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Comparison of a New Multifilament Stainless Steel Suture with Frequently Used Sutures for Flexor Tendon Repair
SCIENTIFIC ARTICLE
Comparison of a New Multifilament Stainless Steel Suture with Frequently Used Sutures for Flexor Tendon Repair Erik McDonald, BS, Joshua A. Gordon, BS, Jenni M. Buckley, PhD, Leonard Gordon, MD
Purpose To investigate the mechanical properties of some common suture materials currently in use and compare them with a new multifilament stainless steel suture. Methods We investigated the mechanical properties of 3-0 and 4-0 Fiberwire, 3-0 Supramid, 3-0 Ethibond, and a new 3-0 and 4-0 multifilament stainless steel suture. All suture material was tested in a knotted configuration and all but the Supramid was tested in an unknotted configuration. We measured the load, elongation at failure, and stiffness during both tests. Results The 4-0 multifilament stainless steel showed the least elongation, whereas the 3-0 multifilament stainless steel withstood the highest load of any material in both the knotted and unknotted tests. There was no difference in stiffness between the 3-0 and 4-0 multifilament stainless steel when untied; however, the 3-0 multifilament stainless steel was stiffer when tied. Soaking in a saline solution had no significant effect on the ultimate load, elongation at failure, or stiffness of any of the sutures. The 3-0 Fiberwire and 3-0 Ethibond required at least 5 throws to resist untying. Conclusions Multifilament stainless steel exhibited promising mechanical advantages over the other sutures tested. More research is needed to determine how this material will affect the clinical outcomes of primary flexor tendon repair. Clinical relevance With a secure attachment to the tendon, the multifilament stainless steel’s lower elongation and better knot-holding ability may result in a higher force to produce a 2-mm gap and a higher ultimate tensile strength in a tendon repair. (J Hand Surg 2011;36A:1028–1034. Copyright © 2011 by the American Society for Surgery of the Hand. All rights reserved.) Key words Biomechanics, Ethibond, Fiberwire, flexor tendon, mechanical properties. properties used to predict the success of a tendon repair are the ultimate tensile strength and the ability to resist gapping.1–10 The characteristics of the suture material
T
WO OF THE BIOMECHANICAL
FromtheUCSF/SFGHOrthopaedicTraumaInstitute,andtheDepartmentofAnatomyandOrthopaedic Surgery,UniversityofCalifornia,SanFrancisco;andtheDavidGeffenSchoolofMedicine,Universityof California, Los Angeles, Los Angeles, CA. Received for publication September 30, 2010; accepted in revised form March 22, 2011. Funding and hardware for this study were provided by Core Essence Orthopaedics, Fort Washington, PA. L.G. owns stock and receives royalties from Core Orthopaedics. Corresponding author: Leonard Gordon, MD, Department of Anatomy and Orthopaedic Surgery, University of California, 2299 Post Street, San Francisco, CA 94115; e-mail: [email protected]. 0363-5023/11/36A06-0011$36.00/0 doi:10.1016/j.jhsa.2011.03.033
1028 䉬 © ASSH 䉬 Published by Elsevier, Inc. All rights reserved.
used for a repair have a noteworthy effect on these parameters, and a number of new suture materials have been developed.11–28 Some of the characteristics of an ideal suture material include nonbioreactivity, a high ultimate tensile strength, and the ability to resist elongation, handle and tie easily, and hold knots well. In 1929, Bunnell29 advocated the use of silk or chromatic catgut, but by 194030 he had begun to suggest monofilament stainless steel in a crisscross configuration for primary flexor tendon repair. This suture was difficult to handle and was ultimately discarded in favor of monofilament nylon and subsequently Ethibond (EB), a multifilament polyester (Ethicon, Somerville, NJ). More recently Fiberwire (FW) (Arthrex, Naples, FL) has demonstrated some advantageous
MULTIFILAMENT STAINLESS STEEL SUTURE
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FIGURE 1: A Side view of the 3-0 MFSS suture (magnification ⫻6.3). B Diagram showing the configuration of the 7 bundles of 7 filaments used in the MFSS suture material.
filaments in this design produces a suture that is easier to handle than the monofilament designs.30,33 The mechanical properties of MFSS may be advantageous in producing strong repairs with secure knots. The purposes of this study were to investigate the mechanical properties of some common suture materials currently in use and to compare them with a new MFSS suture.
FIGURE 2: Test setup showing the load cell and suture clamps.
properties but has some disadvantages including a poor ability to hold knots.20,27,31,32 Recently, a multifilament stainless steel (MFSS) suture was developed for use in flexor tendon repair. Whereas the use of stainless steel as suture material is not a new idea, the configuration of the stainless steel
MATERIALS AND METHODS Suture material physical properties We investigated the mechanical properties of the following 4 suture materials: FW, a multifilament, ultrahigh-molecular-weight polyethylene core with a braided polyester jacket; Supramid (SM), a multifilament nylon core with a nylon jacket (S. Jackson, Inc., Alexandria, VA); EB, a multifilament polyester suture; and an MFSS suture (Core Essence Orthopaedics, Fort Washington, PA). The SM and EB were tested in the 3-0 size, whereas the FW and MFSS were tested in 3-0 and 4-0 configurations. The MFSS cable is composed of 49 filaments of 316L stainless steel. The filaments in the 3-0 size are 0.034 mm in diameter, with a total suture diameter of 0.31 mm. The 4-0 filaments are 0.024 mm in diameter and the total suture diameter is 0.21 mm. The suture is arranged in 7 bundles of 7 filaments each; although technically a cable, it functions as a suture (Fig. 1). Untied suture testing We evaluated the ultimate tensile strength of 5 different suture materials: 3-0 and 4-0 MFSS, 3-0 and 4-0 FW,
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FIGURE 3: A Representative knot showing 3 total throws. B Representative knot showing 5 total throws.
