- Email: [email protected]
Heat Treatment of Arthroscopic Knots and Its Effect on Knot Security
Heat Treatment of Arthroscopic Knots and Its Effect on Knot Security Derfel Pari Williams, M.B.Ch.B.(Hons), M.R.C.S., Peter J. Hughes, F.R.C.S.(Tr&Orth), Anthony C. Fisher, M.Sc., Ph.D., C.Eng., and Patrick Doherty, Ph.D.
Purpose: The purpose of this study was to investigate heat application to arthroscopic knots as a method of improving knot security. Methods: Heat treatment was assessed on 4 suture materials— Ethibond (Ethicon, Somerville, NJ), PDS (Ethicon), Orthocord (DePuy Mitek, Raynham, MA), and FiberWire (Arthrex, Naples, FL)—tied by use of the Duncan loop, compared with untreated controls. A hand-tied surgeon’s knot with Ethibond was included as the gold standard. Knots were tied around a plastic rod immersed in a saline solution–filled water bath at 37°C, with heat treatment performed by use of the Mitek VAPR 3 electrosurgical unit and VAPR S90 electrode (DePuy Mitek), applied directly to the knot body. Loops were subjected to a 5-N preload, followed by loading to clinical failure (⬎3 mm of displacement) and ultimate (breaking) failure by use of a tensile tester. Results: Load to ultimate failure was significantly higher in the FiberWire 1-second heat treatment arm (26.0% increase, 234.25 ⫾ 62.34 N, P ⬍ .03), Orthocord 1-second heat treatment arm (55.6% increase, 204.72 ⫾ 78.47 N, P ⬍ .03), and Orthocord 5-second heat treatment arm (69.2% increase, 222.58 ⫾ 56.57 N, P ⬍ .001) than in controls. Load to clinical failure was significantly higher in the Orthocord 10-second heat treatment arm (34.7% increase, 78.58 ⫾ 13.88 N, P ⬍ .0001) when compared with controls. The FiberWire 5- and 10-second heat treatment arms showed lower load to clinical and ultimate failure (P ⬍ .001). Ethibond, Orthocord, and FiberWire showed higher load to clinical failure than PDS (P ⬍ .0001). Ethibond and Orthocord knots were more likely to fail through knot slippage after heat treatment compared with controls (P ⬍ .01). Conclusions: Heat treatment resulted in greater knot security when combined with Orthocord and FiberWire suture materials. Heat-treated Ethibond and Orthocord knots were more likely to fail through suture breakage than knot slippage. Clinical Relevance: This study presents a simple and novel technique of improving knot security in the arthroscopic repair. The effects of heat were extremely well tolerated in the Orthocord and FiberWire groups, making this technique particularly suitable for clinical use. Key Words: Knot security—Arthroscopy—Heat treatment—Suture—Welding.
A
strong and secure knot is an essential component of any soft-tissue repair, providing soft-tissue apposition required for healing and a good functional
From the Orthopaedic Department, Lancashire Teaching Hospitals NHS Foundation Trust (D.P.W., P.J.H.), Preston; Department of Clinical Engineering, Royal Liverpool University Hospital (A.C.F.), Liverpool; and Department of Clinical Engineering, University of Liverpool (P.D.), Liverpool, England. The authors report no conflict of interest. Address correspondence and reprints requests to Derfel Pari Williams, M.B.Ch.B.(Hons), 54 Dudley Rd, Mossley Hill, Liverpool, Merseyside L18 1ET, England. E-mail: [email protected] © 2008 by the Arthroscopy Association of North America 0749-8063/08/2401-7256$34.00/0 doi:10.1016/j.arthro.2007.10.005
outcome. Arthroscopic surgery, however, presents additional difficulties compared with an open procedure, and knot-tying techniques must be adapted. This difference has necessitated several modifications to the knot configurations,1-14 suture materials,14-17 and instrumentation18,19 used for arthroscopic knots, all with the aim of achieving optimal knot security. However, the arthroscopic knot remains technically more demanding than its hand-tied counterpart, and it is technically difficult to produce an equivalently secure arthroscopic knot.3,7,17 Further improvements in knot security are therefore continually sought to achieve a strong and reliable repair. Heat welding of fibers is an established technique in
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 24, No 1 (January), 2008: pp 7-13
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D. P. WILLIAMS ET AL.
the textile industry. More recently, in the surgical field, ultrasonic energy has been used to weld suture ends together, completely eliminating the knot.20,21 However, there are currently very few data on the application of heat treatment to traditionally tied knots, as well as its role in improving knot security. Previous studies included the use of an electrocautery knife to cut suture ends, forming an enlarged knot ear and thus preventing knot slippage.22,23 Improvements in knot security have also been shown after heat treatment with a carbon dioxide laser.24 Although these studies have shown improved knot security, the techniques have limited application in the clinical setting of an arthroscopic surgeon. There are currently no published data, to our knowledge, on the role of heat application in improving arthroscopic knot security. We hypothesized that heat treatment of arthroscopic knots would result in increased knot security through welding of individual suture strands and, thus, prevent slipping of the knot. The purpose of this study was to evaluate the effect of heat treatment on security of the arthroscopic knot. METHODS Four suture materials commonly used in arthroscopic shoulder surgery were investigated in this study: No. 2 Ethibond (Ethicon, Somerville, NJ); No. 2 PDS (Ethicon); No. 2 Orthocord (DePuy Mitek, Raynham, MA); and No. 2 FiberWire (Arthrex, Naples, FL). Knots were tied by use of the senior surgeon’s preferred knot configuration, the Duncan loop followed by 3 alternating half-hitches.15 An additional group in which Ethibond was hand-tied by use of a standard surgeon’s knot was included as the gold standard, with an initial double-overhand throw followed by 2 single-overhand throws. The senior surgeon, using an arthroscopic knot pusher, tied all knots around a plastic rod immersed in a saline solution– filled water bath at 37°C. Ten knots were tied per group, making a total of 120 knots, with untreated control and treatment arms in each suture group. Heat application was performed with the Mitek VAPR 3 electrosurgical unit and a corresponding VAPR S90 electrode (DePuy Mitek). All heat treatment was undertaken within the saline solution–filled water bath, by use of the vaporization setting at a power of 240 W. Because we were not aware of any previous studies evaluating heat tolerance of suture materials, we initially assessed the suture burn-through time for each material to determine the most appropriate heat treat-
FIGURE 1.
