Technical Briefs

A Nitinol Based Flexor Tendon Fixation Device: Gapping and Tensile Strength Measurements in Cadaver Flexor Tendon

[+] Author and Article Information
Shawn P. Reese

CoNextions Inc.,
Salt Lake City, UT 84104;
Department of Bioengineering,
The University of Utah,
Salt Lake City, UT 84112
e-mail: s.reese@conextionsmed.com

Erik N. Kubiak

CoNextions Inc.,
Salt Lake City, UT 84104;
Division of Orthopaedic Trauma,
Department of Orthopaedic Surgery,
The University of Utah,
Salt Lake City, UT 84112

1Corresponding author.

Contributed by the Bioengineering Division of ASME for publication in the JOURNAL OF BIOMECHANICAL ENGINEERING. Manuscript received May 8, 2013; final manuscript received September 30, 2013; accepted manuscript posted October 19, 2013; published online December 3, 2013. Assoc. Editor: Zong-Ming Li.

J Biomech Eng 136(1), 014501 (Dec 03, 2013) (5 pages) Paper No: BIO-13-1221; doi: 10.1115/1.4025779 History: Received May 08, 2013; Revised September 30, 2013; Accepted October 19, 2013

In this study, a new nitinol based fixation device was investigated for use in repairing severed digital flexor tendons. The device, composed of superelastic nitinol, is tubular in shape with inward facing tines for gripping tissue. Its cellular structure was designed such that it has a large effective Poisson's ratio, which facilitates a “finger trap” effect. This allows for reduced tendon compression during a resting state (to permit vascular perfusion) and increased compression during loading (to drive the tines into the tissue for gripping). To test the feasibility of using this device for flexor tendon repair, it was tested on cadaver flexor digitorum profundus tendons. The tendons were excised, cut in the region corresponding to a zone II laceration, and repaired using the device. The device was easy to install and did not prevent the tendon from bending. Constant strain rate tensile testing revealed a mean tensile strength of 57.6 ± 7.7 N, with a force of 53.2 ± 7.8 N at a 2 mm gap. This exceeds the suggested primary repair strength of 45 N, which has been proposed as the necessary strength for enabling early mobilization. Although considerable future studies will be needed to determine the suitability of the new repair device for clinical use, this study demonstrates the feasibility of utilizing a tubular, nitinol repair device for flexor tendon fixation.

