INTRODUCTION

KNOT TYING IS A BASIC SURGICAL SKILL and is quicklyacquired by the training surgeon.1,2 The ability to

accurately suture and then tie the knot is a complex ma-neuver involving manual dexterity, hand-eye coordina-tion, and depth perception. Tying intracorporeal knots

JOURNAL OF LAPAROENDOSCOPIC & ADVANCED SURGICAL TECHNIQUESVolume 16, Number 4, 2006© Mary Ann Liebert, Inc.

Technical Report

How Reliable Is Intracorporeal Laparoscopic Knot Tying?

PEDRO-JOSE LOPEZ, MD,1 JOHN VENESS, BSc, CEng, MIEE, CSci,2ANDREW WOJCIK, BSc, BA, MA, PhD, ARSM, DIC,2

and JOE CURRY, MBBS, FRCS (Paed Surg)1

ABSTRACT

Background: Are knots tied laparoscopically as reliable as those tied in open surgery? The aim ofour study was to try to answer this question.

Materials and Methods: Using a standardized technique, one senior laparoscopic surgeon tied 3suture materials using 3 methods of knotting: hand, instrument, and laparoscopic (in a simulator).The tension in the knots was measured using a tension gauge at the time of knotting and 5 minuteslater. The surgeon was blinded to the value. The experiment was repeated 4 times. The 36 sutureswere then analyzed using a materials-testing machine. The force achieved prior to breakage, the ex-tension, and the breaking points were recorded. The scientist performing the analysis was blindedas to the method of tying and tensions produced.

Results: There were no significant differences in tension at 5 minutes between suture materialsor method of knot tying. The mean extension achieved prior to breakage for 33 sutures was 29.71mm with a force of 16.09 N. In 3 sutures the knot slipped completely while tension was being in-creased, thus no measure of breakage force could be obtained. These 3 sutures were monofilamentand tied laparoscopically.

Conclusion: There were no significant changes in suture tension after 5 minutes regardless of ma-terial or method of knot tying. Three of the 12 knots tied laparoscopically came undone under straintesting. All 3 knots were monofilament suture. This may have important implications when choos-ing suture material. Further studies are planned to expand the analysis of different knotting tech-niques with different suture materials.

Departments of 1Paediatric Surgery and 2Biomedical Engineering, Great Ormond Street Hospital and University College ofLondon, London, United Kingdom.

using laparoscopy is an equally important skill, butmade more difficult to learn by the lack of depth per-ception and the two-dimensional representation.3,4 Thesurgeon has only visual clues to guide the accuracy andforce of the stitch tying, as much of the tactile sensa-tion is dampened or removed by the ports and the lengthof the laparoscopic instrument.5 This leaves one vital

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INTRACORPOREAL KNOT TYING 429

MATERIALS AND METHODS

Three commonly used suture materials were chosen forthe experiment-Vicryl, Prolene, and Ethilon. The senior au-thor (JC) tied 4 square knots over a custom-made electronictension gauge (Fig. 1) using only his hands; 4 knots usinga standard needle holder; and 4 knots using an intracorpo-real knotting technique incorporating 5-mm laparoscopicinstruments and a camera in a training box (Fig. 2).

The tension produced in the knots was measured at thetime of tying and after 5 minutes. The surgeon wasblinded to the value of the tension. The experiment wasrepeated 4 times for each type of suture material and eachmethod of tying.

The 36 sutures were then analyzed using a HounsfieldH5K-S materials testing machine (Figs. 3 and 4). The ini-tial sample length was set to 35 mm and an extensionrate of 10 mm/min was used. The force was applied un-til the suture broke. The maximum force achieved priorto breakage, the maximum extension, and the breakingpoints were recorded. The scientist supervising this partof the experiment was blinded to the method of tying andtensions produced. The point of suture rupture wasrecorded. Data were analyzed using GraphPad Prism soft-ware. Results are expressed as means. P values �0.05were considered significant.

RESULTS

Table 1 shows the mean tension achieved for the 3 su-ture materials initially and after 5 minutes. The greatestfall in suture tension at 5 minutes was seen with Prolene,although this was not statistically significant (P � 0.49).There was no significant differences in tension after 5

FIG. 1. Homemade electronic tension gauge.

FIG. 2. In the laparoscopic training box.

TABLE 2. MEAN TENSION ACHIEVED FOR THE 3 METHODS OF

KNOT TYING INITIALLY AND AFTER 5 MINUTES

After 5Method of knot tying Initially minutes

Hand 93.33 91.08Instrument 139.5 130.5Laparoscopically 102.2 101.5

TABLE 1. MEAN TENSION ACHIEVED FOR THE THREE SUTURE

MATERIALS INITIALLY AND AFTER 5 MINUTES

After 5Material Initially minutes

Prolene 98.92 86.17Vicryl 88.58 92.67Ethilon 147.33 144.0

question: Are knots tied using laparoscopy as reliableas those tied by more traditional open methods of handor instrument? The aim of our study was to try to ad-dress this issue.

