# Applications of Magnesium and Its Alloys: A Review
## 4 Magnesium and Its Alloys as a Biomaterial
### Biomedical Applications
#### 4.5.1 Musculoskeletal and Orthopedic Applications  
Autografting is the yardstick of contemporary bone repair materials. It contains the necessary elements to stimulate new bone growth. However, it is resource-scarce, and it requires secondary surgeries to remove the implant after the impaired physical functions have been restored [72]. As previously discussed in Section 4.1, the need for secondary surgeries is also a challenge faced by bio-inert metallic implants, in addition to stress shielding [46]. Hence, the medical community has been actively seeking prospective implant solutions that are biocompatible, biodegradable, and exhibit similar characteristics to the human bone. Novel biomaterials like biodegradable polymers have been investigated for their suitability as they also share properties similar to materials found in the human body [61]. However, biodegradable polymers possess inferior mechanical strength and brittleness to magnesium and its alloys, resulting in surgery failure when employed in load-bearing applications [57]. Further, employing biodegradable polymers is also observed to induce long-term inflammatory responses in peri-implant tissue and discourage osseous ingrowth [57; 73]. Hence, except for its rapid corrosive behavior, magnesium remains a more promising biomaterial than biodegradable polymers for bone substitution and scaffolding of bone tissue [56]. Notably, magnesium-based orthopedic implants positively affect the regeneration of new blood vessels and bone tissue. Others could not achieve this feat and, thus, may provide magnesium-based orthopedic implants with an edge over the rest, especially when dealing with challenging bone conditions [73]. Present clinical applications of magnesium-based orthopedic implants remain relatively nascent and sparse. Notable implants in recent years include the MAGNEEZIX(Syntellix AG, Hanover, Germany) MgYREZr alloy bioabsorbable compression screw and the K-METTM(U&i Corporation, Seoul, Korea) MgCaZn alloy bioresorbable bone screw, and both demonstrated positive clinical results in several case applications. For example, the use of MAGNEEZIX(r) MgYREZr alloy screw for osteochondral fracture fixation at the humeral capitulum is reported to be clinically and radiologically uneventful as the degradation of the magnesium alloy did not hinder the healing process [74]. Another case trial (Figure 4A) uses MAGNEEZIX(r), and a similar specification titanium alloy--the incumbent choice--for hallux valgus surgery in 13 patients reported comparable pain assessment and range of motion scores of the first metatarsophalangeal joint [73]. Following these positive results, MAGNEEZIX(r) was accepted for clinical use by the medical community, and its availability proliferated in more than 50 nations. Today, it is explicitly recommended for intra- and extra-articular fractures, nonunions, bone fusion, bunionectomies, and osteotomies treatments. Its average price is reported to be ~20% higher than comparable titanium implants [74; 75]. Similarly, for K-METTM, long term studies were conducted, and favorable results were reported. In a clinical study of 53 cases, K-METTM alloy screws were observed to support early bone healing, leading to the growth of a new bone capable of replacing the K-METTM implant entirely within a year of its implantation (Figure 4B) [76]. Recent developments further include the exploration of using ultra high-purity magnesium orthopedic internal fixation implant to treat avascular necrosis of the femoral head in China [73], using magnesium-based implants to treat facial fractures in Singapore [77], and the first clinical trial to investigate the effects of a coated magnesium implant [78]. In summary, while there has been an initial loss of interest in using magnesium as a biomaterial from the medical community, in part due to its corrosive behavior, interest for clinical applications has since renewed in the recent decade.