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Gelberman, R. H., Boyer, M. I., Brodt, M. D., Winters, S. C., and Silva, M. J., 1999, “The Effect of Gap Formation at the Repair Site on the Strength and Excursion of Intrasynovial Flexor Tendons. An Experimental Study on the Early Stages of Tendon-Healing in Dogs,” J. Bone Joint Surg. Am., 81(7), pp. 975–982. [CrossRef] [PubMed]
Lee, S. K., 2012, “Modern Tendon Repair Techniques,” Hand Clinics, 28(4), pp. 565–570. [CrossRef] [PubMed]
Seiler, J. G., 3rd, 2001, “Flexor Tendon Repair,” J. Am. Soc. Surg. Hand, 1(3), pp. 177–191. [CrossRef]
Tanaka, T., Amadio, P. C., Zhao, C., Zobitz, M. E., Yang, C., and An, K. N., 2004, “Gliding Characteristics and Gap Formation for Locking and Grasping Tendon Repairs: A Biomechanical Study in a Human Cadaver Model,” J. Hand Surg., 29A, pp. 6–14. [CrossRef]
Tang, J. B., Gu, Y. T., Rice, K., Chen, F., and Pan, C. Z., 2001, “Evaluation of Four Methods of Flexor Tendon Repair for Postoperative Active Mobilization,” Plastic Reconstruct. Surg., 107(3), pp. 742–749. [CrossRef]
Bogumill, G. P., 2002, “Functional Anatomy of the Flexor Tendon System of the Hand,” Hand Surg., 7(1), pp. 33–46. [CrossRef] [PubMed]
Boyer, M. I., 2005, “Flexor Tendon Biology,” Hand Clinics, 21(2), pp. 159–166. [CrossRef] [PubMed]
Lilly, S. I., and Messer, T. M., 2006, “Complications After Treatment of Flexor Tendon Injuries,” J. Am. Acad. Orthop. Surg., 14(7), pp. 387–396. [PubMed]
Dy, C. J., Hernandez-Soria, A., Ma, Y., Roberts, T. R., and Daluiski, A., 2012, “Complications After Flexor Tendon Repair: A Systematic Review and Meta-Analysis,” J. Hand Surg., 37(3), pp. 543–551. [CrossRef]
Jaibaji, M., 2000, “Advances in the Biology of Zone II Flexor Tendon Healing and Adhesion Formation,” Ann. Plastic Surg., 45(1), pp. 83–92. [CrossRef]
Boyer, M. I., Meunier, M. J., Lescheid, J., Burns, M. E., Gelberman, R. H., and Silva, M. J., 2001, “The Influence of Cross-Sectional Area on the Tensile Properties of Flexor Tendons,” J. Hand Surg., 26A, pp. 828–832. [CrossRef]
Khanna, A., Friel, M., Gougoulias, N., Longo, U. G., and Maffulli, N., 2009, “Prevention of Adhesions in Surgery of the Flexor Tendons of the Hand: What is the Evidence?,” Br. Med. Bull., 90, pp. 85–109. [CrossRef] [PubMed]
Strick, M. J., Filan, S. L., Hile, M., McKenzie, C., Walsh, W. R., and Tonkin, M. A., 2004, “Adhesion Formation After Flexor Tendon Repair: A Histologic and Biomechanical Comparison of 2- and 4-Strand Repairs in a Chicken Model,” J. Hand Surg., 29(1), pp. 15–21. [CrossRef]
Strickland, J. W., 2000, “Development of Flexor Tendon Surgery: Twenty-Five Years of Progress,” J. Hand Surg., 25(2), pp. 214–235. [CrossRef]
Wolfe, S. W., Willis, A. A., Campbell, D., Clabeaux, J., and Wright, T. M., 2007, “Biomechanic Comparison of the Teno Fix Tendon Repair Device With the Cruciate and Modified Kessler Techniques,” J. Hand Surg., 32(3), pp. 356–366. [CrossRef]
Wong, J. K., Alyouha, S., Kadler, K. E., Ferguson, M. W., and McGrouther, D. A., 2010, “The Cell Biology of Suturing Tendons,” Matrix Biol., 29(6), pp. 525–536. [CrossRef] [PubMed]
Aoki, M., Manske, P. R., Pruitt, D. L., and Larson, B. J., 1994, “Tendon Repair Using Flexor Tendon Splints: An Experimental Study,” J. Hand Surg., 19(6), pp. 984–990. [CrossRef]
Gordon, L., Dysarz, F. A., Venkateswara, K. T., Mok, A. P., Ritchie, R. O., and Rabinowitz, S., 1999, “Flexor Tendon Repair Using a Stainless Steel External Splint. Biomechanical Study on Human Cadaver Flexor Tendons,” J. Hand Surgery Br. Eur., 24(6), pp. 654–657. [CrossRef]
Gordon, L., Tolar, M., Rao, K. T., Ritchie, R. O., Rabinowitz, S., and Lamb, R. P., 1998, “Flexor Tendon Repair Using a Stainless Steel Internal Anchor. Biomechanical Study on Human Cadaver Tendons,” J. Hand Surg., 23(1), pp. 37–40. [CrossRef]
Silfverskiold, K. L., and Andersson, C. H., 1993, “Two New Methods of Tendon Repair: An In Vitro Evaluation of Tensile Strength and Gap Formation,” J. Hand Surg., 18(1), pp. 58–65. [CrossRef]
Gussous, Y. M., Zhao, C., Amadio, P. C., and An, K. N., 2011, “The Resurgence of Barbed Suture and Connecting Devices for Use in Flexor Tendon Tenorrhaphy,” Hand (NY), 6(3), pp. 268–275. [CrossRef]
Rocchi, L., Merolli, A., Genzini, A., Merendi, G., and Catalano, F., 2008, “Flexor Tendon Injuries of the Hand Treated With Tenofix: Mid-Term Results,” J. Orthop. Traumatol., 9(4), pp. 201–208. [CrossRef] [PubMed]
Su, B. W., Protopsaltis, T. S., Koff, M. F., Chang, K. P., Strauch, R. J., Crow, S. A., and Rosenwasser, M. P., 2005, “The Biomechanical Analysis of a Tendon Fixation Device for Flexor Tendon Repair,” J. Hand Surg., 30(2), pp. 237–245. [CrossRef]
