Gesammeltes Wissen

The purpose of this paper is to provide a succinct but nevertheless complete mechanistic overview of the various types of magnesium corrosion. The understanding of the corrosion processes of magnesium alloys builds upon our understanding of the corrosion of pure magnesium. This provides an understanding of the types of corrosion exhibited by magnesium alloys, and also of the environmental factors of most importance. This deep understanding is required as a foundation if we are to produce magnesium alloys much more resistant to corrosion than the present alloys. Much has already been achieved, but there is vast scope for improvement. This present analysis can provide a foundation and a theoretical framework for further, much needed research. There is still vast scope both for better fundamental understanding of corrosion processes, engineering usage of magnesium, and also on the corrosion protection of magnesium alloys in service.

Owing to their mechanical properties, metallic materials present a promising solution in the field of resorbable implants. The magnesium metabolism in humans differs depending on its introduction. The natural, oral administration of magnesium via, for example, food, essentially leads to an intracellular enrichment of Mg2+. In contrast, introducing magnesium-rich substances or implants into the tissue results in a different decomposition behavior. Here, exposing magnesium to artificial body electrolytes resulted in the formation of the following products: magnesium hydroxide, magnesium oxide, and magnesium chloride, as well as calcium and magnesium apatites. Moreover, it can be assumed that Mg2+, OH− ions, and gaseous hydrogen are also present and result from the reaction for magnesium in an aqueous environment. With the aid of physiological metabolic processes, the organism succeeds in either excreting the above mentioned products or integrating them into the natural metabolic process. Only a burst release of these products is to be considered a problem. A multitude of general tissue effects and responses from the Mg's degradation products is considered within this review, which is not targeting specific implant classes. Furthermore, common alloying elements of magnesium and their hazardous potential in vivo are taken into account.

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. Further, 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.

This is the first larger study analyzing the use of magnesium-based screws for fixation of modified Chevron osteotomies in hallux valgus surgery. 44 patients (45 feet) were included in this prospective study. A modified Chevron osteotomy was performed on every patient and a magnesium screw used for fixation. The mean clinical follow up was 21.4 weeks. The mean age of the patients was 45.5 years. 40 patients could be provided with the implant, in 4 patients the surgeon decided to change to a standard metallic implant. The AOFAS, FAAM and pain NRS-scale improved markedly. The hallux valgus angle, intermetatarsal angle and sesamoid position improved significantly. Seven patients showed dorsal subluxation, rotation or medial shifting of the metatarsal heads within the first three months. One of these patients was revised, in all others the findings were considered clinically not significant or the patients refused revision. This study shows the feasibility of using magnesium screws in Hallux valgus-surgery. Surgeons starting with the use of these implants should be aware of the proper handling of these implants and should know about corrosion effects during healing and its radiographic appearance. 

Purpose: Degradable magnesium implants have received increasing interest in recent years. In anterior cruciate ligament reconstruction surgery, the well-known osteoconductive effects of biodegradable magnesium alloys may be useful. The aim of this study was to examine whether interference screws made of MgYREZr have comparable biomechanical properties to commonly used biodegradable screws and whether a different thread on the magnesium screw has an influence on the fixation strength.

Methods: Five magnesium (MgYREZr-alloy) screws were tested per group. Three different groups with variable thread designs (Designs 1, 2, and 3) were produced and compared with the commercially available bioabsorbable Bioacryl rapid polylactic-co-glycolic acid screw Milagro®. In vitro testing was performed in synthetic bone using artificial ligament fixed by an interference screw. The constructs were pretensioned with a constant load of 60 N for 30 s followed by 500 cycles between 60 N and 250 N at 1 Hz. Construct displacements between the 1st and 20th and the 21st and 500th cycles were recorded. After a 30 s break, a maximum load to failure test was performed at 1 mm/s measuring the maximum pull-out force.

Results: The maximum loads to failure of all three types of magnesium interference screws (Design 1: 1,092 ± 133.7 N; Design 2: 1,014 ± 103.3 N; Design 3: 1,001 ± 124 N) were significantly larger than that of the bioabsorbable Milagro® interference screw (786.8 ± 62.5 N) (p < 0.05). However, the greatest maximum load was found with magnesium screw Design 1. Except for a significant difference between Designs 1 and 2, there were no further significant differences among the four groups in displacement after the 20th cycle.

Conclusions: Biomechanical testing showed higher pullout forces for magnesium compared with a commercial polymer screw. Hence, they suggest better stability and are a potential alternative. The thread geometry does not significantly influence the stability provided by the magnesium implants. This study shows the first promising results of a degradable material, which may be a clinical alternative in the future.

