Indian Journal of Fibre & Textile Research Vol. 29, September 2004, pp. 27 1-277

Effect of suture structure on knot performance of polyamide suturesa

A S Hockenbergerb & E Karaca Department of Textile Engineering, University of Uludag, Bursa, T urkey

Received I August 2003; revised received and accepted 7 November 2003

The knot performance of monofi lament and braided polyamide (PA) sutures has been characterised by applying two d iffe rent knots with two, three and four th rows. It is observed that generally granny knot and braided structure have better knot perfo rmance. An additional throw does not increase the fo rce required to break the suture. Suture size is also important for knot performance and the sutu res behave di ffe rently when they are wet.

Keywords: Braided polyamide suture. Granny knot. Knot perfo rmance, Polyamide suture. Sq uare knot IPC Code: Int. C I. 7 D02G 3/00, A6 1 L 17/00

1 Introduction Sutures remain the most common method of

approx imating the divided edges of ti ssue. A suture is defined as a thread that either holds adj acent cut surfaces of the wound or compresses blood vessels to stop bleedi ng.

Suture security is the ability of knot and suture material to maintain ti ssue approx imation during the healing process without s lippage, untying and breaking. Suture failure may be resulted by either knot untying or knot breaking. Untying results from the slippage of knot. The degree to whi ch the knots can slip is influenced by a vari ety of facto rs, including coefficient of friction of the suture materi al, suture di ameter, knot type, length of the cut ears of knot, and moisture. Suture slippage can be coun teracted by usi ng more throws than are necessary fo r knot security, but these additional throws are time consuming and prolong unnecessarily the length of the operati ve procedure. In add ition, considerab ly more suture is added to the wound, further damaging its res istance to infec tion. Therefore, the surgeon must ti e a secure knot with each suture using the fewes t number of th rows 1-4 .

Knot breakage is the other cause of suture failure . The fo rce necessary to break a knotted suture is lower than that required to break an untied suture. The tensile forces exerted on a tied suture are converted into shear forces by the configuration of knot and finally rupture the suture . The magnitude of forces necessary to produce kno t breakage varies with the

"Part of paper presented at Medtex 03 Confe rence, Bolton Institute, UK, 2003. ~o whom all the correspondence should be addressed. Phone: 4428 176; Fax : +90 -224 -442802 1; E-mai l: sengonul @uludag.edu .tr

size of suture loop, kind of suture materi al and d iameter of suture3

.

The handl ing characteri sti cs of surg ical sutures are one of the most important considerations in suture selection . Surgeons evaluate the handling characteri sti cs of sutures by the number of th rows required for secure knot. They prefer a suture that permits two- th row knots to be eas ily advanced to the wound edges, prov iding a preview of the ul timate opposition of wound edges . Therefore, it is essential that quantitati ve info rmation be available concerni ng the expected performance of a surgical suture during wound closure and the number of throws necessary for a secure knot must be optimised5

.6

.

The present work was, therefore, aimed at studying the effect of construction of suture structure, such as number of th rows for secure knot and type of knot , on the knot perfo rmance.

2 Materials and Methods

2.1 Materials

Synthetic, non-absorbable polyamide (PA) sutures were used. To study the effect of suture structure on knot security, the monofil ament and multi filament structures of polyamide sutures were used. Fig. 1 shows SEM photographs of the sutures. The sizes of these sutures were 0 , 2/0 and 3/0 United States Pharmacopoeia (USP). Table I shows the handl ing and mechanical properties of the sutures.

2.2 Methods

2.2.1 Test Procedure Prior to dry tests, all sutures were conditioned

under the standard atmospheric conditions (65% RH and 20DC) for 24 h. Prior to wet tests, all the sutures were conditioned in 0.9% sodium chloride solu tion for 24 h. The instrument used to measure knot

272 INDI AN J. FIB RE TEXT. RES ., SEPTEMBER 2004

Table 1- Properties of suture material s

Suture Surface Size Thickness, tex procedure USP

Monofilament None 0 138 PA

2/0 118

3/0 48

Braided Wax 0 130 PA

2/0 109

3/0 59

bOt,} ;~. ~~'.~ ,. ,-:to, .

