Early results using a biodegradable magnesium screw for modified chevron osteotomies

Biodegradable WE43 Mg alloy/hydroxyapatite interpenetrating phase composites with reduced hydrogen evolution

Biodegradable magnesium implants offer a solution for bone repair without the need for implant removal. However, concerns persist regarding peri-implant gas accumulation, which has limited their widespread clinical acceptance. Consequently, there is a need to minimise the mass of magnesium to reduce the total volume of gas generated around the implants. Incorporating porosity is a direct approach to reducing the mass of the implants, but it also decreases the strength and degradation resistance. This study demonstrates that the infiltration of a calcium phosphate cement into an additively manufactured WE43 Mg alloy scaffold with 75 % porosity, followed by hydrothermal treatment, yields biodegradable magnesium/hydroxyapatite interpenetrating phase composites that generate an order of magnitude less hydrogen gas during degradation than WE43 scaffolds. The enhanced degradation resistance results from magnesium passivation, allowing osteoblast proliferation in indirect contact with composites. Additionally, the composites exhibit a compressive strength 1.8 times greater than that of the scaffolds, falling within the upper range of the compressive strength of cancellous bone. These results emphasise the potential of the new biodegradable interpenetrating phase composites for the fabrication of temporary osteosynthesis devices. Optimizing cement hardening and magnesium passivation during hydrothermal processing is crucial for achieving both high compressive strength and low degradation rate.

Effect of hematoma on early degradation behavior of magnesium after implantation

The corrosion of magnesium (Mg)-based bioabsorbable implanting devices is influenced by implantation environment which dynamically changes by biological response including wound healing. Understanding the corrosion mechanisms along the healing process is essential for the development of Mg-based devices. In this study, a hematoma model was created in a rat femur to analyze Mg corrosion with hematoma in the early stage of implantation. Pure Mg specimen (99.9%,ϕ1.2 × 6 mm) was implanted in rat femur under either hematoma or non-hematoma conditions. After a designated period of implantation, the specimens were collected and weighed. The insoluble salts formed on the specimen surfaces were analyzed using scanning electron microscopy, energy-dispersive x-ray spectroscopy, and Raman spectroscopy on days 1, 3, and 7. The results indicate that hematomas promote Mg corrosion and change the insoluble salt precipitation. The weight loss of the hematoma group (27.31 ± 5.91 µg mm-2) was significantly larger than that of the non-hematoma group (14.77 ± 3.28 µg mm-2) on day 7. In the non-hematoma group, carbonate and phosphate were detected even on day 1, but the only latter was detected on day 7. In the hematoma group, hydroxide was detected on day 1, followed by the formation of carbonate and phosphate on days 3 and 7. The obtained results suggest the hypoxic and acidic microenvironment in hematomas accelerates the Mg corrosion immediately after implantation, and the subsequent hematoma resorption process leads to the formation of phosphate and carbonate with organic molecules. This study revealed the risk of hematomas as an acceleration factor of the corrosion of Mg-based devices leading to the early implant failure. It is important to consider this risk in the design of Mg-based devices and to optimize surgical procedures controlling hemorrhage at implantation and reducing unexpected bleeding after surgery.

Application and Perspectives: Magnesium Materials in Bone Regeneration

The field of bone regeneration has always been a hot and difficult research area, and there is no perfect strategy at present. As a new type of biodegradable material, magnesium alloys have excellent mechanical properties and bone promoting ability. Compared with other inert metals, magnesium alloys have significant advantages and broad application prospects in the field of bone regeneration. By searching the official Web sites and databases of various funds, this paper summarizes the research status of magnesium composites in the field of bone regeneration and introduces the latest scientific research achievements and clinical transformations of scholars in various countries and regions, such as improving the corrosion resistance of magnesium alloys by adding coatings. Finally, this paper points out the current problems and challenges, aiming to provide ideas and help for the development of new strategies for the treatment of bone defects and fractures.

Comparison of Time-Zero Primary Stability Between a Biodegradable Magnesium Bone Staple and Metal Bone Staples for Knee Ligament Fixation: A Biomechanical Study in a Porcine Model

Background

Bone staples have been shown previously to be a viable modality for cortical tendon graft fixation in ligament knee surgery. However, soft tissue reactions have been reported, making implant removal necessary. Magnesium alloys are a promising material for biodegradable orthopaedic implants, with mechanical properties closely resembling those of human bone.

Purpose

To compare the primary stability of a biodegradable bone staple prototype made from magnesium to bone staples made from metal in the cortical fixation of tendon grafts during knee surgery.

Study Design

Controlled laboratory study.

Methods

Primary stability of peripheral tendon graft fixation was assessed in a porcine model of medial collateral ligament reconstruction. Two commercially available metal bone staples (Richards fixation staple with spikes [Me1] and spiked ligament staple [Me2]) were compared with a magnesium bone staple prototype for soft tissue fixation. Primary stability was assessed using a uniaxial materials testing machine. Cyclic loading at 50 and 100 N was applied for 500 cycles each, followed by load-to-failure testing.

Results

After 500 cycles at 50 N, elongation was 1.5 ± 0.5 mm in the Me1 group, 1.9 ± 0.5 mm in the Me2 group, and 1.8 ± 0.4 mm in the magnesium group. After 1000 cycles of loading (500 cycles at 50 N and 500 at 100 N), elongation was 3.6 ± 0.9 mm in the Me1 group, 3.5 ± 0.6 mm in the Me2 group, and 4.1 ± 1.0 mm in the magnesium group. No significant differences regarding elongation were found between the groups. Load to failure was 352 ± 115 N in the Me1 group, 373 ± 77 N in the Me2 group, and 449 ± 92 N in the magnesium group, with no significant difference between the groups.

Conclusion

In this study, the magnesium bone staples provided appropriate time-zero biomechanical primary stability in comparison with metal bone staples and may therefore be a feasible alternative for cortical fixation of tendon grafts in knee surgery.

Clinical Relevance

The biodegradability of magnesium bone staples would eliminate the need for later implant removal.

Prospective evaluation of ultrasound features of magnesium-based bioabsorbable screw resorption in pediatric fractures

OBJECTIVE

Bioabsorbable magnesium-based alloy screws release gas upon resorption. The resulting findings in the adjacent soft tissues and joints may mimic infection. The aim of the study was to evaluate the ultrasound (US) findings in soft tissues and joints during screw resorption.

METHODS

Prospectively acquired US studies from pediatric patients treated with magnesium screws were evaluated for screw head visibility, posterior acoustic shadowing, twinkling artifact, foreign body granuloma, gas (soft tissue, intra-articular), alterations of the skin and subcutaneous fat, perifascial fluid, localized fluid collections, hypervascularization, and joint effusion.

RESULTS

Sixty-six US studies of 28 pediatric patients (nfemale = 9, nmale = 19) were included. The mean age of the patients at the time of surgery was 10.84 years; the mean time between surgery and ultrasound was 128.3 days (range = 6-468 days). The screw head and posterior acoustic shadowing were visible in 100% of the studies, twinkling artifact in 6.1%, foreign body granuloma in 92.4%, gas locules in soft tissue in 100% and intra-articular in 18.2%, hyperechogenicity of the subcutaneous fat in 90.9%, cobblestoning of the subcutaneous fat in 24.2%, loss of normal differentiation between the epidermis/dermis and the subcutaneous fat in 57.6%, localized fluid collection in 9.9%, perifascial fluid in 12.1%, hypervascularization in 27.3%, and joint effusion in 18.2%.

CONCLUSION

US findings in pediatric patients treated with magnesium screws strongly resemble infection, but are normal findings in the setting of screw resorption.

CLINICAL RELEVANCE STATEMENT

Bioabsorbable magnesium-based alloy screws release gas during resorption. The resulting US findings in the adjacent soft tissues and joints in pediatric patients may mimic infection, but are normal findings.

KEY POINTS

• Bioabsorbable magnesium-based alloy screws release gas upon resorption. • The resulting ultrasound findings in children's soft tissues and joints closely resemble those of soft tissue infection or osteosynthesis-associated infection. • Be familiar with these ultrasound findings in order to avoid inadvertently misdiagnosing a soft tissue infection or osteosynthesis-associated infection.

Mechanical Properties and Corrosion Rate of ZnAg3 as a Novel Bioabsorbable Material for Osteosynthesis

Osteosynthesis in fracture treatment typically uses hardware that remains in the patient's body, which brings a permanent risk of negative side effects such as foreign body reactions or chronic inflammation. Bioabsorbable materials, however, can degrade and slowly be replaced by autologous bone tissue. A suitable material is requested to offer great biocompatibility alongside excellent mechanical properties and a reasonable corrosion rate. Zinc-silver alloys provide these characteristics, which makes them a promising candidate for research. This study investigated the aptitude as a bioabsorbable implant of a novel zinc-silver alloy containing 3.3 wt% silver (ZnAg3). Here, the tensile strength as well as the corrosion rate in PBS solution (phosphate buffered solution) of ZnAg3 were assessed. Furthermore, shear tests, including fatigue and quasi-static testing, were conducted with ZnAg3 and magnesium pins (MAGNEZIX®, Syntellix AG, Hannover, Germany), which are already in clinical use. The detected corrosion rate of 0.10 mm/year for ZnAg3 was within the proposed range for bioabsorbable implants. With a tensile strength of 237.5 ± 2.12 MPa and a shear strength of 144.8 ± 13.2 N, ZnAg3 satisfied the mechanical requirements for bioabsorbable implants. The fatigue testing did not show any significant difference between ZnAg3 and magnesium pins, whereas both materials withstood the cyclic loading. Thus, the results support the assumption that ZnAg3 is qualified for further investigation.

