Adjustable- Versus Fixed-Loop Devices for Femoral Fixation in ACL Reconstruction: An In Vitro Full-Construct Biomechanical Study of Surgical Technique-Based Tibial Fixation and Graft Preparation

Background: Femoral suspensory fixation for anterior cruciate ligament (ACL) reconstruction has evolved from fixed- to adjustable-loop devices. However, there are still controversies regarding undesired lengthening of adjustable-loop devices. Hypothesis: Adjustable-loop fixation will achieve similar elongation to that of fixed-loop devices, and intraoperative preconditioning will reduce initial elongation for adjustable-loop constructs. Study Design: Controlled laboratory study. Methods: Three adjustable-loop devices (GraftMax, TightRope, and Ultrabutton) and 2 fixed-loop devices (Endobutton and RetroButton) were used in an intraoperative surgical technique workflow according to an in vitro model with porcine bone and bovine tendons (8 specimens per device; N = 40 constructs tested). Each construct underwent 1000 cycles of position- and force-controlled dynamic loading, whereby a total elongation threshold of 3 mm was defined as clinical failure. Constructs were finally pulled to failure at 50 mm/min. Results: There were no statistically significant differences among the devices for total or dynamic elongation. Total elongation (mean SD) for adjustable-loop constructs was 4.13 1.46 mm for GraftMax, 2.78 +/- 0.85 mm for TightRope, and 2.76 +/- 0.45 mm for Ultrabutton; for the fixed-loop devices, total elongation was 2.85 +/- 0.74 mm for Endobutton and 2.85 +/- 1.03 mm for RetroButton. The GraftMax had a significantly lower initial force (95.5 +/- 58.0 N) after retensioning, with the highest initial elongation (0.99 +/- 0.60 mm). The Ultrabutton showed the greatest force loss (-105.9 +/- 13.5 N) during position control cycling, which was significantly different from the GraftMax (-22.3 +/- 28.2 N), with the smallest force loss (P < .001). The TightRope construct had a significantly smaller initial elongation (-0.36 +/- 0.22 mm) and the greatest pull-to-failure load (958 +/- 40 N) as compared with all of the other devices. Conclusion: Adjustable- and fixed-loop configurations achieved statistically comparable fixation strength for total elongation. However, the GraftMax construct exceeded the total elongation threshold of clinical failure. The Ultrabutton produced the greatest loss of force during position control cycling, and the GraftMax button design prevented proper retensioning. The TightRope had a significant greater ultimate strength when compared with all other devices. Clinical Relevance: Biomechanical testing according to a surgical technique workflow suggests that adjustable-loop devices can be considered a safe alternative to fixed-loop devices in ACL reconstruction.