The Performance of Bio-Integrative Mineral-Fiber Reinforced Screws in a Load Bearing Osteotomy Model in Sheep

Category: Basic Sciences/Biologics Introduction/Purpose: Injuries to weight-bearing bones can be detrimental to patient mobility, often requiring surgical intervention, as mechanical failure leads to non-union, joint stiffness, and compromised function. Metal implants are widely used for fracture fixation; however, stress concentration, irritation, and pain often result in hardware removal, driving the development of non-permanent implants, traditionally polymer-based. These, in turn, lack strength and may cause adverse inflammatory reactions. Thus, an unmet need exists for more robust, safely eliminated fixation devices. This study aimed to evaluate the performance of bio-integrative, mineral fiber-reinforced screws, currently utilized for multiple surgical procedures in Orthopedic Foot and Ankle Surgery, in an in vivo fully load-bearing distal femur fracture model in sheep. Methods: Five sheep were subjected to femur lateral condyle osteotomy. Fixation was performed using two 3.5mm fiber-reinforced compression screws made of mineral fibers comprised of elements found in native bone, bound by PLDLA [poly (L-lactide-co- D, L-lactide)]. Animals recovered to full load-bearing conditions. Micro CT and histopathology were performed at 26, 78, 104, and 130 weeks (W). Osteotomy healing, new bone formation, tissue ingrowth into the implant wall, and biocompatibility measures were evaluated. Results: All animals demonstrated uneventful recovery. Stable reduction was evident by optimal bone healing on imaging and histological evaluation. At 12 weeks, all sites demonstrated anatomical alignment and complete bone bridging across osteotomy sites, with no implant failure. Cellular response was dominated by anti-inflammatory M2 macrophages and multinucleated giant cells associated with the expected phagocytic response. Implant bio-integration was completed by 130W, with no material remaining and no adverse effects. Conclusion: Large animal models are considered benchmarks for the long-term effects of orthopedic implants due to their similarity to humans with respect to bone composition, dimensions, physiology, biomechanics, and remodeling. This fully load-bearing femoral osteotomy sheep model demonstrates the safe and effective use of bio-integrative implant technology, suggesting its applicability in various orthopedic foot and ankle indications.