Knot Security and Tensile Strength of Suture Materials Danielle M. Marturello1, DVM, Michael S. McFadden1, DVM, MS, Diplomate ACVS, R. Avery Bennett2, DVM, MS, Diplomate ACVS, Guillaume R. Ragetly3, DVM, PhD, Diplomate ACVS, ECVS, and Gavin Horn4, PhD 1 Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, Urbana, Illinois ,2 Department of Surgery, Animal Medical Center, New York City, New York ,3 Department of Surgery, Centre Hospitalier Vétérinaire Frégis, Arcueil, France and 4 Fire Service Institute, University of Illinois, Urbana, Illinois
Corresponding Author Danielle M. Marturello, DVM, Aspen Meadow Veterinary Specialists, Longmont, CO. E‐mail: [email protected] Submitted May 2013 Accepted October 2013 DOI:10.1111/j.1532-950X.2013.12076.x
Objective: To evaluate knot security and tensile failure load of suture tied in simple interrupted, beginning continuous, and ending continuous patterns for 11 suture materials commonly used in small animal surgery. Study design: Mechanical study. Methods: For each of 11 suture material types, and 5 knot sizes (2, 3, 4, 5, and 6 throws) 2 surgeons each tied 6 knots (n ¼ 12 for each knot size in 11 suture materials). Three types of patterns were evaluated: a simple interrupted square knot, a square knot beginning a simple continuous pattern, and the knot ending a simple continuous pattern. All knots were incubated in healthy canine donor plasma at 40°C for a minimum of 24 hours. Sutures were evaluated for knot security (knots untied, suture failed by breaking, suture slipped from the clamps, or suture untied before testing) and maximum load carried before knot slippage or knot failure (termed tensile failure load). Results: Significant differences were found in knot security and tensile failure load among suture types. There was no significant difference between the simple interrupted knots and the knots at the beginning of a simple continuous pattern; however, both were significantly less likely to fail than the knots tied at the end of a simple continuous pattern. The number of throws per knot had a significant effect for knot security and tensile failure load. Surgeon experience had a significant effect on failure mode and tensile failure load. Conclusions: Suture type, number of throws per knot (knot size), suture pattern, and surgeon experience play an important role in knot security and should be considered when performing surgery.
All suture materials are evaluated on basic characteristics such as handling properties, degree of inflammatory reaction induced in tissues, cost, initial tensile strength, temporal loss of tensile strength, and knot security. In most surgical procedures, tying knots with suture material is an essential component of maintaining tissue apposition. Security of a knot is crucial to holding tissues together until they have healed, and a secure knot is defined as one that does not untie or slip open before the suture line breaks.1 Tensile breaking strength is commonly defined as the force a suture can withstand before breaking.2 The type of suture and the type of knot that are used affect knot security. Monofilament sutures are less pliable and more susceptible to damage from crushing or nicking,3 and are also smoother, which makes a knot more likely to slip. Therefore, more throws are typically required when using a monofilament suture. Braided sutures have greater strength and pliability3 making a Presented in part at the ACVS Veterinary Symposium, San Antonio TX, October 2013.
knot less likely to slip, meaning fewer throws could result in a secure knot. Square knots are more secure than granny or half hitch knots which are more prone to slipping.4 For different suture materials, the type of knot requires varying numbers of throws to create a secure knot.6 Since that report, different suture materials are commonly used in surgical practice and have not been evaluated mechanically to assess differences in knot security. The earlier study did not evaluate tensile failure load or the effect of surgeon experience on knot security. Our purpose was to determine the minimum number of throws necessary to create a secure knot with 11 suture material types and 3 suture patterns independent of the experience of the person tying the knot. A secure knot was defined as a knot that failed by breaking rather than untying. We hypothesized that the security of the knot would increase as the number of throws increased but that 2 square knots would be sufficient to cause the suture to break instead of failing because of the knot untying. Our 2nd hypothesis was that knots tied with multifilament sutures would require fewer throws than
Veterinary Surgery 43 (2014) 73–79 © Copyright 2013 by The American College of Veterinary Surgeons
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monofilament sutures to form a secure knot. Lastly, we hypothesized that there would not be a difference between a 4th year veterinary student and an ACVS Diplomate with regard to knot security or tensile load to failure.
