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A Biomechanical Comparison of 3 Loop Suture Materials in a 6-Strand Flexor Tendon Repair Technique
SCIENTIFIC ARTICLES
A Biomechanical Comparison of 3 Loop Suture Materials in a 6-Strand Flexor Tendon Repair Technique Aaron W. T. Gan, MMed, Puay Yong Neo, BEng, Min He, PhD, Andrew K. T. Yam, MMed, Alphonsus K. S. Chong, MMed, Shian Chao Tay, MBBS, MSc
Purpose The braided polyblend (FiberWire) suture is recognized for its superiority in tensile strength in flexor tendon repair. The purpose of this study was to compare the biomechanical performance of 3 loop-suture materials used in a locking 6-strand flexor tendon repair configuration: braided polyblend (FiberLoop 4-0), cable nylon (Supramid Extra II 4-0), and braided polyester (Tendo-Loop 4-0). We hypothesized that, using this technique, the braided polyblend suture would give superior tensile strength compared with the other 2 suture materials. Methods We divided 30 fresh porcine flexor tendons transversely and repaired each with 1 of the 3 suture materials using a modified Lim-Tsai 6-strand suture technique. We loaded the repaired tendons to failure using a materials testing machine and collected data on the mechanism of failure, ultimate tensile strength, gap strength, and stiffness. Results Failure mechanisms for the repaired specimens were as follows: the braided polyblend had 50% suture breakage and 50% suture pullout; the cable nylon had 100% suture breakage; and the braided polyester had 80% suture breakage and 20% suture pullout. Specimens repaired with the braided polyblend suture had the highest mean ultimate tensile strength (97 N; standard deviation, 22) and the highest mean gap force (35 N; standard deviation, 7). Conclusions This study supports the findings of previous studies showing superior strength of the braided polyblend suture. Clinical relevance We were able to achieve up to 124 N in ultimate tensile strength and 48 N of gap force with this suture in porcine tendons. This gives greater confidence in starting immediate controlled passive or active rehabilitation after repair of flexor tendon injuries. (J Hand Surg 2012;37A:1830–1834. Copyright © 2012 by the American Society for Surgery of the Hand. All rights reserved.) Key words Six-strand flexor tendon repair, FiberLoop, FiberWire, loopsuture, modified Lim-Tsai technique. OR EARLY ACTIVE REHABILITATION to be successful, flexor tendon repairs must have sufficient tensile strength to withstand the tensile stresses generated by active flexion of the affected digits.1 Flexor
F
From the Department of Hand Surgery, Singapore General Hospital; and the Department of Hand and Reconstructive Microsurgery, National University Hospital, Singapore. Received for publication May 14, 2010; accepted in revised form June 12, 2012. SupportedbySinghealthFoundationGrantSHF/FG446S/2009andNationalMedicalResearchCouncil Grants NMRC/1116/2007 and NMRC/1148/2007.
1830 䉬 © ASSH 䉬 Published by Elsevier, Inc. All rights reserved.
tendon repair strength depends on many aspects, including the repair site, the suture material used,2–5 the location of suture placement,6 –10 and the number of strands crossing the repair site.11–15 Comparative studNo benefits in any form have been received or will be received related directly or indirectly to the subject of this article. Correspondingauthor:ShianChaoTay,MBBS,MSc,DepartmentofHandSurgery,SingaporeGeneral Hospital, Outram Road, Singapore 169608; e-mail: [email protected]. 0363-5023/12/37A09-0010$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2012.06.008
SUTURE MATERIAL IN 6-STRAND REPAIR
ies on the performance of suture materials have reported the superiority in strength of braided polyblend (FiberWire; Arthrex, Naples, FL) compared with other suture materials such as nylon and polyester.16,17 However, there is still no clear consensus on the best choice of suture material for use in different repair techniques. Often, decisions are based on the surgeon’s preference and experience. Superiority in suture strength does not necessarily result in higher flexor tendon repair strength. Previous studies by Barrie et al15 and Miller et al16 have proven that if a suture technique tends to fail by suture pullout, the strength of the suture material provides little improvement to overall repair strength once the load exceeds pullout load values. Consequently, a suture material superior in strength would only provide the greatest influence on repair strength when a repair technique fails first by suture breakage. In current clinical practice, we use a 6-strand core suture technique with a 4-0 cable nylon loop suture for flexor tendon repairs, based on studies demonstrating the superiority in tensile strength of 6-strand repairs over 2- or 4-strand repairs.13,14 Previous studies comparing suture materials were done using 2-strand and 4-strand repair techniques.16,17 The Lim-Tsai technique18 uses a loop suture that crosses the repair site 3 times to achieve a 6-strand repair, unlike the 6-strand repair techniques described in previous comparison studies13,14 that used non-loop sutures crossing the repair site 6 times. The biomechanical properties of a 6-strand repair using non-loop sutures passed 6 times may not be equivalent to that using a loop suture passed 3 times. The purpose of this study was to compare the biomechanical performance of 3 loopsuture materials used in a core locking 6-strand flexor tendon repair configuration. MATERIALS AND METHODS Flexor tendon specimens and repair technique We harvested 30 fresh flexor tendons from the central 2 rays of porcine forelimbs. We then divided the flexor tendons transversely at the level of the A2 pulley and repaired them using a 6-strand, modified version of the Lim-Tsai technique with 1 of the 3 suture materials: (1) cable nylon (Supramid Extra II 4-0; S. Jackson, Inc., Alexandria, VA; n ⫽ 10), (2) braided polyester (Tendo-Loop 4-0; B. Braun, Melsungen AG, Germany; n ⫽ 10); and (3) braided polyblend (FiberLoop 4-0; FiberWire, Arthrex, Naples, FL; n ⫽ 10). We used a measuring tape to measure 10 mm from the cut tendon ends and marked the sites with a transverse line using a permanent marker pen.
