Design of an alternative implant to suturing in ACL reconstruction: a biomechanical in vitro study

Background: Anterior Cruciate Ligament (ACL) reconstruction using a triple hamstring semitendinosus graft is a commonly used technique for optimal hamstring function, flexion strength, and rapid recovery. In the conventional method, the end of the tendon graft is whipstitched to a suspensory loop, which reportedly can lead to graft failure due to tendon laceration or slippage. This study aims to enhance ACL fixation by introducing a novel implant device replacing conventional sutures. Methods: Six initial designs were introduced, and a product design specification (PDS) chart was used to select one. The design named (Zip-Tie) was chosen based on the PDS scoring and three variants of it were prototyped and subjected to in-vitro experiments to optimize the design. The best performing variant was chosen as the final design which underwent additional validation tests. The mechanical experiments consisted of three loading steps, a preconditioning, a main cyclic, and a pull-out loading. Results: The mechanical properties of the three device variants were compared, and the best performing one was selected as the final design. The final design exhibited superior mechanical properties compared to similar studies, with an average cyclic stiffness (ACS) of 37,637 ± 8,910 N/mm, average pull-out stiffness (APS) of 132.8 ± 28.9 N/mm, and cyclic elongation of 1.11 ± 0.27 mm. The load-to-failure results showed that 80% of the samples exceeded 1000 N. Conclusions: The introduced novel implant device for preparing tripled semitendinosus grafts in ACL reconstruction, demonstrated superior mechanical performance compared to conventional suturing methods. The integration of friction plates and straps enhanced graft fixation and stability. These results support the potential of a new fixation approach, laying the groundwork for future in vivo studies and the exploration of optimal biocompatible materials for clinical application.