A Biomechanical Comparison of Femoral Cortical Suspension Devices for Soft Tissue Anterior Cruciate Ligament Reconstruction Under High Loads

Abstract

Background: Graft healing after soft tissue anterior cruciate ligament (ACL) reconstruction requires rigid fixation to allow for soft tissue healing. Cortical suspension devices for femoral fixation should be biomechanically tested under high loads representative of early rehabilitation to evaluate whether they provide sufficient fixation. Purpose/Hypothesis: To biomechanically compare current fixed-loop and adjustable-loop cortical suspension devices for soft tissue femoral fixation under high loads. The hypotheses were that there would be significant differences in cyclic displacement between devices, independent of loop type, and that retensioning of the adjustable-loop devices would not significantly alter the biomechanical properties of these devices. Study Design: Controlled laboratory study. Methods: Five different femoral ACL graft cortical suspension devices (3 fixed and 2 adjustable) were compared under high cyclic forces (100-400 N for 1000 cycles) and then pulled to failure at 50 mm/min. In addition, the effect of retensioning after simulated preconditioning was evaluated for the 2 adjustable-loop devices. Results: On average, the least amount of cumulative peak cyclic displacement (mean ± SD) was observed for the ENDOBUTTON (1.05 ± 0.05 mm), followed by the RIGIDLOOP (1.09 ± 0.16 mm), XO Button (1.65 ± 0.43 mm), TightRope with retensioning (1.81 ± 0.51 mm), TightRope without retensioning (2.20 ± 0.62 mm), ToggleLoc with retensioning (3.22 ± 1.41 mm), and ToggleLoc without retensioning (3.69 ± 2.39 mm). The ENDOBUTTON displaced significantly less after cyclic loading than all adjustable-loop devices (TightRope and ToggleLoc, both with and without retensioning) and the XO Button. The RIGIDLOOP displaced significantly less than the TightRope without retensioning and ToggleLoc with and without retensioning. There was no significant difference in biomechanical properties after retensioning for both adjustable-loop devices. Conclusion: Significant differences were observed between current fixed-loop and adjustable-loop cortical suspension devices for soft tissue femoral fixation when subjected to high loads experienced during rehabilitation. Retensioning did not significantly alter the biomechanical properties of adjustable-loop devices. Clinical Relevance: Early rehabilitation protocols subject the graft construct to higher forces than what has been previously tested biomechanically. Biomechanical testing of cortical suspension devices under simulated high rehabilitation loads demonstrated significant differences between devices. Future studies should investigate the clinical implications of these time zero results.