Surgical Knot Strength in Continuous Wound Closures

doi:10.4236/ss.2011.24043

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Surgical Science, 2011, 2, 195-197

doi:10.4236/ss.2011.24043 Published Online June 2011 (http://www.SciRP.org/journal/ss)

Surgical Knot Strength in Continuous Wound Closures

Anthony Nigliazzo, Rodrigo Arrangoiz, Richard Hutchison, Marc Basson, Andrew Saxe

Department of Surgery, Michigan State University College of

Human Medicine East Lansing, Michigan, USA

E-mail: [email protected]

Received February 4 2011; revised April 25 2011; accepted May 19 2011

Abstract

Background: Forces applied to knots used for interrupted vs. continuous closures are very different. We

studied the knot strength and knot security of three knots when simulating a continuous wound closure: the

square, the sliding, and a hybrid constructed using a surgeon’s square knot followed by a sliding knot. Mate-

rials and Methods: Knot holding capacity (KHC) of single-strand 1-0 polypropylene was determined by slow

distraction on a horizontal testing sled of the strand that would be used to complete a continuous (“running”)

closure following placement of an anchoring knot with six throws. Distraction continued until failure of the

knot defined as breakage or slippage of the knot. Results: The mean and standard deviation of KHC meas-

ured in pounds was determined (n = 30 for each knot): standard square 8.94 +/– 1.04; sliding 10.72 +/– 1.35;

and hybrid 10.95 +/– 1.10. For each knot the relative knot security [(KHC of the knot/Tensile strength of

untied strand) × 100] was calculated: standard square 69.5%; sliding 83.4%; hybrid 85.2%. Significant dif-

ferences (p < 0.0001) in KHC exist between square and sliding knots (favoring sliding knots) and between

square and hybrid knots (favoring hybrid knots). Hybrid and sliding knots were not statistically different.

Conclusions: Sliding knots and hybrid knots are superior to square knots as anchoring knots for single-strand

continuous wound closure.

Keywords: Knot Strength, Continuous Suture, Square Knot, Slip Knot

1. Introduction

Traditionally, the square knot has been taught as the

ideal anchoring surg ical knot regardless of its use in con-

tinuous closure or in an interrupted suture. However, the

mechanical demands on knots differ between interrupted

closures and continuous suturing techniques. We hy-

pothesized that a hybrid knot, an initial square knot fol-

lowed by slip knots, is the best choice for a continuous

suture; that the hybrid knot would combine the square

knot’s resistance to slip with the strength of the sliding

knot. Our study is the first to compare knot security of

standard knots to a novel hybrid knot using an appropri-

ate model for simulating the forces applied to the an-

choring knot of a continuous suture.

2. Materials and Methods

Because of its wide and successful use 1-0 polypropyl-

ene (Prolene; Ethicon, Langhorne, PA) was chosen as

suture material.

Ninety sutures were hand tied by one surgeon. Thirty

knots of each type were tied: square, sliding, and a hy-

brid. Thirty strands were left untied to test the intrinsic

tensile strength of the suture. All knots were tied with six

throws. The hybrid knot was fashioned by tying a sur-

geon’s square knot followed by 4 sliding knots. (Figure

1).

Knots were tested on a horizontal sled type materials

tester. A 0.5 inch loop was placed around a hook with the

axial strand (that which would participate in the con-

tinuous closure) friction locked around a second hook.

(Figure 2) The force applied to each knot was measured

by an Accuforce Cadet 0-50 ± 0.03 lb force gauge

(Ametek, Paoli, PA). The force gauge was calibrated

immediately prior to the project and the force gauge was

“zeroed” prior to each knot or strand tested. The con-

tinuous closure strand was distracted at less than 5

cm/min until failure. Failure was defined as slippage

and/or breakage of the knot. The force applied at the time

of failure was termed the knot holding capacity (KHC).