and 3-0 EB. The SM suture was only available as a loop of suture with a needle attached. When the suture was removed from the needle, the length of remaining suture was insufficient to be attached to the testing clamps. We therefore tested the SM suture only in the tied configuration. A total of 25 strands were tested, 5 of each material. To test the ultimate tensile strength and elongation of the sutures, each suture was loaded in uniaxial tension at 1 mm/s using a servohydraulic testing machine (MTS Mini-Bionix 858; Eden Prairie, MN) until failure. A strand of suture was attached to the MTS by a set of clamps (Fig. 2). The suture was wrapped around each spool 3 times and then held securely with a clamp on each side. Wrapping the suture around the spools ensured that the load was applied to the center of the suture, which had a length of 3 cm between spools. A 5-N preload was applied and the suture was subjected to 10 cycles from 5 to 10 N to allow the suture to settle and eliminate any slack from the system. A load cell (INTERFACE SSM-500, Scottsdale, AZ) recorded force data and the MTS displacement transducer recorded displacement. The ultimate load, elongation at failure, and stiffness were measured for each specimen. Stiffness represents the force per unit displacement and was calculated as the slope of a best fit line from 15 to 30 N on the force versus displacement curve.
Knotted suture testing To test the strength of the suture in a knotted configuration, we tied the suture around a 7.6-cm-diameter cylinder to ensure consistent lengths using a surgeon’s knot with 1 additional throw, for a total of 3 throws (2 ⫻ 1 ⫻ 1) (Fig. 3). In addition, we tested 3-0 FW and 3-0 EB with a surgeon’s knot with 3 additional throws, for a total of 5 throws (2 ⫻ 1 ⫻ 1 ⫻ 1 ⫻ 1) (Fig. 3). The 3-0 SM was tied after cutting the suture loop off of the needle. The loop of suture was placed around the 2 spools for testing. The suture loops were cyclically loaded 10 times from 5 to 10 N, then immediately tested to failure at 1 mm/s. As with the untied suture, this cyclic preloading allowed the suture to settle and removed any slack from the system. We tested 6 samples of each material and configuration. We also tested 6 samples of each suture after soaking them in a physiological saline solution at room temperature for 10 minutes. The ultimate load and elongation at failure were measured for each specimen. Stiffness was calculated for specimens in which the suture failed by breakage, and not calculated for specimens that failed by untying. As with the untied suture, the stiffness was calculated as the slope of a best fit line from 15 to 30 N on the force versus displacement curve.
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TABLE 1.
Ultimate Load, Elongation at Failure, and Stiffness Results for Unknotted Suture Lower 95% Confidence Interval
Upper 95% Confidence Interval
Suture Material
Size
Ultimate Load (N) (mean ⫾ SD)
MFSS
3-0
73.8 ⫾ 0.7
72.5
75.0
A
FW
3-0
41.9 ⫾ 3.3
40.1
43.6
B
MFSS
4-0
39.9 ⫾ 1.3
38.2
41.7
FW
4-0
36.6 ⫾ 2
34.9
38.4
EB
3-0
27.3 ⫾ 2.4
25.5
29.1
*
B
C C D
Elongation at Failure (mm) (mean ⫾ SD) EB
3-0
13.8 ⫾ 1.7
12.9
14.7
FW
4-0
11.9 ⫾ 1.1
10.9
12.8
B B
FW
3-0
11.6 ⫾ 0.3
10.7
12.6
MFSS
3-0
5 ⫾ 0.8
4.4
5.7
MFSS
4-0
2.3 ⫾ 0.9
1.4
3.3
A
C D
Stiffness (N/mm) (mean ⫾ SD) 3-0
18.5 ⫾ 2.8
17.4
19.7
A
MFSS
4-0
16.8 ⫾ 1.5
15.2
18.4
A
FW
3-0
3.4 ⫾ 0.2
1.8
5.0
MFSS
B
FW
4-0
2.8 ⫾ 0.1
1.1
4.4
B
EB
3-0
1.6 ⫾ 0.1
0.0
3.2
B
*Rows not connected by the same letter are statistically different (p ⬍ .05). N ⫽ 5 for all groups.
Statistical analysis To determine which factors significantly affect the mechanical behavior during bench-top testing, stepwise linear regression was conducted with the following initial predictor variables: (1) suture material, (2) suture gauge, (3) number of knots (knotted only), and (4) wet/dry suture material. We ran the stepwise algorithm with p ⬎ .10 as the exclusion criteria. Pairwise comparisons were then made between suture constructs using Student’s t-test with Tukey’s posthoc adjustment for multiple comparisons. We set p ⬍ .05 as the cutoff for significance; only statistically significant findings are reported in the Results section unless otherwise noted. RESULTS Suture only The ultimate load of the 3-0 MFSS was the highest of any suture material tested (Table 1). The ultimate load of the 4-0 MFSS was not statistically different from the 3-0 or 4-0 FW. The EB had the lowest ultimate tensile strength.
The elongation at failure was highest for EB, which was statistically greater than any other suture (Table 1). The 3-0 and 4-0 FW had equivalent elongations at failure. The 4-0 MFSS had the least elongation at failure. The 3-0 MFSS had an elongation that was statistically greater than the 4-0 MFSS but less than any other suture material tested. There was no difference in stiffness between the 3-0 and 4-0 MFSS (p ⬎ .05); however, both were greater than all other suture materials tested (p ⬍ .05) (Table 1). Knotted suture When tied, the 3-0 MFSS withstood 121 N before rupture (Table 2). When tied with 5 throws, the 3-0 FW sustained 53 N before failure, which was not statistically different from the 4-0 MFSS. The double-stranded SM was also not statistically different from the 3-0 FW with 5 knots. The 4-0 MFSS had the least elongation of any material tested; however, it was not different from the 3-0 MFSS. When tied with 5 throws, the 3-0 FW failed at
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TABLE 2.
