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The effect of number of throws on knot security with nonidentical sliding knots
American Journal of Obstetrics and Gynecology (2004) 191, 1618e20
www.ajog.org
The effect of number of throws on knot security with nonidentical sliding knots Joseph J. Ivy, MD,a James B. Unger, MD,a Jason Hurt, MD,a Debi Mukherjee, ScDb Division of Gynecologic Pelvic Surgery, Department of Obstetrics and Gynecology,a and the Department of Orthopedics,b Louisiana State University Health Sciences Center, Shreveport, La Received for publication February 28, 2004; revised May 9, 2004; accepted May 19, 2004
KEY WORDS Nonidentical sliding knot Throws Knot integrity
Objective: The study was undertaken to test the integrity of nonidentical sliding knots made with 3 throws compared with those made with 6 throws with monofilament and braided absorbable suture. Study design: The 3 throw nonidentical sliding knot was compared with the 6 throw nonidentical sliding knot in 4 different suture groups. The groups were 0-0 polydioxanone, 2-0 polydioxanone, 0-0 polyglactin 910, and 2-0 polyglactin 910. Knots were tested to failure with a tensiometer. The proportion of 3 throw knots becoming untied was compared with the 6 throw knot within each group. Ultimate load required to break tied knots within each suture group was also evaluated. Results: The 3 throw knots had very high rates of knot failure and untied significantly more often than the 6 throw knots. Conclusion: The 6 throw nonidentical sliding knot demonstrates superior knot integrity compared with the 3 throw knot with both monofilament and braided absorbable suture. Ó 2004 Elsevier Inc. All rights reserved.
Many gynecologists use sliding knots as their primary surgical knot because of the need to tie in the deep, narrow spaces of the pelvis and vagina. However, according to a study by Trimbos,1 the majority of gynecologists studied who actually used sliding knots believed they were tying flat square knots. The security of sliding knots has been the subject of some study.2-5 For example, we recently reported a significantly greater proportion of knot failure with nonidentical sliding knots with 0-0 monofilament suture compared with flat knots when 6 throws were used.2 However, this was not the case with braided suture or finer gauge monofilament suture. Surgeons should strive to tie the most secure knot while keeping knot bulk to a minimum with the suture Reprints not available from the authors. 0002-9378/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.ajog.2004.05.029
most ideally suited for the task at hand. The goal of this investigation was to compare the integrity of the 6 throw nonidentical sliding knot with that of the 3 throw nonidentical sliding knot. The knots were tested in 4 groups that consisted of combinations of either 0-0 or 2-0 gauge monofilament or braided absorbable suture. We evaluated knot integrity by determining the proportion of knots that untied and by determining the load required for knot breakage using previously described standardized laboratory testing.2
Material and methods In this study, we used the synthetic absorbable monofilament suture polydioxanone and the absorbable braided suture polyglactin 910 (PDS and Vicryl respectively, Ethicon, Somerville, NJ) in 0-0 and 2-0
Ivy et al
1619 Table I Proportion of knots that untied and mean failure load for 0-0 polydioxanone
Failure by untying (n) Failure load* (N)y
3 Throws (n = 10)
6 Throws (n = 10)
9 (90%) 97.7z
3 (30%) 110.2 G 12.6
P value .02 z
* Load required to break the remaining sutures that did not fail by untying. y Data are given as mean G SD. z Only single value, cannot calculate SD or P value.
Table II Proportion of knots that untied and mean failure load for 0-0 polyglactin 910 3 Throws (n = 10)
6 Throws (n = 10)
P value
Failure by untying (n) 8 (80%) 2 (20%) .02 Failure load* (N)y 109.0 G 10.2 117.2 G 5.6 .13 Figure 1 A, Nonidentical siding knot. B, Flat square knot. C, Untied nonidentical sliding knot.