Objective: The purpose of this retrospective study was to evaluate the outcome of medial malleolar fractures treated with magnesium (MgYREZr) bioabsorbable compression screw fixation.

Materials and methods:  Eleven patients with a medial malleolar fracture (either isolated or accompanied by bimalleolar or trimalleolar ankle fractures) who were treated with magnesium bioabsorbable compression screws between 2015 and 2016 in our hospital were retrospectively evaluated. Patients were monitored with a mean follow-up of 17.3 ± 4.1 months (range 12–24 months). The mechanism of injury was ground level falls in all patients. All fractures were classified as closed fractures. American Orthopedic Foot and Ankle Society’s (AOFAS) scale and the visual analog scale (VAS) were used to evaluate the clinical results during the final follow-up. Bone union and a possible loss of reduction were assessed with serial radiographs. Potential complications including revision surgery and infection were recorded and reported.

Results: There were 11 patients (4 female, 7 male) with a mean age of 41 ± 21.9 years (range 20–78 years). Six patients had Herscovici type C and five patients had type B fractures. At the final follow-up the mean AOFAS score was 94.9 ± 5.7 points (range 85–100 points) and the mean VAS score was 0.4 ± 1.2 points (range 0–4 points). Radiographic solid union was achieved in all cases. No complications were seen during the follow-up. No patients required implant removal or revision surgery.

Conclusion: This is the first study that investigates the use of bioabsorbable magnesium compression screws in medial malleolar fractures. The results of this study revealed that fixation of medial malleolar fractures with bioabsorbable magnesium compression screws provides adequate fixation with good functional results.

Level of evidence:Level IV, therapeutic, retrospective case series.

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). TheAmerican 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.

The clinical application of degradable orthopedic magnesium implants is a tangible vision in medical science. This interdisciplinary review discusses many different aspects of magnesium alloys comprising the manufacturing process and the latest research. We present the challenges of the manufacturing process of magnesium implants with the risk of contamination with impurities and its effect on corrosion. Furthermore, this paper provides a summary of the current examination methods used in in vitro and in vivo research of magnesium alloys. The influence of various parameters (most importantly the effect of the corrosive media) in in vitro studies and an overview about the current in vivo research is given.

The aim was to evaluate the biocompatibility of osteosynthesis plates of the MgYREZr/WE43 alloy by using human cells in vitro. Eluates of degradable magnesium osteosynthesis plates as well as halved plates were used for incubation with human osteoblasts, fibroblasts and osteosarcoma cells. The cell viability was evaluated by using FDA/PI-Staining and LDH analysis. Cell proliferation was assessed by MTT, WST-Test and BrdU-ELISA. Scanning electron microscope was used for investigation of the cell adhesion. The number of devitalized cells in all treatment groups did not significantly deviate from the control group. According to MTT results, the number of metabolically active cells was not significantly affected by the addition of the eluates. The number of metabolically active cells was reduced by 24 to 38% compared to the control on incubation in direct contact with the osteosynthesis plates. The proliferation of the cells was inhibited by the addition of the eluates. While the eluate of the half-hour elution has only a very small effect, the 24 h eluate significantly inhibits proliferation by 23-25% compared to the control. The roughened surface of the magnesium osteosynthesis plate after incubation showed adherent cells. However, some areas of the plates were also free of adherent cells. WE43 based magnesium alloys showed favorable biocompatibility considering the viability of the cells evaluated; however, proliferation rates were reduced in a time dependent manner, especially in fibroblast group. This might be a potential clinical benefit of magnesium osteosynthesis plates and their superiority to titanium, thus the fibroblastic ingrowth might negatively influence the bone-plate contact.

Magnesium alloys are currently subject to much research for use in biodegradable implant applications. The challenge in this field of material development comprises the design of an alloy that provides adequate mechanical and corrosion properties combined with an excellent biocompatibility. While there are many approaches in current literature only one Mgbased application shows the potential to hit the market. MAGNEZIX Compression Screws are the world’s first approved/CE-certified magnesium-based implants designed for use in biodegradable osteosyntheses applications in humans. Therefore, this paper focusses on challenges and current clinical results achieved by means of degradable compression screws. Insights into the screws’ process chain and approval processes are given. As these innovative screws have already been on the market for 2 years long-term results based on their use in surgery are discussed.