Absorbable implants in sport medicine and arthroscopic surgery: A narrative review of recent development

Over the past two decades, advances in arthroscopic and minimally invasive surgical techniques have led to significant growth in sports medicine surgery. Implants such as suture anchors, interference screws, and endo-buttons are commonly used in these procedures. However, traditional implants made of metal or inert materials are not absorbable, leading to complications that affect treatment outcomes. To address this issue, absorbable materials with excellent mechanical properties, good biocompatibility, and controlled degradation rates have been developed and applied in clinical practice. These materials include absorbable polymers, absorbable bioceramics, and absorbable metals. In this paper, we will provide a comprehensive summary of these absorbable materials from the perspective of clinicians, and discuss their clinical applications and related research in sport medicine.

Mg-Zn-Ca Alloy (ZX00) Screws Are Resorbed at a Mean of 2.5 Years After Medial Malleolar Fracture Fixation: Follow-up of a First-in-humans Application and Insights From a Sheep Model

BACKGROUND

In the ongoing development of bioresorbable implants, there has been a particular focus on magnesium (Mg)-based alloys. Several Mg alloys have shown promising properties, including a lean, bioresorbable magnesium-zinc-calcium (Mg-Zn-Ca) alloy designated as ZX00. To our knowledge, this is the first clinically tested Mg-based alloy free from rare-earth elements or other elements. Its use in medial malleolar fractures has allowed for bone healing without requiring surgical removal. It is thus of interest to assess the resorption behavior of this novel bioresorbable implant.

QUESTIONS/PURPOSES

(1) What is the behavior of implanted Mg-alloy (ZX00) screws in terms of resorption (implant volume, implant surface, and gas volume) and bone response (histologic evaluation) in a sheep model after 13 months and 25 months? (2) What are the radiographic changes and clinical outcomes, including patient-reported outcome measures, at a mean of 2.5 years after Mg-alloy (ZX00) screw fixation in patients with medial malleolar fractures?

METHODS

A sheep model was used to assess 18 Mg-alloy (ZX00) different-length screws (29 mm, 24 mm, and 16 mm) implanted in the tibiae and compared with six titanium-alloy screws. Micro-CT was performed at 13 and 25 months to quantify the implant volume, implant surface, and gas volume at the implant sites, as well as histology at both timepoints. Between July 2018 and October 2019, we treated 20 patients with ZX00 screws for medial malleolar fractures in a first-in-humans study. We considered isolated, bimalleolar, or trimalleolar fractures potentially eligible. Thus, 20 patients were eligible for follow-up. However, 5% (one patient) of patients were excluded from the analysis because of an unplanned surgery for a pre-existing osteochondral lesion of the talus performed 17 months after ZX00 implantation. Additionally, another 5% (one patient) of patients were lost before reaching the minimum study follow-up period. Our required minimum follow-up period was 18 months to ensure sufficient time to observe the outcomes of interest. At this timepoint, 10% (two patients) of patients were either missing or lost to follow-up. The follow-up time was a mean of 2.5 ± 0.6 years and a median of 2.4 years (range 18 to 43 months).

RESULTS

In this sheep model, after 13 months, the 29-mm screws (initial volume: 198 ± 1 mm 3 ) degraded by 41% (116 ± 6 mm 3 , mean difference 82 [95% CI 71 to 92]; p < 0.001), and after 25 months by 65% (69 ± 7 mm 3 , mean difference 130 [95% CI 117 to 142]; p < 0.001). After 13 months, the 24-mm screws (initial volume: 174 ± 0.2 mm 3 ) degraded by 51% (86 ± 21 mm 3 , mean difference 88 [95% CI 52 to 123]; p = 0.004), and after 25 months by 72% (49 ± 25 mm 3 , mean difference 125 [95% CI 83 to 167]; p = 0.003). After 13 months, the 16-mm screws (initial volume: 112 ± 5 mm 3 ) degraded by 57% (49 ± 8 mm 3 , mean difference 63 [95% CI 50 to 76]; p < 0.001), and after 25 months by 61% (45 ± 10 mm 3 , mean difference 67 [95% CI 52 to 82]; p < 0.001). Histologic evaluation qualitatively showed ongoing resorption with new bone formation closely connected to the resorbing screw without an inflammatory reaction. In patients treated with Mg-alloy screws after a mean of 2.5 years, the implants were radiographically not visible in 17 of 18 patients and the bone had homogenous texture in 15 of 18 patients. No clinical or patient-reported complications were observed.

CONCLUSION

In this sheep model, Mg-alloy (ZX00) screws showed a resorption to one-third of the original volume after 25 months, without eliciting adverse immunologic reactions, supporting biocompatibility during this period. Mg-alloy (ZX00) implants were not detectable on radiographs after a mean of 2.5 years, suggesting full resorption, but further studies are needed to assess environmental changes regarding bone quality at the implantation site after implant resorption.

CLINICAL RELEVANCE

The study demonstrated successful healing of medial malleolar fractures using bioresorbable Mg-alloy screws without clinical complications or revision surgery, resulting in pain-free ankle function after 2.5 years. Future prospective studies with larger samples and extended follow-up periods are necessary to comprehensively assess the long-term effectiveness and safety of ZX00 screws, including an exploration of limitations when there is altered bone integrity, such as in those with osteoporosis. Additional use of advanced imaging techniques, such as high-resolution CT, can enhance evaluation accuracy.

Interference screws manufactured from magnesium display similar primary stability for soft tissue anterior cruciate ligament graft fixation compared to a biocomposite material - a biomechanical study

PURPOSE

Biodegradable interference screws (IFS) can be manufactured from different biomaterials. Magnesium was previously shown to possess osteoinductive properties, making it a promising material to promote graft-bone healing in anterior cruciate ligament reconstruction (ACLR). The purpose of this study was to compare IFS made from magnesium to a contemporary biocomposite IFS.

METHODS

In a porcine model of ACL reconstruction, deep porcine flexor tendons were trimmed to a diameter of 8 mm, sutured in Krackow technique, and fixed with either 8 × 30 mm biocomposite IFS (Bc-IFS) or 8 × 30 mm magnesium IFS (Mg-IFS) in an 8 mm diameter bone tunnel in porcine tibiae. Cyclic loading for 1000 cycles from 0 to 250 N was applied, followed by load to failure testing. Elongation, load to failure and stiffness of the tested constructs was determined.

RESULTS

After 1000 cycles at 250 N, elongation was 4.8 mm ± 1.5 in the Bc-IFS group, and 4.9 mm ± 1.5 in the Mg-IFS group. Load to failure was 649.5 N ± 174.3 in the Bc-IFS group, and 683.8 N ± 116.5 in the Mg-IFS group. Stiffness was 125.3 N/mm ± 21.9 in the Bc-IFS group, and 122.5 N/mm ± 20.3 in the Mg-IFS group. No significant differences regarding elongation, load to failure and stiffness between Bc-IFS and Mg-IFS were observed.

CONCLUSION

Magnesium IFS show comparable biomechanical primary stability in comparison to biocomposite IFS and may therefore be an alternative to contemporary biodegradable IFS.

Magnesium implant degradation provides immunomodulatory and proangiogenic effects and attenuates peri-implant fibrosis in soft tissues

Implants made of magnesium (Mg) are increasingly employed in patients to achieve osteosynthesis while degrading in situ. Since Mg implants and Mg²⁺ have been suggested to possess anti-inflammatory properties, the clinically observed soft tissue inflammation around Mg implants is enigmatic. Here, using a rat soft tissue model and a 1-28 d observation period, we determined the temporo-spatial cell distribution and behavior in relation to sequential changes of pure Mg implant surface properties and Mg²⁺ release. Compared to nondegradable titanium (Ti) implants, Mg degradation exacerbated initial inflammation. Release of Mg degradation products at the tissue-implant interface, culminating at 3 d, actively initiated chemotaxis and upregulated mRNA and protein immunomodulatory markers, particularly inducible nitric oxide synthase and toll-like receptor-4 up to 6 d, yet without a cytotoxic effect. Increased vascularization was demonstrated morphologically, preceded by high expression of vascular endothelial growth factor. The transition to appropriate tissue repair coincided with implant surface enrichment of Ca and P and reduced peri-implant Mg²⁺ concentration. Mg implants revealed a thinner fibrous encapsulation compared with Ti. The detailed understanding of the relationship between Mg material properties and the spatial and time-resolved cellular processes provides a basis for the interpretation of clinical observations and future tailoring of Mg implants.

Biocompatibility Assessment of Zinc Alloys as a New Potential Material for Bioabsorbable Implants for Osteosynthesis

In the last several years, zinc and its alloys have come into focus as bioabsorbable materials by qualifying themselves with an excellent corrosion rate, mechanical properties, anti-bacterial effects. and considerable biocompatibility. In this study, the biocompatibility of zinc-silver alloys containing 3.3 wt% silver (ZnAg3) was assessed by evaluating their cell viability, the proliferation rate, and the cell toxicity. Two alloys were investigated in which one was phosphated and the other was non-phosphated. The alloys were tested on human osteoblasts (hOb), which are, to a large extent, responsible for bone formation and healing processes. The performance of the phosphated alloy did not differ significantly from the non-phosphated alloy. The results showed a promising biocompatibility with hOb for both alloys equally in all conducted assays, qualifying ZnAg3 for further investigations such as in vivo studies.

