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Biomechanical Evaluation of 4-Strand Flexor Tendon Repair Techniques, Including a Combined Kessler–Tsuge Approach
SCIENTIFIC ARTICLE
Biomechanical Evaluation of 4-Strand Flexor Tendon Repair Techniques, Including a Combined KesslereTsuge Approach Christian Renner, MD, Fernando Corella, MD, Nicole Fischer, MSc Purpose To test the ultimate tensile strength and stiffness of 3 flexor tendon repair techniques using looped suture material. Methods Seventeen fresh porcine flexor tendons were randomized to a single-throw, 4-strand Kessler technique with a looped structure, a double-throw, 4-strand Tsuge technique with 2 looped structures, or a single-throw, 4-strand KesslereTsuge technique with a looped structure. Thirty additional fresh porcine flexor tendons were randomized to the same techniques but with a running epitendinous repair. We measured ultimate tensile strength to failure and stiffness and recorded the cause of failure. Results The Tsuge technique had the highest mean ultimate tensile strength at 75 N (SD, 14 N) versus 63 N (SD, 13 N) for the KesslereTsuge method and 46 N (SD, 11 N) for the Kessler technique. Differences between the Tsuge and KesslereTsuge, the KesslereTsuge and Kessler, and the Tsuge and Kessler techniques were significant. Mean suture stiffness was 6.8 N/mm for the Tsuge technique, 5.7 N/mm for the KesslereTsuge technique, and 4.6 N/mm for the Kessler technique. The difference between the Tsuge and Kessler techniques was significant. Analyzing the tests with or without an epitendinous suture separately did not affect the significance of the differences. Conclusions The modified double-throw, 4-strand Tsuge was the strongest suture technique in this study. It may be a clinically acceptable, albeit slightly weaker alternative to the more complicated Tsuge method. Clinical relevance A combined KesslereTsuge approach might be an option for flexor tendon repair. (J Hand Surg Am. 2015;40(2):229e235. Copyright Ó 2015 by the American Society for Surgery of the Hand. All rights reserved.) Key words Flexor tendon, repair, biomechanics, FiberWire, looped suture.
From the Department of Distal Extremities and Product Engineering, Arthrex GmbH, Munich, Germany; and the Hand Surgery Unit, Department of Orthopedics and Traumatology, Infanta Leonor University Hospital; and the Department of Hand Surgery, Beata María Ana Hospital, Madrid, Spain. Received for publication June 30, 2014; accepted in revised form October 28, 2014. C.R. and NF. are employed by Arthrex GmbH (Munich, Germany). Corresponding author: Christian Renner, MD, Arthrex GmbH, Erwin-Hielscherstr 9, 81249 München, Germany; e-mail: [email protected]. 0363-5023/15/4002-0004$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2014.10.055
UTHORS AGREE ON THE GOALS OF a perfect flexor tendon repair: sufficient tensile strength to allow early mobilization,1 prevention of adhesion formation,2 stimulation of tendon healing,3 and improved clinical outcome.4,5 However, consensus is lacking regarding which technique achieves these desired outcomes. Biomechanical studies indicate that the tensile strength of tendon repair is improved by increasing the number of strands crossing the repair site, using larger-caliber sutures and locking suture techniques, and adding an epitendinous suture.6 Current best practice for flexor tendon repair includes an
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TABLE 1.
COMBINED KESSLEReTSUGE APPROACH FOR FLEXOR TENDON REPAIR
Ultimate Tensile Strength Maximum Force (N) Group
Suture Type
N
Mean
SD
Group 1—without epitendinous suture
Modified double-throw 4-strand Tsuge
6
78
11
Single-throw 4-strand Kessler-Tsuge
6
60
13
Modified single-throw 4-strand Kessler
5
54
12
Group 2—with epitendinous suture
Modified double-throw 4-strand Tsuge
10
73
15
Single-throw 4-strand Kessler-Tsuge
10
64
13
Modified single-throw 4-strand Kessler
10
41
9
Groups 1 and 2
P
Modified double-throw 4-strand Tsuge
16
75
14
.026, < .001
Single-throw 4-strand Kessler-Tsuge
16
63
13
.026, .002, < .001
Modified single-throw 4-strand Kessler
15
46
11
.002, < .001
N, Newton; SD, standard deviation.
FIGURE 1: Modified single-throw, 4-strand Kessler with a looped suture.
atraumatic surgical technique7 with tendon anchorage 10 mm or more from the cut surface.8 The suture material should allow easy handling and hold a secure knot9 that can be buried as much as possible inside the tendon.10,11 Furthermore, tendon vascularization should be unaffected by the suture material, as should the gliding of the tendon inside the tendon sheath and pulleys.12 Despite the publication of several alternative techniques,13 the Kirchmayr technique, as modified by Kessler and Zechner and known as the Kessler technique, remains one of the more popular approaches.11,14e16 Because increasing the number of strands increases the strength of the repair,17,18 the Kessler technique may be modified by a doublethrow Kessler technique19 or made even simpler by using a looped suture material such as the Fiberloop (Arthrex, Inc, Naples, FL).20 Other authors prefer a modified double Tsuge technique and report easy placement and excellent strength.12,17,21 Multiplestrand techniques add to the complexity, making accurate coaptation of the tendon ends with an atraumatic suture placement potentially more difficult. It is therefore preferable to create multiple-strand suture patterns with fewer suture passages and no knots on the tendon surface.22 Our aim was to design a looped technique that followed 4 principles: a 4-strand technique using J Hand Surg Am.
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FIGURE 2: Modified double-throw, 4-strand Tsuge with a looped suture.
FiberWire (Arthrex, Inc), because this suture material has superior ultimate strength and pull-out versus other suture materials23; no bulky knots in the repair site, which may improve healing; no bulky knots on the tendon surface, which could improve tendon sliding; and a suture that crosses the repair site only twice, which could make accurate coaptation with an atraumatic technique easier. We examined a modification of a Kessler technique (modified single-throw, 4-strand Kessler), a modification of a Tsuge technique (modified double-throw, 4strand Tsuge) and a combination of both (single-throw, 4-strand KesslereTsuge). All techniques use a looped suture material with 2 strands placed for each pass of the needle. Hypothesizing that the KesslereTsuge technique would not be notably biomechanically weaker than a double Tsuge technique, which has 2 buried knots, we compared the core suture strength of all 3 techniques. We performed the tests with and without an epitendinous suture to determine its impact in the high-tension sector. MATERIALS AND METHODS We used a looped suture with a 3/8 circular tapered point needle (4-0 FiberWire) using the 3 techniques. All techniques were tested without (n ¼ 17; group 1) and with an epitendinous suture (n ¼ 30; group 2). Vol. 40, February 2015
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FIGURE 3: Locking the suture with a loop-lock.