MULTIFILAMENT STAINLESS STEEL SUTURE
Ultimate Load, Elongation at Failure, and Stiffness Results for Knotted Suture
Suture Material
Size
Throws
Ultimate Load (N) (mean ⫾ SD)
Lower 95% Confidence Interval
Upper 95% Confidence Interval
121 ⫾ 3.2
115.2
126.8
A
47.7
58.3
B
*
MFSS
3-0
3
FW
3-0
5
MFSS
4-0
3
49.6 ⫾ 9.3
44.3
54.9
EB
3-0
5
41.3 ⫾ 3.4
36.0
46.6
EB
3-0
3
32.5 ⫾ 12
27.3
37.8
D
E
SM
3-0
3
30.1 ⫾ 8.1
24.3
35.9
D
E
FW
3-0
3
23 ⫾ 6.3
17.7
28.3
E
FW
4-0
3
10.9
25.8
E
53 ⫾ 15.8
18.4 ⫾ 3
B
C C
D
Elongation at Failure (mm) (mean ⫾ SD) MFSS
4-0
3
2.6 ⫾ 1.6
1.4
3.8
A
MFSS
3-0
3
2.8 ⫾ 0.3
1.6
4.1
A
FW
4-0
3
4.2 ⫾ 0.7
2.5
5.8
A
B
FW
3-0
3
4.3 ⫾ 0.9
3.1
5.4
A
B
FW
3-0
5
6.6 ⫾ 1.6
5.5
7.8
EB
3-0
3
10.7 ⫾ 3.2
8.9
11.2
C
EB
3-0
5
11 ⫾ 1
9.8
12.2
C
SM
3-0
3
16.6 ⫾ 3.7
15.3
17.9
49.3
B
D
Stiffness (N/mm) (mean ⫾ SD) MFSS
3-0
3
47.1 ⫾ 6.9
44.9
MFSS
4-0
3
31.4 ⫾ 3.8
29.4
33.5
FW
3-0
5
8.7 ⫾ 0.8
6.7
10.9
EB
3-0
5
2.9 ⫾ 0.2
0.9
4.9
D
SM
3-0
3
1.8 ⫾ 0.1
–0.6
4.1
D
A B C
*Rows not connected by the same letter are statistically different (p ⬍ .05). N ⫽ 12 for all groups.
an elongation greater than those with only 3 throws; however, the ultimate load was also greater. The double-stranded SM showed the most elongation. The 3-0 MFSS was the stiffest material, followed by 4-0 MFSS and 3-0 FW with 5 throws. The 3-0 EB and SM were the least stiff of the materials tested. Both the 3-0 and 4-0 MFSS failed exclusively by breakage at the knot with only 3 throws. With only 3 throws, the 3-0 and 4-0 FW and 3-0 EB typically untied instead of breaking. When tied with 5 throws, the 3-0 FW and EB broke at the knot instead of untying. The SM broke at the knot. DISCUSSION The results of this study indicate MFSS has some favorable mechanical properties compared with several
suture materials currently in clinical use. The elongation of the MFSS was significantly lower than any of the other suture materials, and the stiffness was significantly higher. When tied, the MFSS only required 3 throws to resist untying, whereas Fiberwire needed 5 throws. We are not the first investigators to conclude that Fiberwire has the potential for untying at low loads.20,27,31,32 A metallic suture material may offer benefits of nonviscoelastic properties. Polymer sutures have been shown to exhibit stress relaxation and creep, unlike stainless steel, which does not have these properties.34 In addition, stainless steel may offer other benefits, such as being secured by a means other than a knot—for example, crimping. We are also not the first study to investigate stainless steel for use in primary flexor tendon repair. Trail et al33
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in 1989 investigated multiple suture materials and found that whereas MFSS offered many advantages over the polymer-based sutures they tested, the authors ultimately did not recommend it based on its handling characteristics. This has been a consistent problem with MFSS. Although we did not directly address the handling properties in this study, we noted that the MFSS does not have the memory that makes monofilament so difficult to work with and tie. The configuration of the individual filaments creates an overall construct that does not plastically deform or kink when handled. This design creates a suture that has completely different handling characteristics from monofilament designs used in the past. In 2005, Lawrence and Davis21 compared a braided stainless steel suture with 4 other materials including FW. They concluded that FW and stainless steel were the most biomechanically suitable when performing flexor tendon repairs. Their study was limited in that the authors only investigated 4-0 suture and only in the tied configuration, but their study supports the hypothesis that an MFSS suture could be a viable option for flexor tendon repair. Additional research is necessary to determine how this particular MFSS suture will perform in vivo. Future studies should investigate how the ultimate load and gapping of a tendon repair is affected by the MFSS, as well as the ability of this construct to pass unimpeded through the tendon pulley system. Greater stiffness is generally regarded as an advantage to limit gapping. Nevertheless, studies should be conducted to determine whether the increased stiffness of the MFSS would shield the tendon from tensile forces during healing at the risk of causing tenomalacia. Although we did not perform a formal power analysis, we determined the sample sizes based on numbers used by previous investigators. This is a limitation of the study. Our final data sets were 5 samples per group for the suture only and 12 samples per group for the knotted suture. The straight suture sample sizes are the same as those of Lawerence and Davis,21 who used 5 samples per group when investigating tied suture, which one would expect to have greater variability. For our tied comparisions, we used 12 samples per group. Again, our outcomes were similar to those of Lawrence and Davis, who tested FW, MFSS, and EB, among other materials. Some of our comparisons did not reach significance but we did observe some trends. One example is the lack of significant differences in elongation at failure between the MFSS and FW when tied. However, in cases like these, one should also consider the mode of failure. The mode of failure for the MFSS was
