Int Urogynecol J DOI 10.1007/s00192-017-3393-5
ORIGINAL ARTICLE
Knot integrity using different suture types and different knot-tying techniques for reconstructive pelvic floor procedures Omar F. Dueñas-Garcia 1 & Gina M. Sullivan 1,2 & Katherine Leung 1,2 & Kristen L. Billiar 3 & Michael K. Flynn 1,2
Received: 24 March 2017 / Accepted: 2 June 2017 # The International Urogynecological Association 2017
Abstract Introduction and hypothesis Surgeons use a variety of sutures and knot-tying methods during pelvic reconstructive procedures. We hypothesized that knot-strength integrity will be similar with regards to type of knot, type of suture, and the knot-tying process. Methods Using six different suture materials, flat square knots and slip knots were tied robotically and by hand by two surgeons. Knot integrity was evaluated using an Instron 5544 machine. We measured force and elongation at suture failure or knot slippage (whichever came first) as well as force at 3mm displacement.
* Omar F. Dueñas-Garcia [email protected] Gina M. Sullivan [email protected] Katherine Leung [email protected] Kristen L. Billiar [email protected] Michael K. Flynn [email protected] 1
Obstetrics and Gynecology Department, Female Pelvic Medicine and Reconstructive Surgery Division, University of Massachusetts Medical School, Worcester, MA, USA
2
University of Massachusetts – UMass Memorial Medical Center, 119 Belmont Street, Worcester, MA 01605, USA
3
Biomedical Engineering Department, Worcester Polytechnic Institute, 100 Institute Road Office 4007 Gateway Park, Worcester, MA 01609, USA
Results Four hundred and thirty-two knots were tie; one unraveled before the analysis, and 431 were tested. Three hundred and ninety-two knots reached or surpassed tensile strength of 30 N, the force at which tissue itself will fail. Knots tied with polyglyconate suture achieved the greatest tensile strength and those with OO-polydioxanone had the lowest. Hand-tied knots, regardless of technique and suture material, had greater tensile strength but greater elongation than robotically tied knots. Slip knots and flat square knots have similar integrity regardless of the tying technique. Conclusion Hand-tied knots had greater tensile strength than robotic knots, but the strength to break all knots required supraphysiological conditions. The decision to use a specific type of suture based on strength is not supported by our results, suggesting that surgeons may choose sutures based on other characteristics and personal comfort. Keywords Knot integrity . Robotically tied . Hand tied . Suture
Introduction In medicine, knots are used by surgeons to approximate surfaces or attach implants to tissue. Despite using knots for centuries, the mathematical study of the ideal knot is less than 100 years old, and scientists of different disciplines continue to debate this topic [1]. In medicine, the use of different materials for different purposes increases the complexity of the models. In recent decades, several suture and knot configurations have been explored for female pelvic reconstructive procedures (FPRP) [2–5]. Recent findings suggest that hand-tied flat square knots (FSK) under laboratory conditions have similar strength and knot integrity as surgeon’s knots when using four different suture materials [3, 4]. Similar studies in minimally
Int Urogynecol J
Fig. 1 a Beginning of two flat square knots (FSK) with two identical square throws (1 = 1 = 1 configuration). b Beginning of a slip knot with one square and one sliding throw (1 = 1-S)
invasive procedures found that tensile strength of one-handed, robotically tied knots is inferior to hand-tied knots [6]. Considering the newer suture materials, knot types and knot-tying techniques (one handed vs two handed), we decided to explore tensile strength and elongation (suture; knot strain and stretch before fracture) of the most common combinations of methods of suture knot tying commonly used in FPRP.
