Repair of large segmental bone defects requires implanted scaffolds not only to provide sufficient structural stability but also to accommodate the pronounced spatial heterogeneity, anisotropy, and load-dependent nonlinear behaviour of native bone while establishing a local mechanical microenvironment conducive to tissue regeneration. Mechanical metamaterials offer a distinct design paradigm for precise mechanical regulation by tailoring microstructural topology and deformation mechanisms, including rotation, buckling, and configurational transitions, thereby enabling spatially differentiated responses, auxetic behaviour, nonlinear stiffness, multistability, and reconfigurability. This review first examines the mechanical adaptation requirements of metamaterial scaffolds for bone repair in the context of the heterogeneous, anisotropic, and nonlinear mechanical characteristics of native bone, and systematically summarises the capabilities and key constraints of advanced three-dimensional printing technologies, including powder bed fusion, vat photopolymerisation, and material extrusion, for fabricating complex metamaterial architectures. Building on this foundation, we critically review the structural mechanisms and bone-regenerative effects of spatially heterogeneous and anisotropic, auxetic, nonlinear, multistable, and reconfigurable metamaterials, and further discuss strategies for integrating functional ions, growth factors, and therapeutic agents with metamaterial architectures. We also examine the time-dependent mechanical evolution of degradable metamaterials, highlighting the coupling among material degradation, architectural evolution, and progressive bone regeneration after implantation. By elucidating the intrinsic relationships among structural design, mechanical response, and biological function, this review aims to provide a conceptual framework for the development of next-generation bone repair implants that combine precise mechanical adaptation with regenerative regulation.