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FIGURE 1: Modified Lim-Tsai 6-strand repair technique.
We used a modified technique with a single-looped suture instead of 2 looped sutures, as originally described by Lim and Tsai,18 to create a 6-strand tendon repair that incorporated 4 locking sites in the complete repair (2 locking sites on each side) (Fig. 1). We completed each repair with 1 knot placed on the lateral surface of the flexor tendon (extratendinous), compared with the original technique, which described 2 knots placed within the repair site (intratendinous). We employed a surgeon’s knot followed by 2 simple squared knots (double-single-single throw) for repairs using the cable nylon and braided polyester sutures. For the braided polyblend suture, we used a 5-throw knot including the initial surgeon’s knot (double-single-singlesingle-single throw). We did this to prevent knot unraveling when using this suture material.19 We placed the locking sites at the marked lines, which ensured a suture purchase of 10 mm on each side. No epitendinous repair was done. All the sutures used were nonabsorbable and 4-0 in size with tapered point needles. To promote consistency, the same surgeon performed all repairs using ⫻ 3.3 magnification. Mechanical testing We mounted the ends of the repaired tendons onto an Instron 5543 device (Instron Corp., Canton, MA) using specially designed clamps with blasted surfaces to ensure a secure grip. For each specimen, we set the clamps 30 mm apart and applied a 1-N preload before each static tensile test. We advanced the crosshead of the mechanical tester at a constant rate of 20 mm/min until repair failure. We took continuous video of the repair site using a digital video camera (Fujifilm Finepix F31 fd; Fujifilm Corp., Tokyo, Japan). We recorded the times at the formation of a 1-mm gap
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SUTURE MATERIAL IN 6-STRAND REPAIR
and at failure of the repair site by suture pullout or suture rupture. For each tendon repair specimen, we generated load-displacement curves and recorded the mechanism of failure. We determined the ultimate tensile strength of the repair, or load to failure, by the peak value on the load-displacement curve (N). We calculated the force at which a 1-mm gap formed by frame-by-frame playback of the video taken, and correlated the time to the loading graphs generated by the Instron software program. We calculated the stiffness by taking the gradient of the linear portion of the load-displacement curve. We assessed 4 objective variables for each specimen: mechanism of failure, ultimate tensile strength, load to 1-mm gap formation, and stiffness.
TABLE 1. Pairwise Multiple Comparison Procedures for Ultimate Tensile Strength and Gap Force Difference of Means
p
q
P
Ultimate tensile strength (Tukey test) Comparison FiberLoop vs Supramid
50.7
3 11.7
⬍ .001
FiberLoop vs TendoLoop
44.8
3
9.9
⬍ .001
3
1.4
.610
Tendo-Loop vs Supramid
5.87
Gap force (Tukey test)
Statistical analysis We used a significance level of .05 for all analysis. We analyzed data with a 1-way analysis of variance and performed pairwise comparison between groups using the Tukey test when we found statistical significance between groups for each data set. RESULTS Mechanism of failure The braided polyblend repairs failed by suture breakage (50%) and suture pullout (50%). All of the cable nylon repairs failed by suture breakage. Most of the braided polyester repairs (80%) failed by suture breakage; the remaining 20% failed by suture pullout. There were no knot failures. Ultimate tensile strength Specimens repaired with the braided polyblend suture had the highest mean ultimate tensile strength (97 N; standard deviation [SD] 22), followed by braided polyester (52 N; SD 11) and then cable nylon (47 N; SD 8). The difference was statistically significant (P ⬍ .001). The Tukey test showed a significant difference between the braided polyblend versus the cable nylon groups and between the braided polyblend versus the braided polyester groups, but not between the braided polyester versus the cable nylon groups (Table 1). Load to 1-mm gap formation Specimens repaired with braided polyblend had the highest mean gap force (35 N; SD 7), followed by braided polyester (18 N; SD 6) and cable nylon (17 N; SD 6). The difference was statistically significant (P ⬍ .001). Similarly, the Tukey test showed a significant difference between the
Comparison FiberLoop vs Supramid
17.0
3
7.8
⬍ .001
FiberLoop vs TendoLoop
16.8
3
8.0
⬍ .001
3
0.09
Tendo-Loop vs Supramid
0.19
.998
q, statistic used by SigmaStat (software used to perform the Tukey test); p, number of means spanned in the comparison.