FIGURE 5: Returning the suture to the incision.
FIGURE 4: Placing a cannula between tendon and suture.
We chose porcine forelimbs flexor tendons for this study because they were readily available and cost-effective and have been shown to offer a comparable model for human tendons for the study of flexor tendon repair.23,24 We harvested and randomized 47 fresh porcine flexor tendons from the central 2 rays of the forefeet. All tendons were continuously stored in saline solutionesoaked gauze compress pouches to preserve the tissue uniformly. The tendons were transected immediately before suturing. Table 1 shows the distribution of the repairs. The same surgeon performed all repairs.
FIGURE 6: The needle is shuttled with the cannula under the first pair of sutures.
Modified single-throw, 4-strand Kessler with looped suture Approximately 1 cm distal from the transsection, we made a 3-mm longitudinal incision on the tendon surface to a depth of 2 to 3 mm to bury the eventual knot. The needle of the looped suture was then advanced into the incision and guided to the surface of the tendon. We then used a regular Kessler suture pattern. Appropriate tension was applied to all strands and 5 knots were tied using all 4 strands, employing 2 strands simultaneously (double clockwiseesingle clockwiseesingle counterclockwiseesingle clockwiseesingle counterclockwise) (Fig. 1). In group 2, all tendons received a running epitendinous suture at the repair site using 7 needle passes.
incisions, with 2 mm of tendon fibers included. The needle was then brought through the looped end of the suture to create a loop-lock. The needle was reinserted close to the loop-lock and advanced longitudinally to the cut surface, where it left the tendon and reentered the opposite cut surface at the same level and was passed through the tendon to the level of the longitudinal incision. It was reinserted close to the exit point and guided horizontally into the longitudinal incision. One strand of the looped suture was cut and the needle with the remaining suture was reinserted into the incision to continue across the tendon. The needle was guided out at the side of the tendon and then passed back toward the longitudinal incision. After applying appropriate tension to all suture strands, we tied the 2 ends of the suture using 5 knots in the previously described sequence. The technique was then repeated inversely (Fig. 2). In group 2, all tendons received a running epitendinous suture at the repair site using 7 needle passes.
Modified double-throw, 4-strand Tsuge with looped suture One centimeter from the cut ends of the dissected tendon, we made a 1-cm longitudinal incision to a depth of 2 to 3 mm. The needle of the looped suture was inserted into the tendon adjacent to one of these
Single-throw, 4-strand KesslereTsuge A longitudinal incision was placed at least 1 cm from the cut surface. To one side of the incision, we placed a looped stitch through the tendon and locked it at the side by passing the needle through the loop (Fig. 3).
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FIGURE 7: Five knots are tied including the first pair of sutures.
FIGURE 9: Mean maximum force of each group and technique with statistical values of significance.
FIGURE 8: Final result of the KesslereTsuge technique.
The needle was then passed transversely through the tendon to exit in the longitudinal incision and the sutures were pulled through fully. The needle was reinserted into the longitudinal incision, aimed for the cut surface, and pulled through. Before we pulled the sutures fully tight, we placed an injection cannula (27 gauge 1.5 in) between the tendon and the suture (Fig. 4). The needle was then passed approximately 1 cm from the cut surface of the other tendon end. The suture needle was then passed transversely; and before passing the needle into the cut surface the ends of the tendon were brought into contact. The needle was advanced to the side of the tendon level with the longitudinal incision and then directed back into the incision (Fig. 5). We made sure the cut surfaces had good contact. One strand of the suture was cut and the needle tip was inserted into the sharp opening of the cannula (Fig. 6) using the cannula as a shuttle underneath the first suture pair (Fig. 7). The 5 knots in the previously described sequence were tightened, which automatically included the initial suture pair, thus adding perpendicular tension to the whole suture pattern (Fig. 8). In group 2, all tendons received a running epitendinous suture at the repair site using 7 needle passes. Mechanical testing We used an Instron 5543 Table-top Universal testing device with an Instron 1-kN static load cell (Instron, High Wycombe, United Kingdom) to measure ultimate tensile strength. Tensile force normal to the axis of connection was applied at a loading rate of 20 mm/min. Displacement was measured in millimeters, with loadto-displacement curves calculated. We determined the ultimate load at failure and stiffness using Matlab R2013a (MathWorks, Inc, Natick, MA). Stiffness was measured between 5 and 20 N. J Hand Surg Am.
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We tested all tendons for ultimate load to failure, load to displacement, failure mode, and stiffness. Defined failure mechanisms were suture breakage, suture pull-out from the tendon, and knot failure. Suture breakage was defined as a ruptured suture. Suture pull-out was defined as an intact suture construct that had slipped out of the tendon. Statistical analysis We performed pairwise multiple comparisons between groups using the Tukey test. Statistically significant differences between suture techniques were determined for both approaches using one-way ANOVA. P < .05 was considered significant. RESULTS The highest mean tensile strength was seen with the double-throw, 4-strand Tsuge suture technique, followed by the KesslereTsuge technique (Table 1, Fig. 9). The weakest suture technique was the 4-strand Kessler. These findings were not markedly altered by the presence of an epitendinous suture or by analyzing the groups separately. Table 2 shows the mean suture stiffness in the combined groups and the Table 3 lists the mechanisms of suture failure. DISCUSSION Brockard et al20 reported that single-throw looped suture repairs were weaker than those using a doublethrow single suture. However, the study also showed that a 2-strand Kessler repair with FiberWire was as strong as a 4-strand cruciate repair with Supramid (B. Braun, Tuttlingen, Germany) on all tested parameters. The ultimate strength of FiberWire is superior to that of other suture materials, as reflected in the maximum tensile strength of flexor tendon repairs.23,25 Because Vol. 40, February 2015
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COMBINED KESSLEReTSUGE APPROACH FOR FLEXOR TENDON REPAIR
TABLE 2.
Mean Stiffness of Each Group and Technique Mean Stiffness (N) Group
Group 1—without epitendinous suture
Group 2—with epitendinous suture
Groups 1 and 2
TABLE 3.