MATERIALS AND METHODS Suture Materials Suture materials tested were 3–0 polyglactin 910 (VicrylTM; Ethicon, Johnson and Johnson, Somerville, NJ), 3–0 lactomer (PolysorbTM, Covidien, Mansfield, MA), 3–0 polydioxanone (PDS IITM, Ethicon), 3–0 polyglyconate (MaxonTM, Covidien), 3–0 polyglecaprone 25 (MonocrylTM, Ethicon), 3–0 glycomer (BiosynTM, Covidien), 3–0 polyglytone 6211 (CaprosynTM, Covidien); 3–0 monofilament nylon (EthilonTM, Ethicon; MonosofTM, Covidien) and 3–0 polypropylene (ProleneTM, Ethicon; SurgiproTM Covidien). Knot Tying Square knots (2 throws) were created by tying suture around a 55 mm diameter aluminum cylinder (Fig 1A,B). Subsequent
Figure 1 (A) 1st throw of a knot tied around a cylinder, (B) 2nd throw being tied to form a square knot around a cylinder, (C) a square knot that has already been tied to form the beginning of a simple continuous pattern, with the continuous end of the suture shown around the cylinder. This end was cut to 10 mm for this study, (D) a square knot that has been tied to form the ending of a simple continuous pattern, with the continuous end of the suture shown around the cylinder. This end was also cut to 10 mm for this study.
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throws were then tied in the same manner to create knot with 3, 4, 5, and 6 throws. All knots were made using instrument ties by 2 authors (D.M.M., M.S.M.) and non‐sterile latex gloves were worn whenever handling suture materials. The suture ends (tails) were cut to 3 mm length (measured with a ruler before cutting). For each surgeon (n ¼ 2), 6 samples of each suture type (n ¼ 11), and each knot size (n ¼ 5) were created. For each suture type and each surgeon 3 different square knots were evaluated: (1) a simple interrupted knot, (2) a knot at the beginning of a simple continuous pattern with 1 tail cut to a minimum of 10 mm (Fig 1C), and (3) the knot at the end of a simple continuous pattern using the free loop to tie the knots (Fig 1D). Suture loops and knots were then placed in a 7 mL glass vial (BD Vacutainer1 red top blood collection tubes, BD Vacutainer, Franklin Lakes, NJ) that were filled with healthy canine donor plasma and incubated at 40°C for a minimum of 24 hours. Mechanical Testing A tabletop materials testing machine (Instron Mini 44 Tensile Tester, Instron, Norwood, MA) with a 500 N load cell, was used for mechanical testing of all samples. Just before testing, each suture loop was removed from the Vacutainer1 and cut directly opposite the knot creating 2 strands of equal length, which were inserted into the Instron Mini 44’s pneumatic grips that clamped the suture ends with air pressure at 45 psi. This pressure was chosen to minimize the risk of sutures slipping from the grips as well as breaking in the grips because of excessive pressure (based on a pilot study with these suture materials). The grips were set to a distance such that the suture material was taut, with minimal force (
Corresponding Author Danielle M. Marturello, DVM, Aspen Meadow Veterinary Specialists, Longmont, CO. E‐mail: [email protected] Submitted May 2013 Accepted October 2013 DOI:10.1111/j.1532-950X.2013.12076.x
Objective: To evaluate knot security and tensile failure load of suture tied in simple interrupted, beginning continuous, and ending continuous patterns for 11 suture materials commonly used in small animal surgery. Study design: Mechanical study. Methods: For each of 11 suture material types, and 5 knot sizes (2, 3, 4, 5, and 6 throws) 2 surgeons each tied 6 knots (n ¼ 12 for each knot size in 11 suture materials). Three types of patterns were evaluated: a simple interrupted square knot, a square knot beginning a simple continuous pattern, and the knot ending a simple continuous pattern. All knots were incubated in healthy canine donor plasma at 40°C for a minimum of 24 hours. Sutures were evaluated for knot security (knots untied, suture failed by breaking, suture slipped from the clamps, or suture untied before testing) and maximum load carried before knot slippage or knot failure (termed tensile failure load). Results: Significant differences were found in knot security and tensile failure load among suture types. There was no significant difference between the simple interrupted knots and the knots at the beginning of a simple continuous pattern; however, both were significantly less likely to fail than the knots tied at the end of a simple continuous pattern. The number of throws per knot had a significant effect for knot security and tensile failure load. Surgeon experience had a significant effect on failure mode and tensile failure load. Conclusions: Suture type, number of throws per knot (knot size), suture pattern, and surgeon experience play an important role in knot security and should be considered when performing surgery.
