High-Tensile Strength Tape Versus High-Tensile Strength Suture: A Biomechanical Study LCDR Ryan J. Gnandt, M.D., USN, LT Jennifer L. Smith, M.D., USN, Kim Nguyen-Ta, M.S., LCDR Lucas McDonald, M.D., M.P.H.&T.M., USN, and LCDR Lance E. LeClere, M.D., USN
Purpose: To determine which suture design, high-tensile strength tape or high-tensile strength suture, performed better at securing human tissue across 4 selected suture techniques commonly used in tendinous repair, by comparing the total load at failure measured during a fixed-rate longitudinal single load to failure using a biomechanical testing machine. Methods: Matched sets of tendon specimens with bony attachments were dissected from 15 human cadaveric lower extremities in a manner allowing for direct comparison testing. With the use of selected techniques (simple MasonAllen in the patellar tendon specimens, whip stitch in the quadriceps tendon specimens, and Krackow stitch in the Achilles tendon specimens), 1 sample of each set was sutured with a 2-mm braided, nonabsorbable, high-tensile strength tape and the other with a No. 2 braided, nonabsorbable, high-tensile strength suture. A total of 120 specimens were tested. Each model was loaded to failure at a fixed longitudinal traction rate of 100 mm/min. The maximum load and failure method were recorded. Results: In the whip stitch and the Krackow-stitch models, the high-tensile strength tape had a significantly greater mean load at failure with a difference of 181 N (P ¼ .001) and 94 N (P ¼ .015) respectively. No significant difference was found in the MasonAllen and simple stitch models. Pull-through remained the most common method of failure at an overall rate of 56.7% (suture ¼ 55%; tape ¼ 58.3%). Conclusions: In biomechanical testing during a single load to failure, high-tensile strength tape performs more favorably than high-tensile strength suture, with a greater mean load to failure, in both the whip- and Krackow-stitch models. Although suture pull-through remains the most common method of failure, high-tensile strength tape requires a significantly greater load to pull-through in a whip-stitch and Krakow-stitch model. Clinical Relevance: The biomechanical data obtained in the current study indicates that high-tensile strength tape may provide better repair strength compared with high-tensile strength suture at time-zero simulated testing.
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or the repair of tendon and musculotendinous injuries, surgeons have the options of using different suture materials, suture designs, and repair techniques. The optimal repair also may depend on the anatomy From the Orthopaedic Surgery Department, Dana C. Covey Orthopaedic Biomechanics Laboratory, Naval Medical Center San Diego, San Diego, California, U.S.A. The authors report they have no conflicts of interest in the authorship and publication of this article. The views and opinions expressed in this article are those of the authors and are not necessarily representative of the official policy or views of the Department of the Navy, the Department of Defense, nor the U.S. Government. Received February 10, 2015; accepted August 7, 2015. Address correspondence to LCDR Lance E. LeClere, M.D., USN, US Naval Academy, Naval Health Clinic Annapolis, 250 Wood Road, Annapolis, MD 21402, U.S.A. E-mail: [email protected] Published by Elsevier Inc. on behalf of the Arthroscopy Association of North America 0749-8063/15109/$36.00 http://dx.doi.org/10.1016/j.arthro.2015.08.013
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and mechanics of the specific tendon or musculotendinous unit that is being repaired.1,2 Variability exists in soft-tissue repair and the causes can be multifactorial. Different suture materials, sizes, and designs as well as the different suturing techniques lead to a variability of results. For example, in published reports of pectoralis major repair alone, the use of both absorbable3,4 and nonabsorbable5,6 suture material has been reported with sizes ranging from No. 1 to No. 5.7 In a clinical scenario, one must consider the forces that will be applied to the repair when selecting the suture material, size, technique, and now even design, with the use of polyblend suture and suture tape.7,8 Suture tape consists of a high-strength, nonabsorbable polyblend suture core, centrally incorporated within a flat braided construction of an ultra-high molecular weight polyethylene (UHMWPE) fiber blended with fibers of one or more long chain synthetic polymers, preferably polyester.8 The larger tissue
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contact area of a suture tape theoretically allows force to be spread across a broader tissue area, thereby potentially allowing for improved performance in securing tissue. A variety of clinical and biomechanical studies have compared repair techniques across different tissue types with various materials and methods.1,2,9-18 To our knowledge, no study had been conducted focusing on the suturetendon interface and comparing high-tensile strength suture and high-tensile strength tape across 4 different models of human tissue repair while matching the compared human tissue samples perfectly for anatomic site, tissue quality, and repair technique. In this study we sought to determine which suture design, high-tensile strength tape or high-tensile strength suture, performed better in securing human tissue across 4 selected suture techniques commonly used in tendinous repair, by comparing the total load at failure measured during a fixed-rate longitudinal single load to failure using a biomechanical testing machine. Given the larger surface area of suture to tissue contact, we hypothesized that high-tensile strength tape would perform better at securing human tissue, with a greater total load at failure across all of the suture techniques tested.
Methods Tissue Dissection Tissue specimens were obtained from the lower extremities of 9 cadavers with a mean age of 74 (range, 53 to 89 years), of which 7 were female (11 experimental tissue set groups) and 2 were male (4 experimental tissue set groups). Fifteen individually numbered fresh-frozen human lower extremities available for use were dissected to obtain the knee extensor mechanism (quadriceps muscles, quadriceps tendon, patella, patellar tendon, and tibial tubercle) and the ankle plantarflexion mechanism (gastrocsoleus complex, Achilles tendon, and calcaneus). The samples were thawed overnight and were kept moist with normal saline throughout the testing process. The patella was transected transversely to separate the patellaquadriceps tendon bonetendon unit from the rest of the knee extensor mechanism. The superior hemipatella and quadriceps tendon were then split longitudinally down the midline to create a paired set of specimens. The remainder of the knee extensor mechanism was then transected transversely through the midpoint of the patellar tendon. The 2 resultant specimens were then split longitudinally down the midline, through the inferior hemipatella and proximal patellar tendon, as well as the distal patellar tendon and tibial tubercle. This produced 15 matched sets of patellapatellar tendon specimens and 15 matched sets of tibial tuberclepatellar tendon specimens. Finally,
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Fig 1. The knee extensor mechanism and Achillescalcaneus tissue specimens were dissected and sectioned as illustrated to produce the paired bonetendon tissue samples (illustrations by R.J.G.). Within each matched set, one sample was sutured with a high-tensile strength tape and the other with a hightensile strength suture.