Suture Type
N
Mean
SD
Modified double-throw 4-strand Tsuge
6
7
2
Single-throw 4-strand Kessler-Tsuge
6
5
2
Modified single-throw 4-strand Kessler
5
4
2
Modified double-throw 4-strand Tsuge
10
7
1
Single-throw 4-strand Kessler-Tsuge
10
6
1
Modified single-throw 4-strand Kessler
10
5
1
P
Modified double-throw 4-strand Tsuge
16
7
2
< .001
Single-throw 4-strand Kessler-Tsuge
16
6
2
< .001
Modified single-throw 4-strand Kessler
15
5
1
< .001
Mechanism of Suture Failure Group
Group 1—without epitendinous suture
Suture Type
Suture Breakage
Tsuge (n ¼ 6)
100% (n ¼ 6)
Kessler-Tsuge (n ¼ 6)
100% (n ¼ 6)
Suture Pullout
Kessler (n ¼ 5) Group 2—with epitendinous suture
Groups 1 and 2
Knot Failure
100% (n ¼ 5)
Tsuge (n ¼ 10)
60% (n ¼ 6)
40% (n ¼ 4)
Kessler-Tsuge (n ¼ 10)
70% (n ¼ 7)
30% (n ¼ 3)
Kessler (n ¼ 10)
50% (n ¼ 5)
50% (n ¼ 5)
Tsuge (n ¼ 16)
37.5% (n ¼ 6)
37.5% (n ¼ 6)
25% (n ¼ 4)
Kessler-Tsuge (n ¼ 16)
37.5% (n ¼ 6)
43.7% (n ¼ 7)
18.7% (n ¼ 3)
Kessler (n ¼ 15)
33% (n ¼ 5)
we were seeking a suture technique with the right balance between simplicity and ultimate tension force, we examined only looped suture techniques with the Fiberloop suture for the current analysis. The Kessler and Tsuge techniques are well established in Europe and well-known in the United States. However, modifications have been made to bury the knot in the tendon. The third technique combined both prior approaches, adding strength to the Kessler without the need for additional suture material or additional operating time. The current study was performed to ascertain whether this technique had sufficient tensile strength for flexor tendon repair. To examine whether the epitendinous suture benefits the high-tension sector, we performed the core repairs with and without an epitendinous suture. We found no significant differences in terms of ultimate force, similar to previous reports20,26,27; the epitendinous repair failed before the core repair in each case. Many authors avoid the epitendinous suture in biomechanical testing to eliminate confounding variables.20,23 The epitendinous suture is valuable because J Hand Surg Am.
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66% (n ¼ 10)
it supports the core suture, especially at a tensile range of 2 to 9 N, which occurs during active motion without resistance, and at a tensile range of 8 to 35 N, which occurs during active motion with light resistance.19 Nevertheless, some of the means in group 2 (with an epitendinous suture) were below those in group 1. This suggests that the epitendinous suture has no influence on the high-tension area described previously.20,26,27 It may be that the difference in means was affected by the sample sizes, which made the smaller group 1 vulnerable to outliers. The largest discrepancy between groups 1 and 2 was seen in the Kessler technique. Knot slippage was the most frequent cause of failure. We used the double-strand knot because it seemed the best compromise for creating a small knot instead of 2 single-strand knots, but a different tying technique may well have altered the results. The larger size of group 2 may represent the true performance of the technique. Haimovici et al28 reported a similar Kessler technique (Pennington, without epitendinous suture) with 4-0 Fiberloop and achieved a maximal tensile strength of 33 4 N. Vol. 40, February 2015
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However, for a 4-strand Kessler with 2 single 4-0 FiberWire sutures the repair had a strength of 56 N, which supports our finding. The Kessler technique has high value, although it seemed from our data to be unfavorable for a looped suture technique. Based on the observation that the epitendinous suture did not add ultimate strength to the repair, we combined both groups in the statistical analysis to increase the sample size. Our tests demonstrated in both groups that the modified double-throw, 4-strand Tsuge technique had the highest tensile strength whereas the looped Kessler technique had the lowest. Although our results showed that the combined KesslereTsuge technique was weaker than a doublethrow Tsuge, the tensile strength was still likely to be high enough to allow early mobilization. Schuind et al29 reported a threshold for unresisted active tendon mobilization of above 35 N. Both the doublethrow Tsuge and KesslereTsuge techniques were clearly above this threshold, whereas the mean of the sutures with the modified Kessler technique failed close to this value in 66% of cases owing to knot failure. For the Tsuge and KesslereTsuge techniques, the knot was the reason for failure in 37% and 44% of cases, respectively. However, in the Kessler technique 66% of failures were related to knot slippage. The security of a 4-strand knot, which was used to tie the 4 ends of the looped suture in the Kessler technique, is clearly weaker than that of a 2-strand knot. Internal data from Arthrex, Inc, on the strength of 4-0 FiberWire in a plain test approach showed the ultimate strength of 21 N for a 5-throw surgical knot tied to both ends of a single suture and an ultimate strength of 56 N in a straight pull-out test. These forces are below the mean of the tested repairs with Tsuge and Kesslere Tsuge. For the modified single-throw, 4-strand Kessler technique, however, the mean of the ultimate tensile strength of the repair was 11 N below the ultimate strength of a straight pull-out test of FiberWire. The mode of failure was not suture breakage but rather knot failure (66%) or suture pull-out (33%). Suture breakage in the Tsuge and KesslereTsuge techniques occurred with equal incidence (38%). From these findings, it might be deduced that the Tsuge and KesslereTsuge techniques can add more strength to the repair, with tension levels that let the suture break before the suture construct pulls out of the tendon or before the knot fails. The Tsuge and Kesslere Tsuge techniques take advantage of the looped suture by adding a loop-lock at one end of the suture pair. Each looped suture is therefore fixed with 2 knots versus a single knot with the Kessler technique. This may share the tension load over the overall construct J Hand Surg Am.
