- Email: [email protected]
Real interest rate parity new measures and tests
Enhancing the Strength of the Tendon– Suture Interface Using 1-Ethyl-3-(3Dimethylaminopropyl) Carbodiimide Hydrochloride and Cyanoacrylate Chunfeng Zhao, MD, Yu-Long Sun, PhD, Mark E. Zobitz, MS, Kai-Nan An, PhD, Peter C. Amadio, MD From the Biomechanics Laboratory, Division of Orthopedic Research, Mayo Clinic College of Medicine, Rochester, MN.
Purpose: Preventing gap or rupture is important to achieving a successful outcome after tendon repair. Weak sutures break; strong sutures fail by pull-out at the tendon–suture interface. In this study, we investigated the use of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and cyanoacrylate to enhance the strength of the tendon–suture interface. Methods: Twenty-four canine flexor digitorum profundus tendons were used to test EDC and cyanoacrylate reinforcement methods, with 12 tendons in each group. A single-loop suture technique was used to test the tendon–suture interface strength. Results: The mean ultimate strengths of the EDC group and the cyanoacrylate group were significantly higher than those of their respective control groups. The stiffness of the group with cyanoacrylate-augmented loops was significantly higher than that of its respective control group. There was no significant difference in stiffness between the 2 reinforcement methods. Conclusions: Our results suggest that tendon–suture interface reinforcement may improve the pull-out failure strength of a suture construct and thereby increase the effectiveness of stronger suture materials. Future studies might address the effects of different kinds and methods of reinforcement with various suture materials and constructs and in different tissues. (J Hand Surg 2007;32A:606 – 611. Copyright © 2007 by the American Society for Surgery of the Hand.) Key words: Reinforcement, repair, suture, tendon.
ostoperative mobilization is essential to improve finger function after flexor tendon injury and repair. Mobilization reduces adhesion formation,1–5 improves tendon gliding,5 and enhances healing.6 –9 Postoperative therapy, however, can also induce gap formation or tendon rupture, which can seriously impair the outcome of tendon repair.10 –13 To achieve the benefits of mobilization and avoid its complications, the tensile strength of the repaired tendon should be able to withstand the force applied to the tendon during the crucial early postoperative mobilization period. As a result, many tendon repair techniques have been developed.14 –21 Although multiple suture strands and heavier su-
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ture materials can increase the tensile strength of a repair,20,22–24 this merely shifts the breaking point from the suture material to the tendon–suture interface. Stronger repairs simply fail when the intact suture cuts out from the tendon.25–27 Thus, the current upper limit of repair strength is dictated not by suture material or technique but rather by the holding power of the tendon itself. We believe that increasing tendon holding power is the key to further increasing repair stiffness and strength in tendon. It is not known whether the failure of the tendon–suture interface is due to a mismatch in material properties, with the harder suture cutting through the softer tendon, whether micromo-
Zhao et al / Reinforcement of the Tendon–Suture Interface
Figure 1. (A) Normal tendon. (B) Tendon stiffened by 1-hour immersion in EDC.
tion at the interface allows the suture to saw through the tendon, or whether both effects might occur. The purpose of this study was to investigate 2 methods to reinforce the tendon–suture interface: using (1) 1-ethyl-3-(3-dimethylaminopropy) carbodiimide hydrochloride (EDC) to harden the tendon at the interface and (2) cyanoacrylate to glue the tendon and suture together in an attempt to eliminate micromotion. We hypothesized that suture pull-out strength and stiffness would increase by using these reinforcement methods.
Materials and Methods Twenty-four canine flexor digitorum profundus (FDP) tendons from 4 dogs were used. The dogs were killed for other research studies that had been approved by our Institutional Animal Care and Use Committee. The FDP tendons were dissected from the second, third, and fourth digits and were completely lacerated at the proximal interphalangeal joint level, where the tendon consists of 2 parallel collagen fiber bundles.28 To eliminate variation related to suture technique, which might have a confounding effect on the outcomes of interest, a single suture loop was made 5 mm from the tendon end. In each tendon after laceration, one end was used as a control and the other was used for the experimentally reinforced suture, to eliminate the effect of nonuniformity in tendon size. The proximal and distal tendon ends were randomly assigned to the control and experimental groups. 1-Ethyl-3-(3-Dimethylaminopropy) Carbodiimide Hydrochloride–Reinforced Tendon–Suture Interface 1-ethyl-3-(3-dimethylaminopropy) carbodiimide hydrochloride is a cross-linking activating reagent that can facilitate the covalent bonding between carboxyl and amino groups such as those in collagen molecules. Figure 1 illustrates the effect of prolonged
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immersion of a tendon in EDC: the normally supple tendon has become a rigid rod. In this study, a 22-gauge needle was inserted transversely through the tendon 5 mm from the tendon end. A 4/0 suture (Ticron; Sherwood Medical, St. Louis, MO) was passed through the needle hole. Approximately 0.05 mL of 10% EDC (Sigma Chemical Co., St. Louis, MO) was then injected into the tendon on withdrawing the needle, leaving the suture in place, so that the EDC was deposited around the tendon–suture interface to reinforce the tendon holding strength (Fig. 2). A single loop was made 5 mm from the tendon end. In this EDC group, 12 FDP tendons from 2 dogs were used. In its control group, the same procedure was performed without injection. Cyanoacrylate-Reinforced Tendon–Suture Interface Twelve FDP tendons from 2 dogs were used to study cyanoacrylate reinforcement. Unlike EDC, cyanoacrylate does not affect tendon mechanical properties. Instead, it works as a glue and thereby eliminates any sawing motion of the suture in the tendon. The same general protocol described earlier was used. Instead of injecting EDC, however, approximately 0.01 mL of cyanoacrylate (Nexaband Formulated Cyanoacrylate; VPL, Phoenix, AZ) was injected into the tendon during needle withdrawal. The tendon holding strength of 4/0 suture (Ticron, Sherwood Medical) at a distance of 5 mm from the tendon end was measured. In the control group, 12 tendons had the loop suture placed without cyanoacrylate reinforcement. Mechanical Test Each specimen was mounted on a servohydraulic testing machine (MTS, Minneapolis, MN) with a clamp to secure the tendon and the suture looped around a pulley. The suture was distracted at a rate of 20 mm/min until complete suture pull-out occurred.
