Biomechanical characterisation of a degradable magnesium-based (MgCa0.8) screw

Is the magnesium screw as stable as the titanium screw in the fixation of first metatarsal distal chevron osteotomy? A comparative biomechanical study on sawbones models

Background: Distal chevron osteotomy (DCO) is commonly performed in hallux valgus surgery. The fixation of the osteotomy is provided by various implants. The usage of biodegradable implants such as magnesium is gradually increasing due to the advantages they provide. In this study, we aimed to compare the fixation of DCO with magnesium or titanium screw biomechanically. Methods: Twenty sawbones were used. The samples were divided into two equal groups, including ten sawbones for fixation with single headless titanium (group-1) or magnesium screw (group-2). DCO and screw fixations were performed on all samples using the same technique. Biomechanical testing was applied to five samples in each group in cantilever and the other five in a physiological configuration using a computer connected to the electromechanical test machine. The obtained data were evaluated using the Shapiro-Wilk test, Student's t-test and Mann-Whitney U test on the IBM® SPSS (Statistical Package for the Social Sciences) V22.0 software. Significance was accepted at the p < 0.05 level. Results: There was no statistically significant difference between the magnesium screw and the titanium screw in terms of maximum force, maximum displacement and stiffness measurements in cantilever and physiological loadings (p > 0.05 for all). Conclusion: This study found no significant difference in biomechanical stability between the magnesium and titanium screws in DCO fixation on sawbones. Further studies with real bones are needed.

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.

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.

Research status of biodegradable metals designed for oral and maxillofacial applications: A review

The oral and maxillofacial regions have complex anatomical structures and different tissue types, which have vital health and aesthetic functions. Biodegradable metals (BMs) is a promising bioactive materials to treat oral and maxillofacial diseases. This review summarizes the research status and future research directions of BMs for oral and maxillofacial applications. Mg-based BMs and Zn-based BMs for bone fracture fixation systems, and guided bone regeneration (GBR) membranes, are discussed in detail. Zn-based BMs with a moderate degradation rate and superior mechanical properties for GBR membranes show great potential for clinical translation. Fe-based BMs have a relatively low degradation rate and insoluble degradation products, which greatly limit their application and clinical translation. Furthermore, we proposed potential future research directions for BMs in the oral and maxillofacial regions, including 3D printed BM bone scaffolds, surface modification for BMs GBR membranes, and BMs containing hydrogels for cartilage regeneration, soft tissue regeneration, and nerve regeneration. Taken together, the progress made in the development of BMs in oral and maxillofacial regions has laid a foundation for further clinical translation.

Bioabsorbable high-purity magnesium interbody cage: degradation, interbody fusion, and biocompatibility from a goat cervical spine model

Background

Bioabsorbable Mg-based implants have been a focus of orthopedic researches due to their intrinsic advantages in orthopedics surgeries. This study aimed to investigate the performance of bioabsorbable high-purity magnesium (HP Mg, 99.98 wt.%) interbody cages in anterior cervical discectomy and fusion (ACDF) and to evaluate the degradation of HP Mg cages under an interbody microenvironment.

Methods

ACDF was performed at C2–3 and C4–5, and a HP Mg cage or autologous iliac bone was randomly implanted. At 3, 6, 12 and 24 weeks after surgery, the cervical specimens were harvested to evaluate the fusion status, degradation and biocompatibility by CT, micro-CT, histological examinations and blood tests.

Results

There was no significant difference in the CT fusion score between cage group and autogenous ilium group at 3 and 6 weeks. At 12 and 24 weeks, the mean CT fusion score in the cage group was markedly lower than in the autogenous ilium group. CT and histological examinations showed bony junctions formed through the middle hole of the cage between upper and lower vertebral bodies in the cage group, but the total fusion area was less than 30%. The degradation rate of cages was relatively rapid within the first 3 weeks and thereafter became stable and slow gradually. The HP Mg cage had good biosecurity and biomechanical characteristics.

Conclusions

Implantation of Mg-based interbody cage achieves successful histological fusion, while the total fusion area needs to be improved. More studies are needed to improve the bone-cage interface.

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.