braided polyblend versus the cable nylon groups and between the braided polyblend versus the braided polyester groups, but not between the braided polyester versus the cable nylon groups (Table 1). Stiffness The mean stiffness was 4.7 N/mm (SD 2.3) for the cable nylon group, 5.5 N/mm (SD 1.9) for the braided polyester group, and 5.9 N/mm (SD 1.8) for the braided polyblend group. The difference was not statistically significant (P ⫽ .425). DISCUSSION Pennington20 first suggested the locking loop suture configuration in 1979 as an effective repair technique for flexor tendons, conferring enough strength for an early mobilization protocol. Pennington also emphasized that the correct orientation of the intratendinous (longitudinal and transverse) components was a critical factor affecting a repair’s strength. In 1997, Hotokezaka and Manske21 described locking and grasping suture methods and demonstrated the superiority of the locking suture method over the grasping method. Previous studies have shown that core suture repairs that incor-
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SUTURE MATERIAL IN 6-STRAND REPAIR
porate locking techniques typically do not fail by suture pullout, but rather by suture breakage.15,21,22 In such cases, material properties and strength of the suture become the limiting factor in the biomechanical performance of the repair.17 The original 6-strand locking Lim-Tsai suture technique has been reported to have higher repair strength than 2- or 4-strand repair techniques reported in other studies.23 The modified version used in this study retained the advantages of the original Lim-Tsai technique while having the advantages of requiring only 1 loop suture per repair and having the knot placed away from the repair site in an extratendinous location. Studies involving various types of sutures and repair techniques have shown consistently that single knot repairs are significantly stronger than double knot repairs.24,25 This could be explained by the relative ease of mastering a single knot suture technique compared with a double knot technique, especially by trainees with limited experience in tendon repair. In addition, placement of a single knot away from the repair site outside the tendon has been shown to result in less suture material at the repair site and a 22% increase in strength comparing 2-strand repairs in a canine model.26 We chose porcine forelimbs flexor tendons for this study because they were readily available and costeffective and have demonstrated a comparable model to humans for the study of flexor tendon repair.27 The lack of epitendinous sutures in the repairs done in the study likely accounted for the lower ultimate tensile strength and gap force values exhibited for the cable nylon and braided polyester repairs, compared with previous studies.16,17 We chose not to incorporate an epitendinous repair, to reduce the number of variables influencing the strength of the repair. In our study protocol, we chose a 1-mm gap as a comparative variable, because this was representative of gap force as shown in the Gill et al23 comparative study of repair techniques in cadaveric tendons. In that study, there was minimal difference in tensile force between the 1- and 2-mm gap formation in the testing of the 4 groups of repair techniques, which included the original 6-strand Lim-Tsai double loop suture repair. Those results were 26 ⫾ 9 N at the 1-mm gap formation and 28 ⫾ 8 N at the 2-mm gap formation. We obtained results in ultimate tensile strength and gap force values in our 6-strand looped braided polyblend comparable to those in previous studies using 4-strand repair techniques. Lawrence and Davis17 used a 4-strand locking single-cross repair technique in porcine flexor tendons and showed that repairs using braided polyblend and stainless-steel sutures were sig-
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nificantly stronger than those using nylon, polyester (Ethibond; Ethicon, Edinburgh, UK), and polypropylene (Prolene; Ethicon) sutures. Braided polyblend repairs had a mean ultimate tensile strength of 81 N, compared with those of nylon (47 N), polypropylene (63 N), and polyester (66 N); all repairs failed by suture rupture at the locking site. Miller et al16 used a Massachusetts General Hospital repair technique on human cadaveric flexor tendons and reported a significantly higher ultimate tensile strength in braided polyblend repairs (124 N) compared with polyester (82 N) and nylon repairs (69 N). A total of 99% of the repairs failed by suture rupture, and the remaining ones failed by suture pullout. In our study, we were able to achieve a mean ultimate tensile strength of 97 N (range, 50 –124 N) in the braided polyblend repairs. The mean 1-mm gap force achieved was 35 N (range, 23– 41 N). Half of the repairs failed by suture breakage and half by suture pullout. None failed by suture unraveling at the knot. According to Strickland’s28 –30 studies, the estimated force required for passive motion is 2 to 4 N, for active flexion with mild resistance up to 10 N, for moderate resisted flexion up to 17 N, for strong grip composite grasp up to 70 N, and for tip-pinch using the index finger up to 120 N. Our results support the possibility of starting an immediate active motion protocol limited to light grip with no gapping at the repair site in a braided polyblend 6-strand core suture repair. However, this will still be insufficient to withstand a noncompliant patient’s activity, which could well include strong composite grasp. This study has limitations. We performed the repairs on fresh porcine tendons, not human tendons. The cross-sectional diameter of these tendons was grossly larger than that of human tendons. Anecdotally, this probably introduces a false elevation of the true tensile values, because a larger amount of tendon substance can be captured at the locking sites in the porcine tendons compared with human tendons, although there have been no studies to prove this. We placed no epitendinous sutures, which can improve the repair strength by up to 50% and reduce gapping at the repair site significantly.30 However, we chose not to incorporate an epitendinous repair, to reduce the number of variables influencing the strength of the repair. This study does not take into consideration suture site bulk and adhesion formation. The extratendinous 5 throws used to knot the braided polyblend suture repairs added considerable bulk to the repair site and may