Su, B. W., Raia, F. J., Quitkin, H. M., Parisien, M., Strauch, R. J., and Rosenwasser, M. P., 2006, “Gross and Histological Analysis of Healing After Dog Flexor Tendon Repair With the Teno Fix Device,” J. Hand Surg., 31(5), pp. 524–529. [CrossRef]
Su, B. W., Solomons, M., Barrow, A., Senoge, M. E., Gilberti, M., Lubbers, L., Diao, E., Quitkin, H. M., Grafe, M. W., and Rosenwasser, M. P., 2006, “A Device for Zone-II Flexor Tendon Repair. Surgical Technique,” J. Bone Joint Surg. Am., 88(Suppl 1 Pt 1), pp. 37–49. [CrossRef] [PubMed]
Su, B. W., Solomons, M., Barrow, A., Senoge, M. E., Gilberti, M., Lubbers, L., Diao, E., Quitkin, H. M., and Rosenwasser, M. P., 2005, “Device for Zone-II Flexor Tendon Repair. A Multicenter, Randomized, Blinded, Clinical Trial,” J. Bone Joint Surg. Am., 87(5), pp. 923–935. [CrossRef] [PubMed]
Hirpara, K. M., Sullivan, P. J., and O'Sullivan, M. E., 2010, “A New Barbed Device for Repair of Flexor Tendons,” J. Bone Joint Surg. Br. Eur., 92(8), pp. 1165–1170. [CrossRef]
Duerig, T. P. A., and Stockel, D., 1999, “An Overview of Nitinol Medical Applications,” Mater. Sci. Eng., A273, pp. 149–160. [CrossRef]
Kujala, S., Pajala, A., Kallioinen, M., Pramila, A., Tuukkanen, J., and Ryhanen, J., 2004, “Biocompatibility and Strength Properties of Nitinol Shape Memory Alloy Suture in Rabbit Tendon,” Biomaterials, 25, pp. 353–358. [CrossRef] [PubMed]
Karjalainen, T., Goransson, H., Viinikainen, A., Jamsa, T., and Ryhanen, J., 2010, “Nickel-Titanium Wire as a Flexor Tendon Suture Material: An Ex Vivo Study,” J. Hand Surg. Eur. Vol., 35(6), pp. 469–474. [CrossRef] [PubMed]
Peel, L. D., 2007, “Exploration of High and Negative Poisson's Ratio Elastomer-Matrix Laminates,” Phys. Status Solidi (b), 244(3), pp. 988–1003. [CrossRef]
Sanders, D. W., Milne, A. D., Dobravec, A., MacDermid, J., Johnson, J. A., and King, G. J., 1997, “Cyclic Testing of Flexor Tendon Repairs: An In Vitro Biomechanical Study,” J. Hand Surg., 22(6), pp. 1004–1010. [CrossRef]
Vanhees, M., Thoreson, A. R., Larson, D. R., Amadio, P. C., An, K. N., and Zhao, C., 2013, “The Effect of Suture Preloading on the Force to Failure and Gap Formation After Flexor Tendon Repair,” J. Hand Surg. Am., 38(1), pp. 56–61. [CrossRef] [PubMed]
Zeplin, P. H., Zahn, R. K., Meffert, R. H., and Schmidt, K., 2011, “Biomechanical Evaluation of Flexor Tendon Repair Using Barbed Suture Material: A Comparative Ex Vivo Study,” J. Hand Surg. Am., 36(3), pp. 446–449. [CrossRef] [PubMed]
Karjalainen, T., He, M., Chong, A. K., Lim, A. Y., Goransson, H., and Ryhanen, J., 2012, “Comparison of the Holding Capacity of Round Monofilament, Round Multifilament, and Flat Multifilament Nitinol Suture Loops in Human Cadaveric Flexor Tendon,” J. Hand Surg. Eur. Vol., 37(5), pp. 459–463. [CrossRef] [PubMed]
Lujan, T. J., Underwood, C. J., Henninger, H. B., Thompson, B. M., and Weiss, J. A., 2007, “Effect of Dermatan Sulfate Glycosaminoglycans on the Quasi-Static Material Properties of the Human Medial Collateral Ligament,” J. Orthop. Res., 25(7), pp. 894–903. [CrossRef] [PubMed]
Lynch, H. A., Johannessen, W., Wu, J. P., Jawa, A., and Elliott, D. M., 2003, “Effect of Fiber Orientation and Strain Rate on the Nonlinear Uniaxial Tensile Material Properties of Tendon,” ASME J. Biomech. Eng., 125(5), pp. 726–731. [CrossRef]
Dinopoulos, H. T., Boyer, M. I., Burns, M. E., Gelberman, R. H., and Silva, M. J., 2000, “The Resistance of a Four- and Eight-Strand Suture Technique to Gap Formation During Tensile Testing: An Experimental Study of Repaired Canine Flexor Tendons After 10 Days of In Vivo Healing,” J. Hand Surg., 25(3), pp. 489–498. [CrossRef]
Waitayawinyu, T., Martineau, P. A., Luris, S., Hanel, D. P., and Trumble, T. E., 2008, “Comparative Biomechanic Study of Flexor Tendon Repair Using Fiber Wire,” J. Hand Surg., 33(5), pp. 701–708. [CrossRef]
Reese, S. P., Maas, S. A., and Weiss, J. A., 2010, “Micromechanical Models of Helical Superstructures in Ligament and Tendon Fibers Predict Large Poisson's Ratios,” J. Biomech., 43(7), pp. 1394–1400. [CrossRef] [PubMed]
Reese, S. P., and Weiss, J. A., 2012, “Tendon Fascicles Exhibit a Linear Correlation Between Poisson's Ratio and Force During Uniaxial Stress Relaxation,” ASME J. Biomech. Eng., 135(3), p. 034501. [CrossRef]
Griffin, M., Hindocha, S., Jordan, D., Saleh, M., and Khan, W., 2012, “An Overview of the Management of Flexor Tendon Injuries,” Open Orthop. J., 6, pp. 28–35. [CrossRef] [PubMed]


