Suture end length as a function of knot integrity

Knot Security 101: A Comprehensive Practical Review to Optimal Knot Configuration, Pulling Direction, Throw Count, and Tail Length

Background

Knots are the weakest structural point in a suture line and inevitably weaken almost all suture materials. This practical review critically evaluates the factors, such as suture material properties, gauge, configuration, throw count, and tail length, that affect knot security.

Methods

A PubMed search between the years 1934 and 2023 identified relevant studies that addressed factors relating to knot security. Studies that investigated knots and sutures solely used in laparoscopic and arthroscopic surgery were excluded. Knot configurations assessed were the Aberdeen, sliding, square, and surgeon's.

Results

Eighty-six articles were included in this review article and demonstrated that knot security varies greatly between suture materials and gauge. Knot security also varies by configuration, throw count, conditions, tail length, and stitch type. Throw count differs by knot configuration, with the Aberdeen knot being most secure with three throws and one to two turns compared with three to five throws for surgeon's and square knots. The optimal tail length was 3 mm.

Conclusions

This practical review demonstrates that there are significant differences in knot security based on a variety of factors. It is challenging to propose an ideal knot because most studies did not evaluate knot security using a broad variety of suture materials, gauges, and throws for each of the most common knots. Although this review article demonstrated several applicable findings, additional robust studies are needed to simplify proposals.

Security Comparison of Various Surgical Knots Using Nylon Suture

OBJECTIVE

To evaluate the strengths of various surgical knot techniques, including square knot, surgeon's knot, granny knot, and random knot with the same three throws.

METHODS

The authors tested each of the four knot techniques using four different gauges of nylon (polyamide [Ethicon]): 4-0, 5-0, 6-0, and 7-0. Each knot type was tested 20 times per nylon gauge, for a total of 320 knots tested. The authors used a static pull machine to measure elongation at yield and maximal force to break.

RESULTS

A comparison of elongation at yield revealed that the surgeon's knot was superior to the square knot, granny knot, and random knots across all gauges of nylons. Further, a comparison of maximal force to break revealed that the surgeon's knot was superior to the square knot, granny knot, and random knots when using 4-0, 5-0, and 6-0 nylon but not when using 7-0 nylon.

CONCLUSIONS

The surgeon's knot was the strongest, and random knot was the weakest when the authors used nylon 4-0, 5-0, and 6-0. While handling fine suture materials such as 7-0 nylon, knot failure appears to be unrelated to the knot technique used. This study provides not only fundamental guidance for tying surgical knots using nylon, but also a rational basis for an adequately strong knot choice in various fields of surgery.

Influence of pulling direction on knot security: A laboratory research

BACKGROUND

When tying knots, some surgeons do not pay particular attention to the direction in which they pull to lay down throws. We examine to what extent does pulling direction influence on knot security.

METHODS

A total of 368 residents were instructed to tie knots with from 2 to 7 throws using silk braided suture in 3-0 gauge. The direction in which they pulled to lay down throws was recorded. Only the knots tied either by pulling in alternate directions (Group A) or in constant direction (Group C) from the first throw to the last were involved in statistical analysis. Tensile strength and untying rate of the knots were then measured for comparative analysis.

RESULTS

For knots with from 2 to 7 throws, the tensile strength of the ones from Group A was significantly higher than that of the ones from Group C (p < 0.05), respectively. For knots with from 5 to 7 throws, the untying rate of the ones from Group A was significantly lower than that of the ones from Group C (p < 0.05), respectively. For the unraveled knots with from 2 to 7 throws (except for the ones with 5 throws), the tensile strength of the ones from Group A was significantly higher than that of the ones from Group C (p < 0.05), respectively.

CONCLUSION

Pulling in constant direction results in inferior knot security. Surgeons must ascertain the influence of pulling direction on knot security, and try to achieve superior security with fewer throws to ensure patient safety.

Does quality of novice hand-tied square knots improve with repetition during a single training session?