Heat application to knot body using side electrode.
ment period. For each material under investigation, suture loops were tied with a standard hand-tied surgeon’s knot between 2 rods within the water bath. The electrode was placed in direct contact with a single suture strand at the midportion of the loop. To maintain constant contact with the electrode, this part of the loop was placed under a small amount of tension, by lifting the electrode onto the suture strand. The time to complete division of the suture strand was taken as the burn-through time. This was repeated 10 times for each material under investigation (total of 40 loops). Heat application to the arthroscopic knot was performed by direct application of the electrode to the knot body (Fig 1). All treatment groups were subjected to 1 second of heat application. Given the higher heat tolerance of Orthocord and FiberWire (determined from burn-through testing), these groups were also subjected to 5 and 10 seconds of heat treatment. After heat treatment, all knots were subjected to tensile testing to assess knot security by use of a Nene tensile tester (Nene Instruments, Wellingborough, England) (Fig 2). All knots were initially subjected to a 5-N preload to take up any slack in the knot, with all measurements zeroed at this point for reference. They were then subjected to load, at a displacement rate of 0.3 mm/s, to clinical failure (⬎3 mm of displacement) and load to ultimate failure (knot or suture failure). At the point of ultimate failure, the mode of failure was recorded as knot slippage or suture breakage. To further assess the changes after heat treatment, a sample of control and heat-treated knots were also subjected to scanning electron microscopy analysis.
HEAT TREATMENT OF ARTHROSCOPIC KNOTS
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Load to Clinical Failure The Orthocord 10-second heat treatment group showed a 34.7% increase in load to clinical failure (78.58 ⫾ 13.88 N) compared with controls (58.35 ⫾ 14.87 N), and its load to clinical failure was significantly higher than that in all other Orthocord, Ethibond, and PDS groups (P ⬍ .0001). The highest load at clinical failure was observed in the FiberWire 1-second heat treatment arm (142.65 ⫾ 23.84 N). Although this was significantly higher than that in all other suture groups (P ⬍ .0001), there was no statistically significant difference between control and treatment arms in this group. Loss of knot security was seen in the FiberWire 5-second treatment arm (64.23 ⫾ 39.51 N) and 10-second treatment arm (86.98 ⫾ 40.21 N) (P ⬍ .001). It was also noted that both the PDS control and treatment arms reached clinical failure at a significantly lower load than all other suture materials (P ⬍ .0001). No statistical differences were seen between control and treatment arms for PDS or Ethibond or between the Orthocord control and 1- and 5-second groups (Table 1 and Fig 3). Load to Ultimate Failure FIGURE 2.
Tensile testing of arthroscopic knots.
Statistical analysis was undertaken with the XLSTAT statistical application (Addinsoft, Paris, France). Loads to failure were analyzed via analysis of variance and the Fisher test of least significant difference. The mode of failure was analyzed by use of the 2 test.
RESULTS Suture Burn-Through Time FiberWire showed superior heat tolerance to all other suture materials (83.30 ⫾ 38.69 seconds, P ⬍ .0001). Orthocord showed significantly higher heat tolerance (38.96 ⫾ 12.64 seconds, P ⬍ .0001) in comparison to both Ethibond (0.93 ⫾ 0.06 seconds) and PDS (1.61 ⫾ 0.25 seconds). Although both Ethibond and PDS tolerated heat poorly on single-strand burn-through testing, heat tolerance was improved when applied to the knot body, with none of the main study knots subsequently tested disintegrating after 1 second of heat treatment.
Heat treatment in the Orthocord group resulted in a statistically significant increase in load to ultimate failure in the 1- and 5-second treatment arms. There was a 55.6% increase in the 1-second group (204.72 ⫾ 78.47 N, P ⬍ .03) and a 69.2% increase in the 5-second group (222.58 ⫾ 56.57 N, P ⬍ .001) compared with controls (131.57 ⫾ 52.41 N). In the Orthocord 10-second group, load to ultimate failure (154.89 ⫾ 49.37 N) was increased in comparison to the control group but did not reach statistical significance (P ⫽ .071). FiberWire showed a 26.0% increase in load to ultimate failure after 1 second of heat treatment (234.25 ⫾ 62.34 N) in comparison to the control group (185.91 ⫾ 57.18 N) (P ⬍ .03). However, load to ultimate failure in the 5-second treatment arm (79.77 ⫾ 68.71 N) and 10-second treatment arm (107.95 ⫾ 55.16 N) was significantly inferior to controls (P ⬍ .001). No significant difference was seen between control and treatment arms in the Ethibond or PDS groups (Table 1 and Fig 3). Mode of Failure Comparison of the mode of failure between the control and treatment groups revealed that both Orthocord and Ethibond loops were more likely to fail
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D. P. WILLIAMS ET AL. TABLE 1.