The Potential of Magnesium Based Materials in Mandibular Reconstruction

The future of biomaterial design will rely on development of bioresorbable implant materials that completely and safely degrade in vivo after the tissues grow, without generating harmful degradation products at the targeted anatomic site. Permanent biomaterials such as Ti6Al4V alloy, 316L stainless steel, and Co-based alloys currently used in mandibular reconstruction often result in stress shielding effects due to mismatch in the Young’s modulus values between the bone and the implant, resulting in implant loosening. Also, allergic responses due to metal ion releases necessitates revision surgery to prevent long term exposure of the body to toxic implant contents. Bioresorbable metals are perceived as revolutionary biomaterials that have transformed the nature of metallic biomaterials from bioinert to bioactive and multi-bio functional (anti-bacterial, anti-proliferation, and anti-cancer). In this aspect, magnesium (Mg)-based materials have recently been explored by the biomedical community as potential materials for mandibular reconstruction, as they exhibit favorable mechanical properties, adequate biocompatibility, and degradability. This article reviews the recent progress that has led to advances in developing Mg-based materials for mandibular reconstruction; correlating with the biomechanics of mandible and types of mandibular defects. Mg-based materials are discussed regarding their mechanical properties, corrosion characteristics, and in vivo performance. Finally, the paper summarizes findings from this review, together with a proposed scope for advancing the knowledge in Mg-based materials for mandibular reconstruction.

Biodegradable magnesium Herbert screw - image quality and artifacts with radiography, CT and MRI

Background

Magnesium alloys have recently been rediscovered as biodegradable implants in musculoskeletal surgery. This study is an ex-vivo trial to evaluate the imaging characteristics of magnesium implants in different imaging modalities as compared to conventional metallic implants.

Methods

A CE-approved magnesium Herbert screw (MAGNEZIX®) and a titanium screw of the same dimensions (3.2x20 mm) were imaged using different modalities: digital radiography (DX), multidetector computed tomography (MDCT), high resolution flat panel CT (FPCT) and magnetic resonance imaging (MRI). The screws were scanned in vitro and after implantation in a fresh chicken tibia in order to simulate surrounding bone and soft tissue. The images were quantitatively evaluated with respect to the overall image quality and the extent and intensity of artifacts.

Results

In all modalities, the artifacts generated by the magnesium screw had a lesser extent and were less severe as compared to the titanium screw (mean difference of artifact size of solo scanned screws in DX: 0.7 mm, MDCT: 6.2 mm, FPCT: 5.9 mm and MRI: 4.73 mm; p < 0.05). In MDCT and FPCT multiplanar reformations and 3D reconstructions were superior as compared with the titanium screw and the metal-bone interface after implanting the screws in chicken cadavers was more clearly depicted. While the artifacts of the titanium screw could be effectively reduced using metal-artifact reduction sequences in MRI (WARP, mean reduction of 2.5 mm, p < 0.05), there was no significant difference for the magnesium screw.

Conclusions

Magnesium implants generate significantly less artifacts in common imaging modalities (DX, MDCT, FPCT and MRI) as compared with conventional titanium implants and therefore may facilitate post-operative follow-up.

Electronic supplementary material

The online version of this article (doi:10.1186/s12880-017-0187-7) contains supplementary material, which is available to authorized users.

Magnesium alloys: A stony pathway from intensive research to clinical reality. Different test methods and approval-related considerations

The first degradable implant made of a magnesium alloy, a compression screw, was launched to the clinical market in March 2013. Many different complex considerations are required for the marketing authorization of degradable implant materials. This review gives an overview of existing and proposed standards for implant testing for marketing approval. Furthermore, different common in vitro and in vivo testing methods are discussed. In some cases, animal tests are inevitable to investigate the biological safety of a novel medical material. The choice of an appropriate animal model is as important as subsequent histological examination. Furthermore, this review focuses on the results of various mechanical tests to investigate the stability of implants for temporary use. All the above aspects are examined in the context of development and testing of magnesium-based biomaterials and their progress them from bench to bedside. A brief history of the first market launch of a magnesium-based degradable implant is given. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 105A: 329-347, 2017.

Biodegradable nasal stents (MgF2 -coated Mg-2 wt %Nd alloy)-A long-term in vivo study

Despite innovative surgical techniques and use of current frontal sinus stents from different materials, the problem of treatment failure with consecutive reoperation remains present. The aim of our study is to investigate biocompatibility, degradation kinetics, and functionality of a newly developed fluoride-coated magnesium-based nasal stent. A minipig anatomy of frontal sinus adapted design and an external surgical approach were developed and established. The functionality of the stents was evaluated endoscopically. The stent-tissue blocks were analysed after 90 and 180 days using microcomputed tomography (µ-CT), histology, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). Functional evaluation revealed an unobstructed stent lumen in all cases. Histological analysis showed moderate mucosal hyperplasia with a mild, nonspecific inflammatory response, and nonosteoconductive effect. Rejection reactions or necrosis did not occur. The volumetric analysis of the stents showed 51% volume loss after 180 days. The EDS analysis did not detect any neodymium (Nd) in the mucosa or bone. The Mg-2 wt % Nd stents are a promising option when treating the narrow passages following paranasal sinus surgery. In particular, its good biocompatibility and good functionality facilitate the re-epithelization of these constricted passages. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 350-365, 2017.

