Magnesium-Based Intramedullary Nailing System in a Sheep Model: Biomechanic Evaluation and First In Vivo Results

The tibia is one of the most frequently fractured bones in humans as in animals, and is predominantly treated by
intramedullary nailing. However, existing intramedullary nailing systems are consisting of non-degradable material leading to a second surgery for removal. Therefore degradable implant materials as magnesium alloys have been part of the scientific research for years. Especially the slow degrading magnesium alloy LAE442 showed a good biocompatibility but has not been examined as an osteosynthesis system yet. The present study assessed the in vivo applicability of an intramedullary interlocking LAE442 nail system (nail Ø 9 mm; screw Ø 3.5 mm). Four-point-bending tests and finite element simulation were performed. The possible influence of fixation screw holes´ orientation on the experimental results was tested (change of Young´s modulus during degradation). In vivo biocompatibility and degradation behavior of magnesium implants was examined in a pilot study (sheep, 24 weeks) with clinical, radiographic and computed tomographic investigations. After euthanasia additional micro-computed tomographic, histological and biomechanical examinations were carried out. Four-point-bending tests (three nail-screw compounds)
exhibited a stiffness of 2179.34 N/mm (MV). Bending simulations showed none influence of the fixation screw holes´
orientation but a decreasing bending stiffness over time.