technique were significant (67.43 ± 6.03 vs. 53.55 ± 6.12s, 3.25 ±0.48 vs. 2.37 ± 0.36N, P < 0.01).

Table 1

Comparisons of knot-tying with different techniques x ± s

Table 2 showed the results of the comparison of forces caused the knot to rupture.

Table 2

Comparisons of knots of different techniques x ± s

The intracorporeal one-handed knot-tying knots (8.64 ± 0.29N) can tolerate better distraction forces compared with the intracorporeal “side winding” knot-tying knots and the extracorporeal knot-tying knots (7.81 ± 0.45 and 8.35 ± 0.87N) (P < 0.05).

DISCUSSION

Knot tying has an important place in laparoscopic surgery and LESS. Several methods of creating LESS knots have been developed, which include the two broad categories of those knots created extracorporeally and those created intracorporeally. Intracorporeal knots are formed entirely within the abdomen by using an instrument tie technique. In conventional laparoscopic surgery, the ports are so placed that the instruments introduced through them make an angle of between 45° and 70° with one another, thus facilitating intracorporeal knot tying. Extracorporeal knots are created by removing both ends of the suture outside the laparoscopic ports forming the knot outside of the abdominal cavity and using a laparoscopic knot pusher to cinch down and secure each throw of the knot.

Since the first reports on LESS in 1997 for cholecystectomy and appendectomy, the applications have been varied, including in urology, adrenalectomy, bariatric procedures, and hernia repairs. In the “puppeteer” technique, two-handed knot-tying becomes almost impossible as the instruments lie almost parallel to one another. The problem may be overcome by using one or even two roticulating instruments so that the tips of the instruments meet at an angle and facilitate knot tying. Thanakumar and John introduced “the intracorporeal one-handed knot-tying technique” for LESS, which refers to a knot tied with one end of the suture kept fixed in one hand as the second hand carries out the manoeuvers necessary to form the knot, and the authors hoped that the knot-tying will not only find a place in the armamentarium of the surgeon performing LESS, but also become applicable in conventional laparoscopic as well as in hybrid techniques combining surgery.[4] Ekci B reported the intracorporeal “side winding” knot-tying technique and said even an inexperienced surgeon would be able to execute this knot safely, quickly, simply and cost effectively.[5] Of course, the extracorporeal knot-tying technique which was widely used in articular surgery can also be performed in LESS.

As several knot-tying methods for LESS like above mentioned were introduced and reported, the assessment of these techniques and knots is important. Traditionally, this assessment has been made subjectively by surgical trainers.[67] However, such subjective assessment cannot precisely compare surgical skills since it often differs from trainer to trainer. Thus, there is now increased demand for objective assessment of LESS knot-tying performance and the safety of the knots.

Earlier this year, we set up a mechanical evaluation platform for LESS and assessed the cross-handed approach and manipulation with articulated instruments by performance of two LESS tasks (suture pass-through rings and clip-cut). Results showed that compared with conventional instruments, articulated instruments and the cross-handed manipulation are associated with longer operation time and more workload.[8]

In the current study, the mechanical evaluation platform for LESS was used to assess different knot-tying methods. Results of the present study have demonstrated that the intracorporeal one-handed knot-tying technique consumed less time and average load, indicating that this method was a better one among the three different techniques. Furthermore and interestingly, our results have shown that shorter time was accompanied with less workload, it can be explained that shorter time represented operated smoothly, quickly and simply, and the average load will be less respectively. Moreover, different with conventional laparoscopic surgery which required more two-handed coordination and during to the associated technical challenges of LESS, the three LESS knot-tying techniques we described above were mainly completed by the dominant hand while the nondominant hand is relatively less important as it just hold one end of the suture, especially when performed with the intracorporeal one-handed and the extracorporeal knot-tying techniques. Otherwise, there will be a clash of two instruments of each hand that hinders the knot-tying. Therefore, we just only compared the average load in the dominant hand, as the workload almost the same in the nondominant hand theoretically. Besides, not consistent with deemed result, more time and workload were required for the extracorporeal technique than for the intracorporeal one-handed technique, partially due to the complexity of the technique and the rough suture which need more workload to cinch down.

Although objective assessment using the mechanical evaluation platform for LESS could be efficient, we must keep in mind that this system alone cannot give any information regarding performance quality. For example, it is of no use if a surgeon completes tying a loose knot at a faster speed with a lower workload. Thus, assessment of performance quality should be integrated into objective assessment. Knot strength is the most important considerations in selecting a knot during every surgery. In this study, we used the material testing system to measure the breaking strength of each of these knots. Results showed that the intracorporeal one-handed technique knot can tolerate greater distraction forces than the intracorporeal “side winding” technique knot and the extracorporeal technique knot.

As only silk braided nonabsorbable suture used in this study, further studies are planned to expand the analysis of different knotting techniques with different suture materials. Another limitation of the current study is that an expert LESS surgeon performed all procedures, and possible difficulties in the knot-tying were probably overcome by the higher expertise of the surgeon. Thus, the expected steep learning curve of different knot-tying techniques mentioned in the article could have been easily overcome. Considering the facts that the limitation was present in all methods of knot-tying and the aim of this study was to compare knot-tying with different techniques rather than the differences among surgeons with varying skill levels, the results of the current study are reliable and probably reflect the efficacy of each knot-tying technique.

our results, when tested in laboratory settings, evaluation of knot-tying techniques in LESS using mechanical methods revealed better results for the intracorporeal one-handed knot-tying technique than for the intracorporeal “side winding” and the extracorporeal knot-tying techniques in terms of the time, average load taken and the force caused the knot to rupture. Further clinical studies with patient's postsurgical follow-up are needed to determine true outcome differences between the knot-tying techniques.