Background

Knot tying is a key surgical skill for novices, and repetition over several training sessions improves knot tying. This study examined the effects of repetition within a single training session on quality of knotted loops and compared results of novice trainees and experienced surgeons.

Methods

Using 0.55 mm nylon monofilament fishing line, novices and surgeons each hand-tied 20 knotted loops, using a 2=1=1=1 configuration (surgeon's throw and three square throws). Loops were mechanically tested with a single load to failure.

Results

All loops tolerated five newtons (N) preload. More than 70% of novice and surgeon knots failed by slipping or untying, and 8.8% of novice knots and 2.5% of surgeon's knots were considered dangerous. Surgeons' loops had less extension at preload, indicating better loop security. However, during single test to failure, there was no difference in mean extension or maximum load between surgeons and novices. There was no significant difference in results of mechanical testing or modes of failure for the first and last ten knotted loops, or the first, second, third, and fourth sets of knotted loops.

Discussion

With appropriate training, novices can construct knots as strong and secure as experienced surgeons. A large percentage of knotted loops are insecure under testing conditions; extra throws may be required when using large diameter monofilament nylon. Novices may require extra training in maintenance of loop security when constructing square knots. Tying more than five or 10 knotted loops within a single training session does not provide added benefits for novices.

Effect of Common Mouthwashes on Mechanical Properties of Suture Materials Used in Dental Surgeries: A Laboratory Experiment

Background: Sutures play a pivotal role in promoting healing in any surgical procedure. However, the versatile nature of the oral environment entails additional properties in the suture materials to assure uneventful healing. A surgeon needs to understand these delicate intricacies in the immediate postoperative phase and needs some kind of algorithm in the selection of sutures that suits the different surgical scenarios. Therefore, a study was designed to observe the effect of four different types of mouthwash, viz. Avohex, Aloedent, Parodontax and Betadine, on the mechanical properties of Vicryl (polyglactin 910), PTFE (polytetrafluoroethylene), Prolene (polypropylene) and Mersilk. Methods: A total of 288 suture samples were divided in four equal groups (72 = each group) and used for the experiments. Tensile load, tensile strength as well as percentage elongation of the suture materials were evaluated in the various stated media at 3rd, 7th, 10th and 14th days, which were compared with the controls. The results were analyzed statistically and inferences were drawn. Results: Mersilk in (Avohex, Parodontax and Betadine) solutions showed a statistically significant decrease in tensile load over time. All the sutures had the highest tensile strength in Parodontax and had the lowest in Betadine solution. Vicryl and PTFE presented significant percentage elongation over time as compared to Prolene and Mersilk. Conclusion: The author has given certain recommendations but also states that there is no standard rule for the use of a particular suture material in all clinical situations. However, the selection of the suture material should be based on the type of surgery and preferences of the surgeon.

How to tie dangerous surgical knots: easily. Can we avoid this?

Objective

Secure knots are essential in all areas of surgical, medical and veterinary practice. Our hypothesis was that technique of formation of each layer of a surgical knot was important to its security.

Design

Equal numbers of knots were tied, by each of three groups, using three techniques, for each of four suture materials; a standard flat reef knot (FRK), knots tied under tension (TK) and knots laid without appropriate hand crossing (NHCK). Each knot technique was performed reproducibly, and tested by distraction with increasing force, till each material broke or the knot separated completely.

Setting

Temporary knot tying laboratory.

Materials

The suture materials were, 2/0 polyglactin 910 (Vicryl), 3/0 polydioxanone, 4/0 poliglecaprone 25 (Monocryl) and 1 nylon (Ethilon).

Participants

Three groups comprised, a senior surgeon, a resident surgeon and three medical students.

Outcome measures

Proportion of each knot type that slipped, degree of slippage and length of suture held in loop secured by each knot type.

Results

20% of FRK tied with all suture materials slipped; all knots tied with the other two techniques, with all materials, slipped, TK (100%) and NHCK (100%). The quantitative degree of slip was significantly less for FRK (mean 6.3%–, 95% CI 2.2% to 10.4%) than for TK (mean 312%, 95% CI 280.0% to 344.0%) and NHCK (mean 113.0%, –95% CI 94.3% to 131.0%).

