ORIGINAL REPORTS
The Effect of Instrumentation on Suture Tensile Strength and Knot Pullout Strength of Common Suture Materials Peter C. Johnson, MD, CPT, MC, USA,*,† Aaron D. Roberts, DO, CPT, MC, USA,*,† Justin M. Hire, MD, CPT, MC, USA,*,† and Terry L. Mueller, DO, LTC, MC, USA*,† *
Department of Orthopaedic Surgery, Dwight D. Eisenhower Army Medical Center, Fort Gordon, Georgia; and †Department of Clinical Investigation, Dwight D. Eisenhower Army Medical Center, Fort Gordon, Georgia OBJECTIVE: To determine the effect of instrumentation of suture material on knot security and tensile strength. STUDY DESIGN: In all, 5 types of suture material were
used; 10 knots were tied without any instrumentation and 10 knots were tied with a hemostat holding tension on the first throw while the second throw was made for each suture type. Each group was tested to failure with the maximum load and mode of failure recorded. The maximum load between groups of each suture type was compared; frequency of failure through knot slippage vs material fracture was also compared between groups. RESULTS: There was no significant difference observed in the maximum load to failure for any suture type between instrumented and noninstrumented groups. Additionally, there was no difference between any instrumented and noninstrumented groups for material failure vs failure due to knot slippage. CONCLUSIONS: Instrumentation of suture material dur-
ing two-hand tying does not affect the strength of suture material or knot security. ( J Surg Ed 73:162-165. Published by Elsevier Inc on behalf of the Association of Program Directors in Surgery) KEY WORDS: knot security, suture strength, suture
material COMPETENCIES: Patient Care, Medical Knowledge, Practice-Based Learning and Improvement
The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or reflecting the views of the Department of Defense or US Government. The authors are employees of the US government. This work was prepared as part of their official duties, and as such there is no copyright to be transferred. Correspondence: Inquiries to Peter C. Johnson, MD, Department of Orthopaedic Surgery, 300 East Hospital Road, Fort Gordon, GA 30905. Fax: þ(706) 787-2901; e-mail: [email protected]
162
INTRODUCTION Occasionally during surgery it is necessary to perform closures or repairs of structures that require an exceptionally tight repair for mechanical advantage and stability, or for postoperative wound care. Examples would include the repair of the short external rotators to the greater trochanter during closure of the Moore (posterior) approach to the hip, which must be tightly repaired for hip stability and function of the rotators, or tight closure of the lumbar fascia following posterior lumbar surgery to prevent wound drainage. In both of these examples, the sutures may need to be tied within a very deep surgical field owing to the involved anatomy and may be further complicated by the patient’s body habitus. While two-hand tying within a deep surgical field, it may be technically difficult to maintain the tension on the first throw of the suture material while performing the second throw to lock the knot in place. Some surgeons use a mosquito hemostat or other instrument to clamp the material and maintain the first throw’s tension while the second throw is being made. Other surgeons object to this practice, on the grounds that the instrumentation damages the suture material. This claim is anecdotal, however, and has not been subject to formal scientific investigation. Studies of suture strength and knot security have been relatively limited in literature in recent years despite the advent of new suture materials as well as previous demonstration of the significant effect of handling techniques on suture materials. Previous studies have examined the effect of surgical needle holders on various materials and found that compression from needle holders may significantly affect material strength in running closures.1 However, no study has investigated the effect of instrumentation on knot tying. Studies examining knot security have helped clarify the ideal number of throws, but they have not determined whether instrumentation has any additional effect on knot security. The intent of this study was to examine the effect
Journal of Surgical Education Published by Elsevier Inc on behalf of the 1931-7204/$30.00 Association of Program Directors in Surgery http://dx.doi.org/10.1016/j.jsurg.2015.08.011
FIGURE 1. (A) Detailed look of hemostat with metal grooves, which could abrade suture integrity during use. (B) Example of hemostat placement during two-hand tying technique.
of instrumentation with hemostats on knot security and strength of various suture materials.