Figure 2. A 22-gauge needle (A) was inserted transversely through the tendon 5 mm from the tendon end. A 4/0 suture (B) was passed through the needle hole. During needle withdrawal, approximately 0.05 mL of 10% EDC was injected into the tendon–suture interface.
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Figure 3. Failure strength of the EDC reinforcement (10 N) and its paired control (6 N). *Significant difference (p ⬍ .05).
Tensile force and displacement were collected at a rate of 20 Hz.
Figure 5. Failure strength of the cyanoacrylate reinforcement (19 N) and its paired control (10 N). *Significant difference (p ⬍ .05).
All control tendons failed by suture cutting through the tendon. Two cyanoacrylate-reinforced tendons and 1 EDC-reinforced tendon failed by suture rupture. The rest of the experimentally treated tendons in both groups failed by suture pulling out from tendon, as in the control tendons. In the EDC-reinforced tendon pairs, the mean ultimate strengths of the EDC-reinforced group and the
control group were 6N (4 –9) and 10 N (5–20), respectively. The EDC reinforcement was significantly stronger than the paired control tendons (p ⬍ .05) (Fig. 3). Although the stiffness of the EDC-reinforced tendons (mean, 3 N/mm; range, 2– 4 N/mm) was also increased compared with the control group (mean, 2 N/mm; range, 1– 4 N/mm), the difference in stiffness was not significant (Fig. 4). In the cyanoacrylate-reinforced tendon pairs, the mean maximum failure strength of the loops in the cyanoacrylate tendons and control tendons was 19 N (range, 13–29 N) and 10 N (range, 6 –16 N), respectively. The cyanoacrylate group was significantly stronger than its control group (p ⬍ .05) (Fig. 5). The stiffness of the tendons with cyanoacrylate-reinforced loops (mean, 5 N/mm; range, 4 – 8 N/mm) was also significantly higher than the stiffness of the tendons in the control group (mean, 4 N/mm; range, 2–5 N/mm) (p ⬍ .05) (Fig. 6). The 2 different reinforcement methods were also compared with normalized data (increased percentage ⫽ [reinforcement ⫺ control)/control ⫻ 100%). The cyanoacrylate-reinforced suture loops increased 91% (⫾51%) in strength and 31% (⫾34%) in stiffness. The EDC-reinforced suture loops increased 64% (⫾83%) in strength and 24% (⫾23%) in stiff-
Figure 4. Stiffness of the EDC reinforcement (3 N/mm) and its paired control (2 N/mm).
Figure 6. Stiffness of the cyanoacrylate reinforcement (5 N/mm) and its paired control (4 N/mm). *Significant difference (p ⬍ .05).
Statistical Analysis The maximum failure load and suture pull-out stiffness were analyzed using paired tests for independent samples to assess whether there were measured differences between the cyanoacrylate reinforcement and its control tendon and also between the EDC cross-link reinforcement and its control tendon. Because of the variable size of the different tendons from one animal to another, normalized data (the difference between the reinforcement and it normal control within single tendon) were used to compare 2 different reinforcement methods (EDC vs cyanoacrylate) using 1-way analysis of variance with the level of significance set at p less than .05.
Results
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ness. There was no significant difference between the 2 kinds of reinforcement in percent gain in either strength or stiffness.
Discussion Gap formation or repair-site rupture are common complications after tendon repair with early mobilization.9,15,29 –31 In vitro studies9,21,26,32 have shown that the failure mode of repaired tendons follows a pattern of the suture first cutting through the tendon, followed by either complete suture pull-out or suture breakage. This failure mode also occurs in vivo.5,13,33 Stronger repairs fail by pull-out of the intact suture from the tendon; weaker repairs fail by failure of the suture loop.25–27 Increasing the strength of a tendon repair is thus not simply a matter of suture material or design; strength is also affected by the ability of the tendon to resist the tendency of the intact suture to pull through the tendon under increasing load. In this study we evaluated the ability of (1) a chemical cross-linking agent, EDC, to increase the stiffness of the tendon around the suture in the same way that an eyelet reinforces the lacing of a shoe, and (2) a biocompatible tissue glue, cyanoacrylate, to fix the tendon and suture together and minimize relative motion. Both methods appear to increase the resistance of the tendon to suture cut-out. 1-ethyl-3-(3-dimethylaminopropy) carbodiimide hydrochloride is a carboxyl-activating agent for the coupling of primary amines to yield amide bonds, which commonly occur in collagen or protein crosslinking. Because it has little toxicity,34 –38 EDC is commonly used in tissue-engineering applications.39 – 42 Cyanoacrylate has been used for many years as a tissue adhesive,43,44 including use in dental,45 vascular,46 nerve,47 and skin repair.48 Although there is some controversy regarding the cytotoxicity of cyanoacrylate,49 –51 we were unable to assess that in this in vitro model. As noted in Figure 1, EDC has the potential to stiffen the tendon not only locally around the suture but also diffusely, resulting in altered tendon mechanics. We did not notice any such effect with the tiny dose of EDC used in our study, but clearly the longer-term effects of this reagent must be carefully studied in animal models in vivo before any clinical studies could be undertaken. Although a significant difference was detected between the experimental and control groups, the EDC and cyanoacrylate experimental groups had larger SDs than their respective control groups. We believe