The mean length of suture in loops held within (FRK mean 25.1 mm 95% CI 24.2 to 26.0 mm) was significantly greater than mean lengths held by the other techniques (TK mean 17.0 mm, 95% CI 16.3 to 17.7 mm), (NHCK mean 16.3 mm, 95% CI 15.9 to 16.7 mm). The latter two types of knot may have tightened more than anticipated, in comparison to FRK, with potential undue tissue tension.

Conclusion

Meticulous technique of knot tying is essential for secure knots, appropriate tissue tension and the security of anastomoses and haemostasis effected.

Mechanical Comparison of High-Strength Tape Suture Versus High-Strength Round Suture

Purpose

To compare knot and loop characteristics of commonly used high-strength tapes and high-strength round sutures.

Methods

Twenty tied 30-mm loops were prepared for using suture-knot combinations of 4 common arthroscopic knots or a hand-tied surgeon’s knot and 7 sutures. Two tapes (BroadBand, SutureTape) and three no. 2 sutures (MaxBraid, FiberWire, DynaCord) were compared. Two additional larger tape sutures (FiberTape, PermaTape) not commonly tied arthroscopically were included in the hand-tied group. Each suture-knot combination was evaluated for loop integrity (single load to a specified elongation), knot security (plastic loop deformation with cyclic testing), loop security, and knot volume. Data were compared using analysis of variance followed by Tukey-Kramer post hoc tests.

Results

BroadBand and SutureTape demonstrated superior loop integrity compared to most no. 2 suture-knot combinations. FiberTape (430.48 ± 89.00 N) and PermaTape (545.16 ± 95.09 N) required significantly greater force to undergo 3 mm of displacement than all other hand-tied sutures (P < .001). All suture-knot configurations demonstrated significant plastic deformation (cyclic elongation) over 1000 cycles (P < 0.001). DynaCord displayed the best loop security except when paired with the Duncan loop. Overall, BroadBand and SutureTape had lower knot volumes compared to all other sutures.

Conclusion

This study exhibits the ability of narrow tape sutures to provide reliable tissue apposition and fixation in multiple suture-knot configurations, while decreasing the potential adverse effects accompanying knot prominence. Generally, BroadBand and SutureTape demonstrated an ideal balance of mechanical characteristics to achieve the optimal suture-knot construct among those tested. Dynacord displayed superior loop security and performed best among round sutures. PermaTape and FiberTape showed greater loop integrity, albeit to the detriment of loop security and knot volume.

Clinical Relevance

When securing a rotator cuff repair construct with a knot, one should have a basic understanding of the mechanical properties of the suture and knot being used to provide the best possible repair. This study will provide information about the mechanical characteristics of commonly used high-strength tape suture knots and loops to help determine what knot type may provide the best overall construct.

An educated guess - Distance estimation by surgeons

Introduction

Estimating distance is a common task in surgery, yet development of distance estimation ability receives little attention in surgical training. Although the Small bites versus large bites for closure of abdominal midline incisions (STITCH) trial reinforced the importance of suture spacing by demonstrating reduced incisional hernia incidence in placement of 5-mm fascial sutures over 1 cm, we hypothesize that neither trainee nor attending surgeons possess the ability to estimate these distances with accuracy.

Methods

We distributed a 4-question distance estimation exercise and a 6-question survey to resident and attending surgeons at a single academic medical center. The mean and the absolute error were compared using a t test.

Results

Most participants were trainees (44 vs 16 attendings, N = 60), and 27% used the metric system prior to undergraduate studies. The mean absolute errors for 5-mm and 1-cm mark placement were 1.40 and 2.07 mm, respectively. The 5-mm mark placement estimates ranged from 2.01 to 11.69 mm, and the 1-cm estimates ranged from 4.82 to 19.19 mm. There was no statistically significant difference in the estimates or absolute errors between trainees and attendings (5 mm P = .202; 1 cm P = .302).

