A Mechanical Evaluation of Zone II Flexor Tendon Repair Using a Knotless Barbed Suture Versus a Traditional Braided Suture

A Mechanical Evaluation of Zone II Flexor Tendon Repair Using a Knotless Barbed Suture Versus a Traditional Braided Suture

SCIENTIFIC ARTICLE A Mechanical Evaluation of Zone II Flexor Tendon Repair Using a Knotless Barbed Suture Versus a Traditional Braided Suture Anirudd...

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A Mechanical Evaluation of Zone II Flexor Tendon Repair Using a Knotless Barbed Suture Versus a Traditional Braided Suture Aniruddh N. Nayak, MS,* Dzi-Viet Nguyen, DO,† Robert C. Brabender, MD,† Matthew E. Hiro, MD,‡ Jeremy J. Miles, MD,§ Ian R. Smithson, MD,§ Brandon G. Santoni, PhD,* Jeffery D. Stone, MD,† Alfred V. Hess, MD† Purpose To determine repair site bulk, gliding resistance, work of flexion, and 1-mm gap formation force in zone II flexor tendon lacerations repaired with knotless barbed or traditional braided suture. Methods Transverse zone II lacerations of the flexor digitorum profundus (FDP) tendon were created in 36 digits from 6 matched human cadaveric pairs. Repair was performed with 2-0 barbed suture (n ¼ 18) or 3-0 polyethylene braided suture (n ¼ 18). Pre- and postrepair crosssectional area was measured followed by quantification of gliding resistance and work of flexion during cyclic flexion-extension loading at 10 mm/min. Thereafter, the repaired tendons were loaded to failure. The force at 1 mm of gap formation was recorded. Results Repaired FDP tendon cross-sectional area increased significantly from intact, with no difference noted between suture types. Gliding resistance and work of flexion were significantly higher for both suture repairs; however, we identified no significant differences in either nondestructive biomechanical parameters between repair types. Average 1-mm gap formation force with the knotless barbed suture (52 N) was greater than that of the traditional braided suture (43 N). Conclusions We identified no significant advantage in using knotless barbed suture for zone II FDP repair in our primary, nondestructive mechanical outcomes in this in vitro study. Clinical relevance In vivo studies may be warranted to determine if one suture method has an advantage with respect to the parameters tested at 4, 6, and 12 plus weeks postrepair and the degree of adhesion formation. The combined laboratory and clinical data, in additional to cost considerations, may better define the role of barbed knotless suture for zone II flexor tendon repair. (J Hand Surg Am. 2015;40(7):1355e1362. Copyright Ó 2015 by the American Society for Surgery of the Hand. All rights reserved.) Key words Zone II flexor tendon laceration, flexor tendon repair, knotless barbed sutures, FDP repair strength, gliding resistance.

From the *Foundation for Orthopaedic Research & Education; the †Florida Orthopaedic Institute; the §Department of Orthopaedics & Sports Medicine, University of South Florida; Tampa, FL; and ‡Department of Surgery, Emory School of Medicine, Atlanta, GA. Received for publication January 14, 2015; accepted in revised form April 8, 2015. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article. Corresponding author: Brandon G. Santoni, PhD, Foundation for Orthopaedic Research & Education, 13020 N. Telecom Pkwy., Tampa, FL 33637; e-mail: [email protected] 0363-5023/15/4007-0011$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2015.04.009


have led to stronger suture material and innovative grasping suture technique (weave designs), which have greatly mitigated suture rupture as a primary cause of repair failure.1 Inadequate grasping of the tendon by the suture causing slippage and gap formation in addition to knot failures remain areas of concern because they represent scenarios of potential repair failure that may impair tendon healing.2 In addition, suture knots increase repair site bulk that may increase gliding resistance (GR) DVANCES IN FLEXOR TENDON SURGERY

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Published by Elsevier, Inc. All rights reserved.