each calcaneusAchilles tendon specimen was split longitudinally down the midline through the Achilles tendon and calcaneal bone segment producing 15 matched sets of calcaneusAchilles tendon specimens (Fig 1). Study Design This study was approved the institutional research board (NMCSD.NHU.2013.0006). A braided nonabsorbable polyblend high-tensile strength suture and a braided nonabsorbable polyblend high-tensile strength tape from the same manufacturer were selected to minimize any variances in manufacturing materials and methods. The suture selected was a No. 2 FiberWire (Arthrex, Naples, FL). This suture consists of a multistrand, long-chain UHMWPE core with a braided jacket of polyester and UHMWPE. The suture tape selected was 2-mm FiberTape (Arthrex). This is a 2-mm wide, ultra-high strength tape using a similar long chain polyethylene structure as the FiberWire suture.8 The dissection technique produced 60 paired sets of bonetendon tissue samples, with each set matched for tissue type and quality. One sample of each pair was sutured with high-tensile strength tape and the other with high-tensile strength suture. In total, 120 samples of lower-extremity human cadaveric bonetendon units were tested (15 specimens tested with suture and 15 specimens tested with tape for each of the 4 tissue repair models). The sutured bonetendon tissue samples were loaded onto an ADMET eXpert 2653, 50kN-Q Dual Column Universal Electromechanical Testing Machine (ADMET; Norwood, MA), equipped with ADMET grips and fixtures (Fig 2). The testing system was calibrated according to ASTM International and International
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Fig 2. The picture illustrates the method used to mount the test samples on the biomechanical testing machine. The bone block creates a mechanical stop on the top of the upper grip and the tendon is loose within the grip.
Organization for Standardization standards. The test samples were preloaded at 1 N and tension was applied at a constant longitudinal traction rate of 100 mm/min until failure. The total load at failure and the location of the ultimate failure were recorded. Failure included: tissue rupture, suture pull-through, tissue avulsion from the bony fragment, suture or tape rupture, and loss of bony fragment fixation in the testing device. The failure load was recorded in Newtons (N). The biomechanical testing system’s custom software, MTESTQuattro Software Controller, was used for setting up the parameters for the mechanical test and for data acquisition. A Wilcoxon signed rank test was used to analyze the data. Tissue Repair Model 1: Whip Stitch. One specimen of each matched pair of patellaquadriceps tendon specimens was sutured with a No. 2 braided nonabsorbable polyblend high-tensile strength suture (FiberWire; Arthrex) and the other with a 2-mm braided nonabsorbable polyblend high-tensile strength tape
Fig 3. The illustrated techniques were used for suturing the tendinous portions of the tissue samples (illustrations by R.J.G.).
(FiberTape; Arthrex) using a uniform whip stitch with 4 loops placed at a depth of 5 mm and spaced at 5mm intervals (Fig 3). The 30 specimens were then loaded individually in the mechanical measuring device by the bony segment of the patella at one end, via one of the machine’s mechanical grips. The bone block served as a mechanical stop on the top of the upper grip while the tendon remained loose within the grip. The bone plugs were not gripped directly to eliminate slippage and/or fracture. At the lower grip, the high-tensile strength tape or high-tensile strength suture was passed through and then tied around another of the machine’s mechanical grips, by the use of a uniform knot-tying technique of 7 squared knot throws (Fig 2). All matched groups were tested to failure at a constant longitudinal traction rate of 100 mm/min and the total load at failure and location of the failure were recorded. Tissue Repair Model 2: Simple Stitch. One specimen of each matched pair of patellapatellar tendon specimens was sutured with a No. 2 braided, nonabsorbable, polyblend high-tensile strength suture and the other with a
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2-mm braided, nonabsorbable, polyblend high-tensile strength tape using a uniform simple stitch, centered and placed 1 cm from the cut end of the tendon (Fig 3). Loading, tissue securing, and testing techniques were identical to the process described previously. Tissue Repair Model 3: MasonAllen Stitch. Likewise, 1 specimen of each matched pair of tibial tuberclepatellar tendon specimens was sutured with a No. 2 braided, nonabsorbable, polyblend high-tensile strength suture and the other with a 2-mm braided, nonabsorbable polyblend high-tensile strength tape using a uniform MasonAllen stitch that was thrown in a manner where the horizontal limb was 1 cm from the tendon end and passed through the tendon at 5 mm from the tendon edge on each end. The longitudinal segments entered and exited the tendon end at the midpoint of the tendon thickness and at 5 mm from the edges of the tendon, with the proximal central longitudinal portion passing through and into the tendon 5 mm above and below the horizontal limb (Fig 3). Loading, tissue securing, and testing techniques were identical to the process described previously. Tissue Repair Model 4: Krackow Stitch. One specimen of each matched pair of calcaneusAchilles tendon specimens was sutured with a No. 2 braided, nonabsorbable, polyblend high-tensile strength suture and the other with a 2-mm braided, nonabsorbable, polyblend high-tensile strength tape using a uniform Krackow stitch with 4 locking loops placed at a depth 5 mm and spaced at 5-mm intervals (Fig 3). Loading, tissue securing, and testing techniques were identical to the process described previously. Material Support. Material support was provided by Arthrex, who donated the polyblend suture and tape materials. No outside funds or other resources were used for the completion of the study. Statistical Analysis Before the initiation of this study, a minimum required sample size was estimated by a paired t-test function (sampsizepwr) within MATLAB version 7.8.0.347 R2009a software (MathWorks; Natick, MA) using alpha ¼ 0.05, power ¼ 0.80, and a standard deviation of 47, which was based on the standard deviation found in a similar experimental study (Arthrex; internal research, 2008). To detect a difference of 40 N between the testing groups, 13 matched pairs per suturing model were required. Given the available tissue and the proposed dissection and tissue preparation techniques, 15 matched pairs per tissue suturing model would be available for testing. Therefore, the study would confidently be able to detect a difference of 40 N between the testing groups (tape v suture). In total, 60
Table 1. Results of the Fixed-Rate Longitudinal Single Loadto-Failure Testing Stitch Whip Krackow Simple MasonAllen
Tape 709.34 N ( 91.10 N) 427.58 N ( 125.92 N) 36.76 N ( 24.95 N) 90.32 N ( 46.95 N)
Suture 528.66 N ( 73.63 N) 333.14 N ( 68.59 N) 29.34 N ( 10.42 N) 93.79 N ( 51.13 N)
P Value .001* .015* .233 .532
NOTE. Data are presented as mean ( SD) unless otherwise indicated. *P < .05.
matched tissue pairs would be compared, for a total of 120 tested samples. The data collected for each tissue repair model were analyzed with separate Wilcoxon signed rank tests. Additionally, where applicable, a Wilcoxon signed rank test was used to compare the difference in total load at failure for any specific method of failure. Descriptive statistics are given as Newtons (N) of force for each value with the mean values provided in graphs and listed with their standard deviations.