US Pharmacopeia sizes. Sutures, all with similar expiration dates, were obtained from hospital operating room stock. The major outcome studied was the proportion of knots that became untied during standardized laboratory testing when nonidentical sliding knots consisting of 6 throws were compared with the same knot with 3 throws for each suture type. In addition, the maximum load required to break a tied suture was also determined. A single investigator tied each knot (J.J.I.). The details of tying nonidentical sliding knots have been described elsewhere.2 Briefly, nonidentical sliding knots are made by placing nonidentical throws of suture around a single suture held under tension. Figure 1 illustrates a nonidentical sliding knot (A) compared with a flat square knot (B). A random number generator was used to obtain random number tables. Knots were then tied in the random order that was generated in the tables to avoid performer bias. All knots were tied around 2 polished stainless steel rings that were transferred to a tensiometer (Instron Testing Machine Model 4202; Instron Co, Canton, Mass). An attempt was made to tie all knots with uniform tension by making the suture snug around the steel rings. Once tied, the knot tails were trimmed to 3 mm each. The knots were then placed in 0.9% sodium chloride solution for 60 seconds to attempt to represent in vivo conditions before the knots were tested. The knots were then transferred to the tensiometer. The loops were stretched at 5 mm/min until failure occurred. Failure was defined as either breakage of the suture or the slip of either tail of the knot more than 3 mm (unraveling). The type of failure was recorded for each event. Load displacement curves were also generated for each knot that was tested.
* Load required to break the remaining sutures that did not fail by untying. y Data are given as mean G SD.
Table III Proportion of knots that untied and mean failure load for 2-0 polydioxanone
Failure by untying (n) Failure load* (N)y
3 Throws (n = 10)
6 Throws (n = 10)
P value
5 (50%) 68.4 G 17.0
2 (20%) 76.3 G 9.4
.35 .31
* Load required to break the remaining sutures that did not fail by untying. y Data are given as mean G SD.
Table IV Proportion of knots that untied and mean failure load for 2-0 polyglactin 910 3 Throws (n = 10)
6 Throws (n = 10)
P value
Failure by untying (n) 8 (80%) 3 (30%) .04 Failure load* (N)y 78.1 G 13.0 69.7 G 24.5 .60 * Load required to break the remaining sutures that did not fail by untying. y Data are given as mean G SD.
For knots that did not unravel, the load required for breakage of the suture was recorded. The online data collection from the tensiometer was performed with Lab View software (National Instruments, Austin, Tex). The Fisher exact test was used to determine whether there was a significant difference in the proportion of knots that untied when the 3 throw knot was compared with the 6 throw knot for each suture type and gauge. The failure load (newtons) that was required for breakage was also
1620 compared with the independent t test. A probability value of less than .05 was considered statistically significant.
Results A total of 80 nonidentical sliding knots were tied in this experiment. No knot began unraveling and subsequently broke before the completion of the unraveling process. That is, once beginning to unravel, the knot completely unraveled. Knots untied when the single strand that had been held under tension during the knot tying process slipped through the loops created by the other strand (Figure 1, C).The proportion of knots with 3 throws that became untied compared with the proportion with 6 throws for each of the 4 suture types are presented in Tables I through IV. A smaller proportion of knots became untied for each suture group when 6 throws were used compared with 3 throws, although this did not achieve statistical significance in the 2-0 polydioxanone group. The mean loads that were required for breakage for the knots that did not untie are also presented in Tables I through IV. As expected, the mean loads that were required for breakage were greater for the 0-0 gauge sutures compared with the 2-0 gauge sutures. However, there were no significant differences in the loads required for breakage between the 3 and 6 throw knots for each suture type. In every case, when the suture broke, it did so at or very near the knot.
Comment Surgeons have a nearly limitless number of options available when choosing suture material, suture gauge, knot configuration, and number of knot throws to use when tying suture. One should strive to tie the most secure knot while keeping knot bulk to a minimum with the suture most ideally suited for the task at hand. Thacker et al6 found that optimal knot configuration, including number of throws, was achieved in only 25% of the cases they studied. Knot untying before suture breakage was a common problem. In addition, we have also previously demonstrated that knot integrity is a function of knot configuration as well as the size and type of suture material.2,5 The nonidentical sliding knot is commonly used by gynecologic surgeons because of the need to tie in the deep and narrow spaces of the vagina and pelvis. Sliding knots do not require that the hands or suture cross, as must occur with flat square knots. We have previously reported that the 6 throw nonidentical sliding knot appears to be an acceptable alternative to the flat square knot, especially when braided suture or finer gauge monofilament suture is used. The goal of the current investigation was to determine whether the number of throws used in nonidentical sliding knots could be
Ivy et al decreased to 3 to keep knot bulk to a minimum. Knot bulk is dependent on the gauge of the suture material as well as the number of throws.7 In this study, we studied knot integrity by evaluating the proportion of knots that became untied when stressed under standard laboratory conditions. We tested both monofilament as well as braided absorbable sutures in 0-0 and 2-0 suture gauge. The amount of load required to either unravel or break the knot was also determined from load-displacement curves that were generated. We compared the 3 throw nonidentical sliding knot with the 6 throw nonidentical sliding knot. We chose commonly used absorbable sutures, polydioxanone and polyglactin 910, in suture gauges also routinely used in gynecologic surgery, 0-0 and 2-0. Knot failure by untying for the 6 throw knots was fairly constant across all 4 types of suture tested and consistent with our previous reports.2,5 However, when the number of throws was decreased to 3, knot failure by untying increased dramatically, irrespective of the suture type or gauge. This difference was statistically significant, except for the 2-0 monofilament suture. The load required to break knots that did not untie did not vary significantly between the 6 throw and 3 throw knots. Not surprisingly, the finer gauge sutures required lower loads for breakage. It is clear from our data that the number of throws used to tie nonidentical sliding knots is an important factor in creating a secure knot with either monofilament or braided absorbable suture. Knot integrity is not adequate when 3 throws are used with either suture. This is true even with finer gauge sutures. The current study reinforces that knot security is a function of suture type as well as knot configuration, including the number of throws used to make the knot. It is important that surgeons be cognizant of the knot they are using as well as the limitations that the knot may have.