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much better than the Kessler technique. The hybrid technique is easy to perform, with one looped suture giving a 4-strand pattern. It is similar to the established Kessler method but adds additional strength because an additional non-profile knot fixes the suture directly to the tendon fibers. In conclusion, the results biomechanically support the double-throw, 4-strand Tsuge technique for flexor tendon repair. However, the KesslereTsuge method appears to be a good alternative, with an acceptable reduction in strength and the advantage of only one looped suture required. In contrast, the looped Kessler technique showed the lowest strength, which is in line with the results of other authors.30 ACKNOWLEDGMENTS The authors thank Liam Davenport (Medicalwriters. com GmbH) for editorial support in producing the manuscript. REFERENCES 1. Lawrence TM, Davis TR. A biomechanical analysis of suture materials and their influence on a four-strand flexor tendon repair. J Hand Surg Am. 2005;30(4):836e841. 2. Aoki M, Kubota H, Pruitt DL, Manske PR. Biomechanical and histologic characteristics of canine flexor tendon repair using early postoperative mobilization. J Hand Surg Am. 1997;22(1):107e114. 3. Kubota H, Manske PR, Aoki M, Pruitt DL, Larson BJ. Effect of motion and tension on injured flexor tendons in chickens. J Hand Surg Am. 1996;21(3):456e463. 4. Small JO, Brennen MD, Colville J. Early active mobilisation following flexor tendon repair in zone 2. J Hand Surg Br. 1989;14(4): 383e391. 5. Bainbridge LC, Robertson C, Gillies D, Elliot D. A comparison of post-operative mobilization of flexor tendon repairs with “passive flexion-active extension” and “controlled active motion” techniques. J Hand Surg Br. 1994;19(4):517e521. 6. Waitayawinyu T, Martineau PA, Luria S, Hanel DP, Trumble TE. Comparative biomechanic study of flexor tendon repair using FiberWire. J Hand Surg Am. 2008;33(5):701e708. 7. Le SV, Chiu S, Meineke RC, Williams P, Wongworawat MD. Number of suture throws and its impact on the biomechanical properties of the four-strand cruciate locked flexor tendon repair with FiberWire. J Hand Surg Eur Vol. 2012;37(9):826e831. 8. Lee SK, Goldstein RY, Zingman A, Terranova C, Nasser P, Hausman MR. The effects of core suture purchase on the biomechanical characteristics of a multistrand locking flexor tendon repair: a cadaveric study. J Hand Surg Am. 2010;35(7):1165e1171. 9. Trail IA, Powell ES, Noble J. An evaluation of suture materials used in tendon surgery. J Hand Surg Br. 1989;14(4):422e427. 10. Moriya T, Thoreson AR, Zhao C, An KN, Amadio PC. The effects of oblique or transverse partial excision of the A2 pulley on gliding resistance during cyclic motion following zone II flexor digitorum profundus repair in a cadaveric model. J Hand Surg Am. 2012;37(8): 1634e1638. 11. Zechner W, Buck-Gramcko D, Lohmann H, Goth D, Stock W. [Improvement of suture technic in flexor tendon injuries: clinical and experimental study]. Handchir Mikrochir Plast Chir. 1985;17(1):8e13. 12. Labana N, Messer T, Lautenschlager E, Nagda S, Nagle D. A biomechanical analysis of the modified Tsuge suture technique for repair of flexor tendon lacerations. J Hand Surg Br. 2001;26(4):297e300.
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13. Petri M, Ettinger M, Dratzidis A, et al. Comparison of three suture techniques and three suture materials on gap formation and failure load in ruptured tendons: a human cadaveric study. Arch Orthop Trauma Surg. 2012;132(5):649e654. 14. Langner C, Surke C, Wieskötter B. Prinzipien der Sehnenbehandlung: Beugesehnen. In: Towfigh H, Hierner R, Langer M, Friedel R, eds. Handchirurgie. Heidelberg, Germany: Springer-Verlag; 2011:101e139. 15. Kirchmayr L. Zur Technik der Sehnennaht. In: Borchard G, ed. Zentralblatt für Chirurgie. Leipzig, Germany: Verlag von Johann Ambrosius Barth; 1917:906e907. 16. Kessler I, Nissim F. Primary repair without immobilization of flexor tendon division within the digital sheath: an experimental and clinical study. Acta Orthop Scand. 1969;40(5):587e601. 17. Angeles JG, Heminger H, Mass DP. Comparative biomechanical performances of 4-strand core suture repairs for zone II flexor tendon lacerations. J Hand Surg Am. 2002;27(3):508e517. 18. McLarney E, Hoffman H, Wolfe SW. Biomechanical analysis of the cruciate four-strand flexor tendon repair. J Hand Surg Am. 1999;24(2):295e301. 19. Stephan C, Saalabian A, van Schoonhoven J, Prommersberger KJ. [Acute flexor tendon surgery]. Oper Orthop Traumatol. 2008;20(1):44e54. 20. Brockardt CJ, Sullivan LG, Watkins BE, Wongworawat MD. Evaluation of simple and looped suture and new material for flexor tendon repair. J Hand Surg Eur Vol. 2009;34(3):329e332. 21. Tsuge K, Yoshikazu I, Matsuishi Y. Repair of flexor tendons by intratendinous tendon suture. J Hand Surg Am. 1977;2(6):436e440.
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22. Cao Y, Tang JB. Biomechanical evaluation of a four-strand modification of the Tang method of tendon repair. J Hand Surg Br. 2005;30(4):374e378. 23. Gan AW, Neo PY, He M, Yam AK, Chong AK, Tay SC. A biomechanical comparison of 3 loop suture materials in a 6-strand flexor tendon repair technique. J Hand Surg Am. 2012;37(9):1830e1834. 24. Smith AM, Forder JA, Annapureddy SR, Reddy KS, Amis AA. The porcine forelimb as a model for human flexor tendon surgery. J Hand Surg Br. 2005;30(3):307e309. 25. 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 Am. 2007;32(5): 591e596. 26. Barmakian JT, Lin H, Green SM, Posner MA, Casar RS. Comparison of a suture technique with the modified Kessler method: resistance to gap formation. J Hand Surg Am. 1994;19(5):777e781. 27. Diao E, Hariharan JS, Soejima O, Lotz JC. Effect of peripheral suture depth on strength of tendon repairs. J Hand Surg Am. 1996;21(2):234e239. 28. Haimovici L, Papafragkou S, Lee W, Dagum A, Hurst LC. The impact of fiberwire, fiberloop, and locking suture configuration on flexor tendon repairs. Ann Plast Surg. 2012;69(4):468e470. 29. Schuind F, Garcia-Elias M, Cooney WP III, An KN. Flexor tendon forces: in vivo measurements. J Hand Surg Am. 1992;17(2): 291e298. 30. Choueka J, Heminger H, Mass DP. Cyclical testing of zone II flexor tendon repairs. J Hand Surg Am. 2000;25(6):1127e1134.
