Knot Security: How Many Throws Does It Really Take?

Transcription

1 n Feture Article Knot Security: How Mny Does It Relly Tke? John E. Tidwell, MD; Vincent L. Kish, AS; Julie B. Smor, MD, PhD; Joseph Prud homme, MD strct Full rticle ville online t Helio.com/Orthopedics. Serch: The purpose of this study ws to determine the minimum numer of throws needed for knot security for squre knots using 5 common suture mterils nd 3 common sizes y in vitro single lod to filure iomechnicl testing. The hypothesis ws tht ech suture comintion studied would shre common minimum of t lest 5 throws to gurntee security. Five suture mterils (FierWire [Arthrex, Inc, Nples, Florid], Monosof, Surgipro, Mxon, nd Polysor [Covidien, Mnsfield, Msschusetts]) with vrying suture sizes (#5, #2, 0, 2-0, nd 4-0) were tied in vitro, vrying the numer of squre knot throws (3, 4, 5, nd 6). Twenty knots for ech comintion were stticlly loded to filure in tension; whether the knot filed y frcture or slippge nd the tensile strength t knot filure ws determined. For the tested mterils, t lest 5 flt squre throws should e used to confer knot security sed on inomil proportion score 95% confidence intervl (CI) 0.84 to 1.0 or t lest 4 throws for 95% CI of 0.76 to FierWire requires 6 flt squre throws per knot for security t either 95% CI level. Unless surgeon hs specific knowledge of experimentl evidence tht fewer throws re necessry for specific ppliction, the defult should e minimum of 4 throws, with 5 conferring dditionl security in most situtions, nd FierWire requiring 6 throws. Figure: A flt squre knot with 2 single-turn throws. Drs Tidwell nd Prud homme nd Mr Kish re from the Deprtment of Orthopedics, West Virgini University, Morgntown, West Virgini; nd Dr Smor is from the Deprtment of Orthopedics, The Ohio Stte University, Columus, Ohio. Drs Tidwell, Smor, nd Prud homme nd Mr Kish hve no relevnt finncil reltionships to disclose. This study received no externl funding. The FierWire suture ws donted y Arthrex, Inc, Nples, Florid. The uthors thnk Suznne Smith for her editing help. Correspondence should e ddressed to: John E. Tidwell, MD, Deprtment of Orthopedics, West Virgini University, PO Box 9196, Morgntown, WV (jtidwell@hsc.wvu.edu). doi: / e532 Helio.com The new online home of ORTHOPEDICS Helio.com/Orthopedics

2 Knot Security Tidwell et l Tying surgicl knots is criticl prt of ll surgicl procedures nd should e sic surgicl skill. The 3 modes of filure for surgicl knots re suture rupture, tissue rupture, nd knot filure. Of these, knot filure y slippge is the most controllle y surgeons, sed on the choice of suture mteril, size, nd knot configurtion nd, more importntly, the numer of throws in ech knot. Knot slippge is n underestimted cuse of knot filure nd loss of tissue pproximtion nd correltes positively with the numer of throws in knot. When pproximting tissue edges, whether skin, tendon, or muscle, the surgeon must lso lnce excess foreign mteril with knot security. 1 A throw refers to specific step or lyer used to crete knot, nd knot is composed of >2 throws in succession. 2 Knot security is defined s knot tht fils y suture frcture prior to untying y slippge. Becuse previous studies hve shown flt squre knots to hve superior knot chrcteristics, we chose to study them; they re nonidenticl, nonloose single turn throws in lternting directions. 3-5 A knot tht fils y slippge fils secondry to surgeon knot-tying technique, usully ecuse of too few knot throws. A knot tht fils y frcture fils secondry to choice of suture mteril or size, s determined y suture mechnicl properties. How mny throws should e used in squre knot to ensure tht ny filure is the result of suture mteril properties nd not the surgicl technique? No universl consensus exists for wht constitutes secure knot. Mny surgeons use commonly ccepted necdotl numer of throws tht vry etween surgeons nd trining progrms ut re not sed on complete scientific dt. Vrious studies hve identified the numer of throws required for 1 or 2 suture mterils. Typiclly these studies hve used 1 suture size nd knot configurtion, using single lod to filure tensile testing. These dt conflict, rnging etween 3 nd 5 Figure 1: A flt squre knot with 2 single-turn throws. throws. 