References 1. Trimbos JB. Security of various knots commonly used in surgical practice. Obstet Gynecol 1984;64:274-80. 2. Schubert DC, Unger JB, Mukherjee D, Perrone JF. Mechanical performance of knots using braided and monofilament absorbable sutures. Am J Obstet Gynecol 2002;187:1438-42. 3. van Rijssel EJC, Trimbos JB, Booster MH. Mechanical performance of square knots and sliding knots in surgery: a comparative study. Am J Obstet Gynecol 1990;162:93-7. 4. Trimbos JB, van Rijssel EJC, Klopper PJ. Performance of sliding knots in monofilament and multifilament suture material. Obstet Gynecol 1986;68:425-30. 5. Ivy JJ, Unger JB, Mukherjee D. Knot integrity with nonidentical and parallel sliding knots. Am J Obstet Gynecol 2004;190:83-6. 6. Thacker JG, Rodeheaver G, Kurtz L, Edgerton MT, Edlich RF. Mechanical performance of sutures in surgery. Am J Surg 1977;133:713-5. 7. van Rijssel, Brand R, Admiral C, Smit I, Trimbos JB. Tissue reaction and surgical knots: the effect of suture size, knot configuration and knot volume. Obstet Gynecol 1989;74:64-8.
www.ajog.org
The effect of number of throws on knot security with nonidentical sliding knots Joseph J. Ivy, MD,a James B. Unger, MD,a Jason Hurt, MD,a Debi Mukherjee, ScDb Division of Gynecologic Pelvic Surgery, Department of Obstetrics and Gynecology,a and the Department of Orthopedics,b Louisiana State University Health Sciences Center, Shreveport, La Received for publication February 28, 2004; revised May 9, 2004; accepted May 19, 2004
KEY WORDS Nonidentical sliding knot Throws Knot integrity
Objective: The study was undertaken to test the integrity of nonidentical sliding knots made with 3 throws compared with those made with 6 throws with monofilament and braided absorbable suture. Study design: The 3 throw nonidentical sliding knot was compared with the 6 throw nonidentical sliding knot in 4 different suture groups. The groups were 0-0 polydioxanone, 2-0 polydioxanone, 0-0 polyglactin 910, and 2-0 polyglactin 910. Knots were tested to failure with a tensiometer. The proportion of 3 throw knots becoming untied was compared with the 6 throw knot within each group. Ultimate load required to break tied knots within each suture group was also evaluated. Results: The 3 throw knots had very high rates of knot failure and untied significantly more often than the 6 throw knots. Conclusion: The 6 throw nonidentical sliding knot demonstrates superior knot integrity compared with the 3 throw knot with both monofilament and braided absorbable suture. Ó 2004 Elsevier Inc. All rights reserved.