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SUTURE MATERIAL IN 6-STRAND REPAIR
cause triggering or adhesion formation, especially in zone II flexor tendon repairs in vivo. This study does not taken into consideration the physiologic effects of tendon healing as an influence of study results. Adhesion formation and its influence of work of flexion are important considerations in zone II flexor tendon repair. In clinical practice, given the choice of the 3 suture materials in this study, one might consider using the braided polyblend suture to achieve a stronger repair compared with the cable nylon and braided polyester sutures. This could increase the surgeon’s confidence in starting an early active motion rehabilitation protocol. REFERENCES 1. Elliot D, Moiemen NS, Flemming AF, Harris SB, Foster AJ. The rupture rate of acute flexor tendon repairs mobilized by the controlled active motion regimen. J Hand Surg 1994;19B:607– 612. 2. Taras JS, Raphael JS, Marczyk SC, Bauerle WB. Evaluation of suture caliber in flexor tendon repair. J Hand Surg 2001;26A:1100 – 1104. 3. Alavanja G, Dailey E, Mass DP. Repair of zone II flexor digitorum profundus lacerations using varying suture sizes: a comparative biomechanical study. J Hand Surg 2005;30A:448 – 454. 4. Barrie KA, Tomak SL, Cholewicki J, Merrell GA, Wolfe SW. Effect of suture locking and suture caliber on fatigue strength of flexor tendon repairs. J Hand Surg 2001;26A:340 –346. 5. Momose T, Amadio PC, Zhao C, Zobitz ME, An KN. The effect of knot location, suture material, and suture size on the gliding resistance of flexor tendons. J Biomed Mater Res 2000;53:806 – 811. 6. Cao Y, Zhu B, Xie RG, Tang JB. Influence of core suture purchase length on strength of four-strand tendon repairs. J Hand Surg 2006; 31A:107–112. 7. Wada A, Kubota H, Hatanaka H, Hotokezaka S, Miura H, Iwamoto Y. The mechanical properties of locking and grasping suture loop configurations in four-strand core suture techniques. J Hand Surg 2000;25B:548 –551. 8. Soejima O, Diao E, Lotz JC, Hariharan JS. Comparative mechanical analysis of dorsal versus palmar placement of core suture for flexor tendon repairs. J Hand Surg 1995;20A:801– 807. 9. Aoki M, Manske PR, Pruitt DL, Kubota H, Larson BJ. Work of flexion after flexor tendon repair according to the placement of sutures. Clin Orthop Relat Res 1995;320:205–210. 10. Ketchum LD. Suture materials and suture techniques used in tendon repair. Hand Clin 1985;1:43–53. 11. Angeles JG, Heminger H, Mass DP. Comparative biomechanical performances of 4-strand core suture repairs for zone II flexor tendon lacerations. J Hand Surg 2002;27A:508 –517.
12. Dona E, Gianoutsos MP, Walsh WR. Optimizing biomechanical performance of the 4-strand cruciate flexor tendon repair. J Hand Surg 2004;29A:571–580. 13. Viinikainen A, Göransson H, Huovinen K, Kellomäki M, Rokkanen P. A comparative analysis of the biomechanical behaviour of five flexor tendon core sutures. J Hand Surg 2004;29B:536 –543. 14. Thurman R, Trumble TE, Hanel DP, Tencer AF, Kiser PK. Two-, four-, and six-strand zone II flexor tendon repairs: an in situ biomechanical comparison using a cadaver model. J Hand Surg 1998;23A: 261–265. 15. Barrie KA, Tomak SL, Cholewicki J, Wolfe SW. The role of multiple strands and locking sutures on gap formation of flexor tendon repairs during cyclical loading. J Hand Surg 2000;25A:714 –720. 16. Miller B, Dodds SD, deMars A, Zagoreas N, Waitayawinyu T, Trumble TE. Flexor tendon repairs: the impact of FiberWire on grasping and locking core sutures. J Hand Surg 2007;32A:591–596. 17. Lawrence TM, Davis TRC. A biomechanical analysis of suture materials and their influence on a four-strand flexor tendon repair. J Hand Surg 2005;30A:836 – 841. 18. Lim BH, Tsai TM. The six-strand technique for flexor tendon repair. Atlas Hand Clin 1996;1:65–76. 19. Waitayawinyu T, Martineau PA, Luria S, Hanel DP, Trumble TE. Comparative biomechanic study of flexor tendon repair using FiberWire. J Hand Surg 2008;33A:701–708. 20. Pennington DG. The locking loop tendon suture. Plast Reconstr Surg 1979;63:648 – 652. 21. Hotokezaka S, Manske PR. Differences between locking loops and grasping loops: effects on 2-strand core suture. J Hand Surg 1997; 22A:995–1003. 22. Hatanaka H, Manske PR. Effect of suture size on locking and grasping flexor tendon repair techniques. Clin Orthop Relat Res 2000;375:267–274. 23. Gill RS, Lim BH, Shatford RA, Toth E, Voor MJ, Tsai TM. A comparative analysis of the six-strand double-loop flexor tendon repair and three other techniques: a human cadaveric study. J Hand Surg 1999;24A:1315–1322. 24. Aoki M, Pruitt DL, Kubota H, Manske PR. Effect of suture knots on tensile strength of repaired canine flexor tendons. J Hand Surg 1995;20B:72–75. 25. Rees L, Matthews A, Masouros SD, Bull AMJ, Haywood R. Comparison of 1- and 2-knot, 4-strand, double-modified kessler tendon repairs in a porcine model. J Hand Surg 2009;34A:705–709. 26. Panandrea R, Seitz WH Jr, Shapiro P, Borden B. Biomechanical and clinical evaluation of the epitenon-first technique of flexor tendon repair. J Hand Surg 1995;20A:261–266. 27. Smith AM, Forder JA, Annapureddy SR, Reddy KSK, Amis AA. The porcine forelimb as a model for human flexor tendon surgery. J Hand Surg 2005;30B:307–309. 28. Strickland JW. Flexor tendon injuries: I. Foundations of treatment. J AM Acad Orthop Surg 1995;3:44 –54. 29. Strickland JW. The Indiana method of flexor tendon repair. Atlas Hand Clin 1996;1:77–103. 30. Strickland JW. Development of flexor tendon surgery: twenty-five years in progress. J Hand Surg 2000;25A:214 –235.