Conclusion

These findings suggest that estimation of distance is a challenge, and development of this fundamental skill during surgical training may have important clinical consequences.

Effect of Hyaluronic Acid in Modifying Tensile Strength of Nonabsorbable Suture Materials: An In Vitro Study

Background and Aims:

In periodontics and other surgical disciplines, sutures play a detrimental role in healing of wound. The use of chemical adjuncts to boost healing has been experimented in recent years. The aim of this study was to evaluate the role of hyaluronic acid rinse in influencing the tensile strengths of commonly used sutures.

Materials and Methods:

Two commonly used nonabsorbable suture materials, silk and polyamide, were used for this in vitro study. Tensile strengths of the suture materials were determined by pre- and post-immersion in hyaluronic acid (test) and chlorhexidine (control). A Tinius Olsen Universal Testing Machine was used to assess the tensile strength of the samples. The variables were assessed for normality using the Kolmogorov–Smirnov test. The Wilcoxon signed rank test and Mann–Whitney U test (for quantitative data within two groups) were used for quantitative data comparison of all the clinical indicators. The level of significance was set at P ≤ 0.05.

Results:

Polyamide showed better stability in terms of tensile strength when compared to silk. Hyaluronic acid as a chemical adjunct did not alter the tensile strengths of both suture materials pre- and post-immersion.

Conclusion:

This in vitro study has shown a promising property of hyaluronic acid with relation to stabilization of tensile strength of suture materials, which needs to be evaluated in clinical settings.

Endoscopic Closure of Large Defects With a Novel Clipping Device and a 4S-Modified Roeder Slipknot

Endoscopic closure is an essential procedure in gastrointestinal (GI) surgery, but currently it is difficult to close large defects endoscopically because of the lack of an appropriate device. Previously, we developed an endoscopic clipping device that has multifiring function and is equipped with an independent clamp. The goal of this study is to provide a new closure method with this device and 4S-modified Roeder (4SMR) slipknot. The feasibility of the closure method is examined by deploying two clips during one insertion onto the 4SMR slipknot to close a 5 cm full-thickness linear defect of an ex vivo porcine stomach from the center. Mechanical strengths of clip-knot closure and the slipknot as regards to tensioning forces are also evaluated. Specifically, the mechanical strength of the 4SMR slipknot is verified by mean peak forces to failure, while the knot is tensioning by 2.5, 5, 7.5, and 10 N force (n = 20 for each group), respectively. Experimental results indicate the clip-slipknot closure can withstand a distracting force of 6.3 ± 5.6 N. Tensioning force has a great influence on the mechanical strength of slipknot, with the mean peak force (tensioning force) being 7.1± 6.5, 16.3 ± 9.3, 18.9 ± 10.4, and 24.2 ± 12.0 N, respectively. The proposed closure method can be used for large defects. Tensioning force higher than 5 N is suitable to ensure a stronger 4SMR slipknot.

Causes of Flexor Tendon Repair Failures in Two Common Repair Techniques: A Cadaver Study

BACKGROUND

Flexor tendon repair failures have primarily been attributed to either core suture rupture or core suture pull out. Recent studies have suggested that knot unravelling may also cause failure of a tendon repair. The aim of this study was to investigate the causes of core suture failure in two types of common flexor tendon repairs.

METHODS

Twenty four cadaver tendons were divided into three groups of eight. Each group tested a specific flexor tendon repair. The repairs tested included an Adelaide repair using 4/0 Ethibond (Ethicon), an Adelaide repair using 4/0 Fiberwire (Arthrex) and the Tsai repair with 4/0 Fiberloop (Arthrex). The repaired tendons were pull-tested to failure. The mechanism of failure, maximum tensile strength and 2 mm gap force were recorded.