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the suture breaking at the knot, whereas the FW failed by untying. With a secure attachment to the tendon, the lower elongation and better knot-holding ability of the MFSS may result in higher force to produce a 2-mm gap and higher ultimate tensile strength in tendon repair. More research is needed to determine how this material will affect actual clinical outcomes of primary flexor tendon repair. REFERENCES 1. Amadio PC. Friction of the gliding surface. Implications for tendon surgery and rehabilitation. J Hand Ther 2005;18:112–119. 2. 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. 3. Bhatia D, Tanner KE, Bonfield W, Citron ND. Factors affecting the strength of flexor tendon repair. J Hand Surg 1992;17B:550 –552. 4. 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. 5. Moriya T, Zhao C, An KN, Amadio PC. The effect of epitendinous suture technique on gliding resistance during cyclic motion after flexor tendon repair: a cadaveric study. J Hand Surg 2010;35A:552– 558. 6. Tang JB, Wang B, Chen F, Pan CZ, Xie RG. Biomechanical evaluation of flexor tendon repair techniques. Clin Orthop Relat Res 2001;38:252–259. 7. Walbeehm ET, De Wit T, Hovius SE, McGrouther DA. Influence of core suture geometry on tendon deformation and gap formation in porcine flexor tendons. J Hand Surg 2009;34B:190 –195. 8. Winters SC, Gelberman RH, Woo SL, Chan SS, Grewal R, Seiler JG III. The effects of multiple-strand suture methods on the strength and excursion of repaired intrasynovial flexor tendons: a biomechanical study in dogs. J Hand Surg 1998;23A:97–104. 9. Zhao C, Amadio PC, Momose T, Couvreur P, Zobitz ME, An KN. The effect of suture technique on adhesion formation after flexor tendon repair for partial lacerations in a canine model. J Trauma 2001;51:917–921. 10. Zhao C, Amadio PC, Tanaka T, Kutsumi K, Tsubone T, Zobitz ME, et al. Effect of gap size on gliding resistance after flexor tendon repair. J Bone Joint Surg 2004;86A:2482–2488. 11. Aoki M, Manske PR, Pruitt DL, Kubota H, Larson BJ. Canine cadaveric study of flexor tendon repair using tendon splint: tensile strength and the work of flexion. Nippon Seikeigeka Gakkai Zasshi 1995;69:332–341. 12. Aoki M, Manske PR, Pruitt DL, Larson BJ. Tendon repair using flexor tendon splints: an experimental study. J Hand Surg 1994;19A: 984 –990. 13. 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. 14. Barrie KA, Wolfe SW, Shean C, Shenbagamurthi D, Slade JF III, Panjabi MM. A biomechanical comparison of multistrand flexor tendon repairs using an in situ testing model. J Hand Surg 2000; 25A:499 –506. 15. 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. 16. Gordon L, Tolar M, Rao KT, Ritchie RO, Rabinowitz S, Lamb RP. Flexor tendon repair using a stainless steel internal anchor. Biomechanical study on human cadaver tendons. J Hand Surg 1998; 23B:37– 40.
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17. Greenwald D, Shumway S, Albear P, Gottlieb L. Mechanical comparison of 10 suture materials before and after in vivo incubation. J Surg Res 1994;56:372–377. 18. Karjalainen T, Goransson H, Viinikainen A, Jamsa T, Ryhanen J. Nickel-titanium wire as a flexor tendon suture material: an ex vivo study. J Hand Surg 2010;35B:469 – 474. 19. Kim JC, Lee YK, Lim BS, Rhee SH, Yang HC. Comparison of tensile and knot security properties of surgical sutures. J Mater Sci Mater Med 2007;18:2363–2369. 20. Komatsu F, Mori R, Uchio Y. Optimum surgical suture material and methods to obtain high tensile strength at knots: problems of conventional knots and the reinforcement effect of adhesive agent. J Orthop Sci 2006;11:70 –74. 21. Lawrence TM, Davis TR. A biomechanical analysis of suture materials and their influence on a four-strand flexor tendon repair. J Hand Surg 2005;30A:836 – 841. 22. Scherman P, Haddad R, Scougall P, Walsh WR. Cross-sectional area and strength differences of Fiberwire, Prolene, and Ticron sutures. J Hand Surg 2010;35A:780 –784. 23. Su BW, Protopsaltis TS, Koff MF, Chang KP, Strauch RJ, Crow SA, et al. The biomechanical analysis of a tendon fixation device for flexor tendon repair. J Hand Surg 2005;30A:237–245. 24. Vigler M, Palti R, Goldstein R, Patel VP, Nasser P, Lee SK. Biomechanical study of cross-locked cruciate versus Strickland flexor tendon repair. J Hand Surg 2008;33A:1821833. 25. Viinikainen A, Goransson H, Huovinen K, Kellomaki M, Tormala P, Rokkanen P. Material and knot properties of braided polyester (Ticron) and bioabsorbable poly-L/D-lactide (PLDLA) 96/4 sutures. J Mater Sci Mater Med 2006;17:169 –177.
26. Wada A, Kubota H, Hatanaka H, Miura H, Iwamoto Y. Comparison of mechanical properties of polyvinylidene fluoride and polypropylene monofilament sutures used for flexor tendon repair. J Hand Surg 2001;26B:212–216. 27. 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. 28. Wolfe SW, Willis AA, Campbell D, Clabeaux J, Wright TM. Biomechanic comparison of the Teno Fix tendon repair device with the cruciate and modified Kessler techniques. J Hand Surg 2007;32A:356 – 366. 29. Bunnell S. Treatment of Injuries of the Hand. Cal West Med 1929; 30:1–5. 30. Bunnell S. Primary repair of severed tendons: the use of stainless steel wire. Am J Surg 1940;47:502–516. 31. Ilahi OA, Younas SA, Ho DM, Noble PC. Security of knots tied with ethibond, fiberwire, orthocord, or ultrabraid. Am J Sports Med 2008;36:2407–2414. 32. Wust DM, Meyer DC, Favre P, Gerber C. Mechanical and handling properties of braided polyblend polyethylene sutures in comparison to braided polyester and monofilament polydioxanone sutures. Arthroscopy 2006;22:1146 –1153. 33. Trail IA, Powell ES, Noble J. An evaluation of suture materials used in tendon surgery. J Hand Surg 1989;14B:422– 427. 34. Vizesi F, Jones C, Lotz N, Gianoutsos M, Walsh WR. Stress relaxation and creep: viscoelastic properties of common suture materials used for flexor tendon repair. J Hand Surg 2008;33A:241– 246.