Suture Material PDS Ethibond Orthocord
FiberWire
Ethibond (hand-tied)
Results of Load to Clinical and Ultimate Failure of Arthroscopic Knots Treatment
Load to Clinical Failure ⫾ SD (N)
Load to Ultimate failure ⫾ SD (N)
Control 1s Control 1s Control 1s 5s 10s Control 1s 5s 10s Control 1s
31.43 ⫾ 1.90〫 31.05 ⫾ 1.61〫 53.43 ⫾ 8.47 56.18 ⫾ 5.91 58.35 ⫾ 14.87 53.02 ⫾ 4.27 53.96 ⫾ 4.74 78.58 ⫾ 13.88* 132.00 ⫾ 13.35 142.65 ⫾ 23.84 64.23 ⫾ 39.51‡ 86.98 ⫾ 40.21‡ 51.74 ⫾ 1.19 50.04 ⫾ 7.22
130.40 ⫾ 38.20 123.65 ⫾ 20.14 123.76 ⫾ 45.21 118.33 ⫾ 35.37 131.57 ⫾ 52.41 204.72 ⫾ 78.47† 222.58 ⫾ 56.57§ 154.89 ⫾ 49.37 185.91 ⫾ 57.18 234.25 ⫾ 62.34⬁ 79.77 ⫾ 68.71‡ 107.95 ⫾ 55.16‡ 121.68 ⫾ 26.54 107.33 ⫾ 33.82
Load to clinical failure: *p⬍0.0001 compared with all other control and treatment groups (except FiberWire) 〫p⬍0.001 compared with all other suture groups ‡p⬍0.001 compared to control Load to ultimate failure: §p⬍0.001 compared with all other control and treatment groups (except FiberWire) †p⬍0.03 compared with all other control and treatment groups (except Orthocord 5s, and FiberWire) ⬁p⬍0.03 compared to all groups (except Orthocord 1s and 5s) ‡p⬍0.001 compared to control
Load to Clinical Failure Load to Ultimate failure 200
*
*
*
* p<0.05
150
* 100
* 50
PDS
Fibrewire
1s
Control
10s
5s
1s
Control
5s
Orthocord
10s
1s
1s
Ethibond
Control
Control
0 1s
Heat application to suture materials is not an entirely new concept. Early studies on heat treatment involved cutting suture ends with an electrocautery knife.22,23 This resulted in formation of an amorphous globular mass at the suture ends, which then lodged in the knot, preventing further slippage. This technique produced 2-throw knots with a breaking strength and knot slippage rate similar to 4-throw control knots23 and, in 1 case, an increase in knot-breaking strength of 8.6% after heat treatment.22 Gupta et al.24 investigated the role of a carbon dioxide laser as a method of treating suture materials. When applied to 2-throw square knots, a 16% increase in knot security was obtained. They also noted that knot slippage did not occur in these treated groups, suggesting that a
250
Control
DISCUSSION
weak bond had formed between the suture strands within the knot. The study concluded that heat welding of sutures was possible but that the bond formed was brittle and weaker than a standard surgical knot.
Load (N)
through suture breakage after heat treatment (P ⬍ .03) (Table 2). This effect was particularly evident in the Orthocord group, which showed an increasing progression toward suture breakage with increased heat treatment (Fig 4). In most cases suture failure occurred at the junction between the suture loop and the knot body. The mode of failure remained unchanged in the PDS, FiberWire, and hand-tied Ethibond groups after heat treatment.
Ethibond (hand tied)
FIGURE 3. Mean load to clinical and ultimate failure of control and heat-treated knots. Increased load to clinical failure was seen in the Orthocord 10-second heat treatment group. Load to ultimate failure was increased in the Orthocord 1- and 5-second heat treatment groups and the FiberWire 1-second heat treatment group. The FiberWire 5- and 10-second treatment groups failed at a significantly lower load.
HEAT TREATMENT OF ARTHROSCOPIC KNOTS TABLE 2. Suture Material PDS Ethibond Orthocord
FiberWire
Ethibond (hand-tied)
Mode of Failure of Knots Treatment
Knot Slippage
Suture Breakage
Control 1s Control 1s Control 1s 5s 10s Control 1s 5s 10s Control 1s
2 0 4 0 10 7 1 1 9 10 10 10 3 3
8 10 6 10 0 3 9 9 1 0 0 0 7 7
We chose to evaluate PDS and Ethibond as part of this study because of their differing characteristics and their established use in arthroscopic surgery. In addition, we investigated the effects on Orthocord and FiberWire, which are composite suture materials, consisting of an outer sleeve and an inner core, providing superior strength properties. We hypothesized that these might react in a different way to standard suture materials. Orthocord is, however, a relatively new material, and as such, there are very few published data regarding its clinical use.18,25-27 Load to clinical failure has previously been defined as loop elongation greater than 3 mm, representing the point at which the soft tissue is no longer apposed, and the repair is more likely to fail.15 Increasing the point of clinical failure therefore has important implications in any soft-tissue repair. This outcome was only significantly increased in the Orthocord 10-second heat treatment arm. Analysis of load to ultimate failure showed that heat treatment resulted in improved knot security when both Orthocord and FiberWire were used. On closer evaluation of the Orthocord group, a clear progression in the response to heat is seen, with the greatest overall improvement in the 5- and 10second treatment groups (Fig 3). The pattern seen with Orthocord suggests that the optimum period of heat treatment for this material may lie somewhere between 5 and 10 seconds. FiberWire knots, on the other hand, were compromised after both 5 and 10 seconds of heat treatment, and the optimum period is likely to be much shorter. We hypothesized that because of its monofilament nature, PDS would potentially show a greater response to heat welding. However, no significant dif-
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ference was seen after heat treatment of PDS. It also exhibited a very low tolerance to heat on single-strand burn-through testing and was significantly inferior on loading to clinical failure. This is in keeping with previous work, which has shown PDS to be an inferior suture material for arthroscopic repair.15-17 Although no significant increases were seen in the PDS or Ethibond groups after heat treatment, our work has shown that even for those materials with an apparently low tolerance to heat, knot security is not compromised by local heat application. Interestingly, our gold-standard hand-tied Ethibond knots were shown to be no more secure than the arthroscopically tied Duncan loop. This may reflect the fact that this is the preferred knot of the senior surgeon, which resulted in consistently secure knots. Assessment of the mode of failure showed that both Ethibond and Orthocord heat-treated arthroscopic knots were more likely to fail through suture breakage rather than knot slippage. This suggests that heat treatment has a direct effect on the knot body preventing slippage. We hypothesize that this may occur by 2 possible means. Heat treatment may have a direct welding effect on the suture material by fusing individual strands together, as seen in the work of Gupta et al.24 Increased roughness of the suture surface may also reduce slippage of suture strands within the knot. Microscopic comparison of control and heat-treated knots clearly shows that individual fibers of the outer layer appear to have fused together after heat treatment, with increased surface roughness, which would support this theory (Fig 5). In the case of Orthocord, we also propose a second possible hypothesis. Given the composite nature of Orthocord, it is possible that heat treatment may result in contraction of the inner
Knot Slippage Suture Breakage 12 10 8 6 4 2 0 Ethibond Control
Ethibond 1s
Orthocord Control
Orthocord 1s Orthocord 5s
Orthocord 10s
Suture
FIGURE 4. Mode of failure of Ethibond and Orthocord control and heat-treated knots after tensile testing. Both groups showed progression to decreased knot slippage after heat treatment (P ⬍ .03).
