This review systematically discusses the research progress of magnesium oxide (MgO) nanoparticle (NP) composites in orthopaedic implants, focusing on their material characteristics, biological performance, preparation methods and applications. It also analyses their potential and associated challenges in bone repair. The paper first summarises the mechanisms by which MgO NPs enhance the mechanical strength, corrosion resistance, biocompatibility, osteogenic activity, and antibacterial properties of conventional orthopaedic materials. The results show that MgO NPs significantly improve the overall performance of composites by refining grains, filling surface defects, releasing Mg²⁺, and regulating the local microenvironment. In addition, this paper discusses current applications of MgObased composites in bone fixation, bone defect repair, and drug delivery while outlining the key challenges hindering clinical translation. Finally, it highlights future research directions, emphasising material design, process optimisation, and intelligent release systems to advance the clinical application of MgO NPs composite in orthopaedic repair and regenerative medicine. Consequently, this review provides a theoretical basis and technical foundation for developing next-generation high-performance bone implant materials.