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Biomechanical Evaluation of 4-Strand Flexor Tendon Repair Techniques, Including a Combined KesslereTsuge Approach Christian Renner, MD, Fernando Corella, MD, Nicole Fischer, MSc Purpose To test the ultimate tensile strength and stiffness of 3 flexor tendon repair techniques using looped suture material. Methods Seventeen fresh porcine flexor tendons were randomized to a single-throw, 4-strand Kessler technique with a looped structure, a double-throw, 4-strand Tsuge technique with 2 looped structures, or a single-throw, 4-strand KesslereTsuge technique with a looped structure. Thirty additional fresh porcine flexor tendons were randomized to the same techniques but with a running epitendinous repair. We measured ultimate tensile strength to failure and stiffness and recorded the cause of failure. Results The Tsuge technique had the highest mean ultimate tensile strength at 75 N (SD, 14 N) versus 63 N (SD, 13 N) for the KesslereTsuge method and 46 N (SD, 11 N) for the Kessler technique. Differences between the Tsuge and KesslereTsuge, the KesslereTsuge and Kessler, and the Tsuge and Kessler techniques were significant. Mean suture stiffness was 6.8 N/mm for the Tsuge technique, 5.7 N/mm for the KesslereTsuge technique, and 4.6 N/mm for the Kessler technique. The difference between the Tsuge and Kessler techniques was significant. Analyzing the tests with or without an epitendinous suture separately did not affect the significance of the differences. Conclusions The modified double-throw, 4-strand Tsuge was the strongest suture technique in this study. It may be a clinically acceptable, albeit slightly weaker alternative to the more complicated Tsuge method. Clinical relevance A combined KesslereTsuge approach might be an option for flexor tendon repair. (J Hand Surg Am. 2015;40(2):229e235. Copyright Ó 2015 by the American Society for Surgery of the Hand. All rights reserved.) Key words Flexor tendon, repair, biomechanics, FiberWire, looped suture.
From the Department of Distal Extremities and Product Engineering, Arthrex GmbH, Munich, Germany; and the Hand Surgery Unit, Department of Orthopedics and Traumatology, Infanta Leonor University Hospital; and the Department of Hand Surgery, Beata María Ana Hospital, Madrid, Spain. Received for publication June 30, 2014; accepted in revised form October 28, 2014. C.R. and NF. are employed by Arthrex GmbH (Munich, Germany). Corresponding author: Christian Renner, MD, Arthrex GmbH, Erwin-Hielscherstr 9, 81249 München, Germany; e-mail: [email protected]. 0363-5023/15/4002-0004$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2014.10.055
UTHORS AGREE ON THE GOALS OF a perfect flexor tendon repair: sufficient tensile strength to allow early mobilization,1 prevention of adhesion formation,2 stimulation of tendon healing,3 and improved clinical outcome.4,5 However, consensus is lacking regarding which technique achieves these desired outcomes. Biomechanical studies indicate that the tensile strength of tendon repair is improved by increasing the number of strands crossing the repair site, using larger-caliber sutures and locking suture techniques, and adding an epitendinous suture.6 Current best practice for flexor tendon repair includes an
A
Ó 2015 ASSH
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r
229
230
TABLE 1.
COMBINED KESSLEReTSUGE APPROACH FOR FLEXOR TENDON REPAIR
Ultimate Tensile Strength Maximum Force (N) Group
Suture Type
N
Mean
SD
Group 1—without epitendinous suture
Modified double-throw 4-strand Tsuge
6
78
11
Single-throw 4-strand Kessler-Tsuge
6
60
13
Modified single-throw 4-strand Kessler
5
54
12
Group 2—with epitendinous suture
Modified double-throw 4-strand Tsuge
10
73
15
Single-throw 4-strand Kessler-Tsuge
10
64
13
Modified single-throw 4-strand Kessler
10
41
9
Groups 1 and 2
P
Modified double-throw 4-strand Tsuge
16
75
14
.026, < .001
Single-throw 4-strand Kessler-Tsuge
16
63
13
.026, .002, < .001
Modified single-throw 4-strand Kessler
15
46
11
.002, < .001
N, Newton; SD, standard deviation.
FIGURE 1: Modified single-throw, 4-strand Kessler with a looped suture.
atraumatic surgical technique7 with tendon anchorage 10 mm or more from the cut surface.8 The suture material should allow easy handling and hold a secure knot9 that can be buried as much as possible inside the tendon.10,11 Furthermore, tendon vascularization should be unaffected by the suture material, as should the gliding of the tendon inside the tendon sheath and pulleys.12 Despite the publication of several alternative techniques,13 the Kirchmayr technique, as modified by Kessler and Zechner and known as the Kessler technique, remains one of the more popular approaches.11,14e16 Because increasing the number of strands increases the strength of the repair,17,18 the Kessler technique may be modified by a doublethrow Kessler technique19 or made even simpler by using a looped suture material such as the Fiberloop (Arthrex, Inc, Naples, FL).20 Other authors prefer a modified double Tsuge technique and report easy placement and excellent strength.12,17,21 Multiplestrand techniques add to the complexity, making accurate coaptation of the tendon ends with an atraumatic suture placement potentially more difficult. It is therefore preferable to create multiple-strand suture patterns with fewer suture passages and no knots on the tendon surface.22 Our aim was to design a looped technique that followed 4 principles: a 4-strand technique using J Hand Surg Am.
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FIGURE 2: Modified double-throw, 4-strand Tsuge with a looped suture.
FiberWire (Arthrex, Inc), because this suture material has superior ultimate strength and pull-out versus other suture materials23; no bulky knots in the repair site, which may improve healing; no bulky knots on the tendon surface, which could improve tendon sliding; and a suture that crosses the repair site only twice, which could make accurate coaptation with an atraumatic technique easier. We examined a modification of a Kessler technique (modified single-throw, 4-strand Kessler), a modification of a Tsuge technique (modified double-throw, 4strand Tsuge) and a combination of both (single-throw, 4-strand KesslereTsuge). All techniques use a looped suture material with 2 strands placed for each pass of the needle. Hypothesizing that the KesslereTsuge technique would not be notably biomechanically weaker than a double Tsuge technique, which has 2 buried knots, we compared the core suture strength of all 3 techniques. We performed the tests with and without an epitendinous suture to determine its impact in the high-tension sector. MATERIALS AND METHODS We used a looped suture with a 3/8 circular tapered point needle (4-0 FiberWire) using the 3 techniques. All techniques were tested without (n ¼ 17; group 1) and with an epitendinous suture (n ¼ 30; group 2). Vol. 40, February 2015
COMBINED KESSLEReTSUGE APPROACH FOR FLEXOR TENDON REPAIR
231
FIGURE 3: Locking the suture with a loop-lock.