RESULTS

The predominant mode of failure was by the knot unravelling. This occurred in 50-88% of the tendon repairs. The sequence of failure was initiated with gapping at the repair site followed by failure of the epitendinous suture. Next the core suture knot unravels. Once the knot unravels, the suture thread slips out of the tendon resulting in the repair failure. Failures due to knot slippage occurred at a lower maximum tensile strength in Ethibond and Fiberloop sutures than failure due to core rupture or pull out. However, given the small number of tendons tested, this result was not significant.

CONCLUSIONS

This study has clearly demonstrated one of the main causes of flexor tendon repair failure in two common repair techniques is knot unravelling.

Physical and Mechanical Evaluation of Five Suture Materials on Three Knot Configurations: An in Vitro Study

The aim of this study was to evaluate and compare the mechanical properties of five suture materials on three knot configurations when subjected to different physical conditions. Five 5-0 (silk, polyamide 6/66, polyglycolic acid, glycolide-e-caprolactone copolymer, polytetrafluoroethylene) suture materials were used. Ten samples per group of each material were used. Three knot configurations were compared A.2=1=1 (forward⁻forward⁻reverse), B.2=1=1 (forward⁻reverse⁻forward), C.1=2=1 (forward⁻forward⁻reverse). Mechanical properties (failure load, elongation, knot slippage/breakage) were measured using a universal testing machine. Samples were immersed in three different pH concentrations (4,7,9) at room temperature for 7 and 14 days. For the thermal cycle process, sutures were immersed in two water tanks at different temperatures (5 and 55 °C). Elongation and failure load were directly dependent on the suture material. Polyglycolic acid followed by glycolide-e-caprolactone copolymer showed the most knot failure load, while polytetrafluoroethylene showed the lowest (P < 0.001). Physical conditions had no effect on knot failure load (P = 0.494). Statistically significant differences were observed between knot configurations (P = 0.008). Additionally, individual assessment of suture material showed statistically significant results for combinations of particular knot configurations. Physical conditions, such as pH concentration and thermal cycle process, have no influence on suture mechanical properties. However, knot failure load depends on the suture material and knot configuration used. Consequently, specific suturing protocols might be recommended to obtain higher results of knot security.

The effect of an air knot on surgical knot integrity

OBJECTIVE

Surgical trainees may tie air knots, which have a questionable tensile strength and rate of untying. The purpose of this study was to determine the effect of an air knot on knot integrity.

METHODS

The 5 suture materials tested were 0-0 gauge coated polyethylene, polyglyconate, glycolide/lactide, polypropylene, and silk. The suture was tied between 2 hex screws 50 mm on center. The strands were tied using 5 square throws, and the knot tails were cut at 3-mm length. To create a standardized air knot, a round common nail measuring 3 mm in diameter was inserted between throws before tying square throw #3. The suture loop was positioned around the upper and lower hooks of the tensiometer so the location of the knot was roughly equidistant from the hooks. Ultimately, either the loop broke or the knot slipped. At that time, the peak tensile force as well as the outcome of the knot were recorded.

RESULTS

A total of 480 knots were tied. The presence of an air knot significantly lowered the tension at knot failure in the glycolide/lactide (P = 0.0003), polypropylene (P = 0.0005), and silk (P = 0.0001) knot configurations. Air knots had the same integrity as surgical knots when coated polyethylene and polyglyconate suture were used. Linear regression was performed and identified both suture material (P < 0.0001) and presence of an air knot (P < 0.0001) to be independently associated with a lower tension at failure.

CONCLUSIONS

Under laboratory conditions, an air knot may contribute to a lower tensile strength at failure for certain suture materials.

Parallel alternating sliding knots are effective for ligation of mesenteric arteries during resection and anastomosis of the equine jejunum

Background

In literature only one article describes and compares methods of achieving hemostasis in equine mesenteric arteries during jejunal resection and anastomosis, and most textbooks favor ligating-dividing mechanical devices. The latter method cannot always be used, not least because the devices are expensive and in some cases even contra-indicated. Various types of knots, including sliding knots, are widely used to provide hemostasis in laparoscopy.