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D. P. WILLIAMS ET AL. the optimum conditions. Further work is required to assess different suture materials, knot configurations, and vaporization settings and to determine the optimum period of heat application required for each suture material. This is not an in vivo study, and therefore the results may not be reflective of the clinical reality. Consideration of possible damage to adjacent tissues and its effect on the repair would also be required with use in the clinical setting. However, we believe that there is significant potential to further develop this technique into a useful and safe method of improving knot security by use of standard arthroscopic instruments.
FIGURE 5. Electron microscopy analysis of Orthocord knots after 1 second of heat treatment (original magnification ⫻150). The surface of the suture appears roughened after heat treatment, which may reduce the amount of slippage at the knot through increased friction between strands.
strand, causing tightening of the knot and subsequent improvement in knot security. This, however, has not been directly evaluated by this study, and further work would be required to substantiate this theory. No significant changes were seen in the mode of failure in the hand-tied Ethibond groups. This may reflect the smaller size of the surgeon’s knot in comparison to the Duncan loop. As a result, there will be fewer suture strands in contact at the knot body. Our initial assessment of suture material heat tolerance showed that both FiberWire and Orthocord were very tolerant to heat on burn-through testing (83.30 ⫾ 38.69 seconds and 38.96 ⫾ 12.64 seconds, respectively). This finding in itself is extremely relevant to every arthroscopic surgeon. On completion of an arthroscopic repair, the surgeon must always be extremely cautious with further use of electrocautery, for fear of damaging the suture material and compromising the soft-tissue repair. Combined with the results of loading to failure, we can conclude that a short burst of soft-tissue vaporization after completing a repair is unlikely to have a detrimental effect on the suture material. The surgeon can therefore confidently use electrocautery without the risk of damaging the repair when using Orthocord or FiberWire. However, on the basis of our results, care should be exercised if one is using further electrocautery after repair with PDS or Ethibond. Although this study has shown the described technique to be an effective and simple method of improving knot security, we have not established
CONCLUSIONS This study has shown that direct heat application to the knot body results in increased load to failure of both Orthocord and FiberWire arthroscopic knots. Ethibond and Orthocord heat-treated knots were also less likely to fail from knot slippage. In addition to the increased knot security obtained through heat treatment, we have also shown that both Orthocord and FiberWire have an extremely high tolerance to heat (compared with PDS and Ethibond), making them particularly suitable for heat treatment. This technique offers a simple yet effective way of applying heat by use of standard arthroscopic instruments. Acknowledgment: The authors are grateful to DePuy Mitek for providing the suture materials used in this study.
REFERENCES 1. Kim SH, Ha KI, Kim, SH, Kim JS. Significance of the internal locking mechanism for loop security enhancement in the arthroscopic knot. Arthroscopy 2001;17:850-855. 2. Kim SH, Ha KI. The SMC knot—A new slip knot with locking mechanism. Arthroscopy 2000;16:563-565. 3. Lo IKY, Burkhart SS, Chan C, Athanasiou K. Arthroscopic knots: Determining the optimal balance of loop security and knot security. Arthroscopy 2004;20:489-502. 4. Hahi OA, Younas SA, Alexander J, Noble PC. Cyclic testing of arthroscopic knot security. Arthroscopy 2004;20:62-68. 5. Kim SH, Yoo JC, Wang JH, Choi KW, Bae TS, Lee CY. Arthroscopic sliding knot: How many additional half-hitches are really needed. Arthroscopy 2005;21:405-411. 6. Elkousy HA, Sekiya JK, Stabile KJ, McMahon PJ. A biomechanical comparison of arthroscopic sliding and sliding-locking knots. Arthroscopy 2005;21:204-210. 7. Mishra DK, Cannon D, Lucas DJ, Belzer JP. Elongation of arthroscopically tied knots. Am J Sports Med 1997;25:113117. 8. Burkhart SS, Wirth MA, Simonich M, Salem D, Lanctot D, Athanasiou K. Knot security in simple sliding knots and its relationship to rotator cuff repair: How secure must the knot be? Arthroscopy 2000;16:202-207.
HEAT TREATMENT OF ARTHROSCOPIC KNOTS 9. Nottage WM, Lieurance RK. Arthroscopic knot tying techniques. Arthroscopy 1999;15:515-521. 10. Mochizuki Y, Hachisuka H, Natsu K, Kashiwagi K, Yasunaga Y, Ochi M. The HU knot: A new sliding knot for arthroscopic surgery. Arthroscopy 2005;21:1014.e1-1014.e3. Available online at www.arthroscopyjournal.org. 11. Hassinger SM, Wongworawat MD, Hechanova JW. Biomechanical characteristics of 10 arthroscopic knots. Arthroscopy 2006;22:827-832. 12. Elkousy H, Hasmmerman SM, Edwards B, et al. The arthroscopic square knot: A biomechanical comparison with open and arthroscopic knots. Arthroscopy 2006;22:736-741. 13. Yiannakopoulos CK, Hiotis I, Antonogiannakis E. The triad knot: A new sliding self-locking knot. Arthroscopy 2005;21: 899.e1-899.e3. Available online at www.arthroscopyjournal. org. 14. Abbi G, Espinoza L, Odell T, Mahar A, Pedowitz R. Evaluation of 5 knots and 2 suture materials for arthroscopic rotator cuff repair: Very strong sutures can still slip. Arthroscopy 2006;22:38-43. 15. Loutzenheiser TD, Harryman DT II, Yung SW, France MP, Sidles JA. Optimizing arthroscopic knots. Arthroscopy 1995; 11:199-206. 16. Loutzenheiser TD, Harryman DT II, Ziegler DW, Yung SW. Optimizing arthroscopic knots using braided or monofilament suture. Arthroscopy 1998;14:57-65. 17. Burkhart SS, Wirth MA, Simonich M, Salem D, Lanctot D, Athanasiou K. Loop security as a determinant of tissue fixation security. Arthroscopy 1998;14:773-776. 18. Wüst DM, Meyer DC, Favre P, Gerber C. Mechanical and
19. 20. 21. 22. 23. 24. 25. 26. 27.