Magnesium-Based Temporary Implants: Potential, Current Status, Applications, and Challenges

Biomedical implants are important devices used for the repair or replacement of damaged or diseased tissues or organs. The success of implantation depends on various factors, such as mechanical properties, biocompatibility, and biodegradability of the materials used. Recently, magnesium (Mg)-based materials have emerged as a promising class of temporary implants due to their remarkable properties, such as strength, biocompatibility, biodegradability, and bioactivity. This review article aims to provide a comprehensive overview of current research works summarizing the above-mentioned properties of Mg-based materials for use as temporary implants. The key findings from in-vitro, in-vivo, and clinical trials are also discussed. Further, the potential applications of Mg-based implants and the applicable fabrication methods are also reviewed.

Refixation of a Large Osteochondral Fragment with Magnesium Compression Screws-A Case Report

INTRODUCTION

Osteochondrosis dissecans (OCD) is a disease affecting the subchondral bone and the overlying articular cartilage. The etiology is most likely a combination of biological and mechanical factors. The incidence is highest in children >12 years old and it predominantly affects the knee. In high-grade OCD lesions, free osteochondral fragments usually are refixed via titanium screws or biodegradable screws or pins. In this case, headless compression screws made from magnesium were used for refixation.

CASE REPORT

A thirteen-year-old female patient with a two-year history of knee pain was diagnosed with an OCD lesion of the medial femoral condyle. After initial conservative treatment, displacement of the osteochondral fragment occurred. Refixation was performed using two headless magnesium compression screws. At the 6 months follow up, the patient was pain free, and the fragment showed progressive healing while the implants were biodegrading.

DISCUSSION

Existing implants for refixation of OCD lesions either require subsequent removal or show less stability and possible inflammatory reactions. The new generation of magnesium screws used in this case did not lead to a gas release, as described for previous magnesium implants, while maintaining stability during continuous biodegradation.

CONCLUSIONS

The data available to date on magnesium implants for the treatment of OCD are promising. However, the evidence on the magnesium implants in refixation surgery of OCD lesions is still limited. Further research needs to be conducted to provide data on outcomes and possible complications.

Prospective Evaluation of Magnetic Resonance Imaging Features of Magnesium-Based Alloy Screw Resorption in Pediatric Fractures

BACKGROUND

The resorption of magnesium-based alloy bioabsorbable screws results in the release of hydrogen gas, which can mimic infection and enter the growth plate. The screw itself and the released gas may also affect image quality.

OBJECTIVE

The evaluation of magnetic resonance imaging (MRI) findings during the most active phase of screw resorption is the objective, with particular focus on the growth plate and to assess for the presence of metal-induced artifacts.

MATERIAL AND METHODS

In total, 30 prospectively acquired MRIs from 17 pediatric patients with fractures treated with magnesium screws were assessed for the presence and distribution of intraosseous, extraosseous, and intra-articular gas; gas within the growth plate; osteolysis along the screw; joint effusion; bone marrow edema; periosteal reaction; soft tissue edema; and metal-induced artifacts.

RESULTS

Gas locules were found in the bone and soft tissues in 100% of the examinations, intra-articular in 40%, and in 37% of unfused growth plates. Osteolysis and the periosteal reaction were present in 87%, bone marrow edema in 100%, soft tissue edema in 100%, and joint effusion in 50% of examinations. Pile-up artifacts were present in 100%, and geometric distortion in 0% of examinations. Fat suppression was not significantly impaired in any examination.

CONCLUSIONS

Gas and edema in the bone and soft tissues are normal findings during the resorption of magnesium screws and should not be misinterpreted as infection. Gas can also be detected within growth plates. MRI examinations can be performed without metal artifact reduction sequences. Standard fat suppression techniques are not significantly affected.

High Complication Rate and High Percentage of Regressing Radiolucency in Magnesium Screw Fixation in 18 Consecutive Patients

(1) Background: Magnesium-based implants use has become a research focus in recent years. Radiolucent areas around inserted screws are still worrisome. The objective of this study was to investigate the first 18 patients treated using MAGNEZIX^® CS screws. (2) Methods: This retrospective case series included all 18 consecutive patients treated using MAGNEZIX^® CS screws at our Level-1 trauma center. Radiographs were taken at 3-, 6- and 9-month follow-ups. Osteolysis, radiolucency and material failure were assessed, as were infection and revision surgery. (3) Results: Most patients (61.1%) had surgery in the shoulder region. Radiolucency regressed from 55.6% at 3-month follow-ups to 11.1% at 9-month follow-ups. Material failure occurred in four patients (22.22%) and infection occurred in two patients, yielding a 33.33% complication rate. (4) Conclusion: MAGNEZIX^® CS screws demonstrated a high percentage of radiolucency that regressed and seems to be clinically irrelevant. The material failure rate and infection rate require further research.

Resorbable magnesium screws for fixation of medial epicondyle avulsion fractures in skeletally immature patients: A comparison with Kirschner wires

BACKGROUND

Displaced medial epicondyle fractures are treated with open reduction and internal fixation with K-wires or screws. Rates of implant prominence, failure, or non-union reported are considerable. Magnesium screws have demonstrated biocompatibility, osteoconductivity, and high pull-out strength. The aim of this study was to compare surgical fixation of medial epicondyle fracture using resorbable magnesium Herbert screws to K-wires, in skeletally immature patients.

METHODS

A retrospective analysis was performed from January 2015 to April 2020. Inclusion criteria were as follows displaced medial epicondyle fracture, <15 years, and absence of concomitant ipsilateral upper limb fractures. Two consecutive cohorts based on fixation device were made: Group A (wires) and Group B (magnesium screws). Alignment, pain, range of motion, Mayo Elbow Performance Score, and radiological healing were assessed.

RESULTS

A total of 27 patients were included: 15 in Group A and 12 in Group B. Groups were comparable for age and sex. Mean follow-up was higher in Group A (38.73 ± 3.15 vs 26.18 ± 4.85 months; p < 0.001). No significant differences were observed regarding range of motion, alignment, pain, and Mayo Elbow Performance Score, with excellent results in both groups. Two patients in Group A developed a deep wound pin site infection requiring antibiotics. X-rays revealed three cases of non-union in Group A and one in Group B, all of them asymptomatic. No patient required a second surgical procedure.

CONCLUSION

Open reduction and internal fixation of medial epicondyle fractures with magnesium screws showed comparable results to a widely accepted procedure such as the use of K-wires, potentially with a lower incidence of non-union and infection. No adverse reactions were recorded.

LEVEL OF EVIDENCE

level III.

Systems, Properties, Surface Modification and Applications of Biodegradable Magnesium-Based Alloys: A Review

In recent years, biodegradable magnesium (Mg) alloys have attracted the attention of many researchers due to their mechanical properties, excellent biocompatibility and unique biodegradability. Many Mg alloy implants have been successfully applied in clinical medicine, and they are considered to be promising biological materials. In this article, we review the latest research progress in biodegradable Mg alloys, including research on high-performance Mg alloys, bioactive coatings and actual or potential clinical applications of Mg alloys. Finally, we review the research and development direction of biodegradable Mg alloys. This article has a guiding significance for future development and application of high-performance biodegradable Mg alloys, promoting the future advancement of the magnesium alloy research field, especially in biomedicine.

Microstructural Origins of the Corrosion Resistance of a Mg-Y-Nd-Zr Alloy Processed by Powder Bed Fusion – Laser Beam

Magnesium alloys are biocompatible, biodegradable and have the ability to promote bone ingrowth, making them ideal candidate materials for replacing auto- and allografts in future treatments of large bone defects. Powder bed fusion–laser beam (PBF-LB) additive manufacturing of these alloys would further allow for the production of complex structures, optimized for bone grafting. However, the corrosion rates of structures processed by PBF-LB remain too high. An improved understanding of the influence of the microstructure generated during PBF-LB on the corrosion properties is considered key to their future implementation in implants. In this study, the effect of PBF-LB processing and subsequent hot isostatic pressing (HIP) on the microstructure and texture in different sample directions was studied and related to the corrosion behavior of a Mg-Y-Nd-Zr alloy. The results were compared with an extruded Mg-Y-Nd-Zr alloy. A higher amount of secondary phases resulted in a higher rate of localized corrosion for the PBF-LB processed material compared to that for the extruded one. Due to growth of the secondary phases, the corrosion rate was further increased after HIP. Moreover, a strong texture was observed in the PBF-LB material, and it was also enhanced in the HIP material. While this affected the electrochemical activity as measured by potentiodynamic polarization tests, any texture effect appeared to be masked by the contribution of the secondary phases in the longer-term mass change and hydrogen evolution tests. Future work should look further into the influence of individual process parameters on the microstructure and the resulting corrosion behavior of the material, to further clarify its interdependence.