JHS 䉬 Vol A, June
Comparison of a New Multifilament Stainless Steel Suture with Frequently Used Sutures for Flexor Tendon Repair Erik McDonald, BS, Joshua A. Gordon, BS, Jenni M. Buckley, PhD, Leonard Gordon, MD
Purpose To investigate the mechanical properties of some common suture materials currently in use and compare them with a new multifilament stainless steel suture. Methods We investigated the mechanical properties of 3-0 and 4-0 Fiberwire, 3-0 Supramid, 3-0 Ethibond, and a new 3-0 and 4-0 multifilament stainless steel suture. All suture material was tested in a knotted configuration and all but the Supramid was tested in an unknotted configuration. We measured the load, elongation at failure, and stiffness during both tests. Results The 4-0 multifilament stainless steel showed the least elongation, whereas the 3-0 multifilament stainless steel withstood the highest load of any material in both the knotted and unknotted tests. There was no difference in stiffness between the 3-0 and 4-0 multifilament stainless steel when untied; however, the 3-0 multifilament stainless steel was stiffer when tied. Soaking in a saline solution had no significant effect on the ultimate load, elongation at failure, or stiffness of any of the sutures. The 3-0 Fiberwire and 3-0 Ethibond required at least 5 throws to resist untying. Conclusions Multifilament stainless steel exhibited promising mechanical advantages over the other sutures tested. More research is needed to determine how this material will affect the clinical outcomes of primary flexor tendon repair. Clinical relevance With a secure attachment to the tendon, the multifilament stainless steel’s lower elongation and better knot-holding ability may result in a higher force to produce a 2-mm gap and a higher ultimate tensile strength in a tendon repair. (J Hand Surg 2011;36A:1028–1034. Copyright © 2011 by the American Society for Surgery of the Hand. All rights reserved.) Key words Biomechanics, Ethibond, Fiberwire, flexor tendon, mechanical properties. properties used to predict the success of a tendon repair are the ultimate tensile strength and the ability to resist gapping.1–10 The characteristics of the suture material
T
WO OF THE BIOMECHANICAL
FromtheUCSF/SFGHOrthopaedicTraumaInstitute,andtheDepartmentofAnatomyandOrthopaedic Surgery,UniversityofCalifornia,SanFrancisco;andtheDavidGeffenSchoolofMedicine,Universityof California, Los Angeles, Los Angeles, CA. Received for publication September 30, 2010; accepted in revised form March 22, 2011. Funding and hardware for this study were provided by Core Essence Orthopaedics, Fort Washington, PA. L.G. owns stock and receives royalties from Core Orthopaedics. Corresponding author: Leonard Gordon, MD, Department of Anatomy and Orthopaedic Surgery, University of California, 2299 Post Street, San Francisco, CA 94115; e-mail: [email protected]. 0363-5023/11/36A06-0011$36.00/0 doi:10.1016/j.jhsa.2011.03.033
1028 䉬 © ASSH 䉬 Published by Elsevier, Inc. All rights reserved.
used for a repair have a noteworthy effect on these parameters, and a number of new suture materials have been developed.11–28 Some of the characteristics of an ideal suture material include nonbioreactivity, a high ultimate tensile strength, and the ability to resist elongation, handle and tie easily, and hold knots well. In 1929, Bunnell29 advocated the use of silk or chromatic catgut, but by 194030 he had begun to suggest monofilament stainless steel in a crisscross configuration for primary flexor tendon repair. This suture was difficult to handle and was ultimately discarded in favor of monofilament nylon and subsequently Ethibond (EB), a multifilament polyester (Ethicon, Somerville, NJ). More recently Fiberwire (FW) (Arthrex, Naples, FL) has demonstrated some advantageous
MULTIFILAMENT STAINLESS STEEL SUTURE
1029
FIGURE 1: A Side view of the 3-0 MFSS suture (magnification ⫻6.3). B Diagram showing the configuration of the 7 bundles of 7 filaments used in the MFSS suture material.
filaments in this design produces a suture that is easier to handle than the monofilament designs.30,33 The mechanical properties of MFSS may be advantageous in producing strong repairs with secure knots. The purposes of this study were to investigate the mechanical properties of some common suture materials currently in use and to compare them with a new MFSS suture.
FIGURE 2: Test setup showing the load cell and suture clamps.
properties but has some disadvantages including a poor ability to hold knots.20,27,31,32 Recently, a multifilament stainless steel (MFSS) suture was developed for use in flexor tendon repair. Whereas the use of stainless steel as suture material is not a new idea, the configuration of the stainless steel
MATERIALS AND METHODS Suture material physical properties We investigated the mechanical properties of the following 4 suture materials: FW, a multifilament, ultrahigh-molecular-weight polyethylene core with a braided polyester jacket; Supramid (SM), a multifilament nylon core with a nylon jacket (S. Jackson, Inc., Alexandria, VA); EB, a multifilament polyester suture; and an MFSS suture (Core Essence Orthopaedics, Fort Washington, PA). The SM and EB were tested in the 3-0 size, whereas the FW and MFSS were tested in 3-0 and 4-0 configurations. The MFSS cable is composed of 49 filaments of 316L stainless steel. The filaments in the 3-0 size are 0.034 mm in diameter, with a total suture diameter of 0.31 mm. The 4-0 filaments are 0.024 mm in diameter and the total suture diameter is 0.21 mm. The suture is arranged in 7 bundles of 7 filaments each; although technically a cable, it functions as a suture (Fig. 1). Untied suture testing We evaluated the ultimate tensile strength of 5 different suture materials: 3-0 and 4-0 MFSS, 3-0 and 4-0 FW,
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FIGURE 3: A Representative knot showing 3 total throws. B Representative knot showing 5 total throws.