within the synovial sheath and pulleys, causing increased work of flexion (WF), potential risks for rerupture, and tendon adhesions.3 Barbed suture designs have recently been reintroduced clinically and include barbs that extend from the outer surface in a bidirectional, staggered, or looped unidirectional design.4 With each pass, the barbs lock into the tissue and distribute repair tension along the entire suture-tissue interface, effectively increasing the grasping area. This load-sharing feature may increase the strength of the repair and prevent complications associated with suture knot failure. This supposed advantage has renewed interest in barbed suture use for flexor tendon repairs, and several recent studies in cadaveric tendon models have shown that barbed suture offers similar repair strength characteristics compared with traditional knotted-suture repairs.5e9 The purpose of this study was to compare the efficacy of knotless barbed and traditional sutures in reducing repair site bulk, GR, and improving gapping resistance of flexor digitorum profundus (FDP) tendon repair. In iterative fashion, we measured changes in the GR after partial and complete flexor digitorum superficialis (FDS) resection. We hypothesized that a barbed suture of a similar cross-sectional area (CSA) and equivalent strength characteristics to a traditional braided suture would confer decreased repair site bulk and GR and improved repair strength for a similar repair technique.

FDP tendon was then manually pulled to completely flex the digit and a second mark (C2) was made on the FDP just distal to the A2 pulley. The distance between the 2 marked locations was measured by a single observer and defined as the tendon excursion length. Thereafter, an incision was made through the carpometacarpal joint to separate the rays from the hand. The FDS and FDP tendon insertions on the middle and distal phalanges were left intact. Tendon attachments The point central to the proximal boundary of the A1 pulley and the distal boundary of the A2 pulley was marked using a surgical pen. The FDS and FDP tendons were then cut to 14-cm and 13-cm lengths, respectively, as measured from the center point. High-strength fishing line was passed in both tendons proximally using a Krackow weave10 and distally in the distal phalanx to facilitate biomechanical testing. Bone tunnels were made medial-to-lateral in the middle and proximal phalanges and through the metacarpal. The phalanges were secured onto a test plate using cable ties passed through the bone tunnels (Fig. 1). Once secured, the distal interphalangeal (DIP) joint was disarticulated, and the annular and cruciate pulleys were excised distal to the A2 pulley. The FDP attachment to the distal phalanx was left intact. The vinculae attached to the FDP tendon were resected along the dorsal aspect without disrupting the FDP, thereby allowing it to slide within the A1 and A2 pulleys.

MATERIALS AND METHODS Specimens Six matched pairs of fresh-frozen cadaveric hands (2 male and 4 female) without prior surgery or arthritic deformities were used (average age, 70 y). The ring, middle, and index digits were individually dissected, rendering 36 digits that were allocated for tendon repair using barbed or traditional sutures. The skin and fascia were removed to visualize the flexor tendons and intrinsic muscles. The FDS and FDP tendons for each digit were carefully separated, ensuring that neither the tendons nor the A1 and A2 pulleys were lacerated during dissection. Specimens were periodically sprayed with 0.9% saline or covered in moist gauze during preparation and biomechanical testing to prevent desiccation.

Biomechanical testing Our biomechanical test set-up was based on previously published models.11,12 Load cells (WMC-25; Interface Inc., Scottsdale, AZ) were connected to the proximal (LC1) and distal (LC2) ends of the FDP via pulleys (P1 and P2), which maintained fixed angles of 20 and 30 of the FDP with respect to the horizontal at the proximal and distal ends, respectively (Fig. 2). The proximal load cell (LC1) was interfaced between the FDP and the actuator of a materials testing system (Bionix; MTS, Eden Prairie, MN). A 4.9-N weight attached to the distal end of LC2 maintained tension in the FDP tendon while a 2-N weight maintained tension in the FDS tendon. Using the digit’s excursion length, the FDP was cycled through 5 flexion/extension cycles at 10 mm/ min. Load cell outputs and tendon displacement data were recorded throughout loading to determine GR and WF. The former was calculated using a previously published formula12: GR ¼ (0.5) * (LC1 flexion e LC2 extension). WF was calculated by measuring the

Determination of excursion length With the A1 and A2 pulleys visible and the digit fully extended, FDP tendon location adjacent to the distal boundary of the A2 pulley was marked (C1). The J Hand Surg Am.