Development of a Model System for Gas Cavity Formation Behavior of Magnesium Alloy Implantation

Clinical applications of magnesium (Mg)-based screws have reported gas cavity formation in the surrounding tissue, which sometimes delays the fixation of the bone fracture. The gas cavity formation is considered to depend on the balance between hydrogen generation by Mg corrosion reacting with water in the body fluid and its diffusion into the surrounding tissue by capillary flow. In order to understand the gas cavity formation behavior by Mg-based material implantation, we developed a new in vitro model system to recreate this cavity formation phenomenon: the hydrogen generation by corrosion and its diffusion into the medium. A model tissue is prepared by gelation of the cell culture medium in a sterile condition. The immersion of Mg alloy samples was performed under 5% CO₂ atmosphere with periodic observation by X-ray computed tomography, which enabled us to observe gas cavity growth up to 28 d. For demonstrating the usefulness of our model system, Mg alloy samples with different corrosion rates were prepared by a biodegradable polymer coating. AZ31 screws were spin-coated by poly-l-lactide (PLLA) and classified into three groups by their coating thickness as 1.0 ± 0.0, 1.6 ± 0.2, and 2.0 ± 0.1 μm (ave. ± s.d.). Upon their immersion into the model tissue, the gas cavity volumes formed were 1.57 ± 0.23, 1.06 ± 0.22, and 0.38 ± 0.09 mm³/mm² for 1.0, 1.6, and 2.0 μm coating samples, having the weight loss of 20.2 ± 2.93, 18.5 ± 2.84, and 11.3 ± 3.54 μg/mm², respectively (ave. ± s.d.). This result clearly indicates the dependence of gas cavity formation on the corrosion rate of the sample. The gas cavity volume was only 3.3∼7.5% of the total hydrogen gas volume estimated based on the weight loss of the samples at 28 d, which is in the range of those calculated from the clinical report (3.2∼9.4% at 4w). This system can be an effective tool to investigate the gas cavity formation behavior and contribute to understand the mechanisms and controlling factors of this phenomenon.

Fixation Performance of Bioabsorbable Zn-6Ag Pins for Osteosynthesis

Bioabsorbable implants have become the focus of the latest research for new bone implant materials. With favorable characteristics such as compatible mechanical characteristics, no long-term side effects, and even osteogenesis enhancing properties they seem to be the future of osteosynthesis. Besides these characteristics, they must perform on the same level as traditional implant materials regarding their mechanical support for bone healing. A particular focus in the research for bioabsorbable implants has been on metal alloys, as these have particularly good mechanical properties such as excellent maximum force and high stability. This study focused on the shear strength of new bioabsorbable zinc and magnesium pins in comparison to traditional implants such as K-wires and cancellous bone screws in bone-implant connections. During quasi-static and fatigue loading experiments, magnesium pins (MAGNEZIX, Syntellix AG, Hannover, Germany) and new zinc silver pins (Zn-6Ag) by Limedion (Limedion GmbH., Mannheim, Germany) were compared with conventional osteosynthetic materials. The pins made of the new bioabsorbable alloys withstood the cyclic loads to the same extent as the conventional osteosynthesis materials. In the quasi-static loading, it was shown that the novel Zn-6Ag from Limedion has the same shear strength as the magnesium pin from Syntellix, which is already in clinical use. In addition, the zinc pin showed significantly better shear strength compared to osteosynthesis with K-wires (p < 0.05).

Radiolucent zones of biodegradable magnesium-based screws in children and adolescents-a radiographic analysis

INTRODUCTION

Albeit the implantation of magnesium-based biodegradable implants can avoid a second surgery for implant removal, the postoperative occurrence of radiolucent zones around these implants based on corrosion processes has not been previously investigated in children and adolescents. We sought to characterize the distinct temporal and spatial dynamics for magnesium-based implants based on standard clinical routine radiographs.

MATERIALS AND METHODS

We retrospectively analyzed 29 patients, treated with magnesium-based compression screws (MAGNEZIX^® CS 2.7 mm, CS 3.2 mm, CS^C 4.8 mm; Syntellix AG) for fracture fixation, osteotomy, or osteochondral refixation. During a follow-up examination, the clinical and functional status was evaluated. Based on digital radiographs, the ratio of the area of the radiolucent zone and that of the screw was evaluated to assess implant degradation at two follow-up visits (i.e., after 6-8 weeks and 12-24 weeks).

RESULTS

In 29 patients (16/29 females, 14.03 ± 2.13 years), a total of 57 implants were evaluated that were used for osteotomy (n = 13, screws n = 26), fracture fixation (n = 9, screws n = 18), or osteochondral refixation (n = 7, screws n = 13). All patients healed without complications and regained full function. Radiolucent zones were observed in 27/29 patients at the first follow-up, with significantly decreased ratios at the second follow-up (2.10 ± 0.55 vs 1.64 ± 0.60, p = 0.0006). Regression analyses were performed to assess the temporal dynamics of radiolucent zones and revealed significant logarithmic developments for the 2.7 mm and 3.2 mm screws, marked by a strong ratio decrease during the first weeks and an almost complete disappearance after approximately 100 days and 200 days, respectively. In contrast, the ceramic-coated 4.8 mm screws presented a significant linear and slower decrease of radiolucent zones.

CONCLUSION

Radiolucent zones are a common phenomenon in the course of implant degradation. However, they represent a self-limiting phenomenon. Remarkably, neither implant failure nor affected implant function is noted in this context. Yet, the microstructural changes accompanying the presence of radiolucent zones remain to be analyzed by three-dimensional high-resolution imaging.

Making Hardware Removal Unnecessary by Using Resorbable Implants for Osteosynthesis in Children

Introduction: Following osteosynthesis, children generally require a second surgery to remove the hardware. This becomes unnecessary, by using resorbable implants. Limiting the number of required surgeries and their associated risks, this technique provides critical aspects of minimally invasive surgery. This review focuses on resorbable implants for osteosynthesis for the treatment of fractures in children and discusses their clinical features. Method: We provide an overview of the two most common technologies used in resorbable osteosynthesis materials: polymer- and magnesium-based alloys. Clinical examples of osteosynthesis are presented using polymer-based ActivaTM products and magnesium-based Magnezix^® products. Results: Polymer-based implants demonstrate surgical safety and efficacy. Due to their elasticity, initial placement of polymer-based products may demonstrate technical challenges. However, stability is maintained over the course of healing. While maintaining good biocompatibility, the rate of polymer-resorption may be controlled by varying the composition of polyesters and copolymers. Similarly, magnesium-based implants demonstrate good mechanical stability and resorption rates, while these characteristics may be controlled by varying alloy components. One of the significant shortcomings of magnesium is that metabolism results in the production of hydrogen gas. Both technologies provide equally good results clinically and radiographically, when compared to non-resorbable implants. Conclusion: Resorbable osteosynthesis materials demonstrate similar therapeutic results as conventional materials for osteosynthesis. Resorbable implants may have the potential to improve patient outcomes, by sparing children a second surgery for hardware removal.

Biodegradable magnesium alloy WE43 porous scaffolds fabricated by laser powder bed fusion for orthopedic applications: Process optimization, in vitro and in vivo investigation

Laser powder bed fusion (L-PBF) of magnesium (Mg) alloy porous scaffolds is expected to solve the dual challenges from customized structures and biodegradable functions required for repairing bone defects. However, one of the key technical difficulties lies in the poor L-PBF process performance of Mg, contributed by the high susceptibility to oxidation, vaporization, thermal expansion, and powder attachment etc. This work investigated the influence of L-PBF energy input and scanning strategy on the formation quality of porous scaffolds by using WE43 powder, and characterized the microstructure, mechanical properties, biocompatibility, biodegradation and osteogenic effect of the as-built WE43 porous scaffolds. With the customized energy input and scanning strategy, the relative density of struts reached over 99.5%, and the geometrical error between the designed and the fabricated porosity declined to below 10%. Massive secondary phases including intermetallic precipitates and oxides were observed. The compressive strength (4.37–23.49 MPa) and elastic modulus (154.40–873.02 MPa) were comparable to those of cancellous bone. Good biocompatibility was observed by in vitro cell viability and in vivo implantation. The biodegradation of as-built porous scaffolds promoted the osteogenic effect, but the structural integrity devastated after 12 h by the immersion tests in Hank's solution and after 4 weeks by the implantation in rabbits' femur, indicating an excessively rapid degradation rate.

•

In vitro and in vivo investigations were performed on WE43 porous scaffolds.

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Reliable fusion quality and dimensional accuracy were achieved.

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The compressive strength and Young modulus ranged 4.37–23.49 and 154.40–873.02 MPa.

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Good biocompatibility and improved osteogenic effect were observed.

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The massive secondary phases as well as the enlarged specific surface resulted to a rapid degradation rate.

Mechanical Analysis and Corrosion Analysis of Zinc Alloys for Bioabsorbable Implants for Osteosynthesis

Zinc alloys have recently been researched intensely for their great properties as bioabsorbable implants for osteosynthesis. Pure zinc (Zn) itself has relatively poor strength, which makes it insufficient for most clinical use. Research has already proven that the mechanical strength of zinc can be enhanced significantly by alloying it with silver. This study evaluated zinc silver alloys (ZnAg) as well as novel zinc silver titanium alloys (ZnAgTi) regarding their mechanical properties for the use as bioabsorbable implants. Compared to pure zinc the mechanical strength was enhanced significantly for all tested zinc alloys. The elastic properties were only enhanced significantly for the zinc silver alloys ZnAg6 and ZnAg9. Regarding target values for orthopedic implants proposed in literature, the best mechanical properties were measured for the ZnAg3Ti1 alloy with an ultimate tensile strength of 262 MPa and an elongation at fracture of 16%. Besides the mechanical properties, the corrosion rates are important for bioabsorbable implants. This study tested the corrosion rates of zinc alloys in PBS solution (phosphate buffered solution) with electrochemical corrosion measurement. Zinc and its alloys showed favorable corrosion rates, especially in comparison to magnesium, which has a much lower degradation rate and no buildup of hydrogen gas pockets during the process. Altogether, this makes zinc alloys highly favorable for use as material for bioabsorbable implants for osteosynthesis.