The objective of this study was to compare a triple ligature for mesenteric vessels composed of three sliding knots with a triple ligature composed of a modified transfixing and two surgeon’s knots.

Methods

Portions of jejunum with associated mesenteric vessels were collected from 12 horses at a local abattoir. These were divided into 24 specimens containing five mesenteric arteries each. Each artery was closed with a triple ligature. In group A, a surgeon’s knot was used to tie the ligatures (two circumferential and one modified transfixing) while in group B all ligatures (three circumferential) were tied with a parallel alternating sliding knot. Both groups were divided ino two subgroups depending on suture material used (multifilament or monofilament suture material). Time to perform ligatures for every specimen were recorded and compared between groups.

After closure, arteries were cannulated and intraluminal pressures were increased until ligature failure. Leaking pressures were recorded and compared between groups.

Results

Ligation of mesenteric arteries was significantly faster to perform with sliding knots than with surgeon’s knots, both with monofilament and multifilament suture material. With multifilament suture material, the leaking pressure of sliding knot ligatures was significantly higher than that of surgeon’s knot ligatures. With monofilament suture, there were no statistically significant differences in leaking pressure between ligature methods. Both ligating methods were stronger with monofilament suture material than with multifilament suture material.

Conclusions

Regardless of the ligature used, monofilament suture material performed better than multifilament suture material to achieve hemostatic knots. Independently of the suture material, the sliding knot is comparable or better than the surgeon’s knot in providing hemostasis, and is faster to perform.

Beyond the square knot: a novel knotting technique for surgical use

BACKGROUND

Knot holding strength is essential to maintain wound closure and ensure tissue contact for healing. Knot unraveling can lead to severe complications, especially for high-tension closures such as tendon repairs, which have recently been reported to have knot unraveling rates as high as 86%. In the current study, a novel surgical knot, the two-strand-overhand locking (TSOL) knot, was designed and mechanically evaluated with use of different suture materials and knot configurations and in actual tendon repairs.

METHODS

The knot holding strength of the TSOL knot was compared with that of a 4-throw square knot with use of three different suture materials that are in common clinical use. With use of braided polyblend suture, the TSOL knot was also compared with five other surgical knot configurations. Finally, the strength of tendon repairs performed with use of the TSOL knot and a 4-throw square knot was studied.

RESULTS

Compared with the 4-throw square knot, the holding strength of the TSOL knot was 143% greater for braided polyblend, 216% greater for polydioxanone, and 118% greater for polyester suture, with a significantly lower knot unraveling rate compared with that of the 4-throw square knot regardless of suture material. The TSOL knot holding strength was also greater than that of the other surgical knot configurations. The strength and stiffness of tendon repairs with a TSOL knot were significantly increased over those of repairs with a 4-throw square knot.

CONCLUSIONS

The TSOL knot provided superior knot holding strength compared with some commonly used surgical knots.

CLINICAL RELEVANCE

The TSOL knot has potential clinical applications, especially when knot security is important and high loads are expected, as in tendon or ligament repairs.

Operating room fatigue: is your twentieth surgical knot as strong as your first?

OBJECTIVE

This study aimed to determine the tensile strength in a series of 20 consecutively tied knots. Knot tying is a universally used technique in surgical procedures, and as such, knot integrity and security are essential.

STUDY DESIGN

Twenty was the number of knots chosen as this is the average number of knots required for a vaginal hysterectomy. We used 0-0 gauge, nonexpired, polyglactin 910 to tie 20 knots in succession with less than 20 seconds rest between knots. The knots were tied without a surgeon's knot and 4 additional square knots (1 = 1 = 1 = 1 = 1). The knots were tied by 2 obstetrician/gynecologists investigators over the period of 2 weeks to minimize fatigue. The sutures were then soaked in 0.9% sodium chloride for 60 seconds and subsequently transferred to a Chatillon LTCM-100 tensiometer (Ametek, Largo, Florida) where the tails were cut to 3 mm length. The force required to break the knots was recorded. To detect a difference over time while maintaining power of 80% with a type I error rate of 5%, a minimum of 17 series of knots were needed (thus, 340 total knots after tying 20 knots per series). To buffer against unanticipated variability in the tensile strengths over time, we rounded the number of knot series up to 20, so a total of 400 knots were tied.