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FIGURE 1: A A right index digit with an intact FDS, FDP, and A2-A1 pulley complex secured onto a specimen testing plate using zip ties. B A calibrated template with predrilled holes allows marking of the laceration site and location of transverse suture passes onto the FDP tendon. C Resection of the FDP tendon at the laceration site (15 mm distal to the A2 pulley) using a sharp scalpel blade.

FIGURE 2: Biomechanical test set-up for measurement of GR and WF. Load transducers (LC1 and LC2), although denoted, are not shown in the figure. A 2-N weight is attached to the FDS tendon via pulley P3 to maintain tension in the tendon.

area under the load-displacement curve for the final (fifth) flexion cycle.

transection (intact) and after repair to determine postrepair CSA changes.

Tendon CSA measurements Intact FDP tendon width and thickness were measured in triplicate at the repair/laceration site. Tendon CSA was calculated using the formula for area of an ellipse (area ¼ (pab)/4; where “a” is tendon width [mediallateral length] and “b” is tendon thickness [dorsalvolar length]). Measurements were taken before tendon

Tendon laceration and repair Using a plastic template with predrilled holes to ensure uniform spacing and placement of the repair sutures in all specimens, a complete transverse laceration of the FDP tendon was made using a scalpel (Fig. 1). The lacerated tendons were then allocated into 2 groups (n ¼ 18 each) with an equal number of

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FIGURE 3: Top: Illustration of a 4-core Kessler FDP repair technique using traditional sutures; red- and blue-arrowed lines indicate the location and direction of suture passes. Suture knots were placed in the center of the 2 lacerated ends. Bottom: Illustration of a modified 4-core Kessler FDP repair technique using barbed sutures. Red- and blue-arrowed lines indicate the location and direction of suture passes. The red and blue dot indicates the suture start location for the bidirectional barbed suture.

flexor tendons from the left and the right hands assigned to barbed or traditional suture repair. Traditional knotted suture repairs were performed using a 4-core Kessler technique (Fig. 3) with a 30 braided polyester/monofilament polyethylene composite (FiberWire; Arthrex, Naples, FL). Knots were tied J Hand Surg Am.

between the 2 lacerated tendon ends. The knotless barbed suture repairs were performed using a modified 4-core Kessler technique (Fig. 3). This suture has bidirectional barbs that extend outward in opposite directions from the midpoint of its length (Quill SRS; Angiotech, Vancouver, Canada). In both r

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repairs, the transverse passes were placed at 7 and 10 mm from the laceration and repairs were augmented with a running locking epitendinous suture (6-0 monofilament, SurgiPro II, Covidien, Mansfield, MA). All repairs were performed by fellowship-trained hand surgeons. Thereafter, each tendon was tested to determine GR and WF for the following sequential test conditions (Table 1); (1) Intact FDP w/ intact FDS; (2) repaired FDP w/ intact FDS (REP); (3) repaired FDP w/ partial FDS slip (PFDS); and (4) repaired FDP w/ full FDS resection (FFDS). All partial FDS slip resections were performed on the radial side for both leftand right-hand digits.