Materials and methods The study was deemed exempt by the University of Massachusetts Medical School Institutional Review Board. Six suture materials were studied: 0 polyester-coated material Fig. 2 Knot sets
with polybutilate (Ethibond; Ethicon, Inc., Somerville, NJ, USA), 0 polypropylene (Prolene; Ethicon), 0 and 00 polydioxanone (PDS; Ethicon, 0 polyglyconate (Maxon; Covidien/Medtronic, Mansfield, MA, USA), and CV-0 polytetrafluoroethylene (Gore-Tex; Gore & Associates, Inc., Newark, DE, USA). Based on the nomenclature established by Tera and Aberg, FSK were defined as five consecutive square throws for multifilament suture and six for monofilament suture (Fig. 1a) [4, 7, 8]. Surgeons secured each throw by descending the finger or instrument past each knot. Slip knots were defined two throws Bin the same direction without tightening the knot;^ The initial was a square throw followed by one sliding throw, with the free end pulled to slide the knot tight before securing it. After the knot was cinched down, additional square throws (3 for multifilament and 4 for monofilament sutures) secured the knot (Fig. 1b). These two procedures were performed robotically and conventionally (by hand). For hand tying, surgeons tied the same number of knots by both one-handed and twohanded methods. Two fellows in female pelvic medicine and reconstructive surgery performed all knot tying. To ensure competence and conformity between surgeons, prior to starting the study, each surgeon completed a practice standardization knot-tying session. For each type of suture material, knots were tied around a 0.5in. polished wooden dowel. To minimize bias, knots were randomized in 12 different sets (6 for each type). Figures 2 describes the total number of knots and knotting modality per set. Order of knotting within sets was Planned to tie per surgeon (n=216)
Enrollment Total number of knots
Total number of knots (n=432) Assessed for eligibility (n= )
Tying modality Randomized (n= )
Sets Hand tied sets (n=6) 1 set= 18 knots
Robotic tied Allocated to intervention sets (n=6) (n= ) Received 1 set= 12 knots allocated intervention (n= )
One handed slip using 6 different type of suture material (total 6 knots) One handed square using 6 different type of suture material (total 6 knots) Two handed handed slip using 6 different type of suture material (total 6 knots) Two handed square using 6 different type of suture material (total 6 knots)
Roboc usingallocated 6 different type of suture Did notslip receive intervention (give reasons) (n= ) 6 knots) material (total Roboc square using 6 different type of suture material (total 6 knots)
Int Urogynecol J
randomized, and surgeons tied a maximum of two sets per day with 30 min of separation between each set. The cut ends were trimmed at 10 mm to standardize the measurements. The tied suture was transferred to a uniaxial mechanical test machine (Instron 5544, Instron, Canton, MA, USA. Because 30 N represents the force required to pull sutures out of the vagina, we used it as the cutoff point for our analysis [9]). Each loop was analyzed for: (a) strength required to break the suture (knot) and/or produce slippage (whichever came first) to displace the knot loop at 3 mm; (b) suture elongation at ≥30 N (force measured at knot failure). Statistical analysis Knot characteristics were described with mean and standard deviation (SD) and comparisons made with Wilcoxon ranksum test or Kruskal–Wallis test. Adjusted linear regression was used to determine strength, elongation, and force until breakage/unraveling. Adjusted logistic regression was used to describe knot characteristics if it survived to 30 N.
Table 1 Knot types, tying methods, and suture material
Results Four hundred and thirty-two knots were tied. One knot unraveled before the analysis, and 431 knots were tested. Table 1 shows the unadjusted differences between surgeons, knot types, tying method, and suture material. Hand-tied knots were stronger than robotically tied knots. When comparing one- and two-handed techniques and FSK and slip knot, we found no significant differences in strength. Knots tied with polyglyconate were strongest and OO-polydioxanone the weakest. From the 431 knots tested, 39 (9.05%) did not reach the 30N mark: 27 (6.26%) robotically tied and 12 (2.78%) hand tied. Eleven that did not reach 30 N were polyester (8 robotically and 3 by hand). Adjusted linear regression was performed to investigate suture strength (Table 2). After adjusting for surgeon, material, tying method, and knot type, hand-tied knots were significantly stronger than robotically tied knots (15.89 N, p < 0.001). Hand-tied knots had significantly greater elongation than robotically tied knots (0.96 U, p = 0.030). The odds of achieving
Mean force to knot failure
Mean elongation to knot failure
Newtons (SD)
P value
Surgeon Surgeon 1
79.72 (27.61)
0.012
Surgeon 2
74.05 (28.49)
Suture material Polyglyconate Polyester
93.29 (36.63) 74.48 (30.03)
Polytetrafluoroethylene O-polydioxanone OO-polydioxanone Polypropylene Tying technique Robot Hand Knot type Flat square Slip Robot only (N = 144): Square Slip Hand only (N = 287): Single-handed square Double-handed square Double-handed slip Single-handed slip
MM (SD)
P value
11.48 (4.90)
0.214
12.08 (5.07)
ORIGINAL ARTICLE
Knot integrity using different suture types and different knot-tying techniques for reconstructive pelvic floor procedures Omar F. Dueñas-Garcia 1 & Gina M. Sullivan 1,2 & Katherine Leung 1,2 & Kristen L. Billiar 3 & Michael K. Flynn 1,2
Received: 24 March 2017 / Accepted: 2 June 2017 # The International Urogynecological Association 2017
Abstract Introduction and hypothesis Surgeons use a variety of sutures and knot-tying methods during pelvic reconstructive procedures. We hypothesized that knot-strength integrity will be similar with regards to type of knot, type of suture, and the knot-tying process. Methods Using six different suture materials, flat square knots and slip knots were tied robotically and by hand by two surgeons. Knot integrity was evaluated using an Instron 5544 machine. We measured force and elongation at suture failure or knot slippage (whichever came first) as well as force at 3mm displacement.