In vitro and in vivo studies on the degradation of high-purity Mg (99.99wt.%) screw with femoral intracondylar fractured rabbit model

High-purity magnesium (HP Mg) takes advantage in no alloying toxic elements and slower degradation rate in lack of second phases and micro-galvanic corrosion. In this study, as rolled HP Mg was fabricated into screws and went through in vitro immersion tests, cytotoxicity test and bioactive analysis. The HP Mg screws performed uniform corrosion behavior in vitro, and its extraction promoted cell viability, bone alkaline phosphatase (ALP) activity, and mRNA expression of osteogenic differentiation related gene, i.e. ALP, osteopontin (OPN) and RUNX2 of human bone marrow mesenchymal stem cells (hBMSCs). Then HP Mg screws were implanted in vivo as load-bearing implant to fix bone fracture and subsequently gross observation, range of motion (ROM), X-ray scanning, qualitative micro-computed tomography (μCT) analysis, histological analysis, bending-force test and SEM morphology of retrieved screws were performed respectively at 4, 8, 16 and 24 weeks. As a result, the retrieved HP Mg screws in fixation of rabbit femoral intracondylar fracture showed uniform degradation morphology and enough bending force. However, part of PLLA screws was broken in bolt, although its screw thread was still intact. Good osseointegration was revealed surrounding HP Mg screws and increased bone volume and bone mineral density were detected at fracture gap, indicating the rigid fixation and enhanced fracture healing process provided by HP Mg screws. Consequently, the HP Mg showed great potential as internal fixation devices in intra-articular fracture operation.

An animal experimental study of porous magnesium scaffold degradation and osteogenesis

Our objective was to observe the biodegradable and osteogenic properties of magnesium scaffolding under in vivo conditions. Twelve 6-month-old male New Zealand white rabbits were randomly divided into two groups. The chosen operation site was the femoral condyle on the right side. The experimental group was implanted with porous magnesium scaffolds, while the control group was implanted with hydroxyapatite scaffolds. X-ray and blood tests, which included serum magnesium, alanine aminotransferase (ALT), creatinine (CREA), and blood urea nitrogen (BUN) were performed serially at 1, 2, and 3 weeks, and 1, 2, and 3 months. All rabbits were killed 3 months postoperatively, and the heart, kidney, spleen, and liver were analyzed with hematoxylin and eosin (HE) staining. The bone samples were subjected to microcomputed tomography scanning (micro-CT) and hard tissue biopsy. SPSS 13.0 (USA) was used for data analysis, and values of P<0.05 were considered to be significant. Bubbles appeared in the X-ray of the experimental group after 2 weeks, whereas there was no gas in the control group. There were no statistical differences for the serum magnesium concentrations, ALT, BUN, and CREA between the two groups (P>0.05). All HE-stained slices were normal, which suggested good biocompatibility of the scaffold. Micro-CT showed that magnesium scaffolds degraded mainly from the outside to inside, and new bone was ingrown following the degradation of magnesium scaffolds. The hydroxyapatite scaffold was not degraded and had fewer osteoblasts scattered on its surface. There was a significant difference in the new bone formation and scaffold bioabsorption between the two groups (9.29 ± 1.27 vs 1.40 ± 0.49 and 7.80 ± 0.50 vs 0.00 ± 0.00 mm3, respectively; P<0.05). The magnesium scaffold performed well in degradation and osteogenesis, and is a promising material for orthopedics.

Magnesium alloys as a biomaterial for degradable craniofacial screws

Recently, magnesium (Mg) alloys have received significant attention as potential biomaterials for degradable implants, and this study was directed at evaluating the suitability of Mg for craniofacial bone screws. The objective was to implant screws fabricated from commercially available pure Mg and alloy AZ31 in vivo in a rabbit mandible. First, Mg and AZ31 screws were compared to stainless steel screws in an in vitro pull-out test and determined to have a similar holding strength (∼40N). A finite-element model of the screw was created using the pull-out test data, and this model can be used for future Mg alloy screw design. Then, Mg and AZ31 screws were implanted for 4, 8 and 12weeks, with two controls of an osteotomy site (hole) with no implant and a stainless steel screw implanted for 12weeks. Microcomputed tomography was used to assess bone remodeling and Mg/AZ31 degradation, both visually and qualitatively through volume fraction measurements for all time points. Histological analysis was also completed for the Mg and AZ31 at 12weeks. The results showed that craniofacial bone remodeling occurred around both Mg and AZ31 screws. Pure Mg had a different degradation profile than AZ31; however, bone growth occurred around both screw types. The degradation rate of both Mg and AZ31 screws in the bone marrow space and the muscle were faster than in the cortical bone space at 12weeks. Furthermore, it was shown that by alloying Mg, the degradation profile could be changed. These results indicate the promise of using Mg alloys for craniofacial applications.