2,3,6-12 No study hs presented evidence of squre knots with multiple suture sizes nd suture mterils. Ech suture hs different physicl properties tht dictte knot security, ut no known mgic numer of knots cross ll suture mterils nd sizes cn e tught to surgeons. The purpose of this study ws to determine the minimum numer of throws needed for knot security for squre knots using 5 common suture mterils nd 3 common sizes y in vitro single lod to filure iomechnicl testing. The hypothesis ws tht ech suture comintion studied would shre common minimum of t lest 5 throws to gurntee security. Bsed on prior experimenttion, FierWire (Arthrex, Inc, Nples, Florid) ws expected to require dditionl throws for knot security. 13 The study conditions represented est cse scenrio with dry suture, single lod to filure testing, nd no running suture configurtions. Mterils nd Methods Suture Mterils Five commonly used surgicl suture mterils were seprted into 2 groups. The nonsorle group included rided multifilmentous FierWire (polyester suture with long chin polyethylene core) nd the monofilments Surgipro (polypropylene) nd Monosof (nylon) (Covidien, Mnsfield, Msschusetts). The sorle group included the monofilment Mxon (polyglyconte) nd rided Polysor (glycolide/lctide) (Covidien). United Sttes Phrmcopei suture sizes 0, 2-0, nd 4-0 were used for mechnicl testing for 1 ll suture mterils, plus n dditionl 2 sizes (#2 nd #5) for FierWire. Ech of these ws donted from the locl operting room (purchsed from Syneture, Norwlk, Connecticut), except for FierWire (donted y Arthrex, Inc). Reproducile In Vitro Knot Tying All surgicl knot tying ws performed y n orthopedic surgicl resident (J.E.T.) with initil supervision from n ttending surgeon (J.P.). Severl dys were spent prcticing the hnd-tied knot technique for consistency prior to tying the knots to e tested. We used flt squre knot suture configurtion with n emphsis on qulity tht included only hnd-tied crossed-hnd technique for the cretion of every flt knot (Figure 1). A flt squre knot is knot where oth strnds enter nd leve the knot prllel to ech other, nd susequent throws re in the opposite direction. Using nottion descried y Dinsmore, 2 the knots were represented s 13131, , , nd for 3-, 4-, 5-, nd 6-throw single-turn knots, respectively. Initilly, pilot knots were visulized under microscope to ensure flt squre knots were eing produced. One knot group included 1 suture size/mteril comintion with specific numer of knots thrown, rnging from 3 to 6 knots. In totl, 48 comintions (4 knots34 sutures33 sizes) were studied, plus 20 comintions (4 knots35 sizes) for FierWire. Ech group consisted of 20 knots unless >2 of the first 6 filed, t which point tht group ws considered n overll filure. Ech knot in group ws tied sequentilly, ut overll group order ws rndomly chosen y picking 1 pck of suture out of g with 1 pck ech of ech size nd type. Ech group ws then tied to completion. Ech knot ws hnd tied round cm outside-dimeter polyvinyl chloride (PVC) pipe (Chrlotte Pipe Compny, Chrlotte, North Crolin), creting uniformly sized suture loops, with tils ll cut to 3 mm. APRIL 2012 Volume 35 Numer 4 e533

3 n Feture Article Mechnicl Testing Ech knot ws removed from the end of the PVC pipe for immedite mechnicl testing using the loop method s detiled y Dinsmore. 2 The suture loop ws plced round the 2 hooks of the hydrulic tensiometer (MTS 5 kip lod; Mteril Testing Systems, Minnepolis, Minnesot) with the suture knot ligned equidistnt from oth hooks. Ech knot ws preloded with pproximtely 1.5 N prior to testing, nd tensile strength ws tested t constnt strin rte of 5 mm/s. For ech knot test, rel-time video cmer (Solid Stte Cmer, model ; Cohu, Inc, Powy, Cliforni) with telescope lens (Edmund Scientifics, Tonwnd, New York) ws used for visuliztion of knot filure. The lod vs displcement dt were collected over time using Noteook Acquisition Softwre (LTech, Wilmington, Msschusetts), with which the force required for rupture could e computed (Figure 2). By crefully wtching the video in rel time for ech knot filure nd inspecting the roken suture knot, determintion of knot filure y slippge or frcture ws documented, s well s the loction of suture frcture on the loop, if pplicle. Ech test produced loop-holding cpcity ecuse the loop method ws used for tensile testing. The knot-holding cpcity ws defined s one-hlf the loop-holding cpcity. 