MATERIALS AND METHODS This study was deemed exempt by the Dwight D. Eisenhower Army Medical Center Institutional Review Board. In all, 5 suture materials were tested (FiberWire, Arthrex, Inc., Naples, FL; Ethibond, Ethicon US, LLC, Cincinatti, OH; VICRYL, Ethicon US, LLC; Prolene, Ethicon US, LLC; and Monocryl, Ethicon US, LLC). In all, 20 total pieces of material had knots tied for each suture material tested; 10 pieces were tested for each suture type with a knot tied using a two-hand tie technique without any type of instrumentation to the suture material. All knots were tied by the principal investigator around the posts of a tying board; during knot tying, tension was maintained on the suture material manually by the principal investigator but was not formally measured. An additional 10 pieces of material had knots tied identically by the principal investigator, with the exception of a mosquito hemostat applied to the first throw to maintain the first throw while the second throw was made (Fig. 1). The hemostat was maximally closed with all 3 ratchet teeth engaged for each knot to control the amount of compression on the material, and no slippage of the first throw occurred after the hemostat was applied. Surgeon’s knots as described by Muffly et al.2 were applied using a double first throw with 5 total throws, which has been shown to be the minimum number of throws needed to ensure security.3,4 Tied loops were then tested to failure. Testing was conducted on an Instron E-10000 load tester (Instron, Norwood, MA), with the maximum load recorded. The maximum load was recorded in Newtons at either knot failure or slippage of the knot. Tensile testing was conducted on suture loops using the parameters described by Naleway et al.,5 with 60 mm of suture loop tested at a crosshead speed of
120 mm/min, or twice the working length of suture loop. This conforms to the USP standard for tensile strength testing. Mean maximum load was compared between instrumented and noninstrumented groups for each suture type using a two-tailed Student t-test with significance set at a p o 0.05. Additionally, the mode of failure, either knot slippage or suture breakage, was recorded. Contingency tables were made for each suture group comparing failure via material breakage vs failure via knot slippage. Fisher’s Exact test was
FIGURE 2. Suture loop being tested on Instron Machine.
Journal of Surgical Education Volume 73/Number 1 January/February 2016
163
TABLE. Mean Maximum Load Between Groups Suture Type
Mean Maximum Load at Failure (N) for Noninstrumented Suture ⫾ SD
2 FiberWire 2 Ethibond 0-Vicryl 2-0 Prolene 4-0 Monocryl
275.44 106.43 94.01 66.81 33.26
⫾ ⫾ ⫾ ⫾ ⫾
40.06 38.50 21.46 6.56 4.85
Mean Maximum Load at Failure (N) for Instrumented Suture ⫾ SD 251.35 115.36 97.96 63.35 31.80
⫾ ⫾ ⫾ ⫾ ⫾
61.91 38.36 9.80 11.72 5.08
p Value 0.307 0.678 0.616 0.31 0.473
SD, standard deviation.
used to examine difference with significance set at o0.05 for a two-tailed p-value. An example suture loop being tested on the Instron machine is shown in Figure 2.
RESULTS There was no statistically significant difference observed in mean maximum load between instrumented and noninstrumented groups for any suture material tested. Suture types, mean maximum load (N) ⫾ standard deviation, and calculated p-values are shown in Table 1. Mode of failure, either slippage of the knot or breakage of the material, was recorded for each piece of suture tested. All loops that failed via suture breakage failed just adjacent to the knot and not within the knot where the hemostat had been applied, meaning that no material failed at the site of instrumentation. No significant difference in mode of failure was found between instrumented vs noninstrumented suture groups for any material using Fisher’s Exact test.
CONCLUSION
ROLE OF FUNDING SOURCES
Our results support that there is no significant effect of instrumentation on tensile strength or knot security for the suture types tested. For each suture type tested, there was no significant difference in mean maximum load at failure, and there was no significant difference between number of loops that failed via knot slippage vs material breakage between noninstrumented and instrumented groups. To our knowledge this is the only study that has investigated the specific effect of instrumentation of the knot during tying on knot security and material strength. Naleway et al.5 examined the mechanical properties of various suture types as well as the effect of knotting the material on tensile strength. In addition to describing the mechanical performance of various newer suture materials under stress, they found that knotting the material significantly decreased the maximum tensile strength, which is in agreement with older studies.
164
Kim et al.6 examined the tensile properties and knot security of suture materials as well, with additional investigation of the effect of storage under a tensile load on absorbable sutures. In their study, nonabsorbable suture materials were tested for tensile strength at baseline, and then tested again after tying with propensity for knot slippage examined. Absorbable suture materials were initially tested for the maximum tensile strength, and then stored for varying times with a 100-g tensile load in Hank’s solution and had tensile properties reexamined. Their results showed an increased risk of knot slippage among nonabsorbable monofilament suture materials over braided, and a decrease in tensile strength over time under a tensile load for absorbable sutures. Our study supports that using a hemostat to maintain the tension of the first throw of a two-hand tied knot while the second throw is being made does not have a significant effect on the strength of the material or the propensity for knot slippage. Surgeons may use this technique to ensure quality knots without concern for adversely affecting knot or material performance.