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handling properties of braided polyblend polyethylene sutures in comparison to braided polyester and monofilament polydioxanone sutures. Arthroscopy 2006;22:1146-1153. Milia MJ, Peindl RD, Connor PM. Arthroscopic knot tying: The role of instrumentation in achieving knot security. Arthroscopy 2005;21:69-76. McIntyre LF, Norris M, Weber B. Comparison of suture welding and hand-tied knots in mini-open rotator cuff repair. Arthroscopy 2006;22:833-836. Richmond JC. A comparison of ultrasonic suture welding and traditional knot tying. Am J Sports Med 2001;29:297299. Tadje JP, Kahler DM, Green CW, Rodeheaver GT, Edlich RF. Enhancing knot security by heat treatment of knot ears. J Biomed Mater Res 1999;48:479-481. Masterson TM, Thacker JG, Rodeheaver GT, Edlich RF. Heat welding for surgical sutures. Am J Surg 1985;150:318320. Gupta BS, Milam BL, Patty RR. Use of carbon dioxide laser in improving knot security in polyester sutures. J Appl Biomater 1990;1:121-125. Wright PB, Budoff JE, Yeh ML, Kelm ZS, Luo ZP. Strength of damaged suture: An in vitro study. Arthroscopy 2006;22: 1270-1275. Barber FA, Herbert MA, Coons DA, Boothby MH. Sutures and suture anchors—Update 2006. Arthroscopy 2006;22:10631069. Shah MR, Strauss EJ, Kaplan K, Jazrawi L, Rosen J. Initial loop and knot security of arthroscopic knots using highstrength sutures. Arthroscopy 2007;23:884-888.
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Purpose: The purpose of this study was to investigate heat application to arthroscopic knots as a method of improving knot security. Methods: Heat treatment was assessed on 4 suture materials— Ethibond (Ethicon, Somerville, NJ), PDS (Ethicon), Orthocord (DePuy Mitek, Raynham, MA), and FiberWire (Arthrex, Naples, FL)—tied by use of the Duncan loop, compared with untreated controls. A hand-tied surgeon’s knot with Ethibond was included as the gold standard. Knots were tied around a plastic rod immersed in a saline solution–filled water bath at 37°C, with heat treatment performed by use of the Mitek VAPR 3 electrosurgical unit and VAPR S90 electrode (DePuy Mitek), applied directly to the knot body. Loops were subjected to a 5-N preload, followed by loading to clinical failure (⬎3 mm of displacement) and ultimate (breaking) failure by use of a tensile tester. Results: Load to ultimate failure was significantly higher in the FiberWire 1-second heat treatment arm (26.0% increase, 234.25 ⫾ 62.34 N, P ⬍ .03), Orthocord 1-second heat treatment arm (55.6% increase, 204.72 ⫾ 78.47 N, P ⬍ .03), and Orthocord 5-second heat treatment arm (69.2% increase, 222.58 ⫾ 56.57 N, P ⬍ .001) than in controls. Load to clinical failure was significantly higher in the Orthocord 10-second heat treatment arm (34.7% increase, 78.58 ⫾ 13.88 N, P ⬍ .0001) when compared with controls. The FiberWire 5- and 10-second heat treatment arms showed lower load to clinical and ultimate failure (P ⬍ .001). Ethibond, Orthocord, and FiberWire showed higher load to clinical failure than PDS (P ⬍ .0001). Ethibond and Orthocord knots were more likely to fail through knot slippage after heat treatment compared with controls (P ⬍ .01). Conclusions: Heat treatment resulted in greater knot security when combined with Orthocord and FiberWire suture materials. Heat-treated Ethibond and Orthocord knots were more likely to fail through suture breakage than knot slippage. Clinical Relevance: This study presents a simple and novel technique of improving knot security in the arthroscopic repair. The effects of heat were extremely well tolerated in the Orthocord and FiberWire groups, making this technique particularly suitable for clinical use. Key Words: Knot security—Arthroscopy—Heat treatment—Suture—Welding.
A
strong and secure knot is an essential component of any soft-tissue repair, providing soft-tissue apposition required for healing and a good functional
From the Orthopaedic Department, Lancashire Teaching Hospitals NHS Foundation Trust (D.P.W., P.J.H.), Preston; Department of Clinical Engineering, Royal Liverpool University Hospital (A.C.F.), Liverpool; and Department of Clinical Engineering, University of Liverpool (P.D.), Liverpool, England. The authors report no conflict of interest. Address correspondence and reprints requests to Derfel Pari Williams, M.B.Ch.B.(Hons), 54 Dudley Rd, Mossley Hill, Liverpool, Merseyside L18 1ET, England. E-mail: [email protected] © 2008 by the Arthroscopy Association of North America 0749-8063/08/2401-7256$34.00/0 doi:10.1016/j.arthro.2007.10.005
outcome. Arthroscopic surgery, however, presents additional difficulties compared with an open procedure, and knot-tying techniques must be adapted. This difference has necessitated several modifications to the knot configurations,1-14 suture materials,14-17 and instrumentation18,19 used for arthroscopic knots, all with the aim of achieving optimal knot security. However, the arthroscopic knot remains technically more demanding than its hand-tied counterpart, and it is technically difficult to produce an equivalently secure arthroscopic knot.3,7,17 Further improvements in knot security are therefore continually sought to achieve a strong and reliable repair. Heat welding of fibers is an established technique in
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 24, No 1 (January), 2008: pp 7-13
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D. P. WILLIAMS ET AL.