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that the wider SDs in the experimental groups was caused by the variability of reagent deposition with our needle-withdraw injection technique. Although we used only flexor tendon to test our hypothesis, these methods might be expected to have similar effects in other tendons, in ligaments, or in other soft tissues. Now that we have shown that the 2 reinforcement methods appear to have an effect, we plan to improve the reliability of the deposition methods. This is a preliminary study of potential new treatments, and there are many limitations to consider. The suture technique used in the study was a single loop, which is not a clinically relevant method. We used this method to simplify our model and to enhance the focus on the effect of the changes in the tendon–suture interface. These modifications should now also be tested with other suture materials, sizes, and constructs, including those methods in common clinical use. In addition, the deposition method that we used for the EDC and cyanoacrylate may be difficult to use clinically. We noted variability in the strength of the enhanced loops, which may be the result of uneven deposition of the EDC and cyanoacrylate with our current method. One of the hypotheses for suture pull-out is that it is the result of a sawing motion of the suture through the tendon. Cyanoacrylate may fix the suture to the tendon and reduce this effect, but we did not include a study group to examine that effect, another topic for future study. Finally, any effect in vivo remains to be explored, including the effects on tendon healing, tendon gliding, and adhesion formation. Cyanoacrylate is used clinically on the skin; its effects and biocompatibility in deeper structures are unknown. Despite these limitations, we believe that this work is a useful proof of concept, suggesting that tendon–suture interface reinforcement may improve the strength of a suture construct. Future studies might evaluate different formulations, compounds, and reaction times; different suture materials and suture designs; and the effect on other tissues. We plan to pursue this concept and hope that the publication of these preliminary data may encourage others similarly. Received for publication September 25, 2006; accepted in revised form March 2, 2007. Supported by the Mayo Foundation. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Corresponding author: Chunfeng Zhao, MD, Biomechanics Laboratory, Mayo Clinic College of Medicine, 200 First St SW, Rochester, MN 55905; e-mail: [email protected]. Copyright © 2007 by the American Society for Surgery of the Hand 0363-5023/07/32A05-0003$32.00/0 doi:10.1016/j.jhsa.2007.03.004
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References 1. Strickland JW. Management of acute flexor tendon injuries. Orthop Clin North Am 1983;14:827– 849. 2. Chow JA, Thomes LJ, Dovelle S, Monsivais J, Milnor WH, Jackson JP. Controlled motion rehabilitation after flexor tendon repair and grafting. A multi-centre study. J Bone Joint Surg 1988;70B:591–595. 3. Cullen KW, Tolhurst P, Lang D, Page RE. Flexor tendon repair in zone 2 followed by controlled active mobilisation. J Hand Surg 1989;14B:392–395. 4. May EJ, Silfverskiold KL. Rate of recovery after flexor tendon repair in zone II. A prospective longitudinal study of 145 digits. Scand J Plast Reconstr Surg Hand Surg 1993;27: 89 –94. 5. Erhard L, Schultz FM, Zobitz ME, Zhao C, Amadio PC, An KN. Reproducible volar partial lacerations in flexor tendons: a new device for biomechanical studies. J Biomech 2002; 35:999 –1002. 6. Gelberman RH, Vande Berg JS, Lundborg GN, Akeson WH. Flexor tendon healing and restoration of the gliding surface. An ultrastructural study in dogs. J Bone Joint Surg 1983; 65A:70 – 80. 7. Gelberman RH, Manske PR, Akeson WH, Woo SL, Lundborg G, Amiel D. Flexor tendon repair. J Orthop Res 1986; 4:119 –128. 8. Gelberman RH, Nunley JA II, Osterman AL, Breen TF, Dimick MP, Woo SL. Influences of the protected passive mobilization interval on flexor tendon healing. A prospective randomized clinical study. Clin Orthop 1991;264:189 –196. 9. Wada A, Kubota H, Miyanishi K, Hatanaka H, Miura H, Iwamoto Y. Comparison of postoperative early active mobilization and immobilization in vivo utilising a four-strand flexor tendon repair. J Hand Surg 2001;26B:301–306. 10. Tsuge K, Yoshikazu I, Matsuishi Y. Repair of flexor tendons by intratendinous tendon suture. J Hand Surg 1977;2:436 – 440. 11. LaSalle WB, Strickland JW. An evaluation of the two-stage flexor tendon reconstruction technique. J Hand Surg 1983; 8:263–267. 12. Silfverskiold KL, May EJ. Gap formation after flexor tendon repair in zone II. Results with a new controlled motion programme. Scand J Plast Reconstr Surg Hand Surg 1993; 27:263–268. 13. Silva MJ, Brodt MD, Boyer MI, Morris TS, Dinopoulos H, Amiel D, Gelberman RH. Effects of increased in vivo excursion on digital range of motion and tendon strength following flexor tendon repair. J Orthop Res 1999;17:777– 783. 14. Kessler I. The “grasping” technique for tendon repair. Hand 1973;5:253–255. 15. Silfverskiold KL, May EJ. Flexor tendon repair in zone II with a new suture technique and an early mobilization program combining passive and active flexion. J Hand Surg 1994;19A:53– 60. 16. Becker H. Primary repair of flexor tendons in the hand without immobilisation-preliminary report. Hand 1978;10: 37– 47. 17. Wade PJ, Muir IF, Hutcheon LL. Primary flexor tendon repair: the mechanical limitations of the modified Kessler technique. J Hand Surg 1986;11B:71–76. 18. Banes AJ, Donlon K, Link GW, Gillespie Y, Bevin AG,
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