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A Biomechanical Comparison of 3 Loop Suture Materials in a 6-Strand Flexor Tendon Repair Technique Aaron W. T. Gan, MMed, Puay Yong Neo, BEng, Min He, PhD, Andrew K. T. Yam, MMed, Alphonsus K. S. Chong, MMed, Shian Chao Tay, MBBS, MSc
Purpose The braided polyblend (FiberWire) suture is recognized for its superiority in tensile strength in flexor tendon repair. The purpose of this study was to compare the biomechanical performance of 3 loop-suture materials used in a locking 6-strand flexor tendon repair configuration: braided polyblend (FiberLoop 4-0), cable nylon (Supramid Extra II 4-0), and braided polyester (Tendo-Loop 4-0). We hypothesized that, using this technique, the braided polyblend suture would give superior tensile strength compared with the other 2 suture materials. Methods We divided 30 fresh porcine flexor tendons transversely and repaired each with 1 of the 3 suture materials using a modified Lim-Tsai 6-strand suture technique. We loaded the repaired tendons to failure using a materials testing machine and collected data on the mechanism of failure, ultimate tensile strength, gap strength, and stiffness. Results Failure mechanisms for the repaired specimens were as follows: the braided polyblend had 50% suture breakage and 50% suture pullout; the cable nylon had 100% suture breakage; and the braided polyester had 80% suture breakage and 20% suture pullout. Specimens repaired with the braided polyblend suture had the highest mean ultimate tensile strength (97 N; standard deviation, 22) and the highest mean gap force (35 N; standard deviation, 7). Conclusions This study supports the findings of previous studies showing superior strength of the braided polyblend suture. Clinical relevance We were able to achieve up to 124 N in ultimate tensile strength and 48 N of gap force with this suture in porcine tendons. This gives greater confidence in starting immediate controlled passive or active rehabilitation after repair of flexor tendon injuries. (J Hand Surg 2012;37A:1830–1834. Copyright © 2012 by the American Society for Surgery of the Hand. All rights reserved.) Key words Six-strand flexor tendon repair, FiberLoop, FiberWire, loopsuture, modified Lim-Tsai technique. OR EARLY ACTIVE REHABILITATION to be successful, flexor tendon repairs must have sufficient tensile strength to withstand the tensile stresses generated by active flexion of the affected digits.1 Flexor
F
From the Department of Hand Surgery, Singapore General Hospital; and the Department of Hand and Reconstructive Microsurgery, National University Hospital, Singapore. Received for publication May 14, 2010; accepted in revised form June 12, 2012. SupportedbySinghealthFoundationGrantSHF/FG446S/2009andNationalMedicalResearchCouncil Grants NMRC/1116/2007 and NMRC/1148/2007.
1830 䉬 © ASSH 䉬 Published by Elsevier, Inc. All rights reserved.
tendon repair strength depends on many aspects, including the repair site, the suture material used,2–5 the location of suture placement,6 –10 and the number of strands crossing the repair site.11–15 Comparative studNo benefits in any form have been received or will be received related directly or indirectly to the subject of this article. Correspondingauthor:ShianChaoTay,MBBS,MSc,DepartmentofHandSurgery,SingaporeGeneral Hospital, Outram Road, Singapore 169608; e-mail: [email protected]. 0363-5023/12/37A09-0010$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2012.06.008
SUTURE MATERIAL IN 6-STRAND REPAIR
ies on the performance of suture materials have reported the superiority in strength of braided polyblend (FiberWire; Arthrex, Naples, FL) compared with other suture materials such as nylon and polyester.16,17 However, there is still no clear consensus on the best choice of suture material for use in different repair techniques. Often, decisions are based on the surgeon’s preference and experience. Superiority in suture strength does not necessarily result in higher flexor tendon repair strength. Previous studies by Barrie et al15 and Miller et al16 have proven that if a suture technique tends to fail by suture pullout, the strength of the suture material provides little improvement to overall repair strength once the load exceeds pullout load values. Consequently, a suture material superior in strength would only provide the greatest influence on repair strength when a repair technique fails first by suture breakage. In current clinical practice, we use a 6-strand core suture technique with a 4-0 cable nylon loop suture for flexor tendon repairs, based on studies demonstrating the superiority in tensile strength of 6-strand repairs over 2- or 4-strand repairs.13,14 Previous studies comparing suture materials were done using 2-strand and 4-strand repair techniques.16,17 The Lim-Tsai technique18 uses a loop suture that crosses the repair site 3 times to achieve a 6-strand repair, unlike the 6-strand repair techniques described in previous comparison studies13,14 that used non-loop sutures crossing the repair site 6 times. The biomechanical properties of a 6-strand repair using non-loop sutures passed 6 times may not be equivalent to that using a loop suture passed 3 times. The purpose of this study was to compare the biomechanical performance of 3 loopsuture materials used in a core locking 6-strand flexor tendon repair configuration. MATERIALS AND METHODS Flexor tendon specimens and repair technique We harvested 30 fresh flexor tendons from the central 2 rays of porcine forelimbs. We then divided the flexor tendons transversely at the level of the A2 pulley and repaired them using a 6-strand, modified version of the Lim-Tsai technique with 1 of the 3 suture materials: (1) cable nylon (Supramid Extra II 4-0; S. Jackson, Inc., Alexandria, VA; n ⫽ 10), (2) braided polyester (Tendo-Loop 4-0; B. Braun, Melsungen AG, Germany; n ⫽ 10); and (3) braided polyblend (FiberLoop 4-0; FiberWire, Arthrex, Naples, FL; n ⫽ 10). We used a measuring tape to measure 10 mm from the cut tendon ends and marked the sites with a transverse line using a permanent marker pen.