the textile industry. More recently, in the surgical field, ultrasonic energy has been used to weld suture ends together, completely eliminating the knot.20,21 However, there are currently very few data on the application of heat treatment to traditionally tied knots, as well as its role in improving knot security. Previous studies included the use of an electrocautery knife to cut suture ends, forming an enlarged knot ear and thus preventing knot slippage.22,23 Improvements in knot security have also been shown after heat treatment with a carbon dioxide laser.24 Although these studies have shown improved knot security, the techniques have limited application in the clinical setting of an arthroscopic surgeon. There are currently no published data, to our knowledge, on the role of heat application in improving arthroscopic knot security. We hypothesized that heat treatment of arthroscopic knots would result in increased knot security through welding of individual suture strands and, thus, prevent slipping of the knot. The purpose of this study was to evaluate the effect of heat treatment on security of the arthroscopic knot. METHODS Four suture materials commonly used in arthroscopic shoulder surgery were investigated in this study: No. 2 Ethibond (Ethicon, Somerville, NJ); No. 2 PDS (Ethicon); No. 2 Orthocord (DePuy Mitek, Raynham, MA); and No. 2 FiberWire (Arthrex, Naples, FL). Knots were tied by use of the senior surgeon’s preferred knot configuration, the Duncan loop followed by 3 alternating half-hitches.15 An additional group in which Ethibond was hand-tied by use of a standard surgeon’s knot was included as the gold standard, with an initial double-overhand throw followed by 2 single-overhand throws. The senior surgeon, using an arthroscopic knot pusher, tied all knots around a plastic rod immersed in a saline solution– filled water bath at 37°C. Ten knots were tied per group, making a total of 120 knots, with untreated control and treatment arms in each suture group. Heat application was performed with the Mitek VAPR 3 electrosurgical unit and a corresponding VAPR S90 electrode (DePuy Mitek). All heat treatment was undertaken within the saline solution–filled water bath, by use of the vaporization setting at a power of 240 W. Because we were not aware of any previous studies evaluating heat tolerance of suture materials, we initially assessed the suture burn-through time for each material to determine the most appropriate heat treat-
FIGURE 1.
Heat application to knot body using side electrode.
ment period. For each material under investigation, suture loops were tied with a standard hand-tied surgeon’s knot between 2 rods within the water bath. The electrode was placed in direct contact with a single suture strand at the midportion of the loop. To maintain constant contact with the electrode, this part of the loop was placed under a small amount of tension, by lifting the electrode onto the suture strand. The time to complete division of the suture strand was taken as the burn-through time. This was repeated 10 times for each material under investigation (total of 40 loops). Heat application to the arthroscopic knot was performed by direct application of the electrode to the knot body (Fig 1). All treatment groups were subjected to 1 second of heat application. Given the higher heat tolerance of Orthocord and FiberWire (determined from burn-through testing), these groups were also subjected to 5 and 10 seconds of heat treatment. After heat treatment, all knots were subjected to tensile testing to assess knot security by use of a Nene tensile tester (Nene Instruments, Wellingborough, England) (Fig 2). All knots were initially subjected to a 5-N preload to take up any slack in the knot, with all measurements zeroed at this point for reference. They were then subjected to load, at a displacement rate of 0.3 mm/s, to clinical failure (⬎3 mm of displacement) and load to ultimate failure (knot or suture failure). At the point of ultimate failure, the mode of failure was recorded as knot slippage or suture breakage. To further assess the changes after heat treatment, a sample of control and heat-treated knots were also subjected to scanning electron microscopy analysis.
HEAT TREATMENT OF ARTHROSCOPIC KNOTS
9
Load to Clinical Failure The Orthocord 10-second heat treatment group showed a 34.7% increase in load to clinical failure (78.58 ⫾ 13.88 N) compared with controls (58.35 ⫾ 14.87 N), and its load to clinical failure was significantly higher than that in all other Orthocord, Ethibond, and PDS groups (P ⬍ .0001). The highest load at clinical failure was observed in the FiberWire 1-second heat treatment arm (142.65 ⫾ 23.84 N). Although this was significantly higher than that in all other suture groups (P ⬍ .0001), there was no statistically significant difference between control and treatment arms in this group. Loss of knot security was seen in the FiberWire 5-second treatment arm (64.23 ⫾ 39.51 N) and 10-second treatment arm (86.98 ⫾ 40.21 N) (P ⬍ .001). It was also noted that both the PDS control and treatment arms reached clinical failure at a significantly lower load than all other suture materials (P ⬍ .0001). No statistical differences were seen between control and treatment arms for PDS or Ethibond or between the Orthocord control and 1- and 5-second groups (Table 1 and Fig 3). Load to Ultimate Failure FIGURE 2.
Tensile testing of arthroscopic knots.
Statistical analysis was undertaken with the XLSTAT statistical application (Addinsoft, Paris, France). Loads to failure were analyzed via analysis of variance and the Fisher test of least significant difference. The mode of failure was analyzed by use of the 2 test.
RESULTS Suture Burn-Through Time FiberWire showed superior heat tolerance to all other suture materials (83.30 ⫾ 38.69 seconds, P ⬍ .0001). Orthocord showed significantly higher heat tolerance (38.96 ⫾ 12.64 seconds, P ⬍ .0001) in comparison to both Ethibond (0.93 ⫾ 0.06 seconds) and PDS (1.61 ⫾ 0.25 seconds). Although both Ethibond and PDS tolerated heat poorly on single-strand burn-through testing, heat tolerance was improved when applied to the knot body, with none of the main study knots subsequently tested disintegrating after 1 second of heat treatment.
