Biodegradable Magnesium Bone Plate and Screw Fixation in Jaw Surgery

The purpose of this study is to evaluate the efficacy and safety of using high-purity magnesium bone plates and screws for internal fixation in jaw surgery. The investigators aim to assess whether these biodegradable magnesium devices promote normal bone healing and functional recovery while ensuring the safety of patients undergoing dentoalveolar surgery, fracture fixation, orthognathic surgery, or craniofacial reconstruction. The hypotheses are:

1. High-purity magnesium bone plates and screws are effective in bone fixation, promoting normal bone healing and functional recovery in jaw surgery.
2. High-purity magnesium bone plates and screws are safe in jaw surgery in terms of local side effects and systemic safety.

Participants will undergo jaw surgery based on the clinical indications. High-purity magnesium bone plates and screws will be used for internal fixation during the surgical procedure. Participants will be followed up at 1 week, 3 weeks, 6 weeks, 3 months, 6 months, 1 year, and 2 years after surgery to assess wound healing, functional recovery, and any side effects. If any side effects occur or deemed necessary, participants may be followed up for a longer period. During postoperative follow-up visits, X-ray or CBCT/CT imaging will be conducted routinely or when clinically indicated.

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.

Despite its potential, magnesium-based fixation faces challenges in orthopedics due to its relatively weak mechanical strength when used in weight-bearing areas, and no clinical trials have been conducted in such cases thus far. Theoretically, fixation in the hip joint area must withstand forces exceeding 2000N, or three times the body weight, which may increase during functional mobilization. Researchers have been exploring coating strategies to decelerate the in vivo degradation of magnesium, thereby extending the mechanical support for adequate orthopedic healing. They are also investigating metallurgical techniques to enhance the mechanical strength of magnesium fixation devices. Conversely, jaw surgeries may benefit from magnesium-based fixation due to their comparatively lower force-loading requirements compared to limb or spine fixation. The normal forces for the mandible are approximately 400N, which decrease to 115N at one week and 250N at six weeks after internal reduction. Consequently, magnesium fixation holds promise for successful application in jaw surgery.

Nonetheless, owing to limited clinical research in this domain, considerable efforts are needed to thoroughly comprehend the benefits of magnesium-based materials in jaw surgery and to establish novel surgical protocols for their implementation. This study seeks to investigate the application of magnesium for bone fixation in jaw surgery and to comprehensively assess the surgical outcomes. The study will contribute to a deeper understanding of using magnesium as internal fixation in jaw surgery and is expected to pave the way for new surgical protocols utilizing biodegradable fixation. Ultimately, this could lead to improved patient outcomes and a reduction in healthcare burdens.

Eligibility Criteria:
Inclusion Criteria:

1. Participants must be 18 years of age or older.
2. Participants must have confirmed indications for jaw surgery with internal fixation, such as alveolar onlay bone grafting, fracture fixation, orthognathic surgery, or reconstructive surgery.
3. Participants should have adequate bone quality and sufficient bone volume to support the placement of magnesium bone plates and screws.
4. Participants must provide written informed consent, indicating their understanding of the potential risks and benefits of magnesium bone plate and screw fixation.

Exclusion Criteria:

1. Participants with certain medical conditions that may affect bone healing or increase the risk of complications, such as uncontrolled diabetes, severe osteoporosis, multiple myelomas, or active bone infections.
2. Participants with medical conditions that may exacerbate or predispose them to systemic side effects of magnesium implants, thus contraindicating their use, should be excluded. These conditions include chronic kidney disease, hypermagnesemia, severe electrolyte imbalances, severe heart disease (especially in those with a history of arrhythmias or heart failure), myasthenia gravis, abnormal thyroid functions, hyperparathyroidism, and adrenocortical insufficiency.
3. Participants with known allergies or hypersensitivity to magnesium.
4. Participants with an ASA score of 3 or above, indicating a higher risk for general anesthesia.
5. Participants who are pregnant or breastfeeding.
6. Participants deemed unlikely to comply with the study protocol, such as attending follow-up appointments or adhering to post-operative care instructions.