2 Sttisticl Anlysis Sttisticl clcultions were performed using JMP Sttisticl Softwre (SAS Institute, Cry, North Crolin). Binomil proportion score 95% confidence intervls (CI) sed on inry results (slippge vs no slippge) were computed for n520 with 0 slips per group nd 1 slip per group. Results The primry outcome ws the numer of throws required to chieve sttisticlly significnt knot security. The vlues were clculted with 2 significnce levels nd confidence intervls (Tle 1), with rnges from 3 to 6 throws vrying y suture size Figure 2: Representtive plots of dt collection of lod versus displcement. Tle 1 Numer of Required for Knot Security t 2 Significnce Levels Suture Size Suture Mteril #2 #5 FierWire 6 (6) 6 (6) 6 (6) 6 (6) 6 (6) Surgipro c 3 (3) 4 (4) 4 (4) NP NP Monosof c 5 (4) 4 (4) 5 (4) NP NP Mxon c 4 (4) 5 (4) 3 (3) NP NP Polysor c 4 (4) 5 (4) 5 (4) NP NP Arevition: NP, not performed. Vlues re for 0 filures in 20 trils (95% inomil score confidence intervl [ ]). Vlues in prentheses re for <1 filure in 20 trils (95% inomil score confidence intervl [ ]). Arthrex, Inc, Nples, Florid. c Covidien, Mnsfield, Msschusetts. nd mteril. FierWire required the most throws: 6 t the no-filure significnce level. The knot-holding cpcities nd slippge rtes re shown from the lod displcement curves s secondry outcome, with results tht vried for squre knots sed on suture size nd mteril, s well s numer of throws (Tles 2-6). The knot-holding cpcities were consistent with previously pulished dt, where comprle dt were ville. 4,9,11-13 The knot-holding cpcity for ech group incresed significntly with dditionl flt squre throws until knot security ws reched. Additionl knots fforded smll increses in knot-holding cpcity. Microscopic video llowed complete visuliztion of ech knot filure. Every knot tht strted to slip ws noted to completely fil y slippge nd knot frcture. Nerly every knot frcture took plce immeditely djcent to the knot. Discussion The knot-tying methods were performed under est cse scenrio to 2 e534 Helio.com The new online home of ORTHOPEDICS Helio.com/Orthopedics

4 Knot Security Tidwell et l provide dt for minimum level of knot security for sorle, nonsorle, monofilment, nd rided suture. This includes in vitro experimenttion performed on dry sutures hnd tied in interrupted squre knot configurtions tested Tle 5 Mxon Squre Knot Slippge Rte nd Knot Holding Cpcity Suture Size (15.5) 83.3 (22.0) 0.0 (66.7) (17.7) 5.0 (47.8) 0.0 (72.6) (18.4) 0.0 (48.8) 0.0 (74.8) (18.1) 0.0 (57.3) 0.0 (79.2) Covidien, Mnsfield, Msschusetts. Dt expressed s knot slippge rte, % (knot holding cpcity, N). Tle 2 with single lod to filure. These knots were lso tied without the time pressures of the operting room environment, ensuring flt squre knots creted with equl tension on oth sides of the knot. Although knot-tying speed nd force FierWire Squre Knot Slippge Rte nd Knot Holding Cpcity Suture Size #2 # (6.2) (21.2) (19.1) (44.7) (100.1) (12.9) (46.6) (39.0) (95.3) (155.0) (19.8) (60.2) 35.0 (68.3) 10.0 (68.5) 25.0 (278.8) (22.5) 0.0 (71.7) 0.0 (76.3) 0.0 (158.0) 0.0 (306.0) Arthrex, Inc, Nples, Florid. Dt expressed s knot slippge rte, % (knot holding cpcity, N). Tle 3 Monosof Squre Knot Slippge Rte nd Knot Holding Cpcity Suture Size (7.1) 83.3 (14.0) 67.7 (29.8) (12.2) 0.0 (24.5) 5.0 (41.8) (12.3) 5.0 (23.6) 0.0 (43.8) (16.5) 0.0 (22.9) 0.0 (45.4) Covidien, Mnsfield, Msschusetts. Dt expressed s knot slippge rte, % (knot holding cpcity, N). Tle 4 Surgipro Squre Knot Slippge Rte nd Knot Holding Cpcity Suture Size (10.9) 33.3 (22.2) 33.3 (33.8) (11.3) 0.0 (28.5) 0.0 (39.2) (10.8) 0.0 (29.3) 0.0 (39.4) (10.5) 0.0 (29.2) 0.0 (41.3) Covidien, Mnsfield, Msschusetts. Dt expressed s knot slippge rte, % (knot holding cpcity, N). Tle 6 Polysor Squre Knot Slippge Rte nd Knot Holding Cpcity Suture Size (16.0) (31.8) 83.3 (52.5) (17.1) 5.0 (49.5) 10.0 (68.7) (17.6) 0.0 (52.0) 0.0 (68.8) (17.9) 0.0 (52.1) 0.0 (67.7) Covidien, Mnsfield, Msschusetts. Dt expressed s knot slippge rte, % (knot holding cpcity, N). cn ffect knot security, 1 these prmeters were not investigted in our study ecuse this informtion is not known while pproximting wounds cliniclly, nd it would drmticlly complicte the study design. However, the knot testing displcement ws set t 5 mm per minute to llow for ccurte knot filure video visuliztion; this ws slower thn most other studies, which rnged from 25 to 50 mm per minute. 