TABLE 1. Repair Conditions and the Associated Acronyms Acronym



Repaired FDP tendon with intact FDS tendon


Repaired FDP with partial FDS slip


Repaired FDP with full FDS resection


GR results are reported in Figure 4. No significant difference in GR between the traditional and the barbed suture repairs was identified for any condition. In the traditional suture group, a significant decrease in GR compared with the REP condition was noted with the FFDS test condition. Compared with the REP condition with barbed suture repair, GR significantly decreased in the PFDS and FFDS test conditions. WF results are reported in Figure 5. Tendon repair (REP) resulted in significant increases in WF for both repair groups. As with GR results, no significant difference in WF between the traditional and the barbed suture repairs was identified for any condition. On average, the PFDS and FFDS conditions reduced WF in both groups compared with the REP condition, although it was significant only for the FFDS condition with traditional suture repair. Maximum force at 1 mm of repair gapping for the traditional repair was 43  12 N (range, 22e65 N) and 52  15 N (range, 26e75N) for the barbed suture repair (P < .001). Failure of the epitendinous suture was the primary mode of failure for the traditional suture repairs prior to initiation of repair gapping (6 of 18; 33%). After gapping, in 15 out of 18 specimens (83%), one or more central core sutures tore through the tendon first before suture rupture. In the remaining 3 specimens (17%), failure initiated as rupturing of one or more central core sutures. Similarly, in the barbed suture repair group, the epitendinous sutures failed prior to gapping (7 of 18; 39%). After gapping, in 17 of 18 specimens (94%), one or more central core sutures ruptured first before tearing through the tendon.

Tendon repair strength Following cyclic testing, repaired tendons were mounted within a soft tissue clamp attached to the linear actuator of the test machine. A caliper (millimeter scale) was placed adjacent to the tendon to monitor gap formation at the repair site during testing. Gap formation was recorded with a high-definition video camera that was time synchronized with the load cell’s output. Tendons were then loaded in tension to failure at 20 mm/min. Posttesting, the video images were analyzed frame-by-frame (Image J; NIH, Bethesda, MD) to determine the force (N) at which the tendon ends gapped 1 mm. Data analysis Data are presented as mean  SD. CSA after repair as well as 1-mm gap formation force were compared with a paired t test between the groups. Intra- and intergroup comparisons of GR and WF were compared with a 2way analysis of variance with tendon condition and suture repair type as factors. Post hoc multiple comparisons were performed with Bonferroni correction. Significance was set at the .05 level. Sample sizes were determined a priori using prior GR data published by Zhao et al.11 Using their reported means and SD for the GR of repaired FDP tendons, a minimum sample size of 12 tendons per group would be required to detect what we considered to be a clinical meaningful increase in GR of 30% using a 2-tailed test with 80% power. Our choice of 18 tendons per group powered the nondestructive component of our study at greater than 90%. RESULTS Intact tendon CSA at the repair site was 12.5  2.9 mm2. Compared with intact, repair site CSA significantly increased by 49% (18.7  3.4 mm2) and 47.5% (18.5  2.9 mm2) for the traditional and barbed suture groups, respectively (P < .001). There was no difference in tendon CSA between suture groups after tendon repair (P ¼ .67). J Hand Surg Am.

Test Condition

DISCUSSION The standard of care for zone II flexor tendon injuries is direct repair of the FDP and often FDS with a core and epitendinous suture technique followed by early mobilization.13 This zone has been reported to have a high rate of adhesion formation after operative intervention, and scar adhesion is common postrepair.14 The success of such a repair can be directly r

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FIGURE 4: Graph shows comparison of average GR values for the barbed and traditional suture treatment groups in the intact, REP, PFDS, and FFDS resected test conditions. A For each repair group, P < .001 relative to the REP, PFDS, and FFDS test conditions.

proportional to its response to in vivo loading, which is multifactorial and includes muscle tension, joint stiffness, external loads, and GR within the synovial sheath and the pulley system. To avoid immobilizationassociated adhesions, it is necessary to achieve a quality repair using technique and suture that confers a superior repair strength while minimizing GR and gap formation to allow for early range of motion protocols with decreased risk for rerupture.14 The theoretical advantage of barbed sutures is their unidirectional barbs, which allow unrestricted suture passage in the direction of the barbs while achieving tissue purchase and resistance to suture pull-out in the opposite direction. As such, barbed sutures may distribute loads throughout the barb-tendon contact area along the suture length,4 which greatly mitigates suture slippage and cut-out through the tendon. The GR and repair strength of the barbed sutures are, therefore, of relevant concern. In addition to being knotless, it would be advantageous if this suture resulted in a lower gliding friction and higher repair strength compared with the braided suture. We compared a 3-0 braided FiberWire (traditional) to a 2-0 barbed Quill (barbed) suture because the effective core diameter and tensile strength of a 2-0 barbed suture are equivalent to that of the 3-0 traditional suture.5 We also standardized the repair J Hand Surg Am.