MiniTab (Minitab Inc., State College, PA) statistical

196 A. NIGLIAZZO ET AL.

(a) (b) (c)

Figure 1. Illustrations of the knots tested in this study. (a)

Square knot, (b) Sliding knot, (c) Hy brid knot.

Figure 2. Illustration of the testing device.

software was used for data analysis. One-way ANOVA

with post hoc pair wise analysis using a Bonferroni ad-

justment was performed to compare the means of KHC

of the three types of knots. P values of <0.05 were con-

sidered significant.

3. Results

Comparisons of the knot holding capacity for each type

of knot, measured in pounds, are displayed in Table 1.

The hybrid knot demonstrated the greatest knot holding

capacity and was statistically superior to the square knot

although not statistically significantly superior to the

sliding knot.

For each knot the relative knot security, defined as

[(KHC of the knot/tensile strength of the untied strand) X

100], was calculated and is displayed in Table 1. Results

were similar to those testing knot holding capacity be-

cause the tensile strength of the suture material (12.8

pounds) was the same for each type of knot.

Failure of square knots and hybrid knots occurred ex-

clusively by breakage. Sliding knots failed by either

breakage (23 of 30 knots) or slippage (7 of 30 knots).

4. Discussion

Several authors have investigated the properties of dif-

ferent knot types when applied to tissue approximation.

The majority of these studies used one of two testing

methods described by Dinsmore [1]: the loop method

and the single strand method. These are appropriate for

interrupted sutures where the approximation of tissue is

performed by a loop of suture material and the knot is

stressed equally on both sides.

These methods are not appropriate, however, for the

study of knots securing a continuous suture. In this set-

ting the knot has force applied to one but not the other of

the strands that exit the top of the knot. The asymmetri-

cal force applied to the knot in the running application

differs greatly from the symmetrical forces applied

within the loop to the base of the knot employed in an

interrupted suture. In addition to asymmetry of the forces

applied to the knot of a continuous closure, there are

shear forces spread along the length of the closure. These

tend to elongate the suture and apply additional stress to

the knot. Our study employed a model that appropriately

simulated a continuous closure. We hypothesized that a

hybrid knot, an initial squ are knot fo llowed by slip kno ts,

is the best choice for a continuous suture.

That our study demonstrated the superiority of sliding

to square knots seems at first to be inconsistent with con-

ventional wisdom. Sliding knots hav e drawn criticism on

two fronts. First, sliding knots may tighten the loop. This

property may lead to constriction of tissue within the

loop of the knot leading to necrosis and failure of the

anchor point. This could permit the running suture to

loosen and ultimately lead to dehiscence of the approxi-

mated tissue. Second, sliding knots, used in the tradi-

tional interrup ted fashion, may allow the knot to untie as

the tissue becomes edematous increasing the diameter of

the loop and pulling th e exiting strands through the kno t.

These concerns, however, are not applicable to running

closure as the suture completing the closure is the load

bearing strand. It continues the length of the incision to

be anchored at the opposite end and cannot come undone

at the initial knot.

Others, also, have questioned the superiority generally

afforded the square knot. Schaaf et al. performed a study

in some ways similar to ours [2]. They calculated the

relative knot security (calculated as we did) of square

knots used as the starting knots, square knots used as

ending knots, and Aberdeen knots. Aberdeen knots with

three “throws” and one “turn” and those with four

“throws” and one “turn” had superior RKS to square

knots. The values they reported for square knots (ap-

proximately 60% - 70%) and those for the Aberdeen

knots (approximately 80%) are strikingly similar to those

we found with square and hybrid knots. Richey and Roe

investigated a variety of knots placed in tissue and tested

in-vitro [3]. They, too, endo rsed an Aberde en knot (what

A. NIGLIAZZO ET AL.

197

Table 1. Properties of knots used in the setting of a continuous closure.