1831
FIGURE 1: Modified Lim-Tsai 6-strand repair technique.
We used a modified technique with a single-looped suture instead of 2 looped sutures, as originally described by Lim and Tsai,18 to create a 6-strand tendon repair that incorporated 4 locking sites in the complete repair (2 locking sites on each side) (Fig. 1). We completed each repair with 1 knot placed on the lateral surface of the flexor tendon (extratendinous), compared with the original technique, which described 2 knots placed within the repair site (intratendinous). We employed a surgeon’s knot followed by 2 simple squared knots (double-single-single throw) for repairs using the cable nylon and braided polyester sutures. For the braided polyblend suture, we used a 5-throw knot including the initial surgeon’s knot (double-single-singlesingle-single throw). We did this to prevent knot unraveling when using this suture material.19 We placed the locking sites at the marked lines, which ensured a suture purchase of 10 mm on each side. No epitendinous repair was done. All the sutures used were nonabsorbable and 4-0 in size with tapered point needles. To promote consistency, the same surgeon performed all repairs using ⫻ 3.3 magnification. Mechanical testing We mounted the ends of the repaired tendons onto an Instron 5543 device (Instron Corp., Canton, MA) using specially designed clamps with blasted surfaces to ensure a secure grip. For each specimen, we set the clamps 30 mm apart and applied a 1-N preload before each static tensile test. We advanced the crosshead of the mechanical tester at a constant rate of 20 mm/min until repair failure. We took continuous video of the repair site using a digital video camera (Fujifilm Finepix F31 fd; Fujifilm Corp., Tokyo, Japan). We recorded the times at the formation of a 1-mm gap
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SUTURE MATERIAL IN 6-STRAND REPAIR
and at failure of the repair site by suture pullout or suture rupture. For each tendon repair specimen, we generated load-displacement curves and recorded the mechanism of failure. We determined the ultimate tensile strength of the repair, or load to failure, by the peak value on the load-displacement curve (N). We calculated the force at which a 1-mm gap formed by frame-by-frame playback of the video taken, and correlated the time to the loading graphs generated by the Instron software program. We calculated the stiffness by taking the gradient of the linear portion of the load-displacement curve. We assessed 4 objective variables for each specimen: mechanism of failure, ultimate tensile strength, load to 1-mm gap formation, and stiffness.
TABLE 1. Pairwise Multiple Comparison Procedures for Ultimate Tensile Strength and Gap Force Difference of Means
p
q
P
Ultimate tensile strength (Tukey test) Comparison FiberLoop vs Supramid
50.7
3 11.7
⬍ .001
FiberLoop vs TendoLoop
44.8
3
9.9
⬍ .001
3
1.4
.610
Tendo-Loop vs Supramid
5.87
Gap force (Tukey test)
Statistical analysis We used a significance level of .05 for all analysis. We analyzed data with a 1-way analysis of variance and performed pairwise comparison between groups using the Tukey test when we found statistical significance between groups for each data set. RESULTS Mechanism of failure The braided polyblend repairs failed by suture breakage (50%) and suture pullout (50%). All of the cable nylon repairs failed by suture breakage. Most of the braided polyester repairs (80%) failed by suture breakage; the remaining 20% failed by suture pullout. There were no knot failures. Ultimate tensile strength Specimens repaired with the braided polyblend suture had the highest mean ultimate tensile strength (97 N; standard deviation [SD] 22), followed by braided polyester (52 N; SD 11) and then cable nylon (47 N; SD 8). The difference was statistically significant (P ⬍ .001). The Tukey test showed a significant difference between the braided polyblend versus the cable nylon groups and between the braided polyblend versus the braided polyester groups, but not between the braided polyester versus the cable nylon groups (Table 1). Load to 1-mm gap formation Specimens repaired with braided polyblend had the highest mean gap force (35 N; SD 7), followed by braided polyester (18 N; SD 6) and cable nylon (17 N; SD 6). The difference was statistically significant (P ⬍ .001). Similarly, the Tukey test showed a significant difference between the
Comparison FiberLoop vs Supramid
17.0
3
7.8
⬍ .001
FiberLoop vs TendoLoop
16.8
3
8.0
⬍ .001
3
0.09
Tendo-Loop vs Supramid
0.19
.998
q, statistic used by SigmaStat (software used to perform the Tukey test); p, number of means spanned in the comparison.