Peterson HD, et al. Cell populations of tendon: a simplified method for isolation of synovial cells and internal fibroblasts: confirmation of origin and biologic properties. J Orthop Res 1988;6:83–94. Diao E, Hariharan JS, Soejima O, Lotz JC. Effect of peripheral suture depth on strength of tendon repairs. J Hand Surg 1996;21A:234 –239. Bischoff RJ, Morifusa S, Gelberman RH, Winters SC, Woo SL, Seiller JG III. The effects of proximal load on the excursion of autogenous flexor tendon grafts. J Hand Surg 1998;23A:285–289. McLarney E, Hoffman H, Wolfe SW. Biomechanical analysis of the cruciate four-strand flexor tendon repair. J Hand Surg 1999;24A:295–301. Aoki M, Pruitt DL, Kubota H, Manske PR. Effect of suture knots on tensile strength of repaired canine flexor tendons. J Hand Surg 1995;20B:72–75. Howard RF, Ondrovic L, Greenwald DP. Biomechanical analysis of four-strand extensor tendon repair techniques. J Hand Surg 1997;22A:838 – 842. Boyer MI, Gelberman RH, Burns ME, Dinopoulos H, Hofem R, Silva MJ. Intrasynovial flexor tendon repair. An experimental study comparing low and high levels of in vivo force during rehabilitation in canines. J Bone Joint Surg 2001;83A:891– 899. Hotokezaka S, Manske PR. Differences between locking loops and grasping loops: effects on 2-strand core suture. J Hand Surg 1997;22A:995–1003. Momose T, Amadio P, Zhao C, Zobitz M, Couvreur P, An KN. Suture techniques with high breaking strength and low gliding resistance: experiments in the dog flexor digitorum profundus tendon. Acta Orthop Scand 2001;72:635– 641. Tanaka T, Amadio PC, Zhao C, Zobitz ME, Yang C, An KN. Gliding characteristics and gap formation for locking and grasping tendon repairs: a biomechanical study in a human cadaver model. J Hand Surg 2004;29A:6 –14. Okuda Y, Gorski JP, Amadio PC. Effect of postnatal age on the ultrastructure of six anatomical areas of canine flexor digitorum profundus tendon. J Orthop Res 1987;5:231–241. Pribaz JJ, Morrison WA, Macleod AM. Primary repair of flexor tendons in no-man’s land using the Becker repair. J Hand Surg 1989;14B:400 – 405. Baktir A, Turk CY, Kabak S, Sahin V, Kardas Y. Flexor tendon repair in zone 2 followed by early active mobilization. J Hand Surg 1996;21B:624 – 628. Peck FH, Kennedy SM, Watson JS, Lees VC. An evaluation of the influence of practitioner-led hand clinics on rupture rates following primary tendon repair in the hand. Br J Plast Surg 2004;57:45– 49. Gordon L, Dysarz FA, Venkateswara KT, Mok AP, Ritchie RO, Rabinowitz S. Flexor tendon repair using a stainless steel external splint. Biomechanical study on human cadaver flexor tendons. J Hand Surg 1999;24B:654 – 657. Drape JL, Silbermann-Hoffman O, Houvet P, Dubert T, Thivet A, Benmelha Z, et al. Complications of flexor tendon repair in the hand: MR imaging assessment. Radiology 1996;198:219 –224. Solis D, Vallejo M, Diaz-Maurino T. Reduction of ricin toxicity without impairing the saccharide-binding properties by chemical modification of the carboxyl groups. Anal Biochem 1993;209:117–122.
Zhao et al / Reinforcement of the Tendon–Suture Interface 35. van Wachem PB, van Luyn MJ, Olde Damink LH, Dijkstra PJ, Feijen J, Nieuwenhuis P. Biocompatibility and tissue regenerating capacity of crosslinked dermal sheep collagen. J Biomed Mater Res 1994;28:353–363. 36. Pieper JS, Oosterhof A, Dijkstra PJ, Veerkamp JH, van Kuppevelt TH. Preparation and characterization of porous crosslinked collagenous matrices containing bioavailable chondroitin sulphate. Biomaterials 1999;20:847– 858. 37. Park SN, Park JC, Kim HO, Song MJ, Suh H. Characterization of porous collagen/hyaluronic acid scaffold modified by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide cross-linking. Biomaterials 2002;23:1205–1212. 38. Duan X, Sheardown H. Dendrimer crosslinked collagen as a corneal tissue engineering scaffold: mechanical properties and corneal epithelial cell interactions. Biomaterials 2006; 27:4608 – 4617. 39. van Wachem PB, Plantinga JA, Wissink MJ, Beernink R, Poot AA, Engbers GH, et al. In vivo biocompatibility of carbodiimide-crosslinked collagen matrices: effects of crosslink density, heparin immobilization, and bFGF loading. J Biomed Mater Res 2001;55:368 –378. 40. Angele P, Abke J, Kujat R, Faltermeier H, Schumann D, Nerlich M, et al. Influence of different collagen species on physico-chemical properties of crosslinked collagen matrices. Biomaterials 2004;25:2831–2841. 41. Song E, Yeon Kim S, Chun T, Byun HJ, Lee YM. Collagen scaffolds derived from a marine source and their biocompatibility. Biomaterials 2006;27:2951–2961. 42. Zhao C, Sun YL, Amadio PC, Tanaka T, Ettema AM, An KN. Surface treatment of flexor tendon autografts with car-
43.
44.
45.
46.
47.
48. 49.
50. 51.
611
bodiimide-derivatized hyaluronic acid. An in vivo canine model. J Bone Joint Surg 2006;88A:2181–2191. Bonomo GM, Leggio A, Consiglio L. [Action of methyl-2cyanoacrylate (Eastman 910) in experimental lesions of the liver. Histo-morphological study]. Minerva Chir 1965;20: 43– 446. Dutton J, Yates PO. An experimental study of the effects of a plastic adhesive, methyl 2-cyanoacrylate monomer (M2 C-1) in various tissues. J Neurosurg 1966;24:876 – 882. Leggat PA, Kedjarune U, Smith DR. Toxicity of cyanoacrylate adhesives and their occupational impacts for dental staff. Ind Health 2004;42:207–211. Ong YS, Yap K, Ang ES, Tan KC, Ng RT, Song IC. 2-octylcynanoacrylate-assisted microvascular anastomosis in a rat model: long-term biomechanical properties and histological changes. Microsurgery 2004;24:304 –308. Pineros-Fernandez A, Rodeheaver PF, Rodeheaver GT. Octyl 2-cyanoacrylate for repair of peripheral nerve. Ann Plast Surg 2005;55:188 –195. Eaglstein WH, Sullivan T. Cyanoacrylates for skin closure. Dermatol Clin 2005;23:193–198. Ricci B, Ricci F, Bianchi PE. Octyl 2-cyanoacrylate in sutureless surgery of extraocular muscles: an experimental study in the rabbit model. Graefes Arch Clin Exp Ophthalmol 2000;238:454 – 458. Maw JL, Kartush JM. Ossicular chain reconstruction using a new tissue adhesive. Am J Otol 2000;21:301–305. Kaplan M, Baysal K. In vitro toxicity test of ethyl 2-cyanoacrylate, a tissue adhesive used in cardiovascular surgery, by fibroblast cell culture method. Heart Surg Forum 2005;8: E169 –E172.