RESULTS

A total of 800 knots were tied. All the sutures broke at the knot and 36% untied. For analyses, the data for each series of knots were collapsed into quarters (ie, knots 1-5, 6-10, 11-15, and 16-20). A repeated-measures analysis of variance found that there were no statistically significant differences between the four quartiles (p = 0.87). A paired samples t-test comparing the first knots in each series with the last knots in each series showed no difference (p = 0.99). Similarly, a paired samples t-test comparing the first 10 knots to the last 10 knots showed no difference over time (p = 0.8). To determine whether there was a change in likelihood of knots coming untied, as more knots were tied, Cochran's Q was used to look across the entire series of 20 knots. This analysis of proportions coming untied revealed no differences over time (p = 0.61). To compare across quarters, a Friedman test was used and similarly showed no change over time (p = 0.92). The different investigators were controlled for in the analysis as a covariate, which turned out to be statistically significant, p = 0.003.

CONCLUSIONS

Under laboratory conditions, the order of knots tied does not change the tensile strength of the material. This would infer that fatigue does not influence the tensile strength for a series of 20 knots; however, additional studies with a larger number of knots series may be warranted.

Assessment of four tissue models on knot tensile strength

OBJECTIVE

To determine whether the tissue model onto which a knot is tied influences the knot's tensile strength.

STUDY DESIGN

Zero-gauge, nonexpired, silk, polyglactin 910, polydioxanone, and polypropylene sutures were tied on 4 different mock tissue models. The tissue models were standard metal hex head screw, uncooked chicken breast, a tube of packaged "string" cheese, and a cylinder of bubble wrap. The knots were tied without a surgeon's knot and with 4 additional square knots (1 = 1 = 1 = 1 = 1). The knots were tied by a single obstetrician/gynecologist investigator (J.M.D.) over the period of 1 week to minimize fatigue. We compared the knots when subjected to a tensiometer until the suture broke or untied. A minimum of 20 knots per group were needed to detect a moderate effect size with a power of 85% and a type I error rate of 5%.

RESULTS

A total of 407 knots were tied with 4 types of material (silk, polyglactin 910, polydioxanone, and polypropylene), using 4 different models (chicken, bubble wrap, cheese, and metal). Among the knot failures, 113 of 407 untied rather than broke (28%). No differences in the likelihood of knots coming untied between the different models (p = 0.34) or tension at failure (p = 0.81) were noted. A 4 × 4 factorial analysis of variance (ANOVA) was conducted to determine the effects of the suture material and model type on tension at failure and whether there was any interaction between the 2 factors. No significant difference was observed in the interaction between suture material and model type (p = 0.35), and no effect for model type was found (p = 0.22).

CONCLUSIONS

Tissue models that use materials more similar to human tissue do not seem to influence knot strength when compared with standard metal models. We propose that it is possible to have an accurate understanding of how knots withstand force and to simulate an in vivo environment by using low-cost, easily accessible natural and synthetic materials for the mechanism onto which the knot is tied.

Effect of petroleum gauze packing on the mechanical properties of suture materials

OBJECTIVE

To test the tensile properties of knotted suture made of 4 different suture materials and exposed to petroleum gauze.

STUDY DESIGN

We tested the tensile strength of United States Pharmacopeia size 0-0 gauge polydioxanone, polyglyconate, glycolide/lactide copolymer, and silk when exposed to petroleum packing or saline. Suture materials were randomized, and knots were tied and then evaluated via tensiometer to the point of knot failure.

RESULTS

A total of 285 knots were tied in 8 groups based on material and exposure to saline or petroleum gauze. We found that petroleum exposure knots failed at a mean of 116.7 N (SD = 31.5) and that saline soaked knots failed at 123.8 N (SD = 32.0). We conducted a 4 × 2 factorial analysis of variance, finding knots exposed to petroleum failed at a statistically significantly lower tensile strengths than saline soaked knots (p = 0.002).