FIGURE 5: Returning the suture to the incision.
FIGURE 4: Placing a cannula between tendon and suture.
We chose porcine forelimbs flexor tendons for this study because they were readily available and cost-effective and have been shown to offer a comparable model for human tendons for the study of flexor tendon repair.23,24 We harvested and randomized 47 fresh porcine flexor tendons from the central 2 rays of the forefeet. All tendons were continuously stored in saline solutionesoaked gauze compress pouches to preserve the tissue uniformly. The tendons were transected immediately before suturing. Table 1 shows the distribution of the repairs. The same surgeon performed all repairs.
FIGURE 6: The needle is shuttled with the cannula under the first pair of sutures.
Modified single-throw, 4-strand Kessler with looped suture Approximately 1 cm distal from the transsection, we made a 3-mm longitudinal incision on the tendon surface to a depth of 2 to 3 mm to bury the eventual knot. The needle of the looped suture was then advanced into the incision and guided to the surface of the tendon. We then used a regular Kessler suture pattern. Appropriate tension was applied to all strands and 5 knots were tied using all 4 strands, employing 2 strands simultaneously (double clockwiseesingle clockwiseesingle counterclockwiseesingle clockwiseesingle counterclockwise) (Fig. 1). In group 2, all tendons received a running epitendinous suture at the repair site using 7 needle passes.
incisions, with 2 mm of tendon fibers included. The needle was then brought through the looped end of the suture to create a loop-lock. The needle was reinserted close to the loop-lock and advanced longitudinally to the cut surface, where it left the tendon and reentered the opposite cut surface at the same level and was passed through the tendon to the level of the longitudinal incision. It was reinserted close to the exit point and guided horizontally into the longitudinal incision. One strand of the looped suture was cut and the needle with the remaining suture was reinserted into the incision to continue across the tendon. The needle was guided out at the side of the tendon and then passed back toward the longitudinal incision. After applying appropriate tension to all suture strands, we tied the 2 ends of the suture using 5 knots in the previously described sequence. The technique was then repeated inversely (Fig. 2). In group 2, all tendons received a running epitendinous suture at the repair site using 7 needle passes.
Modified double-throw, 4-strand Tsuge with looped suture One centimeter from the cut ends of the dissected tendon, we made a 1-cm longitudinal incision to a depth of 2 to 3 mm. The needle of the looped suture was inserted into the tendon adjacent to one of these
Single-throw, 4-strand KesslereTsuge A longitudinal incision was placed at least 1 cm from the cut surface. To one side of the incision, we placed a looped stitch through the tendon and locked it at the side by passing the needle through the loop (Fig. 3).
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FIGURE 7: Five knots are tied including the first pair of sutures.
FIGURE 9: Mean maximum force of each group and technique with statistical values of significance.
FIGURE 8: Final result of the KesslereTsuge technique.
The needle was then passed transversely through the tendon to exit in the longitudinal incision and the sutures were pulled through fully. The needle was reinserted into the longitudinal incision, aimed for the cut surface, and pulled through. Before we pulled the sutures fully tight, we placed an injection cannula (27 gauge 1.5 in) between the tendon and the suture (Fig. 4). The needle was then passed approximately 1 cm from the cut surface of the other tendon end. The suture needle was then passed transversely; and before passing the needle into the cut surface the ends of the tendon were brought into contact. The needle was advanced to the side of the tendon level with the longitudinal incision and then directed back into the incision (Fig. 5). We made sure the cut surfaces had good contact. One strand of the suture was cut and the needle tip was inserted into the sharp opening of the cannula (Fig. 6) using the cannula as a shuttle underneath the first suture pair (Fig. 7). The 5 knots in the previously described sequence were tightened, which automatically included the initial suture pair, thus adding perpendicular tension to the whole suture pattern (Fig. 8). In group 2, all tendons received a running epitendinous suture at the repair site using 7 needle passes. Mechanical testing We used an Instron 5543 Table-top Universal testing device with an Instron 1-kN static load cell (Instron, High Wycombe, United Kingdom) to measure ultimate tensile strength. Tensile force normal to the axis of connection was applied at a loading rate of 20 mm/min. Displacement was measured in millimeters, with loadto-displacement curves calculated. We determined the ultimate load at failure and stiffness using Matlab R2013a (MathWorks, Inc, Natick, MA). Stiffness was measured between 5 and 20 N. J Hand Surg Am.
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We tested all tendons for ultimate load to failure, load to displacement, failure mode, and stiffness. Defined failure mechanisms were suture breakage, suture pull-out from the tendon, and knot failure. Suture breakage was defined as a ruptured suture. Suture pull-out was defined as an intact suture construct that had slipped out of the tendon. Statistical analysis We performed pairwise multiple comparisons between groups using the Tukey test. Statistically significant differences between suture techniques were determined for both approaches using one-way ANOVA. P < .05 was considered significant. RESULTS The highest mean tensile strength was seen with the double-throw, 4-strand Tsuge suture technique, followed by the KesslereTsuge technique (Table 1, Fig. 9). The weakest suture technique was the 4-strand Kessler. These findings were not markedly altered by the presence of an epitendinous suture or by analyzing the groups separately. Table 2 shows the mean suture stiffness in the combined groups and the Table 3 lists the mechanisms of suture failure. DISCUSSION Brockard et al20 reported that single-throw looped suture repairs were weaker than those using a doublethrow single suture. However, the study also showed that a 2-strand Kessler repair with FiberWire was as strong as a 4-strand cruciate repair with Supramid (B. Braun, Tuttlingen, Germany) on all tested parameters. The ultimate strength of FiberWire is superior to that of other suture materials, as reflected in the maximum tensile strength of flexor tendon repairs.23,25 Because Vol. 40, February 2015
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TABLE 2.
Mean Stiffness of Each Group and Technique Mean Stiffness (N) Group
Group 1—without epitendinous suture
Group 2—with epitendinous suture
Groups 1 and 2
TABLE 3.