Purpose: Preventing gap or rupture is important to achieving a successful outcome after tendon repair. Weak sutures break; strong sutures fail by pull-out at the tendon–suture interface. In this study, we investigated the use of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride (EDC) and cyanoacrylate to enhance the strength of the tendon–suture interface. Methods: Twenty-four canine flexor digitorum profundus tendons were used to test EDC and cyanoacrylate reinforcement methods, with 12 tendons in each group. A single-loop suture technique was used to test the tendon–suture interface strength. Results: The mean ultimate strengths of the EDC group and the cyanoacrylate group were significantly higher than those of their respective control groups. The stiffness of the group with cyanoacrylate-augmented loops was significantly higher than that of its respective control group. There was no significant difference in stiffness between the 2 reinforcement methods. Conclusions: Our results suggest that tendon–suture interface reinforcement may improve the pull-out failure strength of a suture construct and thereby increase the effectiveness of stronger suture materials. Future studies might address the effects of different kinds and methods of reinforcement with various suture materials and constructs and in different tissues. (J Hand Surg 2007;32A:606 – 611. Copyright © 2007 by the American Society for Surgery of the Hand.) Key words: Reinforcement, repair, suture, tendon.
ostoperative mobilization is essential to improve finger function after flexor tendon injury and repair. Mobilization reduces adhesion formation,1–5 improves tendon gliding,5 and enhances healing.6 –9 Postoperative therapy, however, can also induce gap formation or tendon rupture, which can seriously impair the outcome of tendon repair.10 –13 To achieve the benefits of mobilization and avoid its complications, the tensile strength of the repaired tendon should be able to withstand the force applied to the tendon during the crucial early postoperative mobilization period. As a result, many tendon repair techniques have been developed.14 –21 Although multiple suture strands and heavier su-
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ture materials can increase the tensile strength of a repair,20,22–24 this merely shifts the breaking point from the suture material to the tendon–suture interface. Stronger repairs simply fail when the intact suture cuts out from the tendon.25–27 Thus, the current upper limit of repair strength is dictated not by suture material or technique but rather by the holding power of the tendon itself. We believe that increasing tendon holding power is the key to further increasing repair stiffness and strength in tendon. It is not known whether the failure of the tendon–suture interface is due to a mismatch in material properties, with the harder suture cutting through the softer tendon, whether micromo-
Zhao et al / Reinforcement of the Tendon–Suture Interface
Figure 1. (A) Normal tendon. (B) Tendon stiffened by 1-hour immersion in EDC.
tion at the interface allows the suture to saw through the tendon, or whether both effects might occur. The purpose of this study was to investigate 2 methods to reinforce the tendon–suture interface: using (1) 1-ethyl-3-(3-dimethylaminopropy) carbodiimide hydrochloride (EDC) to harden the tendon at the interface and (2) cyanoacrylate to glue the tendon and suture together in an attempt to eliminate micromotion. We hypothesized that suture pull-out strength and stiffness would increase by using these reinforcement methods.
Materials and Methods Twenty-four canine flexor digitorum profundus (FDP) tendons from 4 dogs were used. The dogs were killed for other research studies that had been approved by our Institutional Animal Care and Use Committee. The FDP tendons were dissected from the second, third, and fourth digits and were completely lacerated at the proximal interphalangeal joint level, where the tendon consists of 2 parallel collagen fiber bundles.28 To eliminate variation related to suture technique, which might have a confounding effect on the outcomes of interest, a single suture loop was made 5 mm from the tendon end. In each tendon after laceration, one end was used as a control and the other was used for the experimentally reinforced suture, to eliminate the effect of nonuniformity in tendon size. The proximal and distal tendon ends were randomly assigned to the control and experimental groups. 1-Ethyl-3-(3-Dimethylaminopropy) Carbodiimide Hydrochloride–Reinforced Tendon–Suture Interface 1-ethyl-3-(3-dimethylaminopropy) carbodiimide hydrochloride is a cross-linking activating reagent that can facilitate the covalent bonding between carboxyl and amino groups such as those in collagen molecules. Figure 1 illustrates the effect of prolonged
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immersion of a tendon in EDC: the normally supple tendon has become a rigid rod. In this study, a 22-gauge needle was inserted transversely through the tendon 5 mm from the tendon end. A 4/0 suture (Ticron; Sherwood Medical, St. Louis, MO) was passed through the needle hole. Approximately 0.05 mL of 10% EDC (Sigma Chemical Co., St. Louis, MO) was then injected into the tendon on withdrawing the needle, leaving the suture in place, so that the EDC was deposited around the tendon–suture interface to reinforce the tendon holding strength (Fig. 2). A single loop was made 5 mm from the tendon end. In this EDC group, 12 FDP tendons from 2 dogs were used. In its control group, the same procedure was performed without injection. Cyanoacrylate-Reinforced Tendon–Suture Interface Twelve FDP tendons from 2 dogs were used to study cyanoacrylate reinforcement. Unlike EDC, cyanoacrylate does not affect tendon mechanical properties. Instead, it works as a glue and thereby eliminates any sawing motion of the suture in the tendon. The same general protocol described earlier was used. Instead of injecting EDC, however, approximately 0.01 mL of cyanoacrylate (Nexaband Formulated Cyanoacrylate; VPL, Phoenix, AZ) was injected into the tendon during needle withdrawal. The tendon holding strength of 4/0 suture (Ticron, Sherwood Medical) at a distance of 5 mm from the tendon end was measured. In the control group, 12 tendons had the loop suture placed without cyanoacrylate reinforcement. Mechanical Test Each specimen was mounted on a servohydraulic testing machine (MTS, Minneapolis, MN) with a clamp to secure the tendon and the suture looped around a pulley. The suture was distracted at a rate of 20 mm/min until complete suture pull-out occurred.