* Omar F. Dueñas-Garcia [email protected] Gina M. Sullivan [email protected] Katherine Leung [email protected] Kristen L. Billiar [email protected] Michael K. Flynn [email protected] 1
Obstetrics and Gynecology Department, Female Pelvic Medicine and Reconstructive Surgery Division, University of Massachusetts Medical School, Worcester, MA, USA
2
University of Massachusetts – UMass Memorial Medical Center, 119 Belmont Street, Worcester, MA 01605, USA
3
Biomedical Engineering Department, Worcester Polytechnic Institute, 100 Institute Road Office 4007 Gateway Park, Worcester, MA 01609, USA
Results Four hundred and thirty-two knots were tie; one unraveled before the analysis, and 431 were tested. Three hundred and ninety-two knots reached or surpassed tensile strength of 30 N, the force at which tissue itself will fail. Knots tied with polyglyconate suture achieved the greatest tensile strength and those with OO-polydioxanone had the lowest. Hand-tied knots, regardless of technique and suture material, had greater tensile strength but greater elongation than robotically tied knots. Slip knots and flat square knots have similar integrity regardless of the tying technique. Conclusion Hand-tied knots had greater tensile strength than robotic knots, but the strength to break all knots required supraphysiological conditions. The decision to use a specific type of suture based on strength is not supported by our results, suggesting that surgeons may choose sutures based on other characteristics and personal comfort. Keywords Knot integrity . Robotically tied . Hand tied . Suture
Introduction In medicine, knots are used by surgeons to approximate surfaces or attach implants to tissue. Despite using knots for centuries, the mathematical study of the ideal knot is less than 100 years old, and scientists of different disciplines continue to debate this topic [1]. In medicine, the use of different materials for different purposes increases the complexity of the models. In recent decades, several suture and knot configurations have been explored for female pelvic reconstructive procedures (FPRP) [2–5]. Recent findings suggest that hand-tied flat square knots (FSK) under laboratory conditions have similar strength and knot integrity as surgeon’s knots when using four different suture materials [3, 4]. Similar studies in minimally
Int Urogynecol J
Fig. 1 a Beginning of two flat square knots (FSK) with two identical square throws (1 = 1 = 1 configuration). b Beginning of a slip knot with one square and one sliding throw (1 = 1-S)
invasive procedures found that tensile strength of one-handed, robotically tied knots is inferior to hand-tied knots [6]. Considering the newer suture materials, knot types and knot-tying techniques (one handed vs two handed), we decided to explore tensile strength and elongation (suture; knot strain and stretch before fracture) of the most common combinations of methods of suture knot tying commonly used in FPRP.