Alterations in magnetic resonance imaging characteristics of bioabsorbable magnesium screws over time in humans: a retrospective single center study

Objectives

This study aimed to examine the alterations in magnetic resonance imaging (MRI) characteristics of bioabsorbable magnesium (Mg) screws over time in a single center study in humans.

Methods

Seventeen patients who underwent medial malleolar (MM) fracture or osteotomy fixation using bioabsorbable Mg screws and had at least one postoperative MRI were included in this retrospective study. Six of them had more than one MRI in the postoperative period and were subject of the artifact reduction measurements. 1.5T or 3T MRI scans were acquired in different periods in each patient. The size and extent of the artifact were assessed independently by two experienced radiologists both quantitatively (distance measurement) and qualitatively (Likert scale).

Results

In the quantitative measurements of the six follow-up patients the screw’s signal loss artifact extent significantly decreased over the time, regardless of the MRI field strength (p<0.001). The mean artifact reduction was 0.06 mm (95% confidence interval [CI]: 0.05–0.07) for proton density weighted [PDw] and 0.04 mm (95% CI: 0.03–0.05) for T1 weighted (T1w) sequences per week. The qualitative assessments similarly showed significant artifact reduction in all MRI sequences. Different imaging findings, like bone marrow edema (BME), liquid collections, and gas formation were reported. The overall inter-reader agreement was high (κ=0.88, p<0.001).

Conclusions

The time-dependent artifact reduction of Mg screws in postoperative controls might indicate the expected self-degradation of the Mg implants. In addition, different MRI findings were reported, which are characteristic of Mg implants. Further MRI studies are required to get a better understanding of Mg imaging properties.

Fixation of Unstable Osteochondritis Dissecans Lesions and Displaced Osteochondral Fragments Using New Biodegradable Magnesium Pins in Adolescents

OBJECTIVE

Fixation of unstable osteochondritis dissecans (OCD) lesions and displaced osteochondral fragments are frequently performed procedures in pediatric orthopedic surgery. Since 2018, CE-certified MAGNEZIX pins are used in our institution in these cases. The aim of this study was (1) to analyze safety, efficiency, and limitations of magnesium-pin-based fixation of unstable OCD lesions and displaced osteochondral fragments and (2) to report clinical and radiological outcomes at short-term follow-up (FU).

DESIGN

In this prospective cohort study, 19 patients (10 girls and 9 boys) were included. Inclusion criteria were (1) magnetic resonance imaging-confirmed unstable OCD lesion or displaced osteochondral fragment, (2) fixation with magnesium-based pins, and (3) minimum FU of 6 months. X-rays were taken 6 weeks and 6 months after operation and magnetic resonance imaging scans every 4 to 6 months to assess the healing progress.

RESULTS

In total 67 pins were used, with a mean of 3.6 ± 1.4 per patient. Average age at surgery was 13.7 years (11-17 years). Mean time of operation was 56 ± 31 minutes, including arthroscopy, fixation, and patellar realignment (n = 6). No intraoperative complications occurred. Average FU was 11.3 ± 4.2 months (6-20 months). No redislocation or new dislocation occurred. Until now a complete radiographic healing occurred in 12 cases. Due to an implant failure in one case 11 weeks after the index surgery a revision became necessary.

CONCLUSIONS

In short-term FU of 11 ± 4 months MAGNEZIX pins provide high stability after fixation of unstable OCDs and displaced osteochondral fragments leading to uncomplicated and timely healing.

Extended Distal Chevron Osteotomy and Akin Osteotomy Using Bioabsorbable Materials for Treatment of Moderate to Severe Hallux Valgus

The purpose of this study was to investigate the suitability of bioabsorbable materials for fixation of extended distal chevron osteotomy and Akin osteotomy for the treatment of moderate to severe hallux valgus. We performed a retrospective analysis of extended distal chevron osteotomy and Akin osteotomy for the treatment of moderate to severe hallux valgus (33 patients, 42 feet). Fixation of extended distal chevron osteotomy and Akin osteotomy was performed using poly-l-lactic acid pins and polylactic acid/polyglycolic acid copolymer sutures, respectively. The radiological outcomes were evaluated based on the preoperative and 3-year follow-up intermetatarsal angle, hallux valgus angle, and hallux interphalangeal angle. The clinical results were assessed according to 3-year follow-up Manchester-Oxford Foot Questionnaire scores, patient satisfaction, and postoperative complications. All radiological and clinical results were compared with those of a control group treated with metallic implants. The mean 3-year follow-up intermetatarsal angle, hallux valgus angle, and hallux interphalangeal angle were significantly corrected from the preoperative values (all p < .001). The mean 3-year follow-up Manchester-Oxford Foot Questionnaire scores score was significantly improved from the preoperative values (p < .001). Regarding patient satisfaction, 88.1% of the patients reported good to excellent results. A total of seven complications were reported. All radiological and clinical results were comparable with those of control group treated with metallic implant. Based on these results, we recommend using bioabsorbable materials as another reliable device for fixation of extended distal chevron osteotomy and Akin osteotomy even for the treatment of moderate to severe hallux valgus.

Enhanced Corrosion Resistance and In Vitro Biocompatibility of Mg-Zn Alloys by Carbonate Apatite Coating

B-type carbonate apatite (CAp) coatings were formed on as-cast and T4-treated Mg-xZn (x = 1, 5, and 7 wt %) alloys containing various sized Zn-rich second phase to improve the corrosion resistance and biocompatibility. The CAp coating grew uniformly on the alloys with a thickness of 1.1-1.3 μm and did not show cracks or pores on 30 μm-sized second-phase particles. The CAp coating retarded corrosion of Mg-Zn substrates for the first 3-5 days in Hanks' solution. Polarization resistance of the CAp-coated alloys was 10-90 and 1-70 times higher than the uncoated and hydroxyapatite (HAp)-coated alloys, respectively. The corrosion rate of CAp-coated alloys was greatly affected by the substrate alloys once the coatings were partly broken. The CAp-coated alloys showed 40-60 and 25-45% lower 14-day average corrosion rates than the uncoated and HAp-coated alloys, respectively, in the immersion test. The CAp coating significantly enhanced the viability of osteoblastic MC3T3-E1 cells on the Mg-Zn alloys for 72 h compared to the uncoated and HAp-coated alloys. The cell densities on CAp-coated alloys were similar for 72 h regardless of substrate alloys. Therefore, the CAp coating can be a superior coating candidate for corrosion-control and biocompatibility improvement for biodegradable Mg alloys.

Matched retrospective analysis of three different fixation devices for chevron osteotomy

Chevron osteotomy with consecutive fixation is a commonly performed operative treatment option for hallux valgus deformities. The present retrospective study aims to compare the clinical and radiological outcome of novel bioabsorbable magnesium screw fixation with metal screw and Kirschner wire fixation. Eighteen matched triplets were assembled according to the following criteria: female gender, age difference less than 5 years, date of operation within 4 months, difference in preoperative intermetatarsal angle less than 5°, and equal experience of the first and second surgeon. These patients, between 18 and 85 years of age and with a minimum follow-up period of 12 months, were invited to a follow-up examination, of which only 16 matched triplets of patients entirely kept the appointment. Thus, 48 feet of 44 patients were clinically evaluated using the American Orthopaedic Foot & Ankle Society scale, Foot Function Index, University of California and Los Angeles Activity Score, as well as a visual analogue scale for pain, satisfaction, cosmetic results, and functional impairment. Radiographical assessment included measuring intermetatarsal angle and first metatarsophalangeal angles. All occurring complications and revision surgeries were noted. Significant differences were observed for postoperative intermetatarsal angle between magnesium screw and pin fixation (p = 0.009). Moreover, patients receiving magnesium screw were significantly more prone to undergo the same procedure again (p = 0.03). In conclusion, if the advantages of bioabsorbable magnesium screws outweigh the drawbacks of increased costs and a higher surgical demand, this implant might serve as possible chevron osteotomy fixation method. Compression screws and Kirschner wires also show comparable satisfactory outcomes. LEVEL OF EVIDENCE: III retrospective comparative study.

Use of resorbable magnesium screws in children: systematic review of the literature and short-term follow-up from our series

PURPOSE

Biodegradable implants are of major interest in orthopaedics, especially in the skeletally immature population. Magnesium (Mg) implants are promising for selected surgical procedure in adults, but evidence is lacking. Thus, the aim of this study is to analyze the safety and efficacy of resorbable Mg screw in different orthopaedic procedures in skeletally immature patients. In addition, we present a systematic review of the current literature on the clinical use of Mg implants.