braided polyblend versus the cable nylon groups and between the braided polyblend versus the braided polyester groups, but not between the braided polyester versus the cable nylon groups (Table 1). Stiffness The mean stiffness was 4.7 N/mm (SD 2.3) for the cable nylon group, 5.5 N/mm (SD 1.9) for the braided polyester group, and 5.9 N/mm (SD 1.8) for the braided polyblend group. The difference was not statistically significant (P ⫽ .425). DISCUSSION Pennington20 first suggested the locking loop suture configuration in 1979 as an effective repair technique for flexor tendons, conferring enough strength for an early mobilization protocol. Pennington also emphasized that the correct orientation of the intratendinous (longitudinal and transverse) components was a critical factor affecting a repair’s strength. In 1997, Hotokezaka and Manske21 described locking and grasping suture methods and demonstrated the superiority of the locking suture method over the grasping method. Previous studies have shown that core suture repairs that incor-
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porate locking techniques typically do not fail by suture pullout, but rather by suture breakage.15,21,22 In such cases, material properties and strength of the suture become the limiting factor in the biomechanical performance of the repair.17 The original 6-strand locking Lim-Tsai suture technique has been reported to have higher repair strength than 2- or 4-strand repair techniques reported in other studies.23 The modified version used in this study retained the advantages of the original Lim-Tsai technique while having the advantages of requiring only 1 loop suture per repair and having the knot placed away from the repair site in an extratendinous location. Studies involving various types of sutures and repair techniques have shown consistently that single knot repairs are significantly stronger than double knot repairs.24,25 This could be explained by the relative ease of mastering a single knot suture technique compared with a double knot technique, especially by trainees with limited experience in tendon repair. In addition, placement of a single knot away from the repair site outside the tendon has been shown to result in less suture material at the repair site and a 22% increase in strength comparing 2-strand repairs in a canine model.26 We chose porcine forelimbs flexor tendons for this study because they were readily available and costeffective and have demonstrated a comparable model to humans for the study of flexor tendon repair.27 The lack of epitendinous sutures in the repairs done in the study likely accounted for the lower ultimate tensile strength and gap force values exhibited for the cable nylon and braided polyester repairs, compared with previous studies.16,17 We chose not to incorporate an epitendinous repair, to reduce the number of variables influencing the strength of the repair. In our study protocol, we chose a 1-mm gap as a comparative variable, because this was representative of gap force as shown in the Gill et al23 comparative study of repair techniques in cadaveric tendons. In that study, there was minimal difference in tensile force between the 1- and 2-mm gap formation in the testing of the 4 groups of repair techniques, which included the original 6-strand Lim-Tsai double loop suture repair. Those results were 26 ⫾ 9 N at the 1-mm gap formation and 28 ⫾ 8 N at the 2-mm gap formation. We obtained results in ultimate tensile strength and gap force values in our 6-strand looped braided polyblend comparable to those in previous studies using 4-strand repair techniques. Lawrence and Davis17 used a 4-strand locking single-cross repair technique in porcine flexor tendons and showed that repairs using braided polyblend and stainless-steel sutures were sig-
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nificantly stronger than those using nylon, polyester (Ethibond; Ethicon, Edinburgh, UK), and polypropylene (Prolene; Ethicon) sutures. Braided polyblend repairs had a mean ultimate tensile strength of 81 N, compared with those of nylon (47 N), polypropylene (63 N), and polyester (66 N); all repairs failed by suture rupture at the locking site. Miller et al16 used a Massachusetts General Hospital repair technique on human cadaveric flexor tendons and reported a significantly higher ultimate tensile strength in braided polyblend repairs (124 N) compared with polyester (82 N) and nylon repairs (69 N). A total of 99% of the repairs failed by suture rupture, and the remaining ones failed by suture pullout. In our study, we were able to achieve a mean ultimate tensile strength of 97 N (range, 50 –124 N) in the braided polyblend repairs. The mean 1-mm gap force achieved was 35 N (range, 23– 41 N). Half of the repairs failed by suture breakage and half by suture pullout. None failed by suture unraveling at the knot. According to Strickland’s28 –30 studies, the estimated force required for passive motion is 2 to 4 N, for active flexion with mild resistance up to 10 N, for moderate resisted flexion up to 17 N, for strong grip composite grasp up to 70 N, and for tip-pinch using the index finger up to 120 N. Our results support the possibility of starting an immediate active motion protocol limited to light grip with no gapping at the repair site in a braided polyblend 6-strand core suture repair. However, this will still be insufficient to withstand a noncompliant patient’s activity, which could well include strong composite grasp. This study has limitations. We performed the repairs on fresh porcine tendons, not human tendons. The cross-sectional diameter of these tendons was grossly larger than that of human tendons. Anecdotally, this probably introduces a false elevation of the true tensile values, because a larger amount of tendon substance can be captured at the locking sites in the porcine tendons compared with human tendons, although there have been no studies to prove this. We placed no epitendinous sutures, which can improve the repair strength by up to 50% and reduce gapping at the repair site significantly.30 However, we chose not to incorporate an epitendinous repair, to reduce the number of variables influencing the strength of the repair. This study does not take into consideration suture site bulk and adhesion formation. The extratendinous 5 throws used to knot the braided polyblend suture repairs added considerable bulk to the repair site and may