430 LOPEZ ET AL.

minutes between the different methods of knot tying(Table 2). Twelve of the 36 sutures (33.3%) showed anincrease in their final tension after 5 minutes; 5 wereEthilon and 7 were Vicryl.

Thirty-three of the sutures broke near the knot fol-lowing application of tension. In the other 3 sutures, theknot slipped and became undone while tension was be-ing increased, thus no measure of breakage force couldbe obtained (Fig. 5). These 3 sutures were all monofila-ment (2 Ethilon and 1 Prolene) and were all tied laparo-scopically. The tension in these 3 sutures on initial tyingwas above the mean for 2 of the 3 sutures.

On strain testing the final mean extension achievedprior to breakage for 33 sutures was 29.71 mm with afinal force of 16.09 N. Ethilon produced the maximalextension under increasing applied force while Vicryltolerated the most force before breakage occurred(Table 3).

DISCUSSION

Accurate and secure suturing is a fundamental skillin surgery. These skills are learned early by surgeonsin training and often deeply ingrained by the time con-sultant practice is achieved.6,7 The quality of the su-turing can frequently be taken for granted by the sur-geon, and often other factors will be blamed for

operative complications such as infection or poorly per-fused tissue. It must be kept in mind that a knot that istied incorrectly and fails gives the tissue no chance ofhealing.

The advent of laparoscopy has revolutionized surgicalpractice and its use by pediatric surgeons is increasingrapidly.8 New skills have to be learned and establishedold skills need to be adapted to laparoscopy. This is es-pecially the case for intracorporeal knot tying:9 the two-dimensional representation and a lack of direct assess-ment of tension can make knot tying a very challengingtask.4,10

Can the surgeon assume that the knots he or she maytie laparoscopically are of the same quality of those tiedat open surgery? We have shown that, while the differ-ence is not statistically significant, the only 3 sutures tountie at the knot on strain testing were all monofilamentand were tied laparoscopically. These suture failures oc-curred at a directly applied tension that would be un-likely to be reproduced in actual surgery in children, butthey do raise a concern. We were unable to ascertainfrom this study whether this is a feature of the methodof knotting, the knot employed, the suture material, ora combination of all these factors. Others have observedslipping of knots during in vitro laparoscopic knot ty-ing.11

Our study also highlighted the fact that the tension ap-plied during knotting can increase with time. This in-

FIG. 3. Hounsfield H5K-S materials testing machine.

TABLE 3. EXTENSION AND FINAL FORCE

ACHIEVED BEFORE BREAKING POINT

Extension ForceMaterial (mm) (newton)

Prolene 27.15 16.19Vicryl 22.65 19.21Ethilon 40.48 14.04

FIG. 4. Hounsfield H5K-S materials testing machine.

INTRACORPOREAL KNOT TYING 431

crease could potentially exacerbate tissue ischemia andinfluence wound healing. Vicryl does dissipate its origi-nal strength (by 75% after 14 days) while Ethilon is non-absorbable and so its applied tension may remain.

Reconstructive procedures that require stitches to op-pose tissue may succeed or fail depending on the qualityand integrity of such stitching. There is little research inthe pediatric population that looks at the potential con-sequences of stitch failure. For instance, Nissen fundo-plication relies on stitches at the crura and for the con-struction of the wrap. It has always been associated witha risk of failure.12 Intermediate-term results have beenreported but the longer term outcomes have yet to be pub-lished.13 Extracorporeal knotting may have some advan-tages in terms of ease and security but possibly at the ex-pense of increased tissue ischemia, although a survey ofsurgical residents showed they preferred intracorporealknotting.14

Laparoscopic knotting is highly suited to in vitro train-ing and the surgeon who is new to laparoscopy is welladvised to fine-tune such skills before attempting themon the patient. Structured training has to be done for anoptimal development of laparoscopic skills,15 especiallyas it has been demonstrated how stressful this method canbe compared to open knotting.16,17

Our model does have certain deficiencies, in that thereare no inherent haptics to allow feedback in relation toapplied forces, and there are no visual clues, which nor-mally guide real knotting in terms of opposed tissues (eg,tissue retraction).

Further work is planned to look at improving themodel. We aim to use different knots and suture materi-als to ascertain if there are any potential risk factors forlaparoscopic suture failure.

REFERENCES

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FIG. 5. In batch 2 (samples 11 to 20), the knot of sample 18 slipped and became undone while tension was being increased.

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16. Berguer R, Smith WD, Chung YH. Performing laparo-scopic surgery is significantly more stressful for the sur-geon than open surgery. Surg Endosc 2001;15:1204–1207.

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Address reprint requests to:Joe Curry, MBBS, FRCS (Paed Surg)

Department of Paediatric SurgeryGreat Ormond Street Hospital

London WC1N 3JHUnited Kingdom

E-mail: curryj@gosh.nhs.uk