METHODS

From 2018 until the writing of this manuscript, consecutive orthopaedic surgical procedures involving the use of Mg screws performed at our centre in patients < 15 years of age were retrospectively reviewed. In addition, a systematic review of the literature was performed in the main databases. We included clinical studies conducted on humans, using Mg-alloy implants for orthopaedic procedures.

RESULTS

A total of 14 patients were included in this retrospective analysis. Mean age at surgery was 10.8 years (sd 2.4), mean follow-up was 13.8 months (sd 7.5). Healing was achieved in all the procedures, with no implant-related adverse reaction. No patients required any second surgical procedure. The systematic review evidenced 20 clinical studies, 19 of which conducted on an adult and one including paediatric patients.

CONCLUSION

Evidence on resorbable Mg implants is low but promising in adults and nearly absent in children. Our series included apophyseal avulsion, epiphyseal fractures, osteochondritis dissecans, displaced osteochondral fragment and tendon-to-bone fixation. Mg screws guaranteed stable fixation, without implant failure, with good clinical and radiological results and no adverse events.

LEVEL OF EVIDENCE

IV - Single cohort retrospective analysis with systematic review.

Bioresorbable Magnesium-Based Alloys as Novel Biomaterials in Oral Bone Regeneration: General Review and Clinical Perspectives

Bone preservation and primary regeneration is a daily challenge in the field of dental medicine. In recent years, bioresorbable metals based on magnesium (Mg) have been widely investigated due to their bone-like modulus of elasticity, their high biocompatibility, antimicrobial, and osteoconductive properties. Synthetic Mg-based biomaterials are promising candidates for bone regeneration in comparison with other currently available pure synthetic materials. Different alloys based on Mg were developed to fit clinical requirements. In parallel, advances in additive manufacturing offer the possibility to fabricate experimentally bioresorbable metallic porous scaffolds. This review describes the promising clinical results of resorbable Mg-based biomaterials for bone repair in osteosynthetic application and discusses the perspectives of use in oral bone regeneration.

In vivo degradation and bone formation behaviors of hydroxyapatite-coated Mg alloys in rat femur

Various coatings have been developed for biodegradable Mg alloys to control the degradation speed and to improve the bone conductivity. In this study, hydroxyapatite (HAp) coatings were formed on pure Mg, Mg-0.8mass% Ca (MgCa), Mg-4mass% Y-3mass% rare earth (RE) (WE43), Mg-3mass% RE-1mass% Y (EW31) and Mg-4mass% RE (RE4) alloy rods with a chemical solution deposition method. The HAp-coated and uncoated Mg/Mg alloy rods were implanted in the femurs of rats for 3-6 months, and the corrosion suppression and bone formation abilities of the HAp coating were examined using a scanning electron microscope. The corrosion rate of WE43 was suppressed by 1/3 with the HAp coating for 6 months, and the corrosion product showed very slow dissolution. The effect of the HAp coating for pure Mg and MgCa disappeared in 1-2 months with the thinning of the rods accompanying with the obvious dissolution of the corrosion products. The effect of the HAp coating for EW31 and RE4 was not stable due to the expansion and collapse of the corrosion products. The bone formation was enhanced on the HAp layers. Eventually, the HAp coating basically suppressed the corrosion initiation and corrosion progress of Mg substrates. The magnitude of the suppression effect depended mainly on the chemical and physical stability of the corrosion products.

Effectiveness and safety of biodegradable Mg-Nd-Zn-Zr alloy screws for the treatment of medial malleolar fractures

Background

/Objective: This study aimed to evaluate the effectiveness and safety of treating medial malleolar fractures using our patented Mg-Nd-Zn-Zr alloy (abbr. JDBM) screws with Ca–P coating, in order to provide a solid basis for their further clinical translation.

Methods

Nine patients with medial malleolar fractures were treated using coated JDBM screws. All patients had closed injuries, and none had open fractures. Postoperative radiography was performed to evaluate fracture healing and degradation of the JDBM screws. The visual analogue scale (VAS) was used to evaluate the degree of postoperative pain perceived by the patients, and the American Orthopedic Foot and Ankle Society (AOFAS) ankle-hindfoot scoring system was used to evaluate their postoperative ankle function. Postoperative complications, including infection, failure of internal fixation, and malunion, were carefully recorded during follow-up.

Results

The mean follow-up time was 12.2 ​± ​4.9 months. After the operation, all patients achieved good medial malleolar fracture alignment, and none of them experienced breakage of the JDBM screws before fracture healing. Postoperative radiography indicated JDBM screws gradually degradated with implantation time, and obvious degradation could be observed 12 months, postoperatively. At the final follow-up, the patients’ mean VAS score was 2.3 ​± ​1.9. The mean AOFAS score was 90.4 ​± ​8.9, with excellent or good rates of 88.9%. None of the patients experienced infection, failure of internal fixation, malunion, or other complications.

Conclusion

Coated biodegradable JDBM screws are effective for the treatment of medial malleolar fractures, and have good prospects for further clinical translation in the future.

Translational potential statement

The results of this study indicates coated biodegradable JDBM screw is an alternative internal fixation instrument for fracture treatment and has excellent prospects for clinical translation.

Is There a Role for Absorbable Metals in Surgery? A Systematic Review and Meta-Analysis of Mg/Mg Alloy Based Implants

Magnesium (Mg) alloys have received attention in the literature as potential biomaterials for use as absorbable implants in oral and maxillofacial and orthopedic surgery applications. This study aimed to evaluate the available clinical studies related to patients who underwent bone fixation (patients), and received conventional fixation (intervention), in comparison to absorbable metals (comparison), in terms of follow-up and complications (outcomes). A systematic review and meta-analysis were performed in accordance with the PRISMA statement and PROSPERO (CRD42020188654), PICO question, ROBINS-I, and ROB scales. The relative risk (RR) of complications and failures were calculated considering a confidence interval (CI) of 95%. Eight studies (three randomized clinical trial (RCT), one retrospective studies, two case-control studies, and two prospective studies) involving 468 patients, including 230 Mg screws and 213 Titanium (Ti) screws, were analyzed. The meta-analysis did not show any significant differences when comparing the use of Mg and Ti screws for complications (p = 0.868). The estimated complication rate was 13.3% (95% CI: 8.3% to 20.6%) for the comparison group who received an absorbable Mg screw. The use of absorbable metals is feasible for clinical applications in bone surgery with equivalent outcomes to standard metal fixation devices.

A lean magnesium-zinc-calcium alloy ZX00 used for bone fracture stabilization in a large growing-animal model

Over the last decade, demand has increased for developing new, alternative materials in pediatric trauma care to overcome the disadvantages associated with conventional implant materials. Magnesium (Mg)-based alloys seem to adequately fulfill the vision of a homogeneously resorbable, biocompatible, load-bearing and functionally supportive implant. The aim of the present study is to introduce the high-strength, lean alloy Mg‒0.45Zn‒0.45Ca, in wt% (ZX00), and for the first time investigate the clinical applicability of screw osteosynthesis using this alloy that contains no rare-earth elements. The alloy was applied in a growing sheep model with osteotomized bone (simulating a fracture) and compared to a non-osteotomy control group regarding degradation behavior and fracture healing. The alloy exhibits an ultimate tensile strength of 285.7 ± 3.1 MPa, an elongation at fracture of 18.2 ± 2.1%, and a reduced in vitro degradation rate compared to alloys containing higher amounts of Zn. In vivo, no significant difference between the osteotomized bone and the control group was found regarding the change in screw volume over implantation time. Therefore, it can be concluded that the fracture healing process, including its effects on the surrounding area, has no significant influence on degradation behavior. There was also no negative influence from hydrogen-gas formation on fracture healing. Despite the proximal and distal screws showing chronologically different gas release, the osteotomy showed complete consolidation. STATEMENT OF SIGNIFICANCE: Conventional implants involve several disadvantages in pediatric trauma care. Magnesium-based alloys seem to overcome these issues as discussed in the recent literature. This study evaluates the clinical applicability of high-strength lean Mg‒0.45Zn‒0.45Ca (ZX00) screws in a growing-sheep model. Two groups, one including a simulated fracture and one group without fracture, underwent implantation of the alloy and were compared to each other. No significant difference regarding screw volume was observed between the groups. There was no negative influence of hydrogen-gas formation on fracture healing and a complete fracture consolidation was found after 12 weeks for all animals investigated.

Advances in Antibacterial Functionalized Coatings on Mg and Its Alloys for Medical Use—A Review

As a revolutionary implant material, magnesium and its alloys have many exciting performances, such as biodegradability, mechanical compatibility, and excellent biosecurity. However, the rapid and uncontrollable degradation rate of magnesium greatly hampers its clinical use. Many efforts have been taken to enhance the corrosion resistance of magnesium. However, it must be noted that improving the corrosion resistance of magnesium will lead to the compromise of its antibacterial abilities, which are attribute and proportional to the alkaline pH during its degradation. Providing antibacterial functionalized coating is one of the best methods for balancing the degradation rate and the antibacterial ability of magnesium. Antibacterial functionalized magnesium is especially well-suited for patients with diabetes and infected wounds. Considering the extremely complex biological environment in the human body and the demands of enhancing corrosion resistance, biocompatibility, osteogenesis, and antibacterial ability, composite coatings with combined properties of different materials may be promising. The aim of this review isto collect and compare recent studies on antibacterial functionalized coatings on magnesium and its alloys. The clinical applications of antibacterial functionalized coatings and their material characteristics, antibacterial abilities, in vitro cytocompatibility, and corrosion resistance are also discussed in detail.