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cause triggering or adhesion formation, especially in zone II flexor tendon repairs in vivo. This study does not taken into consideration the physiologic effects of tendon healing as an influence of study results. Adhesion formation and its influence of work of flexion are important considerations in zone II flexor tendon repair. In clinical practice, given the choice of the 3 suture materials in this study, one might consider using the braided polyblend suture to achieve a stronger repair compared with the cable nylon and braided polyester sutures. This could increase the surgeon’s confidence in starting an early active motion rehabilitation protocol. REFERENCES 1. Elliot D, Moiemen NS, Flemming AF, Harris SB, Foster AJ. The rupture rate of acute flexor tendon repairs mobilized by the controlled active motion regimen. J Hand Surg 1994;19B:607– 612. 2. Taras JS, Raphael JS, Marczyk SC, Bauerle WB. Evaluation of suture caliber in flexor tendon repair. J Hand Surg 2001;26A:1100 – 1104. 3. Alavanja G, Dailey E, Mass DP. Repair of zone II flexor digitorum profundus lacerations using varying suture sizes: a comparative biomechanical study. J Hand Surg 2005;30A:448 – 454. 4. Barrie KA, Tomak SL, Cholewicki J, Merrell GA, Wolfe SW. Effect of suture locking and suture caliber on fatigue strength of flexor tendon repairs. J Hand Surg 2001;26A:340 –346. 5. Momose T, Amadio PC, Zhao C, Zobitz ME, An KN. The effect of knot location, suture material, and suture size on the gliding resistance of flexor tendons. J Biomed Mater Res 2000;53:806 – 811. 6. Cao Y, Zhu B, Xie RG, Tang JB. Influence of core suture purchase length on strength of four-strand tendon repairs. J Hand Surg 2006; 31A:107–112. 7. Wada A, Kubota H, Hatanaka H, Hotokezaka S, Miura H, Iwamoto Y. The mechanical properties of locking and grasping suture loop configurations in four-strand core suture techniques. J Hand Surg 2000;25B:548 –551. 8. Soejima O, Diao E, Lotz JC, Hariharan JS. Comparative mechanical analysis of dorsal versus palmar placement of core suture for flexor tendon repairs. J Hand Surg 1995;20A:801– 807. 9. Aoki M, Manske PR, Pruitt DL, Kubota H, Larson BJ. Work of flexion after flexor tendon repair according to the placement of sutures. Clin Orthop Relat Res 1995;320:205–210. 10. Ketchum LD. Suture materials and suture techniques used in tendon repair. Hand Clin 1985;1:43–53. 11. Angeles JG, Heminger H, Mass DP. Comparative biomechanical performances of 4-strand core suture repairs for zone II flexor tendon lacerations. J Hand Surg 2002;27A:508 –517.
12. Dona E, Gianoutsos MP, Walsh WR. Optimizing biomechanical performance of the 4-strand cruciate flexor tendon repair. J Hand Surg 2004;29A:571–580. 13. Viinikainen A, Göransson H, Huovinen K, Kellomäki M, Rokkanen P. A comparative analysis of the biomechanical behaviour of five flexor tendon core sutures. J Hand Surg 2004;29B:536 –543. 14. Thurman R, Trumble TE, Hanel DP, Tencer AF, Kiser PK. Two-, four-, and six-strand zone II flexor tendon repairs: an in situ biomechanical comparison using a cadaver model. J Hand Surg 1998;23A: 261–265. 15. Barrie KA, Tomak SL, Cholewicki J, Wolfe SW. The role of multiple strands and locking sutures on gap formation of flexor tendon repairs during cyclical loading. J Hand Surg 2000;25A:714 –720. 16. Miller B, Dodds SD, deMars A, Zagoreas N, Waitayawinyu T, Trumble TE. Flexor tendon repairs: the impact of FiberWire on grasping and locking core sutures. J Hand Surg 2007;32A:591–596. 17. Lawrence TM, Davis TRC. A biomechanical analysis of suture materials and their influence on a four-strand flexor tendon repair. J Hand Surg 2005;30A:836 – 841. 18. Lim BH, Tsai TM. The six-strand technique for flexor tendon repair. Atlas Hand Clin 1996;1:65–76. 19. Waitayawinyu T, Martineau PA, Luria S, Hanel DP, Trumble TE. Comparative biomechanic study of flexor tendon repair using FiberWire. J Hand Surg 2008;33A:701–708. 20. Pennington DG. The locking loop tendon suture. Plast Reconstr Surg 1979;63:648 – 652. 21. Hotokezaka S, Manske PR. Differences between locking loops and grasping loops: effects on 2-strand core suture. J Hand Surg 1997; 22A:995–1003. 22. Hatanaka H, Manske PR. Effect of suture size on locking and grasping flexor tendon repair techniques. Clin Orthop Relat Res 2000;375:267–274. 23. Gill RS, Lim BH, Shatford RA, Toth E, Voor MJ, Tsai TM. A comparative analysis of the six-strand double-loop flexor tendon repair and three other techniques: a human cadaveric study. J Hand Surg 1999;24A:1315–1322. 24. Aoki M, Pruitt DL, Kubota H, Manske PR. Effect of suture knots on tensile strength of repaired canine flexor tendons. J Hand Surg 1995;20B:72–75. 25. Rees L, Matthews A, Masouros SD, Bull AMJ, Haywood R. Comparison of 1- and 2-knot, 4-strand, double-modified kessler tendon repairs in a porcine model. J Hand Surg 2009;34A:705–709. 26. Panandrea R, Seitz WH Jr, Shapiro P, Borden B. Biomechanical and clinical evaluation of the epitenon-first technique of flexor tendon repair. J Hand Surg 1995;20A:261–266. 27. Smith AM, Forder JA, Annapureddy SR, Reddy KSK, Amis AA. The porcine forelimb as a model for human flexor tendon surgery. J Hand Surg 2005;30B:307–309. 28. Strickland JW. Flexor tendon injuries: I. Foundations of treatment. J AM Acad Orthop Surg 1995;3:44 –54. 29. Strickland JW. The Indiana method of flexor tendon repair. Atlas Hand Clin 1996;1:77–103. 30. Strickland JW. Development of flexor tendon surgery: twenty-five years in progress. J Hand Surg 2000;25A:214 –235.
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