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Flexor Tendon Repair in an Ex-Vivo Model: An Established Knotless Bidirectional Barbed Suture Technique Does Not Withstand Cyclic Loading Necessary for Early Rehabilitation
Fred O'Brien, MD1; Kenneth Means1; Brent Parks1; Ebrahim Paryavi2
1Curtis National Hand Center, Baltimore, MD; 2University of Maryland Medical Center, Baltimore, MD

Introduction: In a dynamic ex-vivo model, a zone II flexor tendon laceration repaired with knotless, bidirectional barbed suture would provide equivalent resistance to gap formation during cyclic loading as a repair using conventional locking four-strand technique with braided suture of similar strength.

Methods: Flexor digitorum profundus tendons from fifteen fresh frozen cadaver hands were randomly assigned to one of three repair techniques: locking cruciate four-strand repair using braided suture (LC), three-strand repair with transverse passes using braided suture (TS), or three-strand repair with transverse passes using bidirectional barbed suture (BB). Flexor and corresponding extensor tendons were attached to a load generator. The fingers were cycled through a range of motion at a rate of 5.1 mm/s to a load of 5N per finger. Gap formation was assessed and recorded every ten cycles through 100 cycles, and at 100 cycle intervals through 1,000 cycles. Failure of repair was defined as gap formation of greater than 2mm. Tensile loading to failure was performed on each tendon, and the method of failure and required force were recorded.

Results: The BB and TS groups developed an average gap of 2.43 mm (SD 3.29) after 20 cycles, and 2.22 mm (SD 0.85) after 10 cycles, respectively. Over 1,000 cycles, the LC group demonstrated an average gap of 3.21mm (SD 1.51) compared with 9.12 mm (SD 2.80) in the BB group. Due to the consistently wide discrepancy between the cycles to failure between the BB and LC groups, the experiment was terminated at seven tendons per group. Using one-way ANOVA with Fisher LSD, post-hoc analysis was performed. We observed a significant difference in number of cycles until failure (p<0.001) between the LC and BB groups. There was no significant difference in force (N) required to induce catastrophic failure between the LC and BB groups; all repairs in this portion of the study failed by suture pullout.

Discussion and Conclusion: The BB group developed gapping early, with significant differences compared to the LC group at 1,000 cycles. As expected, the TS repairs failed rapidly. Barbed suture was inferior to a conventional repair technique in this low force, cyclic loading scenario, and the results do not support the use of bidirectional barbed suture in the repair of flexor tendons. Additional studies are needed to determine if modifications in techniques or suture materials would provide better resistance to gap formation due to cyclic loading forces encountered in early rehabilitation.

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