Biomechanical Comparison of Three Modified Kessler Techniques for Flexor Tendon Repair: Implications in Surgical Practice and Early Active Mobilization

<b>Objective</b>: Managing flexor tendon injuries surgically remains challenging due to the ongoing debate over the most effective suture technique and materials. An optimal repair must be technically feasible while providing enough strength to allow for early active mobilization during the post-operative phase. This study aimed to assess the biomechanical properties of three modified Kessler repair techniques using two different suture materials: a conventional two-strand and a modified four-strand Kirchmayr-Kessler repair using 3-0 Prolene^® (2s-KK-P and 4s-KK-P respectively), and a four-strand Kessler-Tsuge repair using 4-0 FiberLoop^® (4s-KT-FL). <b>Methods</b>: Human flexor digitorum profundus (FDP) tendons were retrieved from Thiel-embalmed prosections. For each tendon, a full-thickness cross-sectional incision was created, and the ends were reattached using either a 2s-KK-P (n = 30), a 4s-KK-P (n = 30), or a 4s-KT-FL repair (n = 30). The repaired tendons were tested using either a quasi-static (n = 45) or cyclic testing protocol (n = 45). Maximum force (F_max), 2 mm gap force (F_2mm), and primary failure modes were recorded. <b>Results</b>: In both quasi-static and cyclic testing groups, tendons repaired using the 4s-KT-FL approach exhibited higher F_max and F_2mm values compared to the 2s-KK-P or 4s-KK-P repairs. F_max was significantly higher with a 4s-KK-P versus 2s-KK-P repair, but there was no significant difference in F_2mm. Suture pull-out was the main failure mode for the 4s-KT-FL repair, while suture breakage was the primary failure mode in 2s- and 4s-KK-P repairs. <b>Conclusions</b>: FDP tendons repaired using the 4s-KT-FL approach demonstrated superior biomechanical performance compared to 2s- and 4s-KK-P repairs, suggesting that the 4s-KT-FL tendon repair could potentially reduce the risk of gapping or re-rupture during early active mobilization.