Knot Holding Capacity (pounds) Relative Knot Security (%)

Type of knot n Mean Standard Deviation Mean Standard Deviation

Square knot 30 8.9 1.0 69.8 8.1

Sliding knot 30 10.7 1.4 83.8 10.5

Hybrid knot 30 11.0 1.1 85.5 8.6

they termed a “chain-stitch knot”) although the number

of throws was not provided. They found no slippage in

chain-stitch knots, again similar to our findings with a

hybrid knot. Aanning et al. found that a running poly-

propylene suture anchored with half hitches was stronger

than a running suture tied with square knots [4]. Gun-

derson found that half-hitch knots were as secure as

square knots and easier to tie [5]. Fong et al. found that

abdominal wall closure with a running monofilament

suture was stronger when a loop knot was used as anchor

compared to a square knot or surgeons’ knot [6]. Trim-

bos et al. tested three types of sliding knots and found

that when comp ared to earlier data ob tained using square

knots there was little difference in reliability and strength

between sliding knots and square knots [1]. Finally, in an

extensive review Dinsmore et al. demonstrated great

variation in the efficacy of different surgical knots and

emphasized the difficulty in comparing studies because

of lack of standardization in knot terminology and knot

testing methodology [1].

There are several limitations of this study. There are

innumerable variations of knots and we studied only

three. We did, however, select two that are commonly

used and one that we hypothesized might be superior.

Also, as an ex-vivo study it did not incorporate the po-

tential effects of in-vivo degradation and lubrication

upon knot holding capacity. Finally, also as a conse-

quence of conducting an ex-vivo study we did not ac-

count for the effect of suture placement technique.

5. Conclusions

Anchoring knots used for continuous abdominal wall

closures experience asymmetrical forces applied to the

knot. The hybrid knot best resists deformation and has

the favorable knot security characteristics of both square

and sliding knots. It should be used as the an chor ing kno t

for single strand con tinuous abdominal wall closure.

6. Acknowledgements

The authors express gratitude for the graphic artwork of

Mr. William Joy and the statistical analyses by Dr. Alan

Davis

7. References

[1] R. C. Dinsmore, “Understanding Surgical Knot Security:

a Proposal to Standardize the Literature,” Journal of the

American College Surgeons, Vol. 180, 1995, pp. 689-

699.

[2] O. Schaaf, M. Glyde and R. E. Day “In vitro Comparison

of Secure Aberdeen and Square Knots with Plasma- and

Fat-Coated Polydioxanone,” Veterinary Surgery, Vol. 39,

No. 5, 2010, pp. 553-560.

doi:10.1111/j.1532-950X.2009.00640.x

[3] M. L. Richey and S. C. Roe, “Assessment of Knot Secu-

rity in Continuous Intradermal Wound Closures,” Journal

Surgical Researc h, Vol. 123, No. 2, 2005, pp. 284-288.

doi:10.1016/j.jss.2004.08.027

[4] H. L. Aanning, T. Haas, D. R. Jorgensen and W. A.

Corey, “Square not a running knot,” Journal of the Am-

erican College of Surgeons, Vol. 204, No. 3, 2007, pp.

422-425. doi:10.1016/j.jamcollsurg.2006.12.024

[5] P. E. Gunderson, “The Half-Hitch Knot: A Rational Al-

ternative to the Square Knot,” American Journal of Sur-

gery, Vol. 154, 1987, pp. 538-540.

doi:10.1016/0002-9610(87)90273-X

[6] E. D. Fong, A. S. R. Bartlett, S. Malak and I. A. Ander-

son, “Tensile Strength of Surgical Knots in Abdominal

Wall Closure,” ANZ Journal of Surgery, Vol. 78, No. 3,

2008, pp. 164-166.

doi:10.1111/j.1445-2197.2007.04394.x

[7] J. B. Trimbos, E. J. Van Rijssel and P. J. Klopper, “Per-

formance of Sliding Knots in Monofilament and Multi-

filament Suture Material,” Obstet Gynecol, Vol. 68, 1986,

pp. 425-430.