Funding for the purchase of suture materials was provided by the Department of Clinical Investigation, Dwight D. Eisenhower Army Medical Center. DCI provided the funding with the intention of generating an article for publication, and provided facilities and equipment for data collection. DCI had no role in study design, or in data analysis or interpretation.
ACKNOWLEDGMENTS The authors would like to thank Mr. Royce Runner of the Department of Clinical Investigation, DDEAMC, for technical assistance with the Instron load tester and data collection. The authors would also like to thank Dr. Steven D. Zumbrun of the Department of Clinical Investigation, DDEAMC, for assistance with proofreading of the manuscript.
Journal of Surgical Education Volume 73/Number 1 January/February 2016
REFERENCES 1. Stamp CV, McGregor W, Rodeheaver GT, Thacker JG,
Towler MA, Edlich RF. Surgical needle holder damage to sutures. Am Surg. 1988;54(5):300-306. 2. Muffly TM, Kow N, Iqbal I, Barber MD. Minimum
number of throws needed for knot security. J Surg Educ. 2011;68(2):130-133. http://dx.doi.org/10.1016/j.jsurg. 2010.11.001. 3. Muffly TM, Boyce J, Kieweg SL, Bonham AJ. Tensile
strength of a surgeon’s or a square knot. J Surg Educ. 2010;67(4):222-226. http://dx.doi.org/10.1016/j.jsurg. 2010.06.007.
4. Tidwell JE, Kish VL, Samora JB. Knot security: how
many throws does it really take? Orthopedics. 2012; 35(4):532-537. http://dx.doi.org/10.3928/0147744720120327-16. 5. Naleway SE, Lear W, Kruzic JJ, Maughan CB. Mechan-
ical properties of suture materials in general and cutaneous surgery. J Biomed Mater Res Part B. 2015; 103(4):735-742. http://dx.doi.org/10.1002/jbm.b.33171. 6. Kim JC, Lee YK, Lim BS, Rhee SH, Yang HC.
Comparison of tensile and knot security properties of surgical sutures. J Mater Sci Mater Med. 2007; 18(12):2363-2369. http://dx.doi.org/10.1007/s10856007-3114-6.
Journal of Surgical Education Volume 73/Number 1 January/February 2016
165
The Effect of Instrumentation on Suture Tensile Strength and Knot Pullout Strength of Common Suture Materials Peter C. Johnson, MD, CPT, MC, USA,*,† Aaron D. Roberts, DO, CPT, MC, USA,*,† Justin M. Hire, MD, CPT, MC, USA,*,† and Terry L. Mueller, DO, LTC, MC, USA*,† *
Department of Orthopaedic Surgery, Dwight D. Eisenhower Army Medical Center, Fort Gordon, Georgia; and †Department of Clinical Investigation, Dwight D. Eisenhower Army Medical Center, Fort Gordon, Georgia OBJECTIVE: To determine the effect of instrumentation of suture material on knot security and tensile strength. STUDY DESIGN: In all, 5 types of suture material were
used; 10 knots were tied without any instrumentation and 10 knots were tied with a hemostat holding tension on the first throw while the second throw was made for each suture type. Each group was tested to failure with the maximum load and mode of failure recorded. The maximum load between groups of each suture type was compared; frequency of failure through knot slippage vs material fracture was also compared between groups. RESULTS: There was no significant difference observed in the maximum load to failure for any suture type between instrumented and noninstrumented groups. Additionally, there was no difference between any instrumented and noninstrumented groups for material failure vs failure due to knot slippage. CONCLUSIONS: Instrumentation of suture material dur-
ing two-hand tying does not affect the strength of suture material or knot security. ( J Surg Ed 73:162-165. Published by Elsevier Inc on behalf of the Association of Program Directors in Surgery) KEY WORDS: knot security, suture strength, suture
material COMPETENCIES: Patient Care, Medical Knowledge, Practice-Based Learning and Improvement
The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or reflecting the views of the Department of Defense or US Government. The authors are employees of the US government. This work was prepared as part of their official duties, and as such there is no copyright to be transferred. Correspondence: Inquiries to Peter C. Johnson, MD, Department of Orthopaedic Surgery, 300 East Hospital Road, Fort Gordon, GA 30905. Fax: þ(706) 787-2901; e-mail: [email protected]
162