and 3-0 EB. The SM suture was only available as a loop of suture with a needle attached. When the suture was removed from the needle, the length of remaining suture was insufficient to be attached to the testing clamps. We therefore tested the SM suture only in the tied configuration. A total of 25 strands were tested, 5 of each material. To test the ultimate tensile strength and elongation of the sutures, each suture was loaded in uniaxial tension at 1 mm/s using a servohydraulic testing machine (MTS Mini-Bionix 858; Eden Prairie, MN) until failure. A strand of suture was attached to the MTS by a set of clamps (Fig. 2). The suture was wrapped around each spool 3 times and then held securely with a clamp on each side. Wrapping the suture around the spools ensured that the load was applied to the center of the suture, which had a length of 3 cm between spools. A 5-N preload was applied and the suture was subjected to 10 cycles from 5 to 10 N to allow the suture to settle and eliminate any slack from the system. A load cell (INTERFACE SSM-500, Scottsdale, AZ) recorded force data and the MTS displacement transducer recorded displacement. The ultimate load, elongation at failure, and stiffness were measured for each specimen. Stiffness represents the force per unit displacement and was calculated as the slope of a best fit line from 15 to 30 N on the force versus displacement curve.
Knotted suture testing To test the strength of the suture in a knotted configuration, we tied the suture around a 7.6-cm-diameter cylinder to ensure consistent lengths using a surgeon’s knot with 1 additional throw, for a total of 3 throws (2 ⫻ 1 ⫻ 1) (Fig. 3). In addition, we tested 3-0 FW and 3-0 EB with a surgeon’s knot with 3 additional throws, for a total of 5 throws (2 ⫻ 1 ⫻ 1 ⫻ 1 ⫻ 1) (Fig. 3). The 3-0 SM was tied after cutting the suture loop off of the needle. The loop of suture was placed around the 2 spools for testing. The suture loops were cyclically loaded 10 times from 5 to 10 N, then immediately tested to failure at 1 mm/s. As with the untied suture, this cyclic preloading allowed the suture to settle and removed any slack from the system. We tested 6 samples of each material and configuration. We also tested 6 samples of each suture after soaking them in a physiological saline solution at room temperature for 10 minutes. The ultimate load and elongation at failure were measured for each specimen. Stiffness was calculated for specimens in which the suture failed by breakage, and not calculated for specimens that failed by untying. As with the untied suture, the stiffness was calculated as the slope of a best fit line from 15 to 30 N on the force versus displacement curve.
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TABLE 1.
Ultimate Load, Elongation at Failure, and Stiffness Results for Unknotted Suture Lower 95% Confidence Interval
Upper 95% Confidence Interval
Suture Material
Size
Ultimate Load (N) (mean ⫾ SD)
MFSS
3-0
73.8 ⫾ 0.7
72.5
75.0
A
FW
3-0
41.9 ⫾ 3.3
40.1
43.6
B
MFSS
4-0
39.9 ⫾ 1.3
38.2
41.7
FW
4-0
36.6 ⫾ 2
34.9
38.4
EB
3-0
27.3 ⫾ 2.4
25.5
29.1
*
B
C C D
Elongation at Failure (mm) (mean ⫾ SD) EB
3-0
13.8 ⫾ 1.7
12.9
14.7
FW
4-0
11.9 ⫾ 1.1
10.9
12.8
B B
FW
3-0
11.6 ⫾ 0.3
10.7
12.6
MFSS
3-0
5 ⫾ 0.8
4.4
5.7
MFSS
4-0
2.3 ⫾ 0.9
1.4
3.3
A
C D
Stiffness (N/mm) (mean ⫾ SD) 3-0
18.5 ⫾ 2.8
17.4
19.7
A
MFSS
4-0
16.8 ⫾ 1.5
15.2
18.4
A
FW
3-0
3.4 ⫾ 0.2
1.8
5.0
MFSS
B
FW
4-0
2.8 ⫾ 0.1
1.1
4.4
B
EB
3-0
1.6 ⫾ 0.1
0.0
3.2
B
*Rows not connected by the same letter are statistically different (p ⬍ .05). N ⫽ 5 for all groups.
Statistical analysis To determine which factors significantly affect the mechanical behavior during bench-top testing, stepwise linear regression was conducted with the following initial predictor variables: (1) suture material, (2) suture gauge, (3) number of knots (knotted only), and (4) wet/dry suture material. We ran the stepwise algorithm with p ⬎ .10 as the exclusion criteria. Pairwise comparisons were then made between suture constructs using Student’s t-test with Tukey’s posthoc adjustment for multiple comparisons. We set p ⬍ .05 as the cutoff for significance; only statistically significant findings are reported in the Results section unless otherwise noted. RESULTS Suture only The ultimate load of the 3-0 MFSS was the highest of any suture material tested (Table 1). The ultimate load of the 4-0 MFSS was not statistically different from the 3-0 or 4-0 FW. The EB had the lowest ultimate tensile strength.
The elongation at failure was highest for EB, which was statistically greater than any other suture (Table 1). The 3-0 and 4-0 FW had equivalent elongations at failure. The 4-0 MFSS had the least elongation at failure. The 3-0 MFSS had an elongation that was statistically greater than the 4-0 MFSS but less than any other suture material tested. There was no difference in stiffness between the 3-0 and 4-0 MFSS (p ⬎ .05); however, both were greater than all other suture materials tested (p ⬍ .05) (Table 1). Knotted suture When tied, the 3-0 MFSS withstood 121 N before rupture (Table 2). When tied with 5 throws, the 3-0 FW sustained 53 N before failure, which was not statistically different from the 4-0 MFSS. The double-stranded SM was also not statistically different from the 3-0 FW with 5 knots. The 4-0 MFSS had the least elongation of any material tested; however, it was not different from the 3-0 MFSS. When tied with 5 throws, the 3-0 FW failed at
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TABLE 2.