Many gynecologists use sliding knots as their primary surgical knot because of the need to tie in the deep, narrow spaces of the pelvis and vagina. However, according to a study by Trimbos,1 the majority of gynecologists studied who actually used sliding knots believed they were tying flat square knots. The security of sliding knots has been the subject of some study.2-5 For example, we recently reported a significantly greater proportion of knot failure with nonidentical sliding knots with 0-0 monofilament suture compared with flat knots when 6 throws were used.2 However, this was not the case with braided suture or finer gauge monofilament suture. Surgeons should strive to tie the most secure knot while keeping knot bulk to a minimum with the suture Reprints not available from the authors. 0002-9378/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.ajog.2004.05.029
most ideally suited for the task at hand. The goal of this investigation was to compare the integrity of the 6 throw nonidentical sliding knot with that of the 3 throw nonidentical sliding knot. The knots were tested in 4 groups that consisted of combinations of either 0-0 or 2-0 gauge monofilament or braided absorbable suture. We evaluated knot integrity by determining the proportion of knots that untied and by determining the load required for knot breakage using previously described standardized laboratory testing.2
Material and methods In this study, we used the synthetic absorbable monofilament suture polydioxanone and the absorbable braided suture polyglactin 910 (PDS and Vicryl respectively, Ethicon, Somerville, NJ) in 0-0 and 2-0
Ivy et al
1619 Table I Proportion of knots that untied and mean failure load for 0-0 polydioxanone
Failure by untying (n) Failure load* (N)y
3 Throws (n = 10)
6 Throws (n = 10)
9 (90%) 97.7z
3 (30%) 110.2 G 12.6
P value .02 z
* Load required to break the remaining sutures that did not fail by untying. y Data are given as mean G SD. z Only single value, cannot calculate SD or P value.
Table II Proportion of knots that untied and mean failure load for 0-0 polyglactin 910 3 Throws (n = 10)
6 Throws (n = 10)
P value
Failure by untying (n) 8 (80%) 2 (20%) .02 Failure load* (N)y 109.0 G 10.2 117.2 G 5.6 .13 Figure 1 A, Nonidentical siding knot. B, Flat square knot. C, Untied nonidentical sliding knot.
US Pharmacopeia sizes. Sutures, all with similar expiration dates, were obtained from hospital operating room stock. The major outcome studied was the proportion of knots that became untied during standardized laboratory testing when nonidentical sliding knots consisting of 6 throws were compared with the same knot with 3 throws for each suture type. In addition, the maximum load required to break a tied suture was also determined. A single investigator tied each knot (J.J.I.). The details of tying nonidentical sliding knots have been described elsewhere.2 Briefly, nonidentical sliding knots are made by placing nonidentical throws of suture around a single suture held under tension. Figure 1 illustrates a nonidentical sliding knot (A) compared with a flat square knot (B). A random number generator was used to obtain random number tables. Knots were then tied in the random order that was generated in the tables to avoid performer bias. All knots were tied around 2 polished stainless steel rings that were transferred to a tensiometer (Instron Testing Machine Model 4202; Instron Co, Canton, Mass). An attempt was made to tie all knots with uniform tension by making the suture snug around the steel rings. Once tied, the knot tails were trimmed to 3 mm each. The knots were then placed in 0.9% sodium chloride solution for 60 seconds to attempt to represent in vivo conditions before the knots were tested. The knots were then transferred to the tensiometer. The loops were stretched at 5 mm/min until failure occurred. Failure was defined as either breakage of the suture or the slip of either tail of the knot more than 3 mm (unraveling). The type of failure was recorded for each event. Load displacement curves were also generated for each knot that was tested.
* Load required to break the remaining sutures that did not fail by untying. y Data are given as mean G SD.
Table III Proportion of knots that untied and mean failure load for 2-0 polydioxanone
Failure by untying (n) Failure load* (N)y
3 Throws (n = 10)
6 Throws (n = 10)
P value
5 (50%) 68.4 G 17.0
2 (20%) 76.3 G 9.4
.35 .31
* Load required to break the remaining sutures that did not fail by untying. y Data are given as mean G SD.
Table IV Proportion of knots that untied and mean failure load for 2-0 polyglactin 910 3 Throws (n = 10)
6 Throws (n = 10)
P value
Failure by untying (n) 8 (80%) 3 (30%) .04 Failure load* (N)y 78.1 G 13.0 69.7 G 24.5 .60 * Load required to break the remaining sutures that did not fail by untying. y Data are given as mean G SD.
For knots that did not unravel, the load required for breakage of the suture was recorded. The online data collection from the tensiometer was performed with Lab View software (National Instruments, Austin, Tex). The Fisher exact test was used to determine whether there was a significant difference in the proportion of knots that untied when the 3 throw knot was compared with the 6 throw knot for each suture type and gauge. The failure load (newtons) that was required for breakage was also
1620 compared with the independent t test. A probability value of less than .05 was considered statistically significant.
