Development and Application of Biodegradable Magnesium Bone Plate and Screw Fixation in Jaw Surgery

Bone plate and screw fixation is a well-recognized system for internal fixation in jaw surgery, encompassing fracture fixation, orthognathic surgery, and craniofacial reconstruction. Along the development, titanium and its alloys have become the predominant materials for internal fixation, owing to their exceptional mechanical properties and biocompatibility. However, titanium has certain drawbacks, such as excessive rigidity compared to bone, which can result in stress shielding and subsequent bone resorption. Additionally, titanium plate and screw fixation is intended for temporary mechanical support during bone healing and may necessitate removal via a secondary surgery following bone healing, thereby increasing healthcare burdens. If left in situ, titanium can interfere with X-ray imaging due to beam-hardening effects.

In an effort to address the limitations of titanium fixation, researchers have been exploring the development of alternative materials for internal fixation. Bioresorbable systems utilize biodegradable materials for bone plate and screw fixation, thus eliminating the need for a secondary surgery for hardware removal. These biodegradable systems avoid long-term issues associated with stress shielding or X-ray scattering. Commercially available biodegradable osteosynthesis materials include high-molecular-weight polymers such as poly(lactic acid) (PLA), polyglycolic acid (PGA), and poly(lactic-co-glycolic acid) copolymer (PLGA). However, these biodegradable polymers exhibit insufficient mechanical strength, necessitating increased dimensions and resulting in a bulky volume that may impede application. Moreover, the suboptimal biocompatibility can provoke foreign body reactions and hinder normal bone healing. Lastly, controlling the biodegradation rates of polymers is challenging, which may surpass normal bone healing and lead to postoperative complications such as malunion or nonunion.

In recent years, magnesium has emerged as a promising biodegradable metal for internal fixation, as demonstrated by numerous research studies. Magnesium exhibits mechanical properties more closely aligned with human bone than the rigid titanium or stainless-steel materials, effectively mitigating the drawbacks of stress shielding and X-ray scattering. In vivo, magnesium plates and screws gradually dissolve, releasing magnesium ions and hydrogen gas. Magnesium ions, essential to the human body, can be metabolized without causing harm. The accumulation of hydrogen gas in tissues may result in temporary swelling or discomfort, which typically resolves as the gas dissipates over time. More importantly, magnesium has demonstrated remarkable bioactivity in promoting bone regeneration, sparking a surge of interest in basic biomechanical research. Its exceptional bioactivity has even been demonstrated in challenging clinical situations. Consequently, the unique and superior properties of magnesium have positioned it as a promising next-generation biomedical implants for internal fixation in humans.

The application of magnesium-based materials in bone surgery can be traced back to 1906, and recent advancements have led to the development of biodegradable internal fixation devices by companies like Synntellix AG (Germany) and U&I Corporation (South Korea) [7]. These fixation systems, including MAGNEZIX® (Mg-Y-Re-Zr alloy screws) and RESOMET™ (Mg-Ca-Zn alloy screws), have shown promising results in various clinical studies across multiple countries, treating conditions such as hallux valgus, osteonecrosis of the femoral head, and distal radius fractures. However, given the potential health risks of alloy elements to patients, Chinese research teams have been committed to the development of high-purity magnesium for internal fixation purposes.

Numerous human clinical studies utilizing high-purity magnesium have been successfully conducted in China. In 2015, Yu et al. employed high-purity magnesium screws for the fixation of vascularized bone grafts in young adults with displaced femoral neck fractures. Over a 16-month follow-up period, patients achieved satisfactory results in the Harris hip score, a functional index, and experienced a lower incidence of complications such as avascular necrosis and nonunion. In 2016, Zhao et al. implemented high-purity magnesium screws in a clinical trial to fix vascularized bone grafts in osteonecrosis of the femoral head. Within a 12-month follow-up period, patients treated with magnesium screws demonstrated higher satisfactory results in functional scores and reduced bone graft displacement. The serum levels of magnesium remained within the normal physiological range, and potential adverse effects induced by magnesium degradation products were absent. In 2019, Chen et al. utilized high-purity magnesium screws to fix vascularized bone grafts for trauma-induced femoral head necrosis in a case report. Satisfactory outcomes were achieved in terms of functional recovery, and the magnesium screws gradually degraded over more than two years without any noticeable side effects.