Heat treatment in the Orthocord group resulted in a statistically significant increase in load to ultimate failure in the 1- and 5-second treatment arms. There was a 55.6% increase in the 1-second group (204.72 ⫾ 78.47 N, P ⬍ .03) and a 69.2% increase in the 5-second group (222.58 ⫾ 56.57 N, P ⬍ .001) compared with controls (131.57 ⫾ 52.41 N). In the Orthocord 10-second group, load to ultimate failure (154.89 ⫾ 49.37 N) was increased in comparison to the control group but did not reach statistical significance (P ⫽ .071). FiberWire showed a 26.0% increase in load to ultimate failure after 1 second of heat treatment (234.25 ⫾ 62.34 N) in comparison to the control group (185.91 ⫾ 57.18 N) (P ⬍ .03). However, load to ultimate failure in the 5-second treatment arm (79.77 ⫾ 68.71 N) and 10-second treatment arm (107.95 ⫾ 55.16 N) was significantly inferior to controls (P ⬍ .001). No significant difference was seen between control and treatment arms in the Ethibond or PDS groups (Table 1 and Fig 3). Mode of Failure Comparison of the mode of failure between the control and treatment groups revealed that both Orthocord and Ethibond loops were more likely to fail
10
D. P. WILLIAMS ET AL. TABLE 1.
Suture Material PDS Ethibond Orthocord
FiberWire
Ethibond (hand-tied)
Results of Load to Clinical and Ultimate Failure of Arthroscopic Knots Treatment
Load to Clinical Failure ⫾ SD (N)
Load to Ultimate failure ⫾ SD (N)
Control 1s Control 1s Control 1s 5s 10s Control 1s 5s 10s Control 1s
31.43 ⫾ 1.90〫 31.05 ⫾ 1.61〫 53.43 ⫾ 8.47 56.18 ⫾ 5.91 58.35 ⫾ 14.87 53.02 ⫾ 4.27 53.96 ⫾ 4.74 78.58 ⫾ 13.88* 132.00 ⫾ 13.35 142.65 ⫾ 23.84 64.23 ⫾ 39.51‡ 86.98 ⫾ 40.21‡ 51.74 ⫾ 1.19 50.04 ⫾ 7.22
130.40 ⫾ 38.20 123.65 ⫾ 20.14 123.76 ⫾ 45.21 118.33 ⫾ 35.37 131.57 ⫾ 52.41 204.72 ⫾ 78.47† 222.58 ⫾ 56.57§ 154.89 ⫾ 49.37 185.91 ⫾ 57.18 234.25 ⫾ 62.34⬁ 79.77 ⫾ 68.71‡ 107.95 ⫾ 55.16‡ 121.68 ⫾ 26.54 107.33 ⫾ 33.82
Load to clinical failure: *p⬍0.0001 compared with all other control and treatment groups (except FiberWire) 〫p⬍0.001 compared with all other suture groups ‡p⬍0.001 compared to control Load to ultimate failure: §p⬍0.001 compared with all other control and treatment groups (except FiberWire) †p⬍0.03 compared with all other control and treatment groups (except Orthocord 5s, and FiberWire) ⬁p⬍0.03 compared to all groups (except Orthocord 1s and 5s) ‡p⬍0.001 compared to control
Load to Clinical Failure Load to Ultimate failure 200
*
*
*
* p<0.05
150
* 100
* 50
PDS
Fibrewire
1s
Control
10s
5s
1s
Control
5s
Orthocord
10s
1s
1s
Ethibond
Control
Control
0 1s
Heat application to suture materials is not an entirely new concept. Early studies on heat treatment involved cutting suture ends with an electrocautery knife.22,23 This resulted in formation of an amorphous globular mass at the suture ends, which then lodged in the knot, preventing further slippage. This technique produced 2-throw knots with a breaking strength and knot slippage rate similar to 4-throw control knots23 and, in 1 case, an increase in knot-breaking strength of 8.6% after heat treatment.22 Gupta et al.24 investigated the role of a carbon dioxide laser as a method of treating suture materials. When applied to 2-throw square knots, a 16% increase in knot security was obtained. They also noted that knot slippage did not occur in these treated groups, suggesting that a
250
Control
DISCUSSION
weak bond had formed between the suture strands within the knot. The study concluded that heat welding of sutures was possible but that the bond formed was brittle and weaker than a standard surgical knot.
Load (N)
through suture breakage after heat treatment (P ⬍ .03) (Table 2). This effect was particularly evident in the Orthocord group, which showed an increasing progression toward suture breakage with increased heat treatment (Fig 4). In most cases suture failure occurred at the junction between the suture loop and the knot body. The mode of failure remained unchanged in the PDS, FiberWire, and hand-tied Ethibond groups after heat treatment.
Ethibond (hand tied)
FIGURE 3. Mean load to clinical and ultimate failure of control and heat-treated knots. Increased load to clinical failure was seen in the Orthocord 10-second heat treatment group. Load to ultimate failure was increased in the Orthocord 1- and 5-second heat treatment groups and the FiberWire 1-second heat treatment group. The FiberWire 5- and 10-second treatment groups failed at a significantly lower load.