Results The compiled data from the study are reported in Table 1. The mean maximum load at failure in the whip stitch model was 709 N (SD 91 N) for the tape and 529 N (SD 73.63 N) for the suture (P ¼ .001). The mean maximum load at failure in the Krackow stitch model was 428 N (SD 126 N) for the tape and 333 N (SD 69 N) for the suture (P ¼ .015). The mean maximum load at failure in the proximal simple stitch model was 37 N (SD 25 N) for the tape and 29 N (SD 10 N) for the suture (P ¼ .233). The mean maximum load at failure in the Mason-Allen stitch model was 90 N (SD 47 N) for the tape and 94 N (SD 51 N) for the suture (P ¼ .532) (Fig 4). Suture pull-through remained the most common mode of failure at 56.7% across all tissue samples tested (68/120 samples). For each of the suture designs, suture pull-through also remained the most common mode of failure at 55% for the suture (33/60 samples) and 58.3% for the tape (35/60 samples) (Fig 5). No incidences of suture failure were observed in the hightensile strength tape group across all tissue repair models. Additionally, no incidences of suture pullthrough were observed in the Krackow stitch model (Fig 5).
Discussion The major finding of this study is that 2-mm braided, nonabsorbable polyblend high-tensile strength tape has
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Fig 4. Mean loads at failure across all repair models with the standard deviations. The values found to be statistically significant are identified by an asterisk.
a greater maximal load to failure than No. 2 braided, nonabsorbable polyblend high-tensile strength suture when placed in a whip-stitch and Krakow-stitch fashion. There was no statistically significant difference in Simple and MasonAllen suture configurations. Suture pull-through was the most common mode of failure across all suture configurations. With the evolution of suture material and design, there has been an increase in the tensile strength of the sutures available for soft tissue and tendinous repair.
Fig 5. Methods of failure for both the high-tensile strength suture and the high-tensile strength tape in reference to the suture techniques that were tested.
The improved strength of both sutures and suture anchors has resulted in the most common site of failure being the suturetendon interface.13 Krakow, whipstitch, MasonAllen, and simple suture configurations were chosen for this study because of published reports in which authors used these techniques in common tendinous repair scenarios such as quadriceps,19 and patellar tendon repairs,20 pectoralis major repairs,21 and rotator cuff repairs22; however, these reports either describe only the use of suture19,20,22 or do not include
TAPE VERSUS SUTURE: A BIOMECHANICAL STUDY
an analysis of the strength of repair when tape is used.21 Similar to previous studies of suture strength, this study focused on the suturetendon interface while comparing 2 polyblend suture designs in the repair of tendinous human tissue. The primary goal was to demonstrate superiority, or lack thereof, of one suture design over another in the repair of tendinous tissue, and this study was specifically designed to limit the potential for confounding variables to focus on the characteristics of each suture design. The head-to-head comparison of 2 different polyblend suture designs was performed on paired tissue samples from the same donor, which were therefore matched for age, sex, tissue type, tissue quality, and tissue anatomy. The aim was to create surrogate repair examples in order to provide data that would correlate well with the repair of tissues of similar anatomy and quality. In both the whip-stitch and the Krackow-stitch models, the high-tensile strength tape had a significantly greater mean load at failure by 181 N and 94 N, respectively. There was no significant difference in the mean load at failure between high-tensile strength tape and high-tensile strength suture in the simple stitch and MasonAllen stitch models; however, this study was powered to find a difference at 40 N with the number of specimens that were tested. In the simple stitch model, the mean load at failure was only 37 N for the tape and 29 N for the suture, suggesting that the current study was underpowered to find a significant difference in this particular repair model. Previous studies in which authors compared sutures and tapes have been performed with the inclusion of cyclic loading. The current study was designed to test biomechanical strength in a “time-zero” scenario. Bisson et al.14 used a bovine infraspinatus model to evaluate different suture composite materials at the suturetendon interface. They compared No. 2 FiberWire, Ultrabraid (Smith and Nephew, London, England), Orthocord (DePuy Mitek, Raynham, MA), and ETHIBOND (Ethicon, Johnson and Johnson, Piscataway, NJ) through a simple suture technique that was subjected to cyclic testing from 5 to 30 N for 30 cycles, followed by load-to-failure testing. They found no significant difference between polyester and polyblend suture materials in the ultimate tensile load. However, they did find a difference between these materials in the mode of failure, with suture breakage being most common with the polyester suture, and suture pullthrough being most common with the polyblend suture. In the current study, which used polyblend suture materials alone, pull-through was seen at a similar rate in both groups (suture ¼ 55%; tape ¼ 58.3%), which is consistent with the results obtained by Bisson et al. However, the whip-stitch model demonstrated a significant difference in the mean load at pull-through favoring the high-tensile strength tape by 221 N. By
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focusing on the suture design alone, the current study also demonstrated 8 incidences of suture breakage in a polyblend suture and no incidences of suture breakage in a polyblend tape, but it was not powered nor designed to elucidate a statistically significant difference in mode of failure. In their recent study, Deranlot et al.13 identified the suturetendon interface as a critical component of repair security in rotator cuff repair and used a sheep infraspinatus tendon model to compare the abrasive properties of four different suture designs. A simple suture technique was used and the suture was cycled through the tendon with 30 mm of excursion under a 10 N load for 50 cycles or until a tendon tear of greater than 13 mm. They found increased abrasive effects of FiberWire and FiberTape compared with ForceFiber (Tornier, Bloomington, MN) and Orthocord (DePuy Mitek) sutures. The authors acknowledged that although the testing conditions allowed for a comparison of suture abrasiveness, they did not necessarily reflect the intended clinical correlation of a rotator cuff repair. Another admitted limitation of the study is that it lacked the statistical power to further evaluate a difference between FiberWire and FiberTape. In contrast, the