A lean bioabsorbable magnesium-zinc-calcium alloy ZX00 used for operative treatment of medial malleolus fractures: early clinical results of a prospective non-randomized first in man study

Aims

This study is a prospective, non-randomized trial for the treatment of fractures of the medial malleolus using lean, bioabsorbable, rare-earth element (REE)-free, magnesium (Mg)-based biodegradable screws in the adult skeleton.

Methods

A total of 20 patients with isolated, bimalleolar, or trimalleolar ankle fractures were recruited between July 2018 and October 2019. Fracture reduction was achieved through bioabsorbable Mg-based screws composed of pure Mg alloyed with zinc (Zn) and calcium (Ca) ( Mg-Zn0.45-Ca0.45, in wt.%; ZX00). Visual analogue scale (VAS) and the presence of complications (adverse events) during follow-up (12 weeks) were used to evaluate the clinical outcomes. The functional outcomes were analyzed through the range of motion (ROM) of the ankle joint and the American Orthopaedic Foot and Ankle Society (AOFAS) score. Fracture reduction and gas formation were assessed using several plane radiographs.

Results

The follow-up was performed after at least 12 weeks. The mean difference in ROM of the talocrural joint between the treated and the non-treated sites decreased from 39° (SD 12°) after two weeks to 8° (SD 11°) after 12 weeks (p ≤ 0.05). After 12 weeks, the mean AOFAS score was 92.5 points (SD 4.1). Blood analysis revealed that Mg and Ca were within a physiologically normal range. All ankle fractures were reduced and stabilized sufficiently by two Mg screws. A complete consolidation of all fractures was achieved. No loosening or breakage of screws was observed.

Conclusion

This first prospective clinical investigation of fracture reduction and fixation using lean, bioabsorbable, REE-free ZX00 screws showed excellent clinical and functional outcomes.

Cite this article: Bone Joint Res 2020;9(8):477–483.

Osteoclast and osteoblast responsive carbonate apatite coatings for biodegradable magnesium alloys

Corrosion-control coatings which can enhance bone formation and be completely replaced by bone are attractive for biodegradable Mg alloys. Carbonate apatite (CAp) and hydroxyapatite (HAp) coatings were formed on Mg-4 wt% Y-3 wt% rare earth (WE43) alloy as a corrosion-control and bioabsorbable coating in the coating solution with various concentrations of NaHCO₃. The incorporation of carbonate group in apatite structure was examined using X-ray diffraction and Fourier transform infrared spectroscopy. Rat osteoclast precursor and MC3T3-E1 osteoblast cells were cultured on the CAp- and HAp-coated WE43 to examine the osteoclastic resorption and the alkaline phosphatase (ALP) activity, respectively. Mg ions in the used medium were quantified to examine the corrosion-control ability. The NaHCO₃ addition in the solution resulted in the formation of B-type CAp in which the phosphate group of apatite structure was substituted with the carbonate group. The osteoclastic resorption was observed only for the CAp coatings as the cracking of the coatings and the corrosion of substrate WE43 strongly localized under osteoclast cell bodies. The CAp and HAp coatings significantly enhanced the ALP activity of osteoblasts. The CAp-coated WE43 specimens showed 1/5 smaller amount of Mg ion release than the uncoated WE43 on the first day of culturing osteoblasts. For the subsequent 22 days, the Mg ion release was reduced to 1/2 by the CAp coatings. In the presence of osteoclasts, the CAp coatings showed slightly lower corrosion protectiveness than the HAp coating. It was demonstrated that the CAp coatings can be a bioabsorbable and corrosion-control coating for biodegradable Mg alloys.

Are Magnesium Screws Proper for Mandibular Condyle Head Osteosynthesis?

Recently, magnesium alloys have gained a significant amount of recognition as potential biomaterials for degradable implants for craniofacial bone screws. Purpose: The aim of this work was to compare screws made specifically for mandibular head osteosynthesis from different materials. Materials and Methods: Screws measuring 14 mm made by one manufacturer specifically for mandibular head osteosynthesis out of the following materials were selected: magnesium (MgYREZr), titanium (Ti6Al7Nb), and polymer (PLGA). The axial pull-out strength and torsional properties were investigated. Results: Each type of screw presented different pull-out forces (Kruskal–Wallis test, p < 0.001). The magnesium screw had the highest pull-out force of 399 N (cracked without the screw out being pulled out), followed by the titanium screw, with a force of 340 N, and the PLGA screw, with a force of 138 N (always cracked at the base of the screw head without the screw being pulled out). ANOVA was performed for the maximal torques before damage to the screw (torsional properties), revealing that the maximal torque of the magnesium screw was 16 N·cm, while that of the titanium screw was 19 N·cm. The magnesium screw was significantly weaker than the titanium screw (p < 0.05). The measured torque and pull-out force were not related to each other (p > 0.05). Conclusion: Among the screws compared, the metal biodegradable magnesium screw seems to be the most suitable material for multiscrew mandibular head osteosynthesis, considering the condition of the fragile screwdriver socket.

Magnesium-based bioabsorbable screw fixation for hallux valgus surgery - A suitable alternative to metallic implants

BACKGROUND

The primary aim of this pilot study was to prospectively evaluate outcomes of the MgYREZr bioabsorbable screw in the setting of hallux valgus corrective surgery. The secondary aim was to compare the outcomes against a control group treated with conventional titanium screws.

METHODS

A consecutive series of patients with hallux valgus deformity (n=24) underwent forefoot reconstruction surgery with a scarf osteotomy to the first metatarsal using MgYREZr screws. Functional scores, radiological outcomes, and complication profile were recorded over 12 months. Results were compared against a control group of patients (n=69) using titanium alloy screws.

RESULTS

At 1-year post-operative, both functional and radiological outcomes showed significant improvements. Compared to the control group, there was no significant difference in functional outcomes, yet radiological improvements were significantly better in the control group.

CONCLUSIONS

The MgYREZr bioabsorbable screw is a suitable alternative to titanium alloy screws for hallux valgus corrective surgery.

Comparison of SCAphoid fracture osteosynthesis by MAGnesium-based headless Herbert screws with titanium Herbert screws: protocol for the randomized controlled SCAMAG clinical trial

Background

Scaphoid fractures are the most common carpal fractures. They often need to be treated by surgery, where the use of a compression screw is the globally accepted gold standard. Surgeons may choose between different implant materials including titanium alloys, which remain in the body or are removed after healing. An alternative are biodegradable magnesium-based implants. Properties of magnesium alloys include high stability, osteoconductivity, potential reduction of infections and few artifacts in magnetic resonance imaging (MRI). The aim of this trial is to demonstrate non-inferiority of magnesium-based compression screws compared with titanium Herbert screws for scaphoid fractures.

Methods

The trial is designed as a multicenter, blinded observer, randomized controlled parallel two-group post market trial. Approximately 190 patients will be randomized (1:1) with stratification by center either to titanium or magnesium-based compression screws. Follow-up is 1 year per patient. Surgical procedures and aftercare will be performed according to the German treatment guideline for scaphoid fractures. The first primary endpoint is the patient-rated wrist evaluation (PRWE) score after 6 months. The second primary endpoint is a composite safety endpoint including bone union until 6 months, no adverse device effect (ADE) during surgery or wound healing and no serious ADE or reoperation within 1 year. The third primary endpoint is the difference in change MRI artifacts over time. Non-inferiority will be investigated for primary endpoints 1 (t-test confidence interval) and 2 (Wilson’s score interval) using both the full analysis set (FAS) and the per protocol population at the one-sided 2.5% test-level. Superiority of magnesium over titanium screws will be established using the FAS at the two-sided 5% test-level (Welch test) only if non-inferiority has been established for both primary endpoints. Secondary endpoints include quality of life.

Discussion

This study will inform care providers whether biodegradable magnesium-based implants are non-inferior to standard titanium Herbert screws for the treatment of scaphoid fractures in terms of wrist function and safety. Furthermore, superiority of magnesium-based implants may be demonstrated using MRI, which is used as surrogate endpoint for screw degradation.

Trial registration

DRKS, DRKS00013368. Registered Dec 04, 2017.

Electronic supplementary material

The online version of this article (10.1186/s12891-019-2723-9) contains supplementary material, which is available to authorized users.

Comparison of magnesium versus titanium screw fixation for biplane chevron medial malleolar osteotomy in the treatment of osteochondral lesions of the talus

PURPOSE

This retrospective study aimed to compare the clinical and radiological outcomes of patients who underwent biplane chevron medial malleolar osteotomy (MMO) for osteochondral lesions of the talus (OLT), fixed with either magnesium (Mg) or titanium (Ti) screws.

METHODS

A total of 22 patients (12 male and 10 female) with a mean age of 40.6 ± 12.5 years (range 18-56 years) who underwent MMO for OLT treatment were included in this retrospective study. Of the 22 patients, MMO was fixed with bioabsorbable Mg screws (Alloy: MgYREZr) in 11 patients, and in the remaining 11 patients (one bilateral) MMO was fixed with Ti screws. All patients were followed up for at least 1 year with a mean of 20.7 ± 8.9 months (range 12-49 months). The American Orthopedic Foot and Ankle Society (AOFAS) scale and the visual analog scale (VAS) were used to evaluate the clinical results. Union of the osteotomy, postoperative displacement and all other complications were followed and analyzed.