Figure 2. A 22-gauge needle (A) was inserted transversely through the tendon 5 mm from the tendon end. A 4/0 suture (B) was passed through the needle hole. During needle withdrawal, approximately 0.05 mL of 10% EDC was injected into the tendon–suture interface.
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Figure 3. Failure strength of the EDC reinforcement (10 N) and its paired control (6 N). *Significant difference (p ⬍ .05).
Tensile force and displacement were collected at a rate of 20 Hz.
Figure 5. Failure strength of the cyanoacrylate reinforcement (19 N) and its paired control (10 N). *Significant difference (p ⬍ .05).
All control tendons failed by suture cutting through the tendon. Two cyanoacrylate-reinforced tendons and 1 EDC-reinforced tendon failed by suture rupture. The rest of the experimentally treated tendons in both groups failed by suture pulling out from tendon, as in the control tendons. In the EDC-reinforced tendon pairs, the mean ultimate strengths of the EDC-reinforced group and the
control group were 6N (4 –9) and 10 N (5–20), respectively. The EDC reinforcement was significantly stronger than the paired control tendons (p ⬍ .05) (Fig. 3). Although the stiffness of the EDC-reinforced tendons (mean, 3 N/mm; range, 2– 4 N/mm) was also increased compared with the control group (mean, 2 N/mm; range, 1– 4 N/mm), the difference in stiffness was not significant (Fig. 4). In the cyanoacrylate-reinforced tendon pairs, the mean maximum failure strength of the loops in the cyanoacrylate tendons and control tendons was 19 N (range, 13–29 N) and 10 N (range, 6 –16 N), respectively. The cyanoacrylate group was significantly stronger than its control group (p ⬍ .05) (Fig. 5). The stiffness of the tendons with cyanoacrylate-reinforced loops (mean, 5 N/mm; range, 4 – 8 N/mm) was also significantly higher than the stiffness of the tendons in the control group (mean, 4 N/mm; range, 2–5 N/mm) (p ⬍ .05) (Fig. 6). The 2 different reinforcement methods were also compared with normalized data (increased percentage ⫽ [reinforcement ⫺ control)/control ⫻ 100%). The cyanoacrylate-reinforced suture loops increased 91% (⫾51%) in strength and 31% (⫾34%) in stiffness. The EDC-reinforced suture loops increased 64% (⫾83%) in strength and 24% (⫾23%) in stiff-
Figure 4. Stiffness of the EDC reinforcement (3 N/mm) and its paired control (2 N/mm).
Figure 6. Stiffness of the cyanoacrylate reinforcement (5 N/mm) and its paired control (4 N/mm). *Significant difference (p ⬍ .05).
Statistical Analysis The maximum failure load and suture pull-out stiffness were analyzed using paired tests for independent samples to assess whether there were measured differences between the cyanoacrylate reinforcement and its control tendon and also between the EDC cross-link reinforcement and its control tendon. Because of the variable size of the different tendons from one animal to another, normalized data (the difference between the reinforcement and it normal control within single tendon) were used to compare 2 different reinforcement methods (EDC vs cyanoacrylate) using 1-way analysis of variance with the level of significance set at p less than .05.
Results
Zhao et al / Reinforcement of the Tendon–Suture Interface
ness. There was no significant difference between the 2 kinds of reinforcement in percent gain in either strength or stiffness.
Discussion Gap formation or repair-site rupture are common complications after tendon repair with early mobilization.9,15,29 –31 In vitro studies9,21,26,32 have shown that the failure mode of repaired tendons follows a pattern of the suture first cutting through the tendon, followed by either complete suture pull-out or suture breakage. This failure mode also occurs in vivo.5,13,33 Stronger repairs fail by pull-out of the intact suture from the tendon; weaker repairs fail by failure of the suture loop.25–27 Increasing the strength of a tendon repair is thus not simply a matter of suture material or design; strength is also affected by the ability of the tendon to resist the tendency of the intact suture to pull through the tendon under increasing load. In this study we evaluated the ability of (1) a chemical cross-linking agent, EDC, to increase the stiffness of the tendon around the suture in the same way that an eyelet reinforces the lacing of a shoe, and (2) a biocompatible tissue glue, cyanoacrylate, to fix the tendon and suture together and minimize relative motion. Both methods appear to increase the resistance of the tendon to suture cut-out. 1-ethyl-3-(3-dimethylaminopropy) carbodiimide hydrochloride is a carboxyl-activating agent for the coupling of primary amines to yield amide bonds, which commonly occur in collagen or protein crosslinking. Because it has little toxicity,34 –38 EDC is commonly used in tissue-engineering applications.39 – 42 Cyanoacrylate has been used for many years as a tissue adhesive,43,44 including use in dental,45 vascular,46 nerve,47 and skin repair.48 Although there is some controversy regarding the cytotoxicity of cyanoacrylate,49 –51 we were unable to assess that in this in vitro model. As noted in Figure 1, EDC has the potential to stiffen the tendon not only locally around the suture but also diffusely, resulting in altered tendon mechanics. We did not notice any such effect with the tiny dose of EDC used in our study, but clearly the longer-term effects of this reagent must be carefully studied in animal models in vivo before any clinical studies could be undertaken. Although a significant difference was detected between the experimental and control groups, the EDC and cyanoacrylate experimental groups had larger SDs than their respective control groups. We believe