current study was designed to specifically evaluate the mean load at failure difference between these 2 suture designs across various examples of tendinous repair and demonstrated that in both a whip-stitch and a Krackow-stitch model of tendinous repair, the hightensile strength tape had a significantly greater mean load at failure by 180.68 N and 94.44 N, respectively. Compared with previous animal study models, the results of the current study suggest that in human tissue, high-tensile strength tape outperforms No. 2 high tensile strength suture when placed in a Krakow- or whip-stitch configuration. It is likely that the increased surface area and optimal tissue spacing between passes of the suture tape results in the greater load to failure in these scenarios. Unlike the simple stitch model used in this study, the Krakow- and whip-stitch configurations allowed for more passes of suture through the tissue, thus increasing contact area between the tissue and the suture/tape. Each pass of tape through tissue likely serves to increase the “advantage” of the tape and its increased surface area. This may explain the low values and underpowered results of the simple stitch model. Observations of the MasonAllen model at the time of testing indicate that failure may have been due to a large volume of tape in a relatively small area, essentially “severing” the tendon. The Krakow- and whipStitch configurations provided more spacing between passes of suture, therefore distributing force over a larger area which would once again take advantage of the broader suture tape. An advantage of a biomechanical study is the ability to control certain variables in the testing process to help
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narrow the focus of the study. As a result, a major strength of this study was the ability to isolate and specifically test the design of the suture in a head-tohead fashion across multiple repair models. This was accomplished by selecting sutures produced from the same composite materials, by using uniform suture techniques performed by a single investigator (J.L.S.), and by using tissue sample pairs that were identically matched for anatomy and quality as a result of a unique concept for dissection and sample preparation. Another strength of the study was that statistical power was achieved in 3 of 4 testing scenarios. Although 4 different repair models were tested, each repair model was individually powered to find a significant difference of 40 N in the mean load at failure. This was accomplished in all but the simple stitch model by obtaining and preparing an appropriate number of tissue samples for each repair model, as was identified through the pre-study power analysis. Limitations The major weakness of this study stems from the fact that our repair models were chosen based on the ability to procure adequate human tissue specimens for testing. These surrogate models, all of which originated from the lower extremity and were tendinous in nature, may not be absolutely representative of the actual repair scenario being considered in a clinical situation, such as a rotator cuff repair, biceps tendon repair or tenodesis, or pectoralis tendon repair. Additionally, only one specific technique (whip, simple, Krackow, MasonAllen) was used in each anatomic site (quad, patellar, Achilles tendons). Thus the results of Krackow stitch in a quad tendon may not have the same absolute value of pullout strength as other suture configurations in other tissue, and the low average tensile loads to failure seen in this study may be indicative of this (i.e., 333 N and 428 N for suture and tape, respectively). We feel that the value of this study design is not comparison of absolute value of pullout strength, or a comparison between different suture configurations. Rather, the value is in the direct comparison of tape to suture in identical tissue specimens with identical suture configurations, in a true “headto-head” testing scenario. Another weakness is the possibility of the study being underpowered to find a significant difference in the simple stitch model. The mean load at failure was only 37 N for the tape and 29 N for the suture, whereas the study was only powered to find a difference at 40 N. An increase in the sample size would allow for the detection of a significant difference at a lower force value, if one exists. From a clinical perspective, one weakness is the absence of a suture fixation device in the repair models.
This component also can play a role in the overall strength of a repair depending on the type or location of the repair. The decision to not use any suture fixation devices, however, was made to avoid the introduction of confounding variables in the study design. Another potential weakness is the manner with which the load was applied. Specifically, this study used the application of a progressive load to failure at a constant rate of distraction, rather than cyclic loading or a combination thereof. This method was chosen to evaluate the overall strength of the repair at the time the repair is performed, without any degenerative changes in the fixation as could potentially be caused by cyclic loading.
Conclusions In biomechanical testing during a single load to failure, high-tensile strength tape performs more favorably than high-tensile strength suture, with a greater mean load to failure, in both the whip-and Krackow-stitch models. Although suture pull-through remains the most common method of failure, high-tensile strength tape requires a significantly greater load to pull-through in a whip stitch and Krakow model.
Acknowledgment The authors thank Dr. Robert H. Riffenburgh for his invaluable assistance with the statistical analysis of the biomechanical study results.
References 1. Lee SJ, Sileo MJ, Kremenic IJ, et al. Cyclic loading of 3 Achilles tendon repairs simulating early postoperative forces. Am J Sports Med 2009;37:786-790. 2. Rabuck SJ, Lynch JL, Guo X, et al. Biomechanical comparison of 3 methods to repair pectoralis major ruptures. Am J Sports Med 2012;40:1635-1640. 3. Wolfe SW, Wickiewicz TL, Cavanaugh JT. Ruptures of the pectoralis major muscle: An anatomic and clinical analysis. Am J Sports Med 1992;20:587-593. 4. Berson BL. Surgical repair of pectoralis major rupture in an athlete: Case report of an unusual injury in a wrestler. Am J Sports Med 1979;7:348-351. 5. Liu J, Wu JJ, Chang CY, Chou YH, Lo WH. Avulsion of the pectoralis major tendon. Am J Sports Med 1992;20: 366-368. 6. Schepsis AA, Grafe MW, Jones HP, Lemos MJ. Rupture of the pectoralis major muscle: Outcome after repair of acute and chronic injuries. Am J Sports Med 2000;28:9-15. 7. Provencher MT, Handfield K, Boniquit NT, Reiff SN, Sekiya JK, Romeo AA. Injuries to the pectoralis major muscle: Diagnosis and management. Am J Sports Med 2010;38:1693-1705. 8. Grafton RD. High strength suture tape. U.S. Patent Application Publication US20050192631A1. September 1, 2005.
