Biomechanical Comparison of 3 Adjustable-Loop Suspensory Devices for All-Inside ACL Reconstruction: A Time-Zero Full-Construct Model

Abstract

Background: Little is known about the stability of adjustable-loop devices (ALDs) for anterior cruciate ligament (ACL) reconstruction (ACLR). Purpose: To evaluate the stabilization behavior of 3 different types of ALDs for all-inside ACLR in a full-construct surgical technique-based manner. Study Design: Controlled laboratory study. Methods: The femoral and tibial devices of Ultrabutton (Smith & Nephew), Infinity (Conmed), and TightRope II (Arthrex) were applied to quadrupled bovine tendon grafts (n = 8 each) with tibial-sided traction applied (350 N) for graft tensioning in a simulated fully extended knee. Knotless femoral graft fixation was based on either a suture-locking device (SLD; Ultrabutton), button-locking device (BLD; Infinity), or dual-locking device (DLD; TightRope II). All constructs were progressively loaded (50 N/500 cycles) from 50 to 300 N for 3000 cycles (0.75 Hz), including complete unloading situations and pull to failure (50 mm/min). Construct elongation, stiffness, and ultimate load were analyzed. Results: BLD showed significantly greater initial elongation (-2.69 ± 0.15 mm) than DLD (-3.19 ± 0.21 mm; P 1000 N). The predominant failure mode was suture rupture and tibial bone breakage with button subsidence (SLD, n = 4). No significant difference in stiffness between constructs was found. Conclusion: While DLD successfully restricted critical construct elongation, BLD partially and SLD completely exceeded the clinical failure threshold (>3 mm) of plastic elongation with loop lengthening during increasing cyclic peak loading with complete unloading. Higher failure loads of SLD and DLD implants (>1000 N) were achieved at similar construct stiffness to BLD. Clinical Relevance: A detailed biomechanical understanding of the stabilization potential is pertinent to the continued evolution of ALDs to improve clinical outcomes.