MULTIFILAMENT STAINLESS STEEL SUTURE
Ultimate Load, Elongation at Failure, and Stiffness Results for Knotted Suture
Suture Material
Size
Throws
Ultimate Load (N) (mean ⫾ SD)
Lower 95% Confidence Interval
Upper 95% Confidence Interval
121 ⫾ 3.2
115.2
126.8
A
47.7
58.3
B
*
MFSS
3-0
3
FW
3-0
5
MFSS
4-0
3
49.6 ⫾ 9.3
44.3
54.9
EB
3-0
5
41.3 ⫾ 3.4
36.0
46.6
EB
3-0
3
32.5 ⫾ 12
27.3
37.8
D
E
SM
3-0
3
30.1 ⫾ 8.1
24.3
35.9
D
E
FW
3-0
3
23 ⫾ 6.3
17.7
28.3
E
FW
4-0
3
10.9
25.8
E
53 ⫾ 15.8
18.4 ⫾ 3
B
C C
D
Elongation at Failure (mm) (mean ⫾ SD) MFSS
4-0
3
2.6 ⫾ 1.6
1.4
3.8
A
MFSS
3-0
3
2.8 ⫾ 0.3
1.6
4.1
A
FW
4-0
3
4.2 ⫾ 0.7
2.5
5.8
A
B
FW
3-0
3
4.3 ⫾ 0.9
3.1
5.4
A
B
FW
3-0
5
6.6 ⫾ 1.6
5.5
7.8
EB
3-0
3
10.7 ⫾ 3.2
8.9
11.2
C
EB
3-0
5
11 ⫾ 1
9.8
12.2
C
SM
3-0
3
16.6 ⫾ 3.7
15.3
17.9
49.3
B
D
Stiffness (N/mm) (mean ⫾ SD) MFSS
3-0
3
47.1 ⫾ 6.9
44.9
MFSS
4-0
3
31.4 ⫾ 3.8
29.4
33.5
FW
3-0
5
8.7 ⫾ 0.8
6.7
10.9
EB
3-0
5
2.9 ⫾ 0.2
0.9
4.9
D
SM
3-0
3
1.8 ⫾ 0.1
–0.6
4.1
D
A B C
*Rows not connected by the same letter are statistically different (p ⬍ .05). N ⫽ 12 for all groups.
an elongation greater than those with only 3 throws; however, the ultimate load was also greater. The double-stranded SM showed the most elongation. The 3-0 MFSS was the stiffest material, followed by 4-0 MFSS and 3-0 FW with 5 throws. The 3-0 EB and SM were the least stiff of the materials tested. Both the 3-0 and 4-0 MFSS failed exclusively by breakage at the knot with only 3 throws. With only 3 throws, the 3-0 and 4-0 FW and 3-0 EB typically untied instead of breaking. When tied with 5 throws, the 3-0 FW and EB broke at the knot instead of untying. The SM broke at the knot. DISCUSSION The results of this study indicate MFSS has some favorable mechanical properties compared with several
suture materials currently in clinical use. The elongation of the MFSS was significantly lower than any of the other suture materials, and the stiffness was significantly higher. When tied, the MFSS only required 3 throws to resist untying, whereas Fiberwire needed 5 throws. We are not the first investigators to conclude that Fiberwire has the potential for untying at low loads.20,27,31,32 A metallic suture material may offer benefits of nonviscoelastic properties. Polymer sutures have been shown to exhibit stress relaxation and creep, unlike stainless steel, which does not have these properties.34 In addition, stainless steel may offer other benefits, such as being secured by a means other than a knot—for example, crimping. We are also not the first study to investigate stainless steel for use in primary flexor tendon repair. Trail et al33
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in 1989 investigated multiple suture materials and found that whereas MFSS offered many advantages over the polymer-based sutures they tested, the authors ultimately did not recommend it based on its handling characteristics. This has been a consistent problem with MFSS. Although we did not directly address the handling properties in this study, we noted that the MFSS does not have the memory that makes monofilament so difficult to work with and tie. The configuration of the individual filaments creates an overall construct that does not plastically deform or kink when handled. This design creates a suture that has completely different handling characteristics from monofilament designs used in the past. In 2005, Lawrence and Davis21 compared a braided stainless steel suture with 4 other materials including FW. They concluded that FW and stainless steel were the most biomechanically suitable when performing flexor tendon repairs. Their study was limited in that the authors only investigated 4-0 suture and only in the tied configuration, but their study supports the hypothesis that an MFSS suture could be a viable option for flexor tendon repair. Additional research is necessary to determine how this particular MFSS suture will perform in vivo. Future studies should investigate how the ultimate load and gapping of a tendon repair is affected by the MFSS, as well as the ability of this construct to pass unimpeded through the tendon pulley system. Greater stiffness is generally regarded as an advantage to limit gapping. Nevertheless, studies should be conducted to determine whether the increased stiffness of the MFSS would shield the tendon from tensile forces during healing at the risk of causing tenomalacia. Although we did not perform a formal power analysis, we determined the sample sizes based on numbers used by previous investigators. This is a limitation of the study. Our final data sets were 5 samples per group for the suture only and 12 samples per group for the knotted suture. The straight suture sample sizes are the same as those of Lawerence and Davis,21 who used 5 samples per group when investigating tied suture, which one would expect to have greater variability. For our tied comparisions, we used 12 samples per group. Again, our outcomes were similar to those of Lawrence and Davis, who tested FW, MFSS, and EB, among other materials. Some of our comparisons did not reach significance but we did observe some trends. One example is the lack of significant differences in elongation at failure between the MFSS and FW when tied. However, in cases like these, one should also consider the mode of failure. The mode of failure for the MFSS was