2 The effects of slower distrction rtes, if ny, would e to produce more slippge thn fster distrction rtes, 2 strengthening these results. Other ptient fctors not considered in this est cse scenrio include tissue condition (eg, ischemi, inflmmtion) nd the ptient s generl helth s it pplies to wound heling. In ddition, Ter nd Aerg 14 reported tht in vivo knots were more likely to slip compred with those in dry environment, wheres Rodehever et l 15 reported tht in vivo conditions increse knot security. In generl, no good knot testing model hs een developed to study the in vivo effects of the wound nd serum on surgicl knots. A summtion of previously reported dt from the current literture is shown in Tle 7. The current literture provides no comprehensive detils for ll suture mterils nd sizes for squre knots. Although these dt contin some dt similr to ours, the overll picture is not complete in ny 1 prticulr experiment. It ws hypothesized tht knot security would e independent from suture mteril nd size. No trend exists towrd incresed se- APRIL 2012 Volume 35 Numer 4 e535

5 n Feture Article Author curity with suture dimeter differences or etween mterils, with the exception of FierWire, which required 6 throws. Confirming prior study results, incresing knot-holding cpcity ws oserved with incresing suture dimeter, nd incresing numer of knot throws conferred incresing knot security nd knot-holding cpcity. The knot-holding cpcity does not increse significntly with dditionl throws dded to knots tht re deemed secure. Moreover, it ws lso hypothesized (sed on clinicl experience) tht t lest 5 throws per knot would e needed to confer security for ll suture mterils. The results of this question re presented in Tle 1 t 2 significnce levels, depending on the desired security level of the surgeon. These vlues vried for ll suture mterils nd sizes studied nd, ccepting slippge rte of 1 of 20 knot filures y slippge, we concluded tht for ll suture comintions (except FierWire), minimum of 4 throws should e plced for squre knots. Accepting 0 of 20 knot slippges (except FierWire), 7 of 12 knots would e sfe with t lest 4 throws, nd the other 5 of 12 would require minimum of 5 throws. In ddition, no significnt differences were detected etween sorle nd nonsorle sutures or etween rided nd monofilment, except the extr requirements for FierWire. Polysor 4-0 nd Monosof 2-0 testing resulted in n increse in knot slippge t the 5-throw level, from 0% to 5%, with reversion to 0% slippge rte t the 6-throw level. With every knot, the possiility exists of poor technique or mechnicl differences in suture technique. Given 0% slippge rte t the 4-throw level nd results within the other suture sizes of tht type of suture, poor technique or mechnicl differences could hve een responsile for these results. For finl results, the 4-throw significnce level ws used. FierWire is 1 suture type in reltively new clss of rided high-performnce polylend polyethylene suture mterils. With stronger mechnicl properties nd noted resistnce to frying ginst metl, 13 this suture hs n ppliction in tendon repir nd s fixtion for soft tissue to one nchors. Wüst et l 13 reported tht this clss of suture mteril, including FierWire, required 2 dditionl throws for knot security thn more conventionl sutures nd up to 6 throws in single lod to filure testing with #2 FierWire. Our study confirms these results with higher CIs, with defined testing protocol nd extension to ll FierWire suture sizes (#5, #2, 0, 2-0 nd 4-0). A more recent study y Ilhi et l 5 reported tht polylend sutures require 5 flt squre knots for security; however, their testing ws performed using cyclic loding to filure. One limittion of our study ws tht direct extrpoltion of these dt to other knot types ws not