Surgical Science, 2011, 2, 195-197
doi:10.4236/ss.2011.24043 Published Online June 2011 (
Copyright © 2011 SciRes. 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
Received February 4 2011; revised April 25 2011; accepted May 19 2011
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
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
(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
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Copyright © 2011 SciRes. SS
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
7. References
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a Proposal to Standardize the Literature,” Journal of the
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[4] H. L. Aanning, T. Haas, D. R. Jorgensen and W. A.
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[5] P. E. Gunderson, “The Half-Hitch Knot: A Rational Al-
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