RESULTS

An improvement in the AOFAS scale and VAS points were recorded in both groups with no statistically significant difference between the groups (p 0.079 and 0.107, respectively). Complete union of the osteotomy was obtained in all patients. One patient in the Ti group required implant removal due to pain and irritation. There were no other significant complications in either group.

CONCLUSIONS

The results of this study showed that bioabsorbable Mg compression screws have similar therapeutic efficacy to Ti screws in respect of functional and radiological outcomes in MMO fixation. Bioabsorbable Mg screw is an alternative fixation material which can be safely used for MMO in ankle surgery.

LEVEL OF EVIDENCE

Level IV, retrospective case series.

Mechanical and biocorrosive properties of magnesium-aluminum alloy scaffold for biomedical applications

This study investigates the morphology, microstructure, compressive behavior, biocorrosion properties, and cytocompatibility of magnesium (Mg)-aluminum (Al) alloy (AE42) scaffolds for their potential use in biodegradable biomedical applications. Mg alloy scaffolds were successfully synthesized via a camphene-based freeze-casting process with precisely controlled heat treatment. The average porosity was approximately 52% and the median pore diameter was ∼13 μm. Salient deformation mechanisms were identified using acoustic emission (AE) signals and adaptive sequential k-means (ASK) analysis. Twinning, dislocation slip, strut bending, and collapse were dominant during compressive deformation. Nonetheless, the overall compressive behavior and deformation mechanisms were similar to those of bulk Mg based on ASK analysis. The corrosion potential of the Mg alloy scaffold (-1.44 V) was slightly higher than that of bulk AE42 (-1.60 V), but the corrosion rate of the Mg alloy scaffold was faster than that of bulk AE42 due to the enhanced surface area of the Mg alloy scaffold. As a result of cytocompatibility evaluation following ISO10993-5, the concentration of the Mg alloy scaffold extract reducing cell growth rate to 50% (IC₅₀) was 10.7%, which is higher (less toxic) than 5%, suggesting no severe inflammation by implantation into muscle.

Internal fixation of three-dimensional distal metatarsal I osteotomies in the treatment of hallux valgus deformities using biodegradable magnesium screws in comparison to titanium screws

BACKGROUND

Various implants, for example K-wires, screws, plates or staples, have been introduced for the stabilisation of corrective osteotomies in hallux valgus surgery. To provide high initial stability and to avoid subsequent implant removal, a novel biodegradable magnesium screw (MAGNEZIX^® CS, Syntellix AG, Hanover, Germany) has been developed and approved for clinical use.

METHODS

Between October 2014 and June 2016, magnesium screws were used in 100 patients with a symptomatic hallux valgus deformity for the fixation of Chevron and Youngswick osteotomies. The results were compared to a retrospective cohort of 100 patients, in which titanium screws were applied to stabilize the osteotomies in a comparable manner. All follow-up data was collected retrospectively.

RESULTS

Both cohorts showed no differences concerning the age of patients, comorbidities, number of corrected toes and duration of surgery. The median clinical follow up was 12.2 weeks (magnesium) and 11.7 weeks (titanium), respectively. No difference was found between the magnesium screws and the titanium screws in respect to prolonged wound healing or deep infection. One patient complained about a prominent screw head in the titanium group and one screw fracture was noticed in the magnesium group most probably due to early full weight bearing. All patients but four could start full weight bearing in normal shoes at six weeks.

CONCLUSIONS

Early results of 100 cases of biodegradable magnesium screws in hallux valgus surgery show non-inferior results concerning clinical outcome and complications compared to titanium alloy screws. To avoid implant removal, while keeping high initial stability, magnesium screws are an excellent option in hallux valgus surgery.

Radiographic and histologic effects of bone morphogenetic protein-2/hydroxyapatite within bioabsorbable magnesium screws in a rabbit model

Background

Hydrogen gas formed by magnesium (Mg) screw corrosion can accumulate around the implant and create bone cysts, long-term osteolysis lesions, and bone healing delay. Thus, several authors currently do not recommend Mg implants for clinical use. In contrast, bone morphogenetic proteins (BMP)-2 have a very strong osteoinductive activity. The purpose of this study was to evaluate the effect of rhBMP-2/hydroxyapatite (HA) inside specially designed Mg cannulated screws in a rabbit femur model for hydrogen gas formation avoidance.

Methods

Fifteen rabbits underwent randomly different cannulated Mg screw implantation in both distal femora; 30 femora were divided into three groups depending on the materials fill in the cannulated Mg screw: control group (Mg screw with no treatment), HA group (Mg screw with HA), and BMP-2/HA group (Mg screw with a composite BMP-2/HA). Plain radiography, micro-CT, and histological analysis were accomplished, and the ability to release BMP-2 of the screws was evaluated by immersion of both the screw with no treatment and screw with a composite BMP-2/HA into the SBF for up to 7 days.

Results

X-ray assessment found the gas shadow around the implant was slightly smaller in the BMP-2/HA group than the HA and control groups at 8 weeks. Micro-CT analysis demonstrated statistically significant higher new bone formation in the BMP-2/HA group than the other groups, respectively, which also correlated with a decreased gas volume. Histological analysis showed higher osteointegration between implants and host femurs in the BMP-2/HA group than the HA and control groups at 12 weeks.

Conclusions

This study indicates that the combination of BMP-2/HA within Mg screws enhances new bone formation and therefore has the potential to decrease the complications of hydrogen gas formation around these implants.

Bone regeneration of hollow tubular magnesium‑strontium scaffolds in critical-size segmental defects: Effect of surface coatings

Segmental defects are formidable challenges for orthopedic surgeons that are caused by large osseous defects such as open injury, comminuted fracture as well as other severe traumas and infection. Current treatment options have practical and clinical shortcomings, calling for innovative bone graft materials. This study is related to hollow tubular magnesium‑strontium (MgSr) alloy scaffolds with autologous morselized bone filled inside and three different coatings were individually applied on MgSr scaffolds, respectively, to study the effects of degradation and bioactivity of the grafts on new bone growth. The optimal coating method was screened using immersion tests, cell proliferation and adhesion, alkaline phosphatase (ALP) assay in vitro, and 4 weeks' implantation in a critical-size segmental defect in vivo. More new bone formation was observed by radiographic tests and histology along the ulna defects, when magnesium scaffold grafts were implanted. Meanwhile, depression occurred for blank control group with only autologous morselized bone filled, because of rapid absorption rate of morselized bone during initial implantation. Therefore, biodegradable MgSr alloy grafts showed their potential application in treating the critical-size segmental defects. As for different coating methods, CaP chemically deposited (CaP) coated sample showed least H₂ evolution in vivo, demonstrating highest corrosion resistance and relative stable interfaces, however, the least beneficial ion release meanwhile. Micro-arc oxidation coating (MAO) degraded faster comparing with CaP, while with the main composition of MgO. They both indicate insufficient bioactivity in bone formation. The results suggest superior combination of bioactive surface, beneficial ions release and appropriate corrosion rate of Strontium phosphate conversion (SrP) coating, indicating superior comprehensive oeteoconductive and osteoinductive properties of coatings on hollow tubular MgSr alloy scaffold.

Comparison of Bioabsorbable Magnesium versus Titanium Screw Fixation for Modified Distal Chevron Osteotomy in Hallux Valgus

Objective

The purpose of this retrospective study was to compare the clinical and radiological results of magnesium versus titanium screw fixation for modified distal chevron osteotomy in hallux valgus (HV).

Materials and Methods

A total of 31 patients who underwent modified distal chevron osteotomy for HV deformity between 2014 and 2017 were reviewed retrospectively. Headless magnesium (Mg) compression screw fixation was applied in 16 patients (17 feet) and headless titanium (Ti) compression screw in 15 patients (17 feet). Patients were followed up for at least 12 months with a mean of 19.0 ± 6.8 months in the Mg screw group and 16.2 ± 6.19 in the Ti screw group, respectively (p: 0.234). Clinical results were evaluated using the American Orthopedic Foot and Ankle Society Hallux metatarsophalangeal-interphalangeal (AOFAS-MTP-IP) scale and a visual analogue scale (VAS). The hallux valgus angle (HVA) and intermetatarsal angle (IMA) were measured before and after surgery. Time to osteotomy union and any complications were recorded and compared between the groups.

Results

An improvement in the AOFAS-MTP-IP scale and VAS points were recorded in both groups with no statistically significant difference between the groups (p: 0.764 and 0.535, resp.). At the final follow-up examination, HVA and IMA were similar (p: 0.226 and 0.712, resp.). There was no significant loss of correction between the early and final radiographs in respect of HVA and IMA in both groups (p: 0.321 and p: 0.067). Full union of the osteotomy was obtained in all patients. Prolonged (1.5 months) swelling and mild hyperemia around the surgical incision were observed in 1 patient in the Mg group but there was a good response to physical and medical therapy, and the complaints were completely resolved. There were no other significant complications in either group.

Conclusion

The results of this study showed that bioabsorbable Mg compression screw fixation has similar therapeutic efficacy to Ti screw fixation in respect of functional and radiological outcomes. Bioabsorbable Mg screw is an alternative fixation material that can be safely used for modified distal chevron osteotomy in HV surgery.