CONCLUSION

Petroleum-exposed sutures fail at lower tensions than saline-exposed sutures.

Minimum number of throws needed for knot security

OBJECTIVE

The purpose of the study was to determine the optimal number of throws to ensure knot security.

STUDY DESIGN

Knots were tied with 3, 4, 5, or 6 square throws with 0-gauge coated polyester, polydioxanone, polypropylene, and polyglactin 910. The suture was soaked in 0.9% sodium chloride and subsequently transferred to a tensiometer and broken.

RESULTS

A total of 225 knots were tied. Regardless of the suture type, tension at failure for knots with 4 throws, 5 throws, and 6 throws was higher than tension at failure of knots with only 3 throws (p < 0.05 for each). We found no difference in the tensile strength between knots with 4, 5, or 6 throws (p > 0.05 for each). Knots with 4 throws were significantly more likely to come untied than knots with 5 or 6 throws (p < 0.01).

CONCLUSIONS

Under laboratory conditions, the ideal knot has 5 throws to maximize tensile strength and rate of untying. This finding does not seem to vary by type of suture material.

Knot integrity as a function of suture expiration

OBJECTIVE

To test the integrity of knots tied with expired suture and non-expired suture, using 5 different suture materials.

STUDY DESIGN

Knots were tied using expired and non-expired chromic catgut, polyglactin 910, polydioxanone, silk, or coated polyester. Expired sutures were a mean of 10.5 years past the date of expiration stamped on the packaging. Suture packaging was inspected for any flaws or humidity. There were 116 knots with expired suture and 109 non-expired knots. All knots were tied by hand. Suture was soaked in 0.9% sodium chloride for 60 seconds and subsequently transferred to a tensiometer where the tails of the knots were cut to 3 mm length. We compared the tensile strength of knots using a tensiometer to pull the knots until the suture broke or untied. A minimum of 30 knots were needed in order to detect a statistically significant main effect for expired and non-expired sutures with 80% power and a 5% chance of type I error.

RESULTS

A total of 225 knots were tied. Overall, we found no difference in mean tension between expired suture (77.5 ± 31.7 N) and non-expired suture at failure (81.9 ± 30.2 N). All the sutures broke at the knot and none untied. Expired chromic and polydioxanone were significantly weaker than the non-expired suture of the same material (p = 0.002 and p = 0.001, respectively). There was no statistically significant difference in tensile strength between expired absorbable or permanent suture materials. Based on a univariate analysis of variance ([SCAP]ANOVA)[R] there was no difference in the tension at failure between expired and non-expired sutures with suture packet as a covariate. No suture untied when knotted with expired suture.

CONCLUSIONS

Under laboratory conditions, expired chromic and polydioxanone sutures broke at lower tensile strength than non-expired sutures of the same material.

Tensile strength of a surgeon's or a square knot

OBJECTIVE

To test the integrity of surgeon's knots and flat square knots using 4 different suture materials.

STUDY DESIGN

Chromic catgut, polyglactin 910, silk, and polydioxanone sutures were tied in the 2 types of knot configurations. For all sutures, a 0-gauge United States Pharmacopeia suture was used. Knots were tied by a single investigator (J.B.). The suture was soaked in 0.9% sodium chloride for 60 s and subsequently transferred to a tensiometer where the tails were cut to 3-mm length. We compared the knots, measuring knot strength with a tensiometer until the sutures broke or untied.

RESULTS

A total of 119 throws were tied. We found no difference in mean tension at failure between a surgeon's knot (79.7 N) and a flat square knot (82.9 N). Using a chi(2) test, we did not find a statistically significant difference in the likelihood of knots coming untied between surgeon's knots (29%) and flat square knots (38%).

CONCLUSIONS

Under laboratory conditions, surgeon's knots and flat square knots did not differ in tension at failure or in likelihood of untying.