.. : M _ . .. .

.... ~ SKU X270 100fJm WD3i

Fig. 1- (a) Mult ifi lament (braided), and (b) monofilament polyamide sutures

performance (Fig. 2) can be mo unted o n the Instron Tensile Tester. The tests were carri ed o ut in two stages. At the firs t s tage, the samples were mounted around the two bolts and to produce the same knot tension in all samples the knots were made mechanically with a dynamometer. To s imulate rea l­li fe conditi ons, the knot tension was determined on a

Test Max. tenaci ty Max. strain Modulu s cond ition cN/tex % eN/tex

Dry 33.7 1 ± 1.53 62. 15 ± 6.85 86.84 ± 3. 14 Wet 33. 19 ± 1.94 74.29 ± 6.75 83. 15 ±2.96 Dry 33.78 ± 0.5 1 54.59 ± 4.56 86.92 ± 2.46 Wet 30.82 ± 0.56 52.42 ± 1.97 89.49 ± 1.64 Dry 39.29 ± 0.55 52.52 ± 2. 13 127.19 ±4.94 Wet 34.98 ± 1.92 57.24 ± 9.02 11 2.64 ± 8.85

Dry 41.54 ± 1.06 35.88 ± 3. 14 145 .89 ± 9.6 1 Wet 37.39 ± 0.4 1 32.15 ± 1.14 161.37 ± 7.94 Dry 31.80± 1.1 4 30.01 ± 2.49 162.70 ± 5.36 Wet 27.68 ± 0.78 30.46 ± 3.57 16·t50 ± 8.88 Dry 37.67 ± 1.11 39.10 ± 6.25 183.53 ± 9.92 Wet 33.96 ± 0.88 36.54 + 3.79 184.89 + 4.54

tension meter. Ten surgeons were told to make a knot around sy nthet ic ti ssue made from silicon using a dynamometer. Almost all the surgeons applied the tension of ION during knotting . Therefore, 10 was des ignated as the knot tensio n. After the knot had been ti ed tightly eno ugh , the ears of the knot around the two bolts were cut to leave 2 mm for the knot i tse l f. At the second stage, the pi voted bar was c lamped between the upper j aw of Instron and then pulled out until the knot broke (force to break the knot) or untied (ho lding fo rce of the knot). The gauge speed of the Instron was 200mmlmin. All the tests were repeated lOti meso

The mechanical performance of the su tures was dete rmined by the knot ho lding force, the force necessary to break the knot and the number of th rows required for a knot that wi ll reach break. The tenacity value (cN/tex) was used fo r determining knot ho lding and knot breaki ng strengths of sutures .

Optical microscopy was used to record the broken ends of the sutures by using Tri nocu ler Stereo Zoom Microscope (x I 0).

2.2.2 Kllot Types In thi s study, square and granny knots were chosen

as most of the Turki sh surgeons use these two types . A knot is composed of a combination of sequen tial th rows. A single throw is formed by wrapping two strands around each other so that the angle of wrap equals 360°. The process o f construct ing two or more throws completes the knot. T he configuration of a knot can be class ified by the spatia l relationsh ip between the knot ears and the loop. When the right ear and loop of a two th row knot ex it on the same side of the knot and paralle l to each other, the type of knor is square. The tension must be equal in both cars. The knot is considered a gran ny type, if the right ear and loop cross

HOCKENBERGER & KARACA: KNOT PERFORMANCE OF POLYAMIDE SUTURES 273

Fig. 2- Instrument used to measure knot performance [(a) instrument mounted on the Instron tensile tester, and (b) suture sample mounted around the two bolts of instrument]

Fig. 3- (a) Square, and (b) granny knot types

or exit different sides of the knot. Similarly, tension is applied to the both ears3,6,7 (Fig, 3), .