Suture Type
N
Mean
SD
Modified double-throw 4-strand Tsuge
6
7
2
Single-throw 4-strand Kessler-Tsuge
6
5
2
Modified single-throw 4-strand Kessler
5
4
2
Modified double-throw 4-strand Tsuge
10
7
1
Single-throw 4-strand Kessler-Tsuge
10
6
1
Modified single-throw 4-strand Kessler
10
5
1
P
Modified double-throw 4-strand Tsuge
16
7
2
< .001
Single-throw 4-strand Kessler-Tsuge
16
6
2
< .001
Modified single-throw 4-strand Kessler
15
5
1
< .001
Mechanism of Suture Failure Group
Group 1—without epitendinous suture
Suture Type
Suture Breakage
Tsuge (n ¼ 6)
100% (n ¼ 6)
Kessler-Tsuge (n ¼ 6)
100% (n ¼ 6)
Suture Pullout
Kessler (n ¼ 5) Group 2—with epitendinous suture
Groups 1 and 2
Knot Failure
100% (n ¼ 5)
Tsuge (n ¼ 10)
60% (n ¼ 6)
40% (n ¼ 4)
Kessler-Tsuge (n ¼ 10)
70% (n ¼ 7)
30% (n ¼ 3)
Kessler (n ¼ 10)
50% (n ¼ 5)
50% (n ¼ 5)
Tsuge (n ¼ 16)
37.5% (n ¼ 6)
37.5% (n ¼ 6)
25% (n ¼ 4)
Kessler-Tsuge (n ¼ 16)
37.5% (n ¼ 6)
43.7% (n ¼ 7)
18.7% (n ¼ 3)
Kessler (n ¼ 15)
33% (n ¼ 5)
we were seeking a suture technique with the right balance between simplicity and ultimate tension force, we examined only looped suture techniques with the Fiberloop suture for the current analysis. The Kessler and Tsuge techniques are well established in Europe and well-known in the United States. However, modifications have been made to bury the knot in the tendon. The third technique combined both prior approaches, adding strength to the Kessler without the need for additional suture material or additional operating time. The current study was performed to ascertain whether this technique had sufficient tensile strength for flexor tendon repair. To examine whether the epitendinous suture benefits the high-tension sector, we performed the core repairs with and without an epitendinous suture. We found no significant differences in terms of ultimate force, similar to previous reports20,26,27; the epitendinous repair failed before the core repair in each case. Many authors avoid the epitendinous suture in biomechanical testing to eliminate confounding variables.20,23 The epitendinous suture is valuable because J Hand Surg Am.
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66% (n ¼ 10)
it supports the core suture, especially at a tensile range of 2 to 9 N, which occurs during active motion without resistance, and at a tensile range of 8 to 35 N, which occurs during active motion with light resistance.19 Nevertheless, some of the means in group 2 (with an epitendinous suture) were below those in group 1. This suggests that the epitendinous suture has no influence on the high-tension area described previously.20,26,27 It may be that the difference in means was affected by the sample sizes, which made the smaller group 1 vulnerable to outliers. The largest discrepancy between groups 1 and 2 was seen in the Kessler technique. Knot slippage was the most frequent cause of failure. We used the double-strand knot because it seemed the best compromise for creating a small knot instead of 2 single-strand knots, but a different tying technique may well have altered the results. The larger size of group 2 may represent the true performance of the technique. Haimovici et al28 reported a similar Kessler technique (Pennington, without epitendinous suture) with 4-0 Fiberloop and achieved a maximal tensile strength of 33 4 N. Vol. 40, February 2015
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However, for a 4-strand Kessler with 2 single 4-0 FiberWire sutures the repair had a strength of 56 N, which supports our finding. The Kessler technique has high value, although it seemed from our data to be unfavorable for a looped suture technique. Based on the observation that the epitendinous suture did not add ultimate strength to the repair, we combined both groups in the statistical analysis to increase the sample size. Our tests demonstrated in both groups that the modified double-throw, 4-strand Tsuge technique had the highest tensile strength whereas the looped Kessler technique had the lowest. Although our results showed that the combined KesslereTsuge technique was weaker than a doublethrow Tsuge, the tensile strength was still likely to be high enough to allow early mobilization. Schuind et al29 reported a threshold for unresisted active tendon mobilization of above 35 N. Both the doublethrow Tsuge and KesslereTsuge techniques were clearly above this threshold, whereas the mean of the sutures with the modified Kessler technique failed close to this value in 66% of cases owing to knot failure. For the Tsuge and KesslereTsuge techniques, the knot was the reason for failure in 37% and 44% of cases, respectively. However, in the Kessler technique 66% of failures were related to knot slippage. The security of a 4-strand knot, which was used to tie the 4 ends of the looped suture in the Kessler technique, is clearly weaker than that of a 2-strand knot. Internal data from Arthrex, Inc, on the strength of 4-0 FiberWire in a plain test approach showed the ultimate strength of 21 N for a 5-throw surgical knot tied to both ends of a single suture and an ultimate strength of 56 N in a straight pull-out test. These forces are below the mean of the tested repairs with Tsuge and Kesslere Tsuge. For the modified single-throw, 4-strand Kessler technique, however, the mean of the ultimate tensile strength of the repair was 11 N below the ultimate strength of a straight pull-out test of FiberWire. The mode of failure was not suture breakage but rather knot failure (66%) or suture pull-out (33%). Suture breakage in the Tsuge and KesslereTsuge techniques occurred with equal incidence (38%). From these findings, it might be deduced that the Tsuge and KesslereTsuge techniques can add more strength to the repair, with tension levels that let the suture break before the suture construct pulls out of the tendon or before the knot fails. The Tsuge and Kesslere Tsuge techniques take advantage of the looped suture by adding a loop-lock at one end of the suture pair. Each looped suture is therefore fixed with 2 knots versus a single knot with the Kessler technique. This may share the tension load over the overall construct J Hand Surg Am.