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that the wider SDs in the experimental groups was caused by the variability of reagent deposition with our needle-withdraw injection technique. Although we used only flexor tendon to test our hypothesis, these methods might be expected to have similar effects in other tendons, in ligaments, or in other soft tissues. Now that we have shown that the 2 reinforcement methods appear to have an effect, we plan to improve the reliability of the deposition methods. This is a preliminary study of potential new treatments, and there are many limitations to consider. The suture technique used in the study was a single loop, which is not a clinically relevant method. We used this method to simplify our model and to enhance the focus on the effect of the changes in the tendon–suture interface. These modifications should now also be tested with other suture materials, sizes, and constructs, including those methods in common clinical use. In addition, the deposition method that we used for the EDC and cyanoacrylate may be difficult to use clinically. We noted variability in the strength of the enhanced loops, which may be the result of uneven deposition of the EDC and cyanoacrylate with our current method. One of the hypotheses for suture pull-out is that it is the result of a sawing motion of the suture through the tendon. Cyanoacrylate may fix the suture to the tendon and reduce this effect, but we did not include a study group to examine that effect, another topic for future study. Finally, any effect in vivo remains to be explored, including the effects on tendon healing, tendon gliding, and adhesion formation. Cyanoacrylate is used clinically on the skin; its effects and biocompatibility in deeper structures are unknown. Despite these limitations, we believe that this work is a useful proof of concept, suggesting that tendon–suture interface reinforcement may improve the strength of a suture construct. Future studies might evaluate different formulations, compounds, and reaction times; different suture materials and suture designs; and the effect on other tissues. We plan to pursue this concept and hope that the publication of these preliminary data may encourage others similarly. Received for publication September 25, 2006; accepted in revised form March 2, 2007. Supported by the Mayo Foundation. No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. Corresponding author: Chunfeng Zhao, MD, Biomechanics Laboratory, Mayo Clinic College of Medicine, 200 First St SW, Rochester, MN 55905; e-mail: [email protected]. Copyright © 2007 by the American Society for Surgery of the Hand 0363-5023/07/32A05-0003$32.00/0 doi:10.1016/j.jhsa.2007.03.004
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The Journal of Hand Surgery / Vol. 32A No. 5 May–June 2007
References 1. Strickland JW. Management of acute flexor tendon injuries. Orthop Clin North Am 1983;14:827– 849. 2. Chow JA, Thomes LJ, Dovelle S, Monsivais J, Milnor WH, Jackson JP. Controlled motion rehabilitation after flexor tendon repair and grafting. A multi-centre study. J Bone Joint Surg 1988;70B:591–595. 3. Cullen KW, Tolhurst P, Lang D, Page RE. Flexor tendon repair in zone 2 followed by controlled active mobilisation. J Hand Surg 1989;14B:392–395. 4. May EJ, Silfverskiold KL. Rate of recovery after flexor tendon repair in zone II. A prospective longitudinal study of 145 digits. Scand J Plast Reconstr Surg Hand Surg 1993;27: 89 –94. 5. Erhard L, Schultz FM, Zobitz ME, Zhao C, Amadio PC, An KN. Reproducible volar partial lacerations in flexor tendons: a new device for biomechanical studies. J Biomech 2002; 35:999 –1002. 6. Gelberman RH, Vande Berg JS, Lundborg GN, Akeson WH. Flexor tendon healing and restoration of the gliding surface. An ultrastructural study in dogs. J Bone Joint Surg 1983; 65A:70 – 80. 7. Gelberman RH, Manske PR, Akeson WH, Woo SL, Lundborg G, Amiel D. Flexor tendon repair. J Orthop Res 1986; 4:119 –128. 8. Gelberman RH, Nunley JA II, Osterman AL, Breen TF, Dimick MP, Woo SL. Influences of the protected passive mobilization interval on flexor tendon healing. A prospective randomized clinical study. Clin Orthop 1991;264:189 –196. 9. Wada A, Kubota H, Miyanishi K, Hatanaka H, Miura H, Iwamoto Y. Comparison of postoperative early active mobilization and immobilization in vivo utilising a four-strand flexor tendon repair. J Hand Surg 2001;26B:301–306. 10. Tsuge K, Yoshikazu I, Matsuishi Y. Repair of flexor tendons by intratendinous tendon suture. J Hand Surg 1977;2:436 – 440. 11. LaSalle WB, Strickland JW. An evaluation of the two-stage flexor tendon reconstruction technique. J Hand Surg 1983; 8:263–267. 12. Silfverskiold KL, May EJ. Gap formation after flexor tendon repair in zone II. Results with a new controlled motion programme. Scand J Plast Reconstr Surg Hand Surg 1993; 27:263–268. 13. Silva MJ, Brodt MD, Boyer MI, Morris TS, Dinopoulos H, Amiel D, Gelberman RH. Effects of increased in vivo excursion on digital range of motion and tendon strength following flexor tendon repair. J Orthop Res 1999;17:777– 783. 14. Kessler I. The “grasping” technique for tendon repair. Hand 1973;5:253–255. 15. Silfverskiold KL, May EJ. Flexor tendon repair in zone II with a new suture technique and an early mobilization program combining passive and active flexion. J Hand Surg 1994;19A:53– 60. 16. Becker H. Primary repair of flexor tendons in the hand without immobilisation-preliminary report. Hand 1978;10: 37– 47. 17. Wade PJ, Muir IF, Hutcheon LL. Primary flexor tendon repair: the mechanical limitations of the modified Kessler technique. J Hand Surg 1986;11B:71–76. 18. Banes AJ, Donlon K, Link GW, Gillespie Y, Bevin AG,
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