TAPE VERSUS SUTURE: A BIOMECHANICAL STUDY 9. Benthien RA, Aronow MS, Doran-Diaz V, Sullivan RJ, Naujoks R, Adams DJ. Cyclic loading of Achilles tendon repairs: A comparison of polyester and polyblend suture. Foot Ankle Int 2006;27:512-518. 10. Sherman SL, Lin EC, Verma NN, et al. Biomechanical analysis of the pectoralis major tendon and comparison of techniques for tendo-osseous repair. Am J Sports Med 2012;40:1887-1894. 11. Jayamoorthy T, Field JR, Costi JJ, Martin DK, Stanley RM, Hearn TC. Biceps tenodesis: A biomechanical study of fixation methods. J Shoulder Elbow Surg 2004;13: 160-164. 12. Kilicoglu O, Koyuncu O, Demirhan M, et al. Timedependent changes in failure loads of 3 biceps tenodesis techniques. Am J Sports Med 2005;33:1536-1544. 13. Deranlot J, Maurel N, Diop A, et al. Abrasive properties of braided polyblend sutures in cuff tendon repair: An in vitro biomechanical study exploring regular and tape sutures. Arthroscopy 2014;30:1569-1573. 14. Bisson LJ, Manohar LM, Wilkins RD, Gurske-Deperio J, Ehrensberger MT. Influence of suture material on the biomechanical behavior of suture-tendon specimens: A controlled study in bovine rotator cuff. Am J Sports Med 2008;36:907-912. 15. Kowalski MS, Dellenbaugh SG, Erlichman DB, Gardner TR, Levine WN, Ahmad CS. Evaluation of suture
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abrasion against rotator cuff tendon and proximal humerus bone. Arthroscopy 2008;24:329-334. Bak K, Cameron EA, Henderson IJ. Rupture of the pectoralis major: A meta-analysis of 112 cases. Knee Surg Sports Traumatol Arthrosc 2000;8:113-119. Kakwani RG, Matthews JJ, Kumar KM, Pimpalnerkar A, Mohtadi N. Rupture of the pectoralis major muscle: Surgical treatment in athletes. Int Orthop 2007;31:159-163. Quinlan JF, Molloy M, Hurson BJ. Pectoralis major tendon ruptures: When to operate. Br J Sports Med 2002;36:226-228. Ilan DI, Tejwani N, Keschner M, Leibman M. Quadriceps tendon rupture. J Am Acad Orthop Surg 2003;11:192-200. Krushinski EM, Parks BG, Hinton RY. Gap formation in transpatellar patellar tendon repair: Pretensioning Krackow sutures versus standard repair in a cadaver model. Am J Sports Med 2010;38:171-175. Metzger PD, Bailey JR, Filler RD, Waltz RA, Provencher MT, Dewing CB. Pectoralis major muscle rupture repair: Technique using unicortical buttons. Arthrosc Tech 2012;1:e119-e125. Brown MJ, Pula DA, Kluczynski MA, Mashtare T, Bisson LJ. Does suture technique affect re-rupture in arthroscopic rotator cuff repair? A meta-analysis. Arthroscopy 2015;31:1576-1582.
Purpose: To determine which suture design, high-tensile strength tape or high-tensile strength suture, performed better at securing human tissue across 4 selected suture techniques commonly used in tendinous repair, by comparing the total load at failure measured during a fixed-rate longitudinal single load to failure using a biomechanical testing machine. Methods: Matched sets of tendon specimens with bony attachments were dissected from 15 human cadaveric lower extremities in a manner allowing for direct comparison testing. With the use of selected techniques (simple MasonAllen in the patellar tendon specimens, whip stitch in the quadriceps tendon specimens, and Krackow stitch in the Achilles tendon specimens), 1 sample of each set was sutured with a 2-mm braided, nonabsorbable, high-tensile strength tape and the other with a No. 2 braided, nonabsorbable, high-tensile strength suture. A total of 120 specimens were tested. Each model was loaded to failure at a fixed longitudinal traction rate of 100 mm/min. The maximum load and failure method were recorded. Results: In the whip stitch and the Krackow-stitch models, the high-tensile strength tape had a significantly greater mean load at failure with a difference of 181 N (P ¼ .001) and 94 N (P ¼ .015) respectively. No significant difference was found in the MasonAllen and simple stitch models. Pull-through remained the most common method of failure at an overall rate of 56.7% (suture ¼ 55%; tape ¼ 58.3%). Conclusions: In biomechanical testing during a single load to failure, high-tensile strength tape performs more favorably than high-tensile strength suture, with a greater mean load to failure, in both the whip- and Krackow-stitch models. Although suture pull-through remains the most common method of failure, high-tensile strength tape requires a significantly greater load to pull-through in a whip-stitch and Krakow-stitch model. Clinical Relevance: The biomechanical data obtained in the current study indicates that high-tensile strength tape may provide better repair strength compared with high-tensile strength suture at time-zero simulated testing.
See commentary on page 364
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or the repair of tendon and musculotendinous injuries, surgeons have the options of using different suture materials, suture designs, and repair techniques. The optimal repair also may depend on the anatomy From the Orthopaedic Surgery Department, Dana C. Covey Orthopaedic Biomechanics Laboratory, Naval Medical Center San Diego, San Diego, California, U.S.A. The authors report they have no conflicts of interest in the authorship and publication of this article. The views and opinions expressed in this article are those of the authors and are not necessarily representative of the official policy or views of the Department of the Navy, the Department of Defense, nor the U.S. Government. Received February 10, 2015; accepted August 7, 2015. Address correspondence to LCDR Lance E. LeClere, M.D., USN, US Naval Academy, Naval Health Clinic Annapolis, 250 Wood Road, Annapolis, MD 21402, U.S.A. E-mail: [email protected] Published by Elsevier Inc. on behalf of the Arthroscopy Association of North America 0749-8063/15109/$36.00 http://dx.doi.org/10.1016/j.arthro.2015.08.013
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and mechanics of the specific tendon or musculotendinous unit that is being repaired.1,2 Variability exists in soft-tissue repair and the causes can be multifactorial. Different suture materials, sizes, and designs as well as the different suturing techniques lead to a variability of results. For example, in published reports of pectoralis major repair alone, the use of both absorbable3,4 and nonabsorbable5,6 suture material has been reported with sizes ranging from No. 1 to No. 5.7 In a clinical scenario, one must consider the forces that will be applied to the repair when selecting the suture material, size, technique, and now even design, with the use of polyblend suture and suture tape.7,8 Suture tape consists of a high-strength, nonabsorbable polyblend suture core, centrally incorporated within a flat braided construction of an ultra-high molecular weight polyethylene (UHMWPE) fiber blended with fibers of one or more long chain synthetic polymers, preferably polyester.8 The larger tissue
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contact area of a suture tape theoretically allows force to be spread across a broader tissue area, thereby potentially allowing for improved performance in securing tissue. A variety of clinical and biomechanical studies have compared repair techniques across different tissue types with various materials and methods.1,2,9-18 To our knowledge, no study had been conducted focusing on the suturetendon interface and comparing high-tensile strength suture and high-tensile strength tape across 4 different models of human tissue repair while matching the compared human tissue samples perfectly for anatomic site, tissue quality, and repair technique. In this study we sought to determine which suture design, high-tensile strength tape or high-tensile strength suture, performed better in securing human tissue across 4 selected suture techniques commonly used in tendinous repair, by comparing the total load at failure measured during a fixed-rate longitudinal single load to failure using a biomechanical testing machine. Given the larger surface area of suture to tissue contact, we hypothesized that high-tensile strength tape would perform better at securing human tissue, with a greater total load at failure across all of the suture techniques tested.
