Biomechanical comparison of four coupled fixation systems for ACL reconstruction with bone socket or full-tunnel on the tibial side

Background To compare in an animal model the biomechanical properties of four coupled fixation devices currently used in ACL reconstruction. Three out of four devices used a full tibial tunnel with an interference screw, while the other one system used a tibial socket and an adjustable loop suspension device. The null hypothesis is that there are no biomechanical differences between all the techniques tested. Methods Thirty two femur–graft–tibia complexes were mounted on a tensile machine using bovine digital extensor tendons, porcine knees and four different fixation device combinations: – Group A: EndoButton CL and BioRCI– Group B: Rigidfix and Intrafix– Group C: Transfix and Deltascrew– Group D: TightRope-RT with the All-inside GraftLink technique.After a preconditioning with a tensile load of 90 N for five minutes, 1000 cycles between 0 and 150 N were applied to the complex before the final pulled to failure. Stiffness and strength were evaluated at the final pullout, as was the displacement (slippage) at one, 100, 500, and 1000 cycles. Results The multiple mean comparison led to a significant difference for the case of stiffness, with worse results in group C compared to group A (p = 0.037). Conversely, no differences were found in UFL and slippage between all groups (p > 0.05). Conclusion All the tested systems demonstrated in an animal model sufficient properties for a safe postoperative rehabilitation both for strength and for stiffness and slippage under cyclic loading.