A simple code has been devised to describe the configuration of knot. The number of wraps involved in each throw is indicated by the appropriate arabic number. The relationship between each throw to another, being either crossed or parallel, is signified

I '( _/ I I. .- ,I I I ~ C~ , 1 ~ 1 ~ 1 ~ 1 '~ 1X1X1X19 1 I rr i~1 ~quare Granny

Fig. 4- Knot types used for the sutures

by the symbols 'X or =' respectively, In accordance with this code, the square knot with two throws is designated 1 = 1, and the granny knot with two throws 1 x 1 (ref. 8),

In this study, two, three and four throws for both the knot types were formed (Fig, 4) ,

3 Results and Discussion Tables 2 and 3 show knot performance results tn

dry and wet states respectively.

3.1 Dry Analysis

3.1.1 Monofilament Polyamide

Four throws are necessary for both granny and square knots to reach knot break, regardless of the suture size.

274 INDIAN 1. FIBRE TEXT. RES., SEPTEMBER 2004

Table 2- Results of dry knot performance

Suture Size Type of Number of Max. tenacity Result USP knot throws (mean±SD)

cNltex

Monofilament PA 0 Square 2 (1=1) 9.84 ± 0.49 Knot un ty ing 3 ( 1=1=1) 30.30 ± 3.29 Knot untying 4 (1=1=1=1 ) 49.81 ± 0.95 Knot breaking

Granny 2 (IXI) 10.28 ± 1.00 Knot untying ~ (IXIXI) 22.36 ± 1.57 Knot un ty ing 4 (IXIXIXI) 52.60 ± 2.56 Knot breaking

2/0 Square 2 (1=1) 9.74 ± 0.31 Knot unlying 3 (1=1=1 ) 28.36 ± 2.63 Knot untying 4 ( 1=1=1=1) 48.62 ± 1.16 Knot breaking

Granny 2 (IXI) 11.40 ± 0.89 Knot untying 3 (lXIXl) 25.05 ± 1.67 Knot untying 4 (lXIXIXI) 48.27 ± 1.96 Knot breaking

3/0 Square 2(1= 1) 16.41 ±0.58 Knot unrying 3 (1=1=1) 56.64 ± 6.46 Knot un ty ing 4 (1=1 =1=1 ) 72.14 ± 2.55 Knot brea king

Granny 2 (lXl) 24.62 ± 0.89 Knot un ty ing 3 (lXIXI) 50.71 ± 3.22 Knot untying 4(1XIXIXI) 75.91 ± 2.67 Knot breaking

Braided PA 0 Square 2(1=1) 47 .41 ± 3.50 Knot untying 3 (1=1=1) 61.13 ± 1.19 Knot breaking 4 (1=1=1=1) 64.18± 1.44 Knot breaking

Granny 2 (IX I) 18.67 ± 0.40 Knot untying 3 ( IXIXI) 63.40 ± 1.81 Knot breaking 4 (lXIXIXI) 66.45 ± 0.55 Knot breaking

2/0 Square 2 (1=1) 27.6 1 ±3.48 Knot untying 3 (1=1=1) 57.11 ± 1.34 Knot breaking 4 ( 1=1=1=1) 61.62 ± 1.08 Knot breaking

Granny 2 ( IX1) 13.94 ± 0.40 Kilot untying 3 (IXIXI ) 55.17±3.17 Knot breaking 4 ( IXIXIXI) 67.48 ± 1.32 Knot breaking

3/0 Square 2(1=1) 45.63 ± 5.82 Knot untying 3 (1=1=1) 68.73 ± 2.38 Knot breaking 4 (1=1=1=1) 69.57 ± 1.10 Knot breaking

Granny 2 (IXl) 20.39 ± 1.53 Knot untyi ng 3 (IXIXI) 59.46 ± 4.58 Knot breaking 4 (lXIXIXI) 75.02 ± 1.91 Knot breaking