Methods Tissue Dissection Tissue specimens were obtained from the lower extremities of 9 cadavers with a mean age of 74 (range, 53 to 89 years), of which 7 were female (11 experimental tissue set groups) and 2 were male (4 experimental tissue set groups). Fifteen individually numbered fresh-frozen human lower extremities available for use were dissected to obtain the knee extensor mechanism (quadriceps muscles, quadriceps tendon, patella, patellar tendon, and tibial tubercle) and the ankle plantarflexion mechanism (gastrocsoleus complex, Achilles tendon, and calcaneus). The samples were thawed overnight and were kept moist with normal saline throughout the testing process. The patella was transected transversely to separate the patellaquadriceps tendon bonetendon unit from the rest of the knee extensor mechanism. The superior hemipatella and quadriceps tendon were then split longitudinally down the midline to create a paired set of specimens. The remainder of the knee extensor mechanism was then transected transversely through the midpoint of the patellar tendon. The 2 resultant specimens were then split longitudinally down the midline, through the inferior hemipatella and proximal patellar tendon, as well as the distal patellar tendon and tibial tubercle. This produced 15 matched sets of patellapatellar tendon specimens and 15 matched sets of tibial tuberclepatellar tendon specimens. Finally,
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Fig 1. The knee extensor mechanism and Achillescalcaneus tissue specimens were dissected and sectioned as illustrated to produce the paired bonetendon tissue samples (illustrations by R.J.G.). Within each matched set, one sample was sutured with a high-tensile strength tape and the other with a hightensile strength suture.
each calcaneusAchilles tendon specimen was split longitudinally down the midline through the Achilles tendon and calcaneal bone segment producing 15 matched sets of calcaneusAchilles tendon specimens (Fig 1). Study Design This study was approved the institutional research board (NMCSD.NHU.2013.0006). A braided nonabsorbable polyblend high-tensile strength suture and a braided nonabsorbable polyblend high-tensile strength tape from the same manufacturer were selected to minimize any variances in manufacturing materials and methods. The suture selected was a No. 2 FiberWire (Arthrex, Naples, FL). This suture consists of a multistrand, long-chain UHMWPE core with a braided jacket of polyester and UHMWPE. The suture tape selected was 2-mm FiberTape (Arthrex). This is a 2-mm wide, ultra-high strength tape using a similar long chain polyethylene structure as the FiberWire suture.8 The dissection technique produced 60 paired sets of bonetendon tissue samples, with each set matched for tissue type and quality. One sample of each pair was sutured with high-tensile strength tape and the other with high-tensile strength suture. In total, 120 samples of lower-extremity human cadaveric bonetendon units were tested (15 specimens tested with suture and 15 specimens tested with tape for each of the 4 tissue repair models). The sutured bonetendon tissue samples were loaded onto an ADMET eXpert 2653, 50kN-Q Dual Column Universal Electromechanical Testing Machine (ADMET; Norwood, MA), equipped with ADMET grips and fixtures (Fig 2). The testing system was calibrated according to ASTM International and International
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Fig 2. The picture illustrates the method used to mount the test samples on the biomechanical testing machine. The bone block creates a mechanical stop on the top of the upper grip and the tendon is loose within the grip.
Organization for Standardization standards. The test samples were preloaded at 1 N and tension was applied at a constant longitudinal traction rate of 100 mm/min until failure. The total load at failure and the location of the ultimate failure were recorded. Failure included: tissue rupture, suture pull-through, tissue avulsion from the bony fragment, suture or tape rupture, and loss of bony fragment fixation in the testing device. The failure load was recorded in Newtons (N). The biomechanical testing system’s custom software, MTESTQuattro Software Controller, was used for setting up the parameters for the mechanical test and for data acquisition. A Wilcoxon signed rank test was used to analyze the data. Tissue Repair Model 1: Whip Stitch. One specimen of each matched pair of patellaquadriceps tendon specimens was sutured with a No. 2 braided nonabsorbable polyblend high-tensile strength suture (FiberWire; Arthrex) and the other with a 2-mm braided nonabsorbable polyblend high-tensile strength tape
Fig 3. The illustrated techniques were used for suturing the tendinous portions of the tissue samples (illustrations by R.J.G.).