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the suture breaking at the knot, whereas the FW failed by untying. With a secure attachment to the tendon, the lower elongation and better knot-holding ability of the MFSS may result in higher force to produce a 2-mm gap and higher ultimate tensile strength in tendon repair. More research is needed to determine how this material will affect actual clinical outcomes of primary flexor tendon repair. REFERENCES 1. Amadio PC. Friction of the gliding surface. Implications for tendon surgery and rehabilitation. J Hand Ther 2005;18:112–119. 2. 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. 3. Bhatia D, Tanner KE, Bonfield W, Citron ND. Factors affecting the strength of flexor tendon repair. J Hand Surg 1992;17B:550 –552. 4. 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. 5. Moriya T, Zhao C, An KN, Amadio PC. The effect of epitendinous suture technique on gliding resistance during cyclic motion after flexor tendon repair: a cadaveric study. J Hand Surg 2010;35A:552– 558. 6. Tang JB, Wang B, Chen F, Pan CZ, Xie RG. Biomechanical evaluation of flexor tendon repair techniques. Clin Orthop Relat Res 2001;38:252–259. 7. Walbeehm ET, De Wit T, Hovius SE, McGrouther DA. Influence of core suture geometry on tendon deformation and gap formation in porcine flexor tendons. J Hand Surg 2009;34B:190 –195. 8. Winters SC, Gelberman RH, Woo SL, Chan SS, Grewal R, Seiler JG III. The effects of multiple-strand suture methods on the strength and excursion of repaired intrasynovial flexor tendons: a biomechanical study in dogs. J Hand Surg 1998;23A:97–104. 9. Zhao C, Amadio PC, Momose T, Couvreur P, Zobitz ME, An KN. The effect of suture technique on adhesion formation after flexor tendon repair for partial lacerations in a canine model. J Trauma 2001;51:917–921. 10. Zhao C, Amadio PC, Tanaka T, Kutsumi K, Tsubone T, Zobitz ME, et al. Effect of gap size on gliding resistance after flexor tendon repair. J Bone Joint Surg 2004;86A:2482–2488. 11. Aoki M, Manske PR, Pruitt DL, Kubota H, Larson BJ. Canine cadaveric study of flexor tendon repair using tendon splint: tensile strength and the work of flexion. Nippon Seikeigeka Gakkai Zasshi 1995;69:332–341. 12. Aoki M, Manske PR, Pruitt DL, Larson BJ. Tendon repair using flexor tendon splints: an experimental study. J Hand Surg 1994;19A: 984 –990. 13. 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. 14. Barrie KA, Wolfe SW, Shean C, Shenbagamurthi D, Slade JF III, Panjabi MM. A biomechanical comparison of multistrand flexor tendon repairs using an in situ testing model. J Hand Surg 2000; 25A:499 –506. 15. 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. 16. Gordon L, Tolar M, Rao KT, Ritchie RO, Rabinowitz S, Lamb RP. Flexor tendon repair using a stainless steel internal anchor. Biomechanical study on human cadaver tendons. J Hand Surg 1998; 23B:37– 40.
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17. Greenwald D, Shumway S, Albear P, Gottlieb L. Mechanical comparison of 10 suture materials before and after in vivo incubation. J Surg Res 1994;56:372–377. 18. Karjalainen T, Goransson H, Viinikainen A, Jamsa T, Ryhanen J. Nickel-titanium wire as a flexor tendon suture material: an ex vivo study. J Hand Surg 2010;35B:469 – 474. 19. Kim JC, Lee YK, Lim BS, Rhee SH, Yang HC. Comparison of tensile and knot security properties of surgical sutures. J Mater Sci Mater Med 2007;18:2363–2369. 20. Komatsu F, Mori R, Uchio Y. Optimum surgical suture material and methods to obtain high tensile strength at knots: problems of conventional knots and the reinforcement effect of adhesive agent. J Orthop Sci 2006;11:70 –74. 21. Lawrence TM, Davis TR. A biomechanical analysis of suture materials and their influence on a four-strand flexor tendon repair. J Hand Surg 2005;30A:836 – 841. 22. Scherman P, Haddad R, Scougall P, Walsh WR. Cross-sectional area and strength differences of Fiberwire, Prolene, and Ticron sutures. J Hand Surg 2010;35A:780 –784. 23. Su BW, Protopsaltis TS, Koff MF, Chang KP, Strauch RJ, Crow SA, et al. The biomechanical analysis of a tendon fixation device for flexor tendon repair. J Hand Surg 2005;30A:237–245. 24. Vigler M, Palti R, Goldstein R, Patel VP, Nasser P, Lee SK. Biomechanical study of cross-locked cruciate versus Strickland flexor tendon repair. J Hand Surg 2008;33A:1821833. 25. Viinikainen A, Goransson H, Huovinen K, Kellomaki M, Tormala P, Rokkanen P. Material and knot properties of braided polyester (Ticron) and bioabsorbable poly-L/D-lactide (PLDLA) 96/4 sutures. J Mater Sci Mater Med 2006;17:169 –177.
26. Wada A, Kubota H, Hatanaka H, Miura H, Iwamoto Y. Comparison of mechanical properties of polyvinylidene fluoride and polypropylene monofilament sutures used for flexor tendon repair. J Hand Surg 2001;26B:212–216. 27. 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. 28. Wolfe SW, Willis AA, Campbell D, Clabeaux J, Wright TM. Biomechanic comparison of the Teno Fix tendon repair device with the cruciate and modified Kessler techniques. J Hand Surg 2007;32A:356 – 366. 29. Bunnell S. Treatment of Injuries of the Hand. Cal West Med 1929; 30:1–5. 30. Bunnell S. Primary repair of severed tendons: the use of stainless steel wire. Am J Surg 1940;47:502–516. 31. Ilahi OA, Younas SA, Ho DM, Noble PC. Security of knots tied with ethibond, fiberwire, orthocord, or ultrabraid. Am J Sports Med 2008;36:2407–2414. 32. Wust DM, Meyer DC, Favre P, Gerber C. Mechanical and handling properties of braided polyblend polyethylene sutures in comparison to braided polyester and monofilament polydioxanone sutures. Arthroscopy 2006;22:1146 –1153. 33. Trail IA, Powell ES, Noble J. An evaluation of suture materials used in tendon surgery. J Hand Surg 1989;14B:422– 427. 34. Vizesi F, Jones C, Lotz N, Gianoutsos M, Walsh WR. Stress relaxation and creep: viscoelastic properties of common suture materials used for flexor tendon repair. J Hand Surg 2008;33A:241– 246.
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