INTRODUCTION Occasionally during surgery it is necessary to perform closures or repairs of structures that require an exceptionally tight repair for mechanical advantage and stability, or for postoperative wound care. Examples would include the repair of the short external rotators to the greater trochanter during closure of the Moore (posterior) approach to the hip, which must be tightly repaired for hip stability and function of the rotators, or tight closure of the lumbar fascia following posterior lumbar surgery to prevent wound drainage. In both of these examples, the sutures may need to be tied within a very deep surgical field owing to the involved anatomy and may be further complicated by the patient’s body habitus. While two-hand tying within a deep surgical field, it may be technically difficult to maintain the tension on the first throw of the suture material while performing the second throw to lock the knot in place. Some surgeons use a mosquito hemostat or other instrument to clamp the material and maintain the first throw’s tension while the second throw is being made. Other surgeons object to this practice, on the grounds that the instrumentation damages the suture material. This claim is anecdotal, however, and has not been subject to formal scientific investigation. Studies of suture strength and knot security have been relatively limited in literature in recent years despite the advent of new suture materials as well as previous demonstration of the significant effect of handling techniques on suture materials. Previous studies have examined the effect of surgical needle holders on various materials and found that compression from needle holders may significantly affect material strength in running closures.1 However, no study has investigated the effect of instrumentation on knot tying. Studies examining knot security have helped clarify the ideal number of throws, but they have not determined whether instrumentation has any additional effect on knot security. The intent of this study was to examine the effect
Journal of Surgical Education Published by Elsevier Inc on behalf of the 1931-7204/$30.00 Association of Program Directors in Surgery http://dx.doi.org/10.1016/j.jsurg.2015.08.011
FIGURE 1. (A) Detailed look of hemostat with metal grooves, which could abrade suture integrity during use. (B) Example of hemostat placement during two-hand tying technique.
of instrumentation with hemostats on knot security and strength of various suture materials.
MATERIALS AND METHODS This study was deemed exempt by the Dwight D. Eisenhower Army Medical Center Institutional Review Board. In all, 5 suture materials were tested (FiberWire, Arthrex, Inc., Naples, FL; Ethibond, Ethicon US, LLC, Cincinatti, OH; VICRYL, Ethicon US, LLC; Prolene, Ethicon US, LLC; and Monocryl, Ethicon US, LLC). In all, 20 total pieces of material had knots tied for each suture material tested; 10 pieces were tested for each suture type with a knot tied using a two-hand tie technique without any type of instrumentation to the suture material. All knots were tied by the principal investigator around the posts of a tying board; during knot tying, tension was maintained on the suture material manually by the principal investigator but was not formally measured. An additional 10 pieces of material had knots tied identically by the principal investigator, with the exception of a mosquito hemostat applied to the first throw to maintain the first throw while the second throw was made (Fig. 1). The hemostat was maximally closed with all 3 ratchet teeth engaged for each knot to control the amount of compression on the material, and no slippage of the first throw occurred after the hemostat was applied. Surgeon’s knots as described by Muffly et al.2 were applied using a double first throw with 5 total throws, which has been shown to be the minimum number of throws needed to ensure security.3,4 Tied loops were then tested to failure. Testing was conducted on an Instron E-10000 load tester (Instron, Norwood, MA), with the maximum load recorded. The maximum load was recorded in Newtons at either knot failure or slippage of the knot. Tensile testing was conducted on suture loops using the parameters described by Naleway et al.,5 with 60 mm of suture loop tested at a crosshead speed of
120 mm/min, or twice the working length of suture loop. This conforms to the USP standard for tensile strength testing. Mean maximum load was compared between instrumented and noninstrumented groups for each suture type using a two-tailed Student t-test with significance set at a p o 0.05. Additionally, the mode of failure, either knot slippage or suture breakage, was recorded. Contingency tables were made for each suture group comparing failure via material breakage vs failure via knot slippage. Fisher’s Exact test was
FIGURE 2. Suture loop being tested on Instron Machine.
Journal of Surgical Education Volume 73/Number 1 January/February 2016
163
TABLE. Mean Maximum Load Between Groups Suture Type
Mean Maximum Load at Failure (N) for Noninstrumented Suture ⫾ SD
2 FiberWire 2 Ethibond 0-Vicryl 2-0 Prolene 4-0 Monocryl
275.44 106.43 94.01 66.81 33.26
⫾ ⫾ ⫾ ⫾ ⫾
40.06 38.50 21.46 6.56 4.85
Mean Maximum Load at Failure (N) for Instrumented Suture ⫾ SD 251.35 115.36 97.96 63.35 31.80
⫾ ⫾ ⫾ ⫾ ⫾
61.91 38.36 9.80 11.72 5.08
p Value 0.307 0.678 0.616 0.31 0.473
SD, standard deviation.
used to examine difference with significance set at o0.05 for a two-tailed p-value. An example suture loop being tested on the Instron machine is shown in Figure 2.
