In vitro and in vivo degradation behavior of an assembled magnesium alloy suture anchor for ligament-bone reconstruction.

Abstract

Biodegradable magnesium alloys suture anchors face rapid anchor eyelet degradation, compromising mechanical strength. In this study, an assembled-structure magnesium alloy suture anchor was proposed to mitigate the fast failure of anchor eyelet. In vitro and in vivo experiments were conducted to evaluate the degradation behavior and biomechanical performance of assembled ZE21C magnesium alloy suture anchors. In vitro, mechanical tests revealed stable fixation with a pull-out force of 123.1 ± 5.9 N and fracture strength of 213.3 ± 3.6 N, ensuring no risk of anchor breakage under physiological loads. Immersion in Hanks' solution demonstrated the screw and tail regions degraded progressively over 14 days, while the anchor eyelet retained structural integrity. The in vivo degradation behavior mirrored in vitro findings and suture anchor maintained its mechanical integrity for 12 weeks post-surgery. Micro-CT and histological analyses confirmed successful functional recovery and fibrocartilage regeneration at the ligament-bone interface. Gas cavities observed post-implantation resolved by week 12 without anchor dislocation. The rapid degradation of threaded region released magnesium ions to facilitate osteogenesis, while the slower degradation of anchor eyelet maintained structural integrity for stable fixation. The gradual decline in fracture force of eyelet parts remained higher than the initial pull-out force within 12 weeks implantation. Furthermore, progressive integration occurred in the connection of assembled anchor further highlighted its reliable fixation performance. This study offers a framework for further design and research of biodegradable magnesium alloy suture anchors for clinical applications. STATEMENT OF SIGNIFICANCE: Achieving clinical efficacy for biodegradable magnesium alloy anchors requires maintaining long-term mechanical stability post-surgery. Delaying degradation at suture-contact anchor eyelet can prolong service life. In this study, we designed an assembled anchor with external full threads to enhance fixation strength while preventing body fluid infiltration into internal anchor eyelet to retard its degradation. Multi-scale in vitro/vivo studies revealed that rapid degradation of external threads promoted bone-tissue integration, whereas slower-degrading anchor eyelet preserved structural stability. Notably, the fracture strength at 12 weeks post-implantation remained superior to the initial pull-out strength. These findings demonstrate the potential for broadening clinical applications of magnesium alloy anchors in future trials.