Biomechanical evaluation of magnesium-based resorbable metallic screw system in a bilateral sagittal split ramus osteotomy model using three-dimensional finite element analysis

PURPOSE

The aim of this study was to evaluate the stress distribution of a magnesium (Mg)-based resorbable screw system in a bilateral sagittal split ramus osteotomy (BSSO) and to compare its biomechanical stability with those of titanium (Ti)-based and polymer (IN)-based systems.

MATERIALS AND METHODS

A 3-dimensional BSSO model (10-mm advancement and setback) was constructed with Mimics. Bicortical screw fixation using Ti, IN, and Mg screws was performed with 4 different geometries of fixation. With an occlusal load of 132 N on the lower first molar, the von Mises stress (VMS) distribution was calculated using ANSYS.

RESULTS

The VMS distribution of Mg was more similar to that of Ti than to that of IN. In all cases, the highest VMS was concentrated on the screw at the most posterior and superior area. Stress was distributed mainly around the screw holes (cancellous bone) and the retromolar area (cortical bone). In the advancement surgery, fixation with 5 Mg screws (5A-Mg, 99.810 MPa at cortical bone) showed biomechanical stability, whereas fixation with the same number of IN screws did not (5A-IN, 109.021 MPa at cortical bone). In the setback surgery, although the maximum VMSs at cortical bone for Mg, IN, and Ti were lower than 108 MPa (yield strength of cortical bone), Mg screws showed more favorable results than IN screws because the maximum VMSs of Mg at cancellous bone were lower than those of IN.

CONCLUSION

The Mg-based resorbable screw system is a promising alternative to the IN-based system.

Biodegradable magnesium-based screw clinically equivalent to titanium screw in hallux valgus surgery: short term results of the first prospective, randomized, controlled clinical pilot study

Purpose

Nondegradable steel-and titanium-based implants are commonly used in orthopedic surgery. Although they provide maximal stability, they are also associated with interference on imaging modalities, may induce stress shielding, and additional explantation procedures may be necessary. Alternatively, degradable polymer implants are mechanically weaker and induce foreign body reactions. Degradable magnesium-based stents are currently being investigated in clinical trials for use in cardiovascular medicine. The magnesium alloy MgYREZr demonstrates good biocompatibility and osteoconductive properties. The aim of this prospective, randomized, clinical pilot trial was to determine if magnesium-based MgYREZr screws are equivalent to standard titanium screws for fixation during chevron osteotomy in patients with a mild hallux valgus.

Methods

Patients (n=26) were randomly assigned to undergo osteosynthesis using either titanium or degradable magnesium-based implants of the same design. The 6 month follow-up period included clinical, laboratory, and radiographic assessments.

Results

No significant differences were found in terms of the American Orthopaedic Foot and Ankle Society (AOFAS) score for hallux, visual analog scale for pain assessment, or range of motion (ROM) of the first metatarsophalangeal joint (MTPJ). No foreign body reactions, osteolysis, or systemic inflammatory reactions were detected. The groups were not significantly different in terms of radiographic or laboratory results.

Conclusion

The radiographic and clinical results of this prospective controlled study demonstrate that degradable magnesium-based screws are equivalent to titanium screws for the treatment of mild hallux valgus deformities.

Magnesium-based bone implants: immunohistochemical analysis of peri-implant osteogenesis by evaluation of osteopontin and osteocalcin expression

The functions of some bone proteins, as osteopontin (OPN) and osteocalcin (OC), have been discovered by the latest studies. This fact suggests the possibility of their immunodetection to characterize peri-implant osteogenesis and implant impact on it. Cylindrical pins of Mg alloys (MgCa0.8, LAE442, ZEK100, LANd442) and titanium alloy (TiAl6V4) were implanted into the tibial medullae of 46 rabbits. Each group was divided regarding to implant duration (3 and 6 months). Bone samples adjacent to the implants were decalcified and treated with routine histological and immunohistochemical protocols using OC and OPN-antibodies. OC was detected in matrix of compact bone, but very rarely in osteoid and bone cells. OPN was detected intracellularly and in osteoid. After 3 months, the highest level of both markers was found in titanium group, followed by LAE442-group. In contrast to LAE442 and TiAl6V4, the other Mg alloys showed increasing levels of OC after 6 months. Lower levels of OP and OC compared to the control group are related to the continuous implant degradation and instability of bone-implant interface in early post-surgical period. Reduced marker's expression in LAE442 and TiAl6V4 groups after 6 months may indicate stabilization of bone-implant interface and completion of peri-implant neo-osteogenesis. Declining characters of OC and OPN expression over the implantation time, as well as their lowest levels in late post-surgical term, suggest a more appropriate biocompatibility of LAE442, which therefore seems to be the most preferable of the tested materials for the use in orthopaedic applications.