Table 3- Results of wet knot performance

Suture Size Ty pe of Number of Max . tenacity Resu lt USP knot throws (mean±SD)

cN/tex

Monofilament PA 0 Square 2 (1=1) 11.36 ± 0.53 Knot untying 3 ( 1=1=1 ) 26.40 ± 2.64 Knot untying 4 ( 1=1=1=1) 47.1O± 1.07 Knot breaki ng

Granny 2 (lXI) 9.59 ± 0.85 Knot un tying 3 (lXIXI) 26.78 ± 2.09 Knot untying 4 (lXIXIXI) 46.89 ± 2. 15 Knot breaking

2/0 Square 2 (1=1) 20.51 ± 2.03 Knot un tyi ng 3 (1=1=1) 28.85 ± 2.35 Knot untying 4 (1=1=1=1) 43.13 ± 2.09 Knot breaking

Granny 2 (lXI) 9.06 ± 0.39 Knot !lntying 3 (1XIX1) 28.77 ± 1.89 Knot untying 4 (lXIXIX1) 46.69 ± 2.37 Knot breaking

-Collld

HOCKENBERGER & KARACA: KNOT PERFORMANCE OF POLY AMIDE SUTURES 275

Table 3- Results of wet knot performance-Colltd

Suture Size Type of Number of Max. tenacity Result USP knot throws (mean±SD)

cNltex

3/0 Square 2 (1=1) 9.14 ± 4.47 Knot untying 3 (1 =1=1 ) 55.33 ± 3.67 Knot untying 4 (1=1=1=1) 65.16 ± 3.89 Knot breaking

Granny 2(IXl) 12.80 ± 1.39 Knot untying 3 (lXIXI) 38.62 ± 1.89 Knot untying 4 (1XIXIXI) 69.18±4.08 Knot breaking

Braided PA 0 Square 2 (1=1) 25.01 ± 3.64 Knot untying 3 (1=1=1) 55.77 ± 1.38 Knot breaking 4 (1=1=1=1) 56.11 ± 2.33 Knot breaking

Granny 2 (lXI) 12.06 ± 0.60 Knot untying 3 (1XIXl) 43 .93 ± 1.99 Knot breaking 4 (IXIXIXI) 54.05 ± 1.62 Knot breaking

2/0 Square 2 (1 =1 ) 21.34 ± 1.89 Knot untying 3 (1=1=1) 33.22 ± 2.25 Knot breaking 4 (1= 1=1=1 ) 48.25 ± 0.81 Knot breaking

Granny 2 (IX l ) 7.97 ± 1.46 Knot untying 3 (IXIXI) 34.85 ± 3.56 Knot untying 4 (lXIXIX I) 49.63 ± 1.26 Knot breaking

3/0 Square 2 (1=1) 25 .60 ± 1.10 Knot untying 3 (1=1=1) 62.52 ± 2.33 Knot breaking 4 (1=1=1=1) 63.64 ± 2.73 Knot breaking

Granny 2 (lXI) 10.13 ± 0.73 Knot untying 3 (IXIXl) 31.62 ± 1.63 Knot untying 4 (1XIXIXI) 5l.21 ± 1.06 Knot breaking

For all the suture sizes, when two and three throws are applied, the knots slip and the sutures do not reach knot break. For both the knot types, the holding force of these two-throws knots is almost 60% lower than the holding force of three-throws knots and almost 70% lower than the force necessary to break the square knot. This is observed for all the suture sizes.

Once the knot is secure and held, for all the suture sizes, excluding 2/0 USP size, the force necessary to break the granny knot is slightly higher than that of the square knot as granny knot shows better knot holding performance (Fig. 5). In 0 and 2/0 USP sizes, four-throws knots are broken at almost the same value. However, for 3/0 USP size the force required to break the knot is 50% higher as compared to that for 0 and 2/0 USP sizes as the knots hold each other better for thinner sizes (Fig. 5).