HEAT TREATMENT OF ARTHROSCOPIC KNOTS TABLE 2. Suture Material PDS Ethibond Orthocord
FiberWire
Ethibond (hand-tied)
Mode of Failure of Knots Treatment
Knot Slippage
Suture Breakage
Control 1s Control 1s Control 1s 5s 10s Control 1s 5s 10s Control 1s
2 0 4 0 10 7 1 1 9 10 10 10 3 3
8 10 6 10 0 3 9 9 1 0 0 0 7 7
We chose to evaluate PDS and Ethibond as part of this study because of their differing characteristics and their established use in arthroscopic surgery. In addition, we investigated the effects on Orthocord and FiberWire, which are composite suture materials, consisting of an outer sleeve and an inner core, providing superior strength properties. We hypothesized that these might react in a different way to standard suture materials. Orthocord is, however, a relatively new material, and as such, there are very few published data regarding its clinical use.18,25-27 Load to clinical failure has previously been defined as loop elongation greater than 3 mm, representing the point at which the soft tissue is no longer apposed, and the repair is more likely to fail.15 Increasing the point of clinical failure therefore has important implications in any soft-tissue repair. This outcome was only significantly increased in the Orthocord 10-second heat treatment arm. Analysis of load to ultimate failure showed that heat treatment resulted in improved knot security when both Orthocord and FiberWire were used. On closer evaluation of the Orthocord group, a clear progression in the response to heat is seen, with the greatest overall improvement in the 5- and 10second treatment groups (Fig 3). The pattern seen with Orthocord suggests that the optimum period of heat treatment for this material may lie somewhere between 5 and 10 seconds. FiberWire knots, on the other hand, were compromised after both 5 and 10 seconds of heat treatment, and the optimum period is likely to be much shorter. We hypothesized that because of its monofilament nature, PDS would potentially show a greater response to heat welding. However, no significant dif-
11
ference was seen after heat treatment of PDS. It also exhibited a very low tolerance to heat on single-strand burn-through testing and was significantly inferior on loading to clinical failure. This is in keeping with previous work, which has shown PDS to be an inferior suture material for arthroscopic repair.15-17 Although no significant increases were seen in the PDS or Ethibond groups after heat treatment, our work has shown that even for those materials with an apparently low tolerance to heat, knot security is not compromised by local heat application. Interestingly, our gold-standard hand-tied Ethibond knots were shown to be no more secure than the arthroscopically tied Duncan loop. This may reflect the fact that this is the preferred knot of the senior surgeon, which resulted in consistently secure knots. Assessment of the mode of failure showed that both Ethibond and Orthocord heat-treated arthroscopic knots were more likely to fail through suture breakage rather than knot slippage. This suggests that heat treatment has a direct effect on the knot body preventing slippage. We hypothesize that this may occur by 2 possible means. Heat treatment may have a direct welding effect on the suture material by fusing individual strands together, as seen in the work of Gupta et al.24 Increased roughness of the suture surface may also reduce slippage of suture strands within the knot. Microscopic comparison of control and heat-treated knots clearly shows that individual fibers of the outer layer appear to have fused together after heat treatment, with increased surface roughness, which would support this theory (Fig 5). In the case of Orthocord, we also propose a second possible hypothesis. Given the composite nature of Orthocord, it is possible that heat treatment may result in contraction of the inner
Knot Slippage Suture Breakage 12 10 8 6 4 2 0 Ethibond Control
Ethibond 1s
Orthocord Control
Orthocord 1s Orthocord 5s
Orthocord 10s
Suture
FIGURE 4. Mode of failure of Ethibond and Orthocord control and heat-treated knots after tensile testing. Both groups showed progression to decreased knot slippage after heat treatment (P ⬍ .03).
12
D. P. WILLIAMS ET AL. the optimum conditions. Further work is required to assess different suture materials, knot configurations, and vaporization settings and to determine the optimum period of heat application required for each suture material. This is not an in vivo study, and therefore the results may not be reflective of the clinical reality. Consideration of possible damage to adjacent tissues and its effect on the repair would also be required with use in the clinical setting. However, we believe that there is significant potential to further develop this technique into a useful and safe method of improving knot security by use of standard arthroscopic instruments.
FIGURE 5. Electron microscopy analysis of Orthocord knots after 1 second of heat treatment (original magnification ⫻150). The surface of the suture appears roughened after heat treatment, which may reduce the amount of slippage at the knot through increased friction between strands.
strand, causing tightening of the knot and subsequent improvement in knot security. This, however, has not been directly evaluated by this study, and further work would be required to substantiate this theory. No significant changes were seen in the mode of failure in the hand-tied Ethibond groups. This may reflect the smaller size of the surgeon’s knot in comparison to the Duncan loop. As a result, there will be fewer suture strands in contact at the knot body. Our initial assessment of suture material heat tolerance showed that both FiberWire and Orthocord were very tolerant to heat on burn-through testing (83.30 ⫾ 38.69 seconds and 38.96 ⫾ 12.64 seconds, respectively). This finding in itself is extremely relevant to every arthroscopic surgeon. On completion of an arthroscopic repair, the surgeon must always be extremely cautious with further use of electrocautery, for fear of damaging the suture material and compromising the soft-tissue repair. Combined with the results of loading to failure, we can conclude that a short burst of soft-tissue vaporization after completing a repair is unlikely to have a detrimental effect on the suture material. The surgeon can therefore confidently use electrocautery without the risk of damaging the repair when using Orthocord or FiberWire. However, on the basis of our results, care should be exercised if one is using further electrocautery after repair with PDS or Ethibond. Although this study has shown the described technique to be an effective and simple method of improving knot security, we have not established
CONCLUSIONS This study has shown that direct heat application to the knot body results in increased load to failure of both Orthocord and FiberWire arthroscopic knots. Ethibond and Orthocord heat-treated knots were also less likely to fail from knot slippage. In addition to the increased knot security obtained through heat treatment, we have also shown that both Orthocord and FiberWire have an extremely high tolerance to heat (compared with PDS and Ethibond), making them particularly suitable for heat treatment. This technique offers a simple yet effective way of applying heat by use of standard arthroscopic instruments. Acknowledgment: The authors are grateful to DePuy Mitek for providing the suture materials used in this study.
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handling properties of braided polyblend polyethylene sutures in comparison to braided polyester and monofilament polydioxanone sutures. Arthroscopy 2006;22:1146-1153. Milia MJ, Peindl RD, Connor PM. Arthroscopic knot tying: The role of instrumentation in achieving knot security. Arthroscopy 2005;21:69-76. McIntyre LF, Norris M, Weber B. Comparison of suture welding and hand-tied knots in mini-open rotator cuff repair. Arthroscopy 2006;22:833-836. Richmond JC. A comparison of ultrasonic suture welding and traditional knot tying. Am J Sports Med 2001;29:297299. Tadje JP, Kahler DM, Green CW, Rodeheaver GT, Edlich RF. Enhancing knot security by heat treatment of knot ears. J Biomed Mater Res 1999;48:479-481. Masterson TM, Thacker JG, Rodeheaver GT, Edlich RF. Heat welding for surgical sutures. Am J Surg 1985;150:318320. Gupta BS, Milam BL, Patty RR. Use of carbon dioxide laser in improving knot security in polyester sutures. J Appl Biomater 1990;1:121-125. Wright PB, Budoff JE, Yeh ML, Kelm ZS, Luo ZP. Strength of damaged suture: An in vitro study. Arthroscopy 2006;22: 1270-1275. Barber FA, Herbert MA, Coons DA, Boothby MH. Sutures and suture anchors—Update 2006. Arthroscopy 2006;22:10631069. Shah MR, Strauss EJ, Kaplan K, Jazrawi L, Rosen J. Initial loop and knot security of arthroscopic knots using highstrength sutures. Arthroscopy 2007;23:884-888.
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