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much better than the Kessler technique. The hybrid technique is easy to perform, with one looped suture giving a 4-strand pattern. It is similar to the established Kessler method but adds additional strength because an additional non-profile knot fixes the suture directly to the tendon fibers. In conclusion, the results biomechanically support the double-throw, 4-strand Tsuge technique for flexor tendon repair. However, the KesslereTsuge method appears to be a good alternative, with an acceptable reduction in strength and the advantage of only one looped suture required. In contrast, the looped Kessler technique showed the lowest strength, which is in line with the results of other authors.30 ACKNOWLEDGMENTS The authors thank Liam Davenport (Medicalwriters. com GmbH) for editorial support in producing the manuscript. REFERENCES 1. Lawrence TM, Davis TR. A biomechanical analysis of suture materials and their influence on a four-strand flexor tendon repair. J Hand Surg Am. 2005;30(4):836e841. 2. Aoki M, Kubota H, Pruitt DL, Manske PR. Biomechanical and histologic characteristics of canine flexor tendon repair using early postoperative mobilization. J Hand Surg Am. 1997;22(1):107e114. 3. Kubota H, Manske PR, Aoki M, Pruitt DL, Larson BJ. Effect of motion and tension on injured flexor tendons in chickens. J Hand Surg Am. 1996;21(3):456e463. 4. Small JO, Brennen MD, Colville J. Early active mobilisation following flexor tendon repair in zone 2. J Hand Surg Br. 1989;14(4): 383e391. 5. Bainbridge LC, Robertson C, Gillies D, Elliot D. A comparison of post-operative mobilization of flexor tendon repairs with “passive flexion-active extension” and “controlled active motion” techniques. J Hand Surg Br. 1994;19(4):517e521. 6. Waitayawinyu T, Martineau PA, Luria S, Hanel DP, Trumble TE. Comparative biomechanic study of flexor tendon repair using FiberWire. J Hand Surg Am. 2008;33(5):701e708. 7. Le SV, Chiu S, Meineke RC, Williams P, Wongworawat MD. Number of suture throws and its impact on the biomechanical properties of the four-strand cruciate locked flexor tendon repair with FiberWire. J Hand Surg Eur Vol. 2012;37(9):826e831. 8. Lee SK, Goldstein RY, Zingman A, Terranova C, Nasser P, Hausman MR. The effects of core suture purchase on the biomechanical characteristics of a multistrand locking flexor tendon repair: a cadaveric study. J Hand Surg Am. 2010;35(7):1165e1171. 9. Trail IA, Powell ES, Noble J. An evaluation of suture materials used in tendon surgery. J Hand Surg Br. 1989;14(4):422e427. 10. Moriya T, Thoreson AR, Zhao C, An KN, Amadio PC. The effects of oblique or transverse partial excision of the A2 pulley on gliding resistance during cyclic motion following zone II flexor digitorum profundus repair in a cadaveric model. J Hand Surg Am. 2012;37(8): 1634e1638. 11. Zechner W, Buck-Gramcko D, Lohmann H, Goth D, Stock W. [Improvement of suture technic in flexor tendon injuries: clinical and experimental study]. Handchir Mikrochir Plast Chir. 1985;17(1):8e13. 12. Labana N, Messer T, Lautenschlager E, Nagda S, Nagle D. A biomechanical analysis of the modified Tsuge suture technique for repair of flexor tendon lacerations. J Hand Surg Br. 2001;26(4):297e300.
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13. Petri M, Ettinger M, Dratzidis A, et al. Comparison of three suture techniques and three suture materials on gap formation and failure load in ruptured tendons: a human cadaveric study. Arch Orthop Trauma Surg. 2012;132(5):649e654. 14. Langner C, Surke C, Wieskötter B. Prinzipien der Sehnenbehandlung: Beugesehnen. In: Towfigh H, Hierner R, Langer M, Friedel R, eds. Handchirurgie. Heidelberg, Germany: Springer-Verlag; 2011:101e139. 15. Kirchmayr L. Zur Technik der Sehnennaht. In: Borchard G, ed. Zentralblatt für Chirurgie. Leipzig, Germany: Verlag von Johann Ambrosius Barth; 1917:906e907. 16. Kessler I, Nissim F. Primary repair without immobilization of flexor tendon division within the digital sheath: an experimental and clinical study. Acta Orthop Scand. 1969;40(5):587e601. 17. Angeles JG, Heminger H, Mass DP. Comparative biomechanical performances of 4-strand core suture repairs for zone II flexor tendon lacerations. J Hand Surg Am. 2002;27(3):508e517. 18. McLarney E, Hoffman H, Wolfe SW. Biomechanical analysis of the cruciate four-strand flexor tendon repair. J Hand Surg Am. 1999;24(2):295e301. 19. Stephan C, Saalabian A, van Schoonhoven J, Prommersberger KJ. [Acute flexor tendon surgery]. Oper Orthop Traumatol. 2008;20(1):44e54. 20. Brockardt CJ, Sullivan LG, Watkins BE, Wongworawat MD. Evaluation of simple and looped suture and new material for flexor tendon repair. J Hand Surg Eur Vol. 2009;34(3):329e332. 21. Tsuge K, Yoshikazu I, Matsuishi Y. Repair of flexor tendons by intratendinous tendon suture. J Hand Surg Am. 1977;2(6):436e440.
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22. Cao Y, Tang JB. Biomechanical evaluation of a four-strand modification of the Tang method of tendon repair. J Hand Surg Br. 2005;30(4):374e378. 23. Gan AW, Neo PY, He M, Yam AK, Chong AK, Tay SC. A biomechanical comparison of 3 loop suture materials in a 6-strand flexor tendon repair technique. J Hand Surg Am. 2012;37(9):1830e1834. 24. Smith AM, Forder JA, Annapureddy SR, Reddy KS, Amis AA. The porcine forelimb as a model for human flexor tendon surgery. J Hand Surg Br. 2005;30(3):307e309. 25. 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 Am. 2007;32(5): 591e596. 26. Barmakian JT, Lin H, Green SM, Posner MA, Casar RS. Comparison of a suture technique with the modified Kessler method: resistance to gap formation. J Hand Surg Am. 1994;19(5):777e781. 27. Diao E, Hariharan JS, Soejima O, Lotz JC. Effect of peripheral suture depth on strength of tendon repairs. J Hand Surg Am. 1996;21(2):234e239. 28. Haimovici L, Papafragkou S, Lee W, Dagum A, Hurst LC. The impact of fiberwire, fiberloop, and locking suture configuration on flexor tendon repairs. Ann Plast Surg. 2012;69(4):468e470. 29. Schuind F, Garcia-Elias M, Cooney WP III, An KN. Flexor tendon forces: in vivo measurements. J Hand Surg Am. 1992;17(2): 291e298. 30. Choueka J, Heminger H, Mass DP. Cyclical testing of zone II flexor tendon repairs. J Hand Surg Am. 2000;25(6):1127e1134.
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