Materials and methods The study was deemed exempt by the University of Massachusetts Medical School Institutional Review Board. Six suture materials were studied: 0 polyester-coated material Fig. 2 Knot sets
with polybutilate (Ethibond; Ethicon, Inc., Somerville, NJ, USA), 0 polypropylene (Prolene; Ethicon), 0 and 00 polydioxanone (PDS; Ethicon, 0 polyglyconate (Maxon; Covidien/Medtronic, Mansfield, MA, USA), and CV-0 polytetrafluoroethylene (Gore-Tex; Gore & Associates, Inc., Newark, DE, USA). Based on the nomenclature established by Tera and Aberg, FSK were defined as five consecutive square throws for multifilament suture and six for monofilament suture (Fig. 1a) [4, 7, 8]. Surgeons secured each throw by descending the finger or instrument past each knot. Slip knots were defined two throws Bin the same direction without tightening the knot;^ The initial was a square throw followed by one sliding throw, with the free end pulled to slide the knot tight before securing it. After the knot was cinched down, additional square throws (3 for multifilament and 4 for monofilament sutures) secured the knot (Fig. 1b). These two procedures were performed robotically and conventionally (by hand). For hand tying, surgeons tied the same number of knots by both one-handed and twohanded methods. Two fellows in female pelvic medicine and reconstructive surgery performed all knot tying. To ensure competence and conformity between surgeons, prior to starting the study, each surgeon completed a practice standardization knot-tying session. For each type of suture material, knots were tied around a 0.5in. polished wooden dowel. To minimize bias, knots were randomized in 12 different sets (6 for each type). Figures 2 describes the total number of knots and knotting modality per set. Order of knotting within sets was Planned to tie per surgeon (n=216)
Enrollment Total number of knots
Total number of knots (n=432) Assessed for eligibility (n= )
Tying modality Randomized (n= )
Sets Hand tied sets (n=6) 1 set= 18 knots
Robotic tied Allocated to intervention sets (n=6) (n= ) Received 1 set= 12 knots allocated intervention (n= )
One handed slip using 6 different type of suture material (total 6 knots) One handed square using 6 different type of suture material (total 6 knots) Two handed handed slip using 6 different type of suture material (total 6 knots) Two handed square using 6 different type of suture material (total 6 knots)
Roboc usingallocated 6 different type of suture Did notslip receive intervention (give reasons) (n= ) 6 knots) material (total Roboc square using 6 different type of suture material (total 6 knots)
Int Urogynecol J
randomized, and surgeons tied a maximum of two sets per day with 30 min of separation between each set. The cut ends were trimmed at 10 mm to standardize the measurements. The tied suture was transferred to a uniaxial mechanical test machine (Instron 5544, Instron, Canton, MA, USA. Because 30 N represents the force required to pull sutures out of the vagina, we used it as the cutoff point for our analysis [9]). Each loop was analyzed for: (a) strength required to break the suture (knot) and/or produce slippage (whichever came first) to displace the knot loop at 3 mm; (b) suture elongation at ≥30 N (force measured at knot failure). Statistical analysis Knot characteristics were described with mean and standard deviation (SD) and comparisons made with Wilcoxon ranksum test or Kruskal–Wallis test. Adjusted linear regression was used to determine strength, elongation, and force until breakage/unraveling. Adjusted logistic regression was used to describe knot characteristics if it survived to 30 N.
Table 1 Knot types, tying methods, and suture material
Results Four hundred and thirty-two knots were tied. One knot unraveled before the analysis, and 431 knots were tested. Table 1 shows the unadjusted differences between surgeons, knot types, tying method, and suture material. Hand-tied knots were stronger than robotically tied knots. When comparing one- and two-handed techniques and FSK and slip knot, we found no significant differences in strength. Knots tied with polyglyconate were strongest and OO-polydioxanone the weakest. From the 431 knots tested, 39 (9.05%) did not reach the 30N mark: 27 (6.26%) robotically tied and 12 (2.78%) hand tied. Eleven that did not reach 30 N were polyester (8 robotically and 3 by hand). Adjusted linear regression was performed to investigate suture strength (Table 2). After adjusting for surgeon, material, tying method, and knot type, hand-tied knots were significantly stronger than robotically tied knots (15.89 N, p < 0.001). Hand-tied knots had significantly greater elongation than robotically tied knots (0.96 U, p = 0.030). The odds of achieving
Mean force to knot failure
Mean elongation to knot failure
Newtons (SD)
P value
Surgeon Surgeon 1
79.72 (27.61)
0.012
Surgeon 2
74.05 (28.49)
Suture material Polyglyconate Polyester
93.29 (36.63) 74.48 (30.03)
Polytetrafluoroethylene O-polydioxanone OO-polydioxanone Polypropylene Tying technique Robot Hand Knot type Flat square Slip Robot only (N = 144): Square Slip Hand only (N = 287): Single-handed square Double-handed square Double-handed slip Single-handed slip
MM (SD)
P value
11.48 (4.90)
0.214
12.08 (5.07)