(FiberTape; Arthrex) using a uniform whip stitch with 4 loops placed at a depth of 5 mm and spaced at 5mm intervals (Fig 3). The 30 specimens were then loaded individually in the mechanical measuring device by the bony segment of the patella at one end, via one of the machine’s mechanical grips. The bone block served as a mechanical stop on the top of the upper grip while the tendon remained loose within the grip. The bone plugs were not gripped directly to eliminate slippage and/or fracture. At the lower grip, the high-tensile strength tape or high-tensile strength suture was passed through and then tied around another of the machine’s mechanical grips, by the use of a uniform knot-tying technique of 7 squared knot throws (Fig 2). All matched groups were tested to failure at a constant longitudinal traction rate of 100 mm/min and the total load at failure and location of the failure were recorded. Tissue Repair Model 2: Simple Stitch. One specimen of each matched pair of patellapatellar tendon specimens was sutured with a No. 2 braided, nonabsorbable, polyblend high-tensile strength suture and the other with a
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2-mm braided, nonabsorbable, polyblend high-tensile strength tape using a uniform simple stitch, centered and placed 1 cm from the cut end of the tendon (Fig 3). Loading, tissue securing, and testing techniques were identical to the process described previously. Tissue Repair Model 3: MasonAllen Stitch. Likewise, 1 specimen of each matched pair of tibial tuberclepatellar tendon specimens was sutured with a No. 2 braided, nonabsorbable, polyblend high-tensile strength suture and the other with a 2-mm braided, nonabsorbable polyblend high-tensile strength tape using a uniform MasonAllen stitch that was thrown in a manner where the horizontal limb was 1 cm from the tendon end and passed through the tendon at 5 mm from the tendon edge on each end. The longitudinal segments entered and exited the tendon end at the midpoint of the tendon thickness and at 5 mm from the edges of the tendon, with the proximal central longitudinal portion passing through and into the tendon 5 mm above and below the horizontal limb (Fig 3). Loading, tissue securing, and testing techniques were identical to the process described previously. Tissue Repair Model 4: Krackow Stitch. One specimen of each matched pair of calcaneusAchilles tendon specimens was sutured with a No. 2 braided, nonabsorbable, polyblend high-tensile strength suture and the other with a 2-mm braided, nonabsorbable, polyblend high-tensile strength tape using a uniform Krackow stitch with 4 locking loops placed at a depth 5 mm and spaced at 5-mm intervals (Fig 3). Loading, tissue securing, and testing techniques were identical to the process described previously. Material Support. Material support was provided by Arthrex, who donated the polyblend suture and tape materials. No outside funds or other resources were used for the completion of the study. Statistical Analysis Before the initiation of this study, a minimum required sample size was estimated by a paired t-test function (sampsizepwr) within MATLAB version 7.8.0.347 R2009a software (MathWorks; Natick, MA) using alpha ¼ 0.05, power ¼ 0.80, and a standard deviation of 47, which was based on the standard deviation found in a similar experimental study (Arthrex; internal research, 2008). To detect a difference of 40 N between the testing groups, 13 matched pairs per suturing model were required. Given the available tissue and the proposed dissection and tissue preparation techniques, 15 matched pairs per tissue suturing model would be available for testing. Therefore, the study would confidently be able to detect a difference of 40 N between the testing groups (tape v suture). In total, 60
Table 1. Results of the Fixed-Rate Longitudinal Single Loadto-Failure Testing Stitch Whip Krackow Simple MasonAllen
Tape 709.34 N ( 91.10 N) 427.58 N ( 125.92 N) 36.76 N ( 24.95 N) 90.32 N ( 46.95 N)
Suture 528.66 N ( 73.63 N) 333.14 N ( 68.59 N) 29.34 N ( 10.42 N) 93.79 N ( 51.13 N)
P Value .001* .015* .233 .532
NOTE. Data are presented as mean ( SD) unless otherwise indicated. *P < .05.
matched tissue pairs would be compared, for a total of 120 tested samples. The data collected for each tissue repair model were analyzed with separate Wilcoxon signed rank tests. Additionally, where applicable, a Wilcoxon signed rank test was used to compare the difference in total load at failure for any specific method of failure. Descriptive statistics are given as Newtons (N) of force for each value with the mean values provided in graphs and listed with their standard deviations.
Results The compiled data from the study are reported in Table 1. The mean maximum load at failure in the whip stitch model was 709 N (SD 91 N) for the tape and 529 N (SD 73.63 N) for the suture (P ¼ .001). The mean maximum load at failure in the Krackow stitch model was 428 N (SD 126 N) for the tape and 333 N (SD 69 N) for the suture (P ¼ .015). The mean maximum load at failure in the proximal simple stitch model was 37 N (SD 25 N) for the tape and 29 N (SD 10 N) for the suture (P ¼ .233). The mean maximum load at failure in the Mason-Allen stitch model was 90 N (SD 47 N) for the tape and 94 N (SD 51 N) for the suture (P ¼ .532) (Fig 4). Suture pull-through remained the most common mode of failure at 56.7% across all tissue samples tested (68/120 samples). For each of the suture designs, suture pull-through also remained the most common mode of failure at 55% for the suture (33/60 samples) and 58.3% for the tape (35/60 samples) (Fig 5). No incidences of suture failure were observed in the hightensile strength tape group across all tissue repair models. Additionally, no incidences of suture pullthrough were observed in the Krackow stitch model (Fig 5).
Discussion The major finding of this study is that 2-mm braided, nonabsorbable polyblend high-tensile strength tape has
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Fig 4. Mean loads at failure across all repair models with the standard deviations. The values found to be statistically significant are identified by an asterisk.
a greater maximal load to failure than No. 2 braided, nonabsorbable polyblend high-tensile strength suture when placed in a whip-stitch and Krakow-stitch fashion. There was no statistically significant difference in Simple and MasonAllen suture configurations. Suture pull-through was the most common mode of failure across all suture configurations. With the evolution of suture material and design, there has been an increase in the tensile strength of the sutures available for soft tissue and tendinous repair.
Fig 5. Methods of failure for both the high-tensile strength suture and the high-tensile strength tape in reference to the suture techniques that were tested.