RESULTS There was no statistically significant difference observed in mean maximum load between instrumented and noninstrumented groups for any suture material tested. Suture types, mean maximum load (N) ⫾ standard deviation, and calculated p-values are shown in Table 1. Mode of failure, either slippage of the knot or breakage of the material, was recorded for each piece of suture tested. All loops that failed via suture breakage failed just adjacent to the knot and not within the knot where the hemostat had been applied, meaning that no material failed at the site of instrumentation. No significant difference in mode of failure was found between instrumented vs noninstrumented suture groups for any material using Fisher’s Exact test.
CONCLUSION
ROLE OF FUNDING SOURCES
Our results support that there is no significant effect of instrumentation on tensile strength or knot security for the suture types tested. For each suture type tested, there was no significant difference in mean maximum load at failure, and there was no significant difference between number of loops that failed via knot slippage vs material breakage between noninstrumented and instrumented groups. To our knowledge this is the only study that has investigated the specific effect of instrumentation of the knot during tying on knot security and material strength. Naleway et al.5 examined the mechanical properties of various suture types as well as the effect of knotting the material on tensile strength. In addition to describing the mechanical performance of various newer suture materials under stress, they found that knotting the material significantly decreased the maximum tensile strength, which is in agreement with older studies.
164
Kim et al.6 examined the tensile properties and knot security of suture materials as well, with additional investigation of the effect of storage under a tensile load on absorbable sutures. In their study, nonabsorbable suture materials were tested for tensile strength at baseline, and then tested again after tying with propensity for knot slippage examined. Absorbable suture materials were initially tested for the maximum tensile strength, and then stored for varying times with a 100-g tensile load in Hank’s solution and had tensile properties reexamined. Their results showed an increased risk of knot slippage among nonabsorbable monofilament suture materials over braided, and a decrease in tensile strength over time under a tensile load for absorbable sutures. Our study supports that using a hemostat to maintain the tension of the first throw of a two-hand tied knot while the second throw is being made does not have a significant effect on the strength of the material or the propensity for knot slippage. Surgeons may use this technique to ensure quality knots without concern for adversely affecting knot or material performance.
Funding for the purchase of suture materials was provided by the Department of Clinical Investigation, Dwight D. Eisenhower Army Medical Center. DCI provided the funding with the intention of generating an article for publication, and provided facilities and equipment for data collection. DCI had no role in study design, or in data analysis or interpretation.
ACKNOWLEDGMENTS The authors would like to thank Mr. Royce Runner of the Department of Clinical Investigation, DDEAMC, for technical assistance with the Instron load tester and data collection. The authors would also like to thank Dr. Steven D. Zumbrun of the Department of Clinical Investigation, DDEAMC, for assistance with proofreading of the manuscript.
Journal of Surgical Education Volume 73/Number 1 January/February 2016
REFERENCES 1. Stamp CV, McGregor W, Rodeheaver GT, Thacker JG,
Towler MA, Edlich RF. Surgical needle holder damage to sutures. Am Surg. 1988;54(5):300-306. 2. Muffly TM, Kow N, Iqbal I, Barber MD. Minimum
number of throws needed for knot security. J Surg Educ. 2011;68(2):130-133. http://dx.doi.org/10.1016/j.jsurg. 2010.11.001. 3. Muffly TM, Boyce J, Kieweg SL, Bonham AJ. Tensile
strength of a surgeon’s or a square knot. J Surg Educ. 2010;67(4):222-226. http://dx.doi.org/10.1016/j.jsurg. 2010.06.007.
4. Tidwell JE, Kish VL, Samora JB. Knot security: how
many throws does it really take? Orthopedics. 2012; 35(4):532-537. http://dx.doi.org/10.3928/0147744720120327-16. 5. Naleway SE, Lear W, Kruzic JJ, Maughan CB. Mechan-
ical properties of suture materials in general and cutaneous surgery. J Biomed Mater Res Part B. 2015; 103(4):735-742. http://dx.doi.org/10.1002/jbm.b.33171. 6. Kim JC, Lee YK, Lim BS, Rhee SH, Yang HC.
Comparison of tensile and knot security properties of surgical sutures. J Mater Sci Mater Med. 2007; 18(12):2363-2369. http://dx.doi.org/10.1007/s10856007-3114-6.
Journal of Surgical Education Volume 73/Number 1 January/February 2016
165