All suture materials are evaluated on basic characteristics such as handling properties, degree of inflammatory reaction induced in tissues, cost, initial tensile strength, temporal loss of tensile strength, and knot security. In most surgical procedures, tying knots with suture material is an essential component of maintaining tissue apposition. Security of a knot is crucial to holding tissues together until they have healed, and a secure knot is defined as one that does not untie or slip open before the suture line breaks.1 Tensile breaking strength is commonly defined as the force a suture can withstand before breaking.2 The type of suture and the type of knot that are used affect knot security. Monofilament sutures are less pliable and more susceptible to damage from crushing or nicking,3 and are also smoother, which makes a knot more likely to slip. Therefore, more throws are typically required when using a monofilament suture. Braided sutures have greater strength and pliability3 making a Presented in part at the ACVS Veterinary Symposium, San Antonio TX, October 2013.
knot less likely to slip, meaning fewer throws could result in a secure knot. Square knots are more secure than granny or half hitch knots which are more prone to slipping.4 For different suture materials, the type of knot requires varying numbers of throws to create a secure knot.6 Since that report, different suture materials are commonly used in surgical practice and have not been evaluated mechanically to assess differences in knot security. The earlier study did not evaluate tensile failure load or the effect of surgeon experience on knot security. Our purpose was to determine the minimum number of throws necessary to create a secure knot with 11 suture material types and 3 suture patterns independent of the experience of the person tying the knot. A secure knot was defined as a knot that failed by breaking rather than untying. We hypothesized that the security of the knot would increase as the number of throws increased but that 2 square knots would be sufficient to cause the suture to break instead of failing because of the knot untying. Our 2nd hypothesis was that knots tied with multifilament sutures would require fewer throws than
Veterinary Surgery 43 (2014) 73–79 © Copyright 2013 by The American College of Veterinary Surgeons
73
Knot Security and Tensile Strength of Suture Materials
Marturello et al.
monofilament sutures to form a secure knot. Lastly, we hypothesized that there would not be a difference between a 4th year veterinary student and an ACVS Diplomate with regard to knot security or tensile load to failure.
MATERIALS AND METHODS Suture Materials Suture materials tested were 3–0 polyglactin 910 (VicrylTM; Ethicon, Johnson and Johnson, Somerville, NJ), 3–0 lactomer (PolysorbTM, Covidien, Mansfield, MA), 3–0 polydioxanone (PDS IITM, Ethicon), 3–0 polyglyconate (MaxonTM, Covidien), 3–0 polyglecaprone 25 (MonocrylTM, Ethicon), 3–0 glycomer (BiosynTM, Covidien), 3–0 polyglytone 6211 (CaprosynTM, Covidien); 3–0 monofilament nylon (EthilonTM, Ethicon; MonosofTM, Covidien) and 3–0 polypropylene (ProleneTM, Ethicon; SurgiproTM Covidien). Knot Tying Square knots (2 throws) were created by tying suture around a 55 mm diameter aluminum cylinder (Fig 1A,B). Subsequent
Figure 1 (A) 1st throw of a knot tied around a cylinder, (B) 2nd throw being tied to form a square knot around a cylinder, (C) a square knot that has already been tied to form the beginning of a simple continuous pattern, with the continuous end of the suture shown around the cylinder. This end was cut to 10 mm for this study, (D) a square knot that has been tied to form the ending of a simple continuous pattern, with the continuous end of the suture shown around the cylinder. This end was also cut to 10 mm for this study.
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throws were then tied in the same manner to create knot with 3, 4, 5, and 6 throws. All knots were made using instrument ties by 2 authors (D.M.M., M.S.M.) and non‐sterile latex gloves were worn whenever handling suture materials. The suture ends (tails) were cut to 3 mm length (measured with a ruler before cutting). For each surgeon (n ¼ 2), 6 samples of each suture type (n ¼ 11), and each knot size (n ¼ 5) were created. For each suture type and each surgeon 3 different square knots were evaluated: (1) a simple interrupted knot, (2) a knot at the beginning of a simple continuous pattern with 1 tail cut to a minimum of 10 mm (Fig 1C), and (3) the knot at the end of a simple continuous pattern using the free loop to tie the knots (Fig 1D). Suture loops and knots were then placed in a 7 mL glass vial (BD Vacutainer1 red top blood collection tubes, BD Vacutainer, Franklin Lakes, NJ) that were filled with healthy canine donor plasma and incubated at 40°C for a minimum of 24 hours. Mechanical Testing A tabletop materials testing machine (Instron Mini 44 Tensile Tester, Instron, Norwood, MA) with a 500 N load cell, was used for mechanical testing of all samples. Just before testing, each suture loop was removed from the Vacutainer1 and cut directly opposite the knot creating 2 strands of equal length, which were inserted into the Instron Mini 44’s pneumatic grips that clamped the suture ends with air pressure at 45 psi. This pressure was chosen to minimize the risk of sutures slipping from the grips as well as breaking in the grips because of excessive pressure (based on a pilot study with these suture materials). The grips were set to a distance such that the suture material was taut, with minimal force (