Results A total of 80 nonidentical sliding knots were tied in this experiment. No knot began unraveling and subsequently broke before the completion of the unraveling process. That is, once beginning to unravel, the knot completely unraveled. Knots untied when the single strand that had been held under tension during the knot tying process slipped through the loops created by the other strand (Figure 1, C).The proportion of knots with 3 throws that became untied compared with the proportion with 6 throws for each of the 4 suture types are presented in Tables I through IV. A smaller proportion of knots became untied for each suture group when 6 throws were used compared with 3 throws, although this did not achieve statistical significance in the 2-0 polydioxanone group. The mean loads that were required for breakage for the knots that did not untie are also presented in Tables I through IV. As expected, the mean loads that were required for breakage were greater for the 0-0 gauge sutures compared with the 2-0 gauge sutures. However, there were no significant differences in the loads required for breakage between the 3 and 6 throw knots for each suture type. In every case, when the suture broke, it did so at or very near the knot.
Comment Surgeons have a nearly limitless number of options available when choosing suture material, suture gauge, knot configuration, and number of knot throws to use when tying suture. One should strive to tie the most secure knot while keeping knot bulk to a minimum with the suture most ideally suited for the task at hand. Thacker et al6 found that optimal knot configuration, including number of throws, was achieved in only 25% of the cases they studied. Knot untying before suture breakage was a common problem. In addition, we have also previously demonstrated that knot integrity is a function of knot configuration as well as the size and type of suture material.2,5 The nonidentical sliding knot is commonly used by gynecologic surgeons because of the need to tie in the deep and narrow spaces of the vagina and pelvis. Sliding knots do not require that the hands or suture cross, as must occur with flat square knots. We have previously reported that the 6 throw nonidentical sliding knot appears to be an acceptable alternative to the flat square knot, especially when braided suture or finer gauge monofilament suture is used. The goal of the current investigation was to determine whether the number of throws used in nonidentical sliding knots could be
Ivy et al decreased to 3 to keep knot bulk to a minimum. Knot bulk is dependent on the gauge of the suture material as well as the number of throws.7 In this study, we studied knot integrity by evaluating the proportion of knots that became untied when stressed under standard laboratory conditions. We tested both monofilament as well as braided absorbable sutures in 0-0 and 2-0 suture gauge. The amount of load required to either unravel or break the knot was also determined from load-displacement curves that were generated. We compared the 3 throw nonidentical sliding knot with the 6 throw nonidentical sliding knot. We chose commonly used absorbable sutures, polydioxanone and polyglactin 910, in suture gauges also routinely used in gynecologic surgery, 0-0 and 2-0. Knot failure by untying for the 6 throw knots was fairly constant across all 4 types of suture tested and consistent with our previous reports.2,5 However, when the number of throws was decreased to 3, knot failure by untying increased dramatically, irrespective of the suture type or gauge. This difference was statistically significant, except for the 2-0 monofilament suture. The load required to break knots that did not untie did not vary significantly between the 6 throw and 3 throw knots. Not surprisingly, the finer gauge sutures required lower loads for breakage. It is clear from our data that the number of throws used to tie nonidentical sliding knots is an important factor in creating a secure knot with either monofilament or braided absorbable suture. Knot integrity is not adequate when 3 throws are used with either suture. This is true even with finer gauge sutures. The current study reinforces that knot security is a function of suture type as well as knot configuration, including the number of throws used to make the knot. It is important that surgeons be cognizant of the knot they are using as well as the limitations that the knot may have.
References 1. Trimbos JB. Security of various knots commonly used in surgical practice. Obstet Gynecol 1984;64:274-80. 2. Schubert DC, Unger JB, Mukherjee D, Perrone JF. Mechanical performance of knots using braided and monofilament absorbable sutures. Am J Obstet Gynecol 2002;187:1438-42. 3. van Rijssel EJC, Trimbos JB, Booster MH. Mechanical performance of square knots and sliding knots in surgery: a comparative study. Am J Obstet Gynecol 1990;162:93-7. 4. Trimbos JB, van Rijssel EJC, Klopper PJ. Performance of sliding knots in monofilament and multifilament suture material. Obstet Gynecol 1986;68:425-30. 5. Ivy JJ, Unger JB, Mukherjee D. Knot integrity with nonidentical and parallel sliding knots. Am J Obstet Gynecol 2004;190:83-6. 6. Thacker JG, Rodeheaver G, Kurtz L, Edgerton MT, Edlich RF. Mechanical performance of sutures in surgery. Am J Surg 1977;133:713-5. 7. van Rijssel, Brand R, Admiral C, Smit I, Trimbos JB. Tissue reaction and surgical knots: the effect of suture size, knot configuration and knot volume. Obstet Gynecol 1989;74:64-8.