Magnesium and magnesium alloys have great application potential in the field of orthopaedics. Compared with traditional inorganic nonmetallic materials and medical polymer materials, magnesium alloys have many advantages, such as better strength, toughness, fatigue resistance, and easy processing. Its mechanical properties are suitable and controllable. It can meet the same elastic modulus, cell compatibility, and biodegradability as human cortical bone. There are also some drawbacks for biodegradability, as magnesium and its alloys, with their high degradation rate, can cause insufficient integrity of the mechanical properties. This paper summarises the research on magnesium and its magnesium alloy materials in the field of bone implantation, looking at what magnesium and its magnesium alloys are, the history of magnesium alloys in bone implant materials, the manufacturing of magnesium alloys, the mechanical properties of magnesium alloys, the bio-compatibility and clinical applications of magnesium alloys, the shortcomings, and the progress of research in recent years.

As osteoarthritis is a common disease in elderly people and large cartilage defects can only be treated by joint replacement surgery, a scaffold is seen as a potential treatment that could help patients to delay or avoid surgery. An ideal scaffold should have similar properties to the surrounding tissues. Thus, for different levels of OA, patients with different bone properties should use different scaffold structures with different mechanical or biological properties. In this paper five structures (A–E) are designed for young OA patients or patients with good bone mechanical properties, middle-age OA patients with weak bone mechanical properties or patients with little osteoporosis, and elderly OA patients who have severer OA and osteoporosis who are not able to perform normal activities. And these five scaffold structures are 3D-printed by an EOS machine with Ti6Al4V powder and evaluated by experiments based on a biomechanical bioreactor simulating the human knee joint and simulation through ANSYS. Structure D with a solid thick beam in the middle has the highest loading force, which is 3707.835 N, and structure E, composed of the polyhedron with the highest specific surface area, has the lowest loading force, which is 1837.402 N. Structures A, B, and C are intended for young OA patients or patients with good bone mechanical properties. Structures D and E are designed for patients who need to avoid or delay joint replacement surgery.