3.1.2 Braided Polyamide Three throws are enough to reach knot break,

independent of the size, for both knot types. For all the suture sizes, when two throws are employed the knots slip. For both knot types, the holding force of two throws is lower than the force necessary to break the secure knot, but much higher than the same forces required in monofilament form.

Once the knot is secure and held, an additional throw does not increase the force required to break square knot, but results in an increase in granny "Knot that is clearly observed in 2/0 and 3/0 USP sizes.

Generally, the force necessary to break the granny knot is higher than that of square knot for the same reason as explained in case of monofilament form . However, thjs is not easily observed in the photographs (Fig. 6). Here, 3/0 USP size suture does not behave different than the rest of the sutures as explained in case of monofilament form. This is due to the fact that the knot holding performance is the same for all the sizes and both knot types (Fig. 7).

3.2 Wet Analysis It is very important to know the wet knot

performance of sutures as they are in wet state after operation throughout healing. Therefore, the wet analysis is also performed . to complete the knot performance analysis. It is observed that both the holding force of the knot and the force necessary to break the knot are about 50% lower for wet sutures compared to dry state as water causes reduction in strength for most polymeric materials. This reduction is slightly more for the braided sutures and the finest sizes.

276 INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2004

Broken end

Broklnlnd

Granny knot in USP 0 size Square knot in USP 0 size

-Granny knot in USP2/0 size Square knot in USP 210 size

Elr Broken end -., . ..

Granny knot in USP3/0 size Square knot in USP 3/0 size

Fig. S-Compari son of four-throw granny and square knots with regard to suture size

Granny knot Square knot

Fig. 6- Comparison of three-throw granny and square knots in USP 2/0 size

HOCKENBERGER & KARACA: KNOT PERFORMANCE OF POLYAMIDE SUTURES 277

U SP 0 size

Broken end Ear

Fig. 7-Compari son of granny knot with regard to sutu re sizes

3.2. 1 Monofilament Polyamide

Four throws are necessary for both granny and square knots to get knot break regardless of the suture size as in dry state. The suture size seems to have no effec t on the nu mber of throws necessary for the knot break. For all the suture sizes, when two and three th rows are applied the knots slip.

Once the knot is secure and held, for all the suture sizes, excluding 0 USP size, the force necessary to break the granny knot is s lightly higher than that of square knot. As in dry state, in 0 and 2/0 USP sizes, four-throws knots are broken at almost the same value. However, for 3/0 US P size the force required to break the knot is 50% higher than that of 0 and 2/0 USP sizes. This is because in the fine suture, each throw snags against another (Fig. 5).

3.2.2 Braided Polyamide Three throws are enough to get knot break in square

knot for all suture sizes and in granny knot for only 0 USP. However, four throws are necessary in granny knot for 2/0 and 3/0 USP sizes . For all the suture sizes, when two throws are employed the knots slip and the sutures do not reach knot break.

The size of the suture is important for wet braided PA sutures compared to wet monofilament PA sutures in terms of number of throws necessary for the secure knot. It can be concluded that for the smallest size suture, water can act as a lubricant between the filaments, causing slippage and results in more throws for secure knot.

4 Conclusions The type of knot configuration affects the knot

security of sutures in both dry and, more obviously, wet state. The knot security has been achieved with three- throws granny and square knots in 0 USP size and with a three-throws square and four-throws granny knots in 2/0 and 3/0 USP sizes braided P A in wet state

In wet state for some of sizes, four throws are needed for secure knot in braided PA sutures which is higher as compared to that in dly state. In dlY state, only three throws are enough to reach knot break independent of the size for both knot types. In contrast, four-throws square and granny knots in all sizes for monofi lament P A fail by breakage in wet and dlY states.

Generally, granny knot has better knot performance for both braided and monofil ament PA sutures . Suture size al so plays an important ro le in the knot perfo rmance, especially in monofilament PA sutu res. Sutures do behave different when they are wet. Once the knot is secure and held, an additional th row does not increase the force necessary to break the suture, as expected. It has been clearl y observed that braided structure has better knot performance.

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