Peterson HD, et al. Cell populations of tendon: a simplified method for isolation of synovial cells and internal fibroblasts: confirmation of origin and biologic properties. J Orthop Res 1988;6:83–94. Diao E, Hariharan JS, Soejima O, Lotz JC. Effect of peripheral suture depth on strength of tendon repairs. J Hand Surg 1996;21A:234 –239. Bischoff RJ, Morifusa S, Gelberman RH, Winters SC, Woo SL, Seiller JG III. The effects of proximal load on the excursion of autogenous flexor tendon grafts. J Hand Surg 1998;23A:285–289. McLarney E, Hoffman H, Wolfe SW. Biomechanical analysis of the cruciate four-strand flexor tendon repair. J Hand Surg 1999;24A:295–301. Aoki M, Pruitt DL, Kubota H, Manske PR. Effect of suture knots on tensile strength of repaired canine flexor tendons. J Hand Surg 1995;20B:72–75. Howard RF, Ondrovic L, Greenwald DP. Biomechanical analysis of four-strand extensor tendon repair techniques. J Hand Surg 1997;22A:838 – 842. Boyer MI, Gelberman RH, Burns ME, Dinopoulos H, Hofem R, Silva MJ. Intrasynovial flexor tendon repair. An experimental study comparing low and high levels of in vivo force during rehabilitation in canines. J Bone Joint Surg 2001;83A:891– 899. Hotokezaka S, Manske PR. Differences between locking loops and grasping loops: effects on 2-strand core suture. J Hand Surg 1997;22A:995–1003. Momose T, Amadio P, Zhao C, Zobitz M, Couvreur P, An KN. Suture techniques with high breaking strength and low gliding resistance: experiments in the dog flexor digitorum profundus tendon. Acta Orthop Scand 2001;72:635– 641. Tanaka T, Amadio PC, Zhao C, Zobitz ME, Yang C, An KN. Gliding characteristics and gap formation for locking and grasping tendon repairs: a biomechanical study in a human cadaver model. J Hand Surg 2004;29A:6 –14. Okuda Y, Gorski JP, Amadio PC. Effect of postnatal age on the ultrastructure of six anatomical areas of canine flexor digitorum profundus tendon. J Orthop Res 1987;5:231–241. Pribaz JJ, Morrison WA, Macleod AM. Primary repair of flexor tendons in no-man’s land using the Becker repair. J Hand Surg 1989;14B:400 – 405. Baktir A, Turk CY, Kabak S, Sahin V, Kardas Y. Flexor tendon repair in zone 2 followed by early active mobilization. J Hand Surg 1996;21B:624 – 628. Peck FH, Kennedy SM, Watson JS, Lees VC. An evaluation of the influence of practitioner-led hand clinics on rupture rates following primary tendon repair in the hand. Br J Plast Surg 2004;57:45– 49. Gordon L, Dysarz FA, Venkateswara KT, Mok AP, Ritchie RO, Rabinowitz S. Flexor tendon repair using a stainless steel external splint. Biomechanical study on human cadaver flexor tendons. J Hand Surg 1999;24B:654 – 657. Drape JL, Silbermann-Hoffman O, Houvet P, Dubert T, Thivet A, Benmelha Z, et al. Complications of flexor tendon repair in the hand: MR imaging assessment. Radiology 1996;198:219 –224. Solis D, Vallejo M, Diaz-Maurino T. Reduction of ricin toxicity without impairing the saccharide-binding properties by chemical modification of the carboxyl groups. Anal Biochem 1993;209:117–122.
Zhao et al / Reinforcement of the Tendon–Suture Interface 35. van Wachem PB, van Luyn MJ, Olde Damink LH, Dijkstra PJ, Feijen J, Nieuwenhuis P. Biocompatibility and tissue regenerating capacity of crosslinked dermal sheep collagen. J Biomed Mater Res 1994;28:353–363. 36. Pieper JS, Oosterhof A, Dijkstra PJ, Veerkamp JH, van Kuppevelt TH. Preparation and characterization of porous crosslinked collagenous matrices containing bioavailable chondroitin sulphate. Biomaterials 1999;20:847– 858. 37. Park SN, Park JC, Kim HO, Song MJ, Suh H. Characterization of porous collagen/hyaluronic acid scaffold modified by 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide cross-linking. Biomaterials 2002;23:1205–1212. 38. Duan X, Sheardown H. Dendrimer crosslinked collagen as a corneal tissue engineering scaffold: mechanical properties and corneal epithelial cell interactions. Biomaterials 2006; 27:4608 – 4617. 39. van Wachem PB, Plantinga JA, Wissink MJ, Beernink R, Poot AA, Engbers GH, et al. In vivo biocompatibility of carbodiimide-crosslinked collagen matrices: effects of crosslink density, heparin immobilization, and bFGF loading. J Biomed Mater Res 2001;55:368 –378. 40. Angele P, Abke J, Kujat R, Faltermeier H, Schumann D, Nerlich M, et al. Influence of different collagen species on physico-chemical properties of crosslinked collagen matrices. Biomaterials 2004;25:2831–2841. 41. Song E, Yeon Kim S, Chun T, Byun HJ, Lee YM. Collagen scaffolds derived from a marine source and their biocompatibility. Biomaterials 2006;27:2951–2961. 42. Zhao C, Sun YL, Amadio PC, Tanaka T, Ettema AM, An KN. Surface treatment of flexor tendon autografts with car-
43.
44.
45.
46.
47.
48. 49.
50. 51.
611
bodiimide-derivatized hyaluronic acid. An in vivo canine model. J Bone Joint Surg 2006;88A:2181–2191. Bonomo GM, Leggio A, Consiglio L. [Action of methyl-2cyanoacrylate (Eastman 910) in experimental lesions of the liver. Histo-morphological study]. Minerva Chir 1965;20: 43– 446. Dutton J, Yates PO. An experimental study of the effects of a plastic adhesive, methyl 2-cyanoacrylate monomer (M2 C-1) in various tissues. J Neurosurg 1966;24:876 – 882. Leggat PA, Kedjarune U, Smith DR. Toxicity of cyanoacrylate adhesives and their occupational impacts for dental staff. Ind Health 2004;42:207–211. Ong YS, Yap K, Ang ES, Tan KC, Ng RT, Song IC. 2-octylcynanoacrylate-assisted microvascular anastomosis in a rat model: long-term biomechanical properties and histological changes. Microsurgery 2004;24:304 –308. Pineros-Fernandez A, Rodeheaver PF, Rodeheaver GT. Octyl 2-cyanoacrylate for repair of peripheral nerve. Ann Plast Surg 2005;55:188 –195. Eaglstein WH, Sullivan T. Cyanoacrylates for skin closure. Dermatol Clin 2005;23:193–198. Ricci B, Ricci F, Bianchi PE. Octyl 2-cyanoacrylate in sutureless surgery of extraocular muscles: an experimental study in the rabbit model. Graefes Arch Clin Exp Ophthalmol 2000;238:454 – 458. Maw JL, Kartush JM. Ossicular chain reconstruction using a new tissue adhesive. Am J Otol 2000;21:301–305. Kaplan M, Baysal K. In vitro toxicity test of ethyl 2-cyanoacrylate, a tissue adhesive used in cardiovascular surgery, by fibroblast cell culture method. Heart Surg Forum 2005;8: E169 –E172.