Grahic Jump Location
Fig. 1

Palmar view of the hand, with flexor tendons (red) overlaid on the bones. Zones I–V are labeled and delineated with a black line. The five pulleys (shown as blue rectangles) are shown on the index finger and labeled, but omitted from the other fingers for clarity.

Grahic Jump Location
Fig. 2

Nitinol fixation device. (a) 2D CAD drawing of the laser cut sheet component, with the center region and regions 1–3 delineated. (b) Side view schematic of the assembled device showing the top and bottom sheet components (heat set tines represented with dotted lines) connected on the sides with nitinol wire. Two separate wires were used for each side and were laced through the holes in the two opposing sheet parts. The ends of the wire lace were passed through a stainless steel swage (dark gray boxes at the ends). (c) Overhead view of a sheet component after the tines were heat set into a downward facing position. (d) Close up view of a tine. (e) Side view of a device ready for use.

Grahic Jump Location
Fig. 3

Application of nitinol fixation device. (a) The tendon stumps were pulled into the opened device using loops of suture material (direction of pull indicated by yellow arrows) such that an overlap of approximately 3 mm was obtained. The side laces were tightened, swages were crimped tight, excess wire was trimmed, and suture loops pulled out. (b) Overhead image of the device after application to a severed tendon. (c) Overhead image of the repaired tendon in the tissue clamps prior to testing.

Grahic Jump Location
Fig. 4

Force–strain response of repaired tendons. The force–strain response was nearly linear for all samples tested (R2 values ranged from 0.98 to 1.00, best fit lines not shown). Curves were truncated at the failure point for each curve for the purpose of clarity.

Grahic Jump Location
Fig. 5

Mean gapping and tensile strength. Force at 2 mm of gapping exceeded 45 N (represented by the dotted line), which is considered the necessary repair strength for early mobilization. No significant differences were present between the failure force, force at 2 mm of gapping or force at 1 mm of gapping. Error bars represent the standard deviation.

Grahic Jump Location
Fig. 6

Typical failure behavior of a repaired tendon. Most samples failed near the 2 mm gapping point. After failure, load decreased in an erratic manner as strain was increased. The locations of 1 mm gap formation, 2 mm gap formation, and failure are overlaid on the plot.



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