possile. However, s Tle 7 Previously Reported Numers of for Knot Security for Squre Knots Suture Mteril Filure Limits Suture Size Brown 9 Nylon 0/ Polyglctin 3 Polyglyconte 3 Rosin & Roinson 8 Nylon 0/ Polyglctin 3 Polyglycolic cid 3 Vn Rijssel et l 11 Polyglyconte 0/10 3-0, 0 4 Polyglycolic cid 3 Trimos 12 Polyglctin 0/ Polyglycolic cid 3 Tril et l 7 Nylon 0/ Polyglycolic cid 3 Polyglyconte 3 Annunzit et l 16 Nylon 0/ previously shown, squre knots provide the most relile knot security for knots tht re otherwise equl. Therefore, for other common knot types (surgeon s knots nd sliding knots), more throws should e required. An dditionl study limittion ws tht the numer of knots tht would e required to improve sttisticl significnce is not fesile. During our study, 20 knots were tied for ech suture comintion, wheres t lest 80 knots with no knot slippge would e needed to crete lower ound 95% CI sed on inomil distriution of Another issue not ddressed in n ex vivo study is the clinicl effect of the ulk of the suture knot. Depending on the loction of the suture in the ody, this my hve potentil mechnicl effects t tht site or on wound heling. Future investigtion is wrrnted to study the in vivo effects on knot security e536 Helio.com The new online home of ORTHOPEDICS Helio.com/Orthopedics

6 Knot Security Tidwell et l ecuse mny suture studies hve hd this limittion. Squre knots tied t the end of running suture should lso e investigted in similr fshion ecuse this is nother common technique of wound closure. Conclusion This study serves s reminder tht our surgicl knots re perhps not s secure s we ssume, especilly when sutured edges re under tension. This study is ment to provide specific minimum numer of throws per knot for knot security. Regrding high-tensile-strength requirements, FierWire requires dditionl throws for security. Medicl trining progrms should use these dt when teching students nd residents out throw requirements for knot security. References 1. Im JN, Kim JK, Kim HK, Lee KY, Prk WH. Effect of tying conditions on the knot security of suture mterils. J App Polymer Sci. 2008; 109(2): Dinsmore RC. Understnding surgicl knot security: proposl to stndrdize the literture. J Am Coll Surg. 1995; 180(6): Lee AC, Fhmy RR, Hnn GB. Ojective evidence for optimum knot configurtion. World J Surg. 2008; 32(12): Schuert DC, Unger JB, Mukherjee D, Perrone JF. Mechnicl performnce of knots using rided nd monofilment sorle sutures. Am J Ostet Gynecol. 2002; 187(6): Ilhi OA, Youns SA, Ho DM, Nole PC. Security of knots tied with ethiond, fierwire, orthocord, or ultrrid [pulished online hed of print Septemer 30, 2008]. Am J Sports Med. 2008; 36(12): Fong ED, Brtlett AS, Mlk S, Anderson IA. Tensile strength of surgicl knots in dominl wound closure. ANZ J Surg. 2008; 78(3): Tril IA, Powell ES, Nole J. An evlution of suture mterils used in tendon surgery. J Hnd Surg Br. 1989; 14(4): Rosin E, Roinson GM. Knot security of suture mterils. Vet Surg. 1989; 18(4): Brown RP. Knotting technique nd suture mterils. Br J Surg. 1992; 79(5): Ivy JJ, Unger JB, Hurt J, Mukherjee D. The effect of numer of throws on knot security with nonidenticl sliding knots. Am J Ostet Gynecol. 2004; 191(5): Vn Rijssel EJ, Trimos JB, Booster MH. Mechnicl performnce of squre knots nd sliding knots in surgery: comprtive study. Am J Ostet Gynecol. 1990; 162(1): Trimos JB. Security of vrious knots commonly used in surgicl prctice. Ostet Gynecol. 1984; 64(2): Wüst DM, Jeyer DC, Fvre P, Gerer C. Mechnicl nd hndling properties of rided polylend polyethylene sutures in comprison to rided polyester nd monofilment polydioxnone sutures. Arthroscopy. 2006; 22(11): Ter H, Aerg C. Strength of knots in surgery in reltion to type of knot, type of suture mteril nd dimension of suture thred. Act Chir Scnd. 1977; 143(2): Rodehever GT, Beltr KA, Green CW, et l. Biomechnicl nd clinicl performnce of new synthetic monofilment sorle suture. J Long Term Eff Med Implnts. 1996; 6(3-4): Annunzit CC, Drke DB, Woods JA, Ger AJ, Rodehever GT, Edlich RF. Technicl considertion in knot construction. Prt 1. Continuous percutneous nd derml suture closure. J Emerg Med. 1997; 15(3): APRIL 2012 Volume 35 Numer 4 e537