technique (Kessler) by using the same number of core passes for the control and the experimental groups. Because a knotless technique was warranted for the barbed suture, the Kessler technique was slightly modified; the location of transverse suture passes was consistent for both groups. CSA after tendon repair was not significantly different between the suture groups, although CSA at the repair site increased by roughly 48% for each group relative to the intact tendon. We initially hypothesized that the increase in CSA for the barbed suture group would be significantly less than the traditional suture group owing to the absence of the centrally placed knots. However, we were unable to confirm this hypothesis. The reason is likely multifactorial and attributable to the Quill fiber being larger (2-0) than the traditional suture (3-0), an increase in the amount of fraying of the lacerated tendon by the barbs when passing the throws, and slight overtensioning at the repair site when bringing the tendon ends into apposition with the barbed suture. The GR values for the traditional and barbed suture groups were similar for all testing modes. Although interventions with partial and complete resection of the FDS yielded improved GR values, neither suture group exhibited a significantly lower GR for a given test condition. One of the explanations to this could r

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FIGURE 5: Graph shows comparison of average WF values for the barbed and traditional suture treatment groups in the intact, REP, PFDS resected, and FFDS resected test conditions. A For the fiberwire group, P < .001 relative to the REP and PFDS conditions and P = .178 compared to the FFDS condition. B For the quill group, P < .001 relative to all test conditions.

again be that overall CSA at the repair site (bulk) was comparable across both groups. We also observed that the barbs often were exposed at the volar aspect of the tendon at the site where the transverse suture passes were made. These barbs could potentially add friction while passing through the A2 pulley. Although these are based on conjecture, additional studies may be needed to assess the possibility of potential friction and tissue irritation caused by barbs sticking away from the repair site. In our study, we were unable to demonstrate a significant difference in WF between the 2 suture groups. The difficulty of demonstrating such changes may have resulted in our inability to re-create factors associated with the tendon healing process such as edema and adhesion formation in an in vitro test setup. Although we did notice an increase in WF for both test groups compared with the intact and data trends were similar to those of GR for the various test conditions, we conclude that WF may be more appropriately studied in vivo. Gap formation is an intrinsic factor associated with adhesion formation and is directly proportional to the quality of the repair and strength of the suture material used. We identified a significant increase in the 1-mm gap formation force in the barbed suture J Hand Surg Am.

group compared with the traditional suture group, a finding similar to that of McClellan et al,7 who performed failure testing on repaired porcine FDP tendons using a similar failure testing protocol and suture repair materials as that used in our study. The barbed sutures rarely (1 of 18 specimens) slipped through the tendon fibrils during the tendon pull-out tests. One or more core strands ruptured prior to slippage within the tendon. We also observed that, in both suture repair groups, the epitendinous sutures ruptured prior to failure of the core sutures. The running epitendinous sutures were in a way the primary resistance to tensile loads before the core sutures were subject to applied loads. Additional in vivo studies may be warranted to determine if one suture method has an advantage with respect to the parameters tested at various time intervals after repair as well as degree of adhesion formation. The combined laboratory and clinical data, in additional to cost considerations, may better define the role, if any, of barbed knotless suture for zone II tendon repair. ACKNOWLEDGMENT This study was funded by a research grant from the Division of Plastic Surgery, University of South r

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Florida, Morsani College of Medicine, Tampa, FL. The funding agency was not involved in any aspect of the study. The authors would like to thank Jacob Cox, MD, and Kaitlyn Christmas, BS, for their invaluable assistance with literature review, study design, specimen preparation, biomechanical testing, and data processing.





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