Optimizing Technique for Onlay Fixation: A Rip-stop Configuration Outperforms Other Configurations For Soft Tissue Graft Fixation Using Knotless All-Suture Anchors

Background: Knotless all-suture anchor (ASA) constructs have been proposed for soft tissue onlay fixation in knee ligament procedures. Purpose: To determine the optimal configuration of soft tissue onlay fixation with knotless ASAs that minimizes cyclic elongation and maximizes load-to-failure performance. Study Design: Controlled laboratory study. Methods: Six onlay fixation constructs (n = 7 per group) were biomechanically evaluated in 2 phases using bovine extensor tendons and a polyurethane foam bone replicate. Phase 1 examined 4 knotless ASA configurations using a 2.6-mm double-loaded knotless ASA. The construct with the least cyclic elongation and greatest failure load was advanced to phase 2, where the repair suture limbs were passed back through the tendon tissue and tied for additional fixation. Grafts were incrementally loaded from 10 to 50 N, 10 to 75 N, and 10 to 100 N for 100 cycles, each at 1 Hz, to simulate progressive rehabilitative loading and then loaded to failure at 50 mm/min on a materials testing system. Outcomes included cyclic elongation (millimeters), stiffness (newtons per millimeter), maximum load (newtons) to 5-mm displacement (clinical failure load), maximum load (newtons) to 10-mm displacement (ultimate load), and mode of failure. One-way analysis of variance tests with post hoc Student-Newman-Keuls pairwise comparisons (α = .05) were performed. Results: In phase 1, the knotless rip-stop configuration had the least total cyclic elongation (mean ± SD, 2.21 ± 0.67 mm), greatest ultimate stiffness (130 ± 12 N/mm), greatest clinical failure load (216 ± 35 N), and greatest ultimate load (246 ± 47 N) of knotless constructs. Although the rip-stop showed lower mean cyclic elongation, the performance observed in cyclic loading of the rip-stop configuration was not significantly smaller than 2 of the other 3 techniques. In phase 2, using the repair suture limbs to perform 2 Krackow passes and then tying the limbs together performed the best, further reducing total cyclic elongation to 1.78 ± 0.27 mm ( P = .048), increasing clinical failure load to 269 ± 37 N ( P = .019), and increasing ultimate load to 407 ± 64 N ( P < .001). Conclusion: The rip-stop configuration had the best biomechanical profile of knotless constructs, with equal or less cyclic elongation as well as superior stiffness and failure loads. Passing the repair sutures back through the tissue and tying them together increased the failure load. Clinical Relevance: Knotless onlay fixation has technique-dependent time-zero biomechanical performance, which should be considered intraoperatively.