Objectives: Satisfactory clinical outcome following flexor tendon repair remains a challenge to the hand surgeon. Advances in surgical technique as well as accelerated postoperative rehabilitation protocols have been responsible for improvements in postoperative motion, but re-rupture rates continue to be problematic. A novel tendon repair technique (Teno Fix^TM, Ortheon Medical, LLC, FL) has been developed that employs embedded soft tissue anchors and a multifilament wire to provide a high-strength and low-profile repair. The purpose of our study was to compare the mechanical profile of Teno Fix^TM tendon repair system to current 2- and 4-strand 3-0 suture repair techniques during cyclic loading.

Methods: Thirty zone II cadaveric flexor digitorum profundus tendon lacerations (index, middle, and ring digits) were randomized to three different tendon repair techniques (3-0 Modified Kessler, 3-0 locked Cruciate 4-strand, or Teno Fix^TM) performed in situ by a single surgeon. Mechanical behavior of each repair was studied under cyclic load in an attempt to simulate in vivo forces during active motion. The specimens were excised and initially cycled in tension, under load control, between 5N and 25N for 8000 cycles at 2Hz. The peak load was increased by 10N and specimen cycled for an additional 4000 cycles. This 10N increase was repeated every 4000 cycles to 65N for a total of 24000 cycles. If the specimen did not fail by final load step of 65N and 24000 cycles, it was loaded in displacement control, at a rate of 0.2mm/sec until failure. Displacement at repair site was monitored using a DVRT gage (Microstrain, Burlington, VT), and gap formation was recorded using serial digital photography. Failure was defined as repair rupture or 4mm gap displacement. Cycles to failure were recorded and weighted by the load step at which specimen was cycling at time of failure (N-Cycles).

Results: The 3-0 locked Cruciate 4-strand repair demonstrated a significant increase in N-cycles to failure when compared with either of the other two suture repairs (p=0.018). The cruciate repair exhibited increased resistance to 1 mm gap (16,200 cycles) compared with the Kessler (7200 cycles) or the Teno Fix^TM (6000 cycles) (p=0.003). DVRT analysis demonstrated less displacement of the cruciate repair at 35N and 45N load steps when compared with the two other repairs (p< 0.01). Conclusions: Inadequate initial repair strength can lead to separation of flexor tendon repairs under the stress of cyclic loading, thus increasing the chance for failure. The Teno Fix^TM implant has previously demonstrated promising laboratory and clinical results in range of motion and decreased rupture rates, and may lead to improvements over conventional suture techniques. In this high force cyclical loading protocol, however, neither the Teno Fix^TM nor the Kessler repair conferred mechanical advantages over a 3-0 locked cruciate 4-strand suture repair. The cyclic forces in this testing protocol exceed load demands of unresisted active motion protocols, but the information provided by protocol establishes safe boundaries for active motion rehabilitation of the Teno Fix^TM device.