The improved strength of both sutures and suture anchors has resulted in the most common site of failure being the suturetendon interface.13 Krakow, whipstitch, MasonAllen, and simple suture configurations were chosen for this study because of published reports in which authors used these techniques in common tendinous repair scenarios such as quadriceps,19 and patellar tendon repairs,20 pectoralis major repairs,21 and rotator cuff repairs22; however, these reports either describe only the use of suture19,20,22 or do not include
TAPE VERSUS SUTURE: A BIOMECHANICAL STUDY
an analysis of the strength of repair when tape is used.21 Similar to previous studies of suture strength, this study focused on the suturetendon interface while comparing 2 polyblend suture designs in the repair of tendinous human tissue. The primary goal was to demonstrate superiority, or lack thereof, of one suture design over another in the repair of tendinous tissue, and this study was specifically designed to limit the potential for confounding variables to focus on the characteristics of each suture design. The head-to-head comparison of 2 different polyblend suture designs was performed on paired tissue samples from the same donor, which were therefore matched for age, sex, tissue type, tissue quality, and tissue anatomy. The aim was to create surrogate repair examples in order to provide data that would correlate well with the repair of tissues of similar anatomy and quality. In both the whip-stitch and the Krackow-stitch models, the high-tensile strength tape had a significantly greater mean load at failure by 181 N and 94 N, respectively. There was no significant difference in the mean load at failure between high-tensile strength tape and high-tensile strength suture in the simple stitch and MasonAllen stitch models; however, this study was powered to find a difference at 40 N with the number of specimens that were tested. In the simple stitch model, the mean load at failure was only 37 N for the tape and 29 N for the suture, suggesting that the current study was underpowered to find a significant difference in this particular repair model. Previous studies in which authors compared sutures and tapes have been performed with the inclusion of cyclic loading. The current study was designed to test biomechanical strength in a “time-zero” scenario. Bisson et al.14 used a bovine infraspinatus model to evaluate different suture composite materials at the suturetendon interface. They compared No. 2 FiberWire, Ultrabraid (Smith and Nephew, London, England), Orthocord (DePuy Mitek, Raynham, MA), and ETHIBOND (Ethicon, Johnson and Johnson, Piscataway, NJ) through a simple suture technique that was subjected to cyclic testing from 5 to 30 N for 30 cycles, followed by load-to-failure testing. They found no significant difference between polyester and polyblend suture materials in the ultimate tensile load. However, they did find a difference between these materials in the mode of failure, with suture breakage being most common with the polyester suture, and suture pullthrough being most common with the polyblend suture. In the current study, which used polyblend suture materials alone, pull-through was seen at a similar rate in both groups (suture ¼ 55%; tape ¼ 58.3%), which is consistent with the results obtained by Bisson et al. However, the whip-stitch model demonstrated a significant difference in the mean load at pull-through favoring the high-tensile strength tape by 221 N. By
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focusing on the suture design alone, the current study also demonstrated 8 incidences of suture breakage in a polyblend suture and no incidences of suture breakage in a polyblend tape, but it was not powered nor designed to elucidate a statistically significant difference in mode of failure. In their recent study, Deranlot et al.13 identified the suturetendon interface as a critical component of repair security in rotator cuff repair and used a sheep infraspinatus tendon model to compare the abrasive properties of four different suture designs. A simple suture technique was used and the suture was cycled through the tendon with 30 mm of excursion under a 10 N load for 50 cycles or until a tendon tear of greater than 13 mm. They found increased abrasive effects of FiberWire and FiberTape compared with ForceFiber (Tornier, Bloomington, MN) and Orthocord (DePuy Mitek) sutures. The authors acknowledged that although the testing conditions allowed for a comparison of suture abrasiveness, they did not necessarily reflect the intended clinical correlation of a rotator cuff repair. Another admitted limitation of the study is that it lacked the statistical power to further evaluate a difference between FiberWire and FiberTape. In contrast, the current study was designed to specifically evaluate the mean load at failure difference between these 2 suture designs across various examples of tendinous repair and demonstrated that in both a whip-stitch and a Krackow-stitch model of tendinous repair, the hightensile strength tape had a significantly greater mean load at failure by 180.68 N and 94.44 N, respectively. Compared with previous animal study models, the results of the current study suggest that in human tissue, high-tensile strength tape outperforms No. 2 high tensile strength suture when placed in a Krakow- or whip-stitch configuration. It is likely that the increased surface area and optimal tissue spacing between passes of the suture tape results in the greater load to failure in these scenarios. Unlike the simple stitch model used in this study, the Krakow- and whip-stitch configurations allowed for more passes of suture through the tissue, thus increasing contact area between the tissue and the suture/tape. Each pass of tape through tissue likely serves to increase the “advantage” of the tape and its increased surface area. This may explain the low values and underpowered results of the simple stitch model. Observations of the MasonAllen model at the time of testing indicate that failure may have been due to a large volume of tape in a relatively small area, essentially “severing” the tendon. The Krakow- and whipStitch configurations provided more spacing between passes of suture, therefore distributing force over a larger area which would once again take advantage of the broader suture tape. An advantage of a biomechanical study is the ability to control certain variables in the testing process to help
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narrow the focus of the study. As a result, a major strength of this study was the ability to isolate and specifically test the design of the suture in a head-tohead fashion across multiple repair models. This was accomplished by selecting sutures produced from the same composite materials, by using uniform suture techniques performed by a single investigator (J.L.S.), and by using tissue sample pairs that were identically matched for anatomy and quality as a result of a unique concept for dissection and sample preparation. Another strength of the study was that statistical power was achieved in 3 of 4 testing scenarios. Although 4 different repair models were tested, each repair model was individually powered to find a significant difference of 40 N in the mean load at failure. This was accomplished in all but the simple stitch model by obtaining and preparing an appropriate number of tissue samples for each repair model, as was identified through the pre-study power analysis. Limitations The major weakness of this study stems from the fact that our repair models were chosen based on the ability to procure adequate human tissue specimens for testing. These surrogate models, all of which originated from the lower extremity and were tendinous in nature, may not be absolutely representative of the actual repair scenario being considered in a clinical situation, such as a rotator cuff repair, biceps tendon repair or tenodesis, or pectoralis tendon repair. Additionally, only one specific technique (whip, simple, Krackow, MasonAllen) was used in each anatomic site (quad, patellar, Achilles tendons). Thus the results of Krackow stitch in a quad tendon may not have the same absolute value of pullout strength as other suture configurations in other tissue, and the low average tensile loads to failure seen in this study may be indicative of this (i.e., 333 N and 428 N for suture and tape, respectively). We feel that the value of this study design is not comparison of absolute value of pullout strength, or a comparison between different suture configurations. Rather, the value is in the direct comparison of tape to suture in identical tissue specimens with identical suture configurations, in a true “headto-head” testing scenario. Another weakness is the possibility of the study being underpowered to find a significant difference in the simple stitch model. The mean load at failure was only 37 N for the tape and 29 N for the suture, whereas the study was only powered to find a difference at 40 N. An increase in the sample size would allow for the detection of a significant difference at a lower force value, if one exists. From a clinical perspective, one weakness is the absence of a suture fixation device in the repair models.
This component also can play a role in the overall strength of a repair depending on the type or location of the repair. The decision to not use any suture fixation devices, however, was made to avoid the introduction of confounding variables in the study design. Another potential weakness is the manner with which the load was applied. Specifically, this study used the application of a progressive load to failure at a constant rate of distraction, rather than cyclic loading or a combination thereof. This method was chosen to evaluate the overall strength of the repair at the time the repair is performed, without any degenerative changes in the fixation as could potentially be caused by cyclic loading.
Conclusions In biomechanical testing during a single load to failure, high-tensile strength tape performs more favorably than high-tensile strength suture, with a greater mean load to failure, in both the whip-and Krackow-stitch models. Although suture pull-through remains the most common method of failure, high-tensile strength tape requires a significantly greater load to pull-through in a whip stitch and Krakow model.
Acknowledgment The authors thank Dr. Robert H. Riffenburgh for his invaluable assistance with the statistical analysis of the biomechanical study results.
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