Measurement of degradation progression of biodegradable metals such as magnesium in vivo is of great importance for customer satisfaction and regulatory purposes. Current methods are based on x-ray/CT (computed tomography) or MRI (magnetic resonance imaging) and have only limited validity. MRI results are heavily impacted by the implant’s position and orientation in the magnetic field. CT scans expose patients to radiation and, due to similar attenuation, precisely distinguishing between bone, magnesium degradation products or metal, makes proper degradation tracking impossible. Both methods rely on subjective assessments of the results. In this work, we describe two non-invasive methods to prospectively overcome these adverse and often inaccurate methods: hydrogen measurement and metal detection. We validated both methods and assessed their feasibility for a clinical application. Both methods are suitable to detect the state of degradation of magnesium implants in vivo directly or indirectly by means of periodically recurring standardized measurements in future studies.

In recent years, much progress has been made on the development of biodegradable magnesium alloys as “smart” implants in cardiovascular and orthopedic applications. Mg-based alloys as biodegradable implants have outstanding advantages over Fe-based and Zn-based ones. However, the extensive applications of Mg-based alloys are still inhibited mainly by their high degradation rates and consequent loss in mechanical integrity. Consequently, extensive studies have been conducted to develop Mg-based alloys with superior mechanical and corrosion performance. This review focuses on the following topics: (i) the design criteria of biodegradable materials; (ii) alloy development strategy; (iii) in vitro performances of currently developed Mg-based alloys; and (iv) in vivo performances of currently developed Mg-based implants, especially Mg-based alloys under clinical trials.

Magnesium-based implants are re-emerging as a substantial amendment to standard orthopaedic implants. A brief introduction of magnesium (Mg) as a biodegradable material and basic magnetic resonance imaging (MRI) principles are discussed. This review aims to highlight the current performance of these implants during examinations with MRI. We also aim to summarise comparisons between Mg-based implants with current standards to emphasise the promotion of biodegradable implants in clinical practice. A comprehensive search of current literature on Mg-based implants and the utilisation of MRI in the studies was performed. Additionally, recorded artefact behaviour of Mg-based implants during MRI was investigated. A total of nine studies were included in which MRI was employed to image Mg-based implants. Of those studies, four of the nine discuss artefact production caused by the implants. MRI successfully imaged regions of interest over all and produced fewer artefacts than other materials used in the studies. MRI was employed in contrast angiography, bone growth observation, bone infection healing, and blood perfusion. Imaging capabilities of an implant material are vital to translating products into clinical application. Positive findings presented in this review suggest and support the use of Mg-based implants due to their successful visual compatibility with MRI techniques.

Magnesium (Mg) implants have shown to cause image artefacts or distortions in magnetic resonance imaging (MRI). Yet, there is a lack of information on how the degradation of Mg-based implants influences the image quality of MRI examinations. In this study, Mg-based implants are analysed in vitro, ex vivo, and in the clinical setting for various magnetic field strengths with the aim to quantify metallic artefact behaviour. In vitro corroded Mg-based screws and a titanium (Ti) equivalent were imaged according to the ASTM F2119. Mg-based and Ti pins were also implanted into rat femurs for different time points and scanned to provide insights on the influence of soft and hard tissue on metallic artefact. Additionally, MRI data of patients with scaphoid fractures treated with CE-approved Mg-based compression screws (MAGNEZIX®) were analysed at various time points post-surgery. The artefact production of the Mg-based material decreased as implant material degraded in all settings. The worst-case imaging scenario was determined to be when the imaging plane was selected to be perpendicular to the implant axis. Moreover, the Mg-based implant outperformed the Ti equivalent in all experiments by producing lower metallic artefact (p < 0.05). This investigation demonstrates that Mg-based implants generate significantly lower metallic distortion in MRI when compared to Ti. Our positive findings suggest and support further research into the application of Mg-based implants including post-operative care facilitated by MRI monitoring of degradation kinetics and bone/tissue healing processes.

Degrading metal alloys are a new class of implant materials suitable for bone surgery. The aim of this study was to investigate the degradation mechanism at the bone–implant interface of different degrading magnesium alloys in bone and to determine their effect on the surrounding bone. Sample rods of four different magnesium alloys and a degradable polymer as a control were implanted intramedullary into the femora of guinea pigs. After 6 and 18 weeks, uncalcified sections were generated for histomorphologic analysis. The bone–implant interface was characterized in uncalcified sections by scanning electron microscopy (SEM), element mapping and X-ray diffraction. Results showed that metallic implants made of magnesium alloys degrade in vivo depending on the composition of the alloying elements. While the corrosion layer of all magnesium alloys accumulated with biological calcium phosphates, the corrosion layer was in direct contact with the surrounding bone. The results further showed high mineral apposition rates and an increased bone mass around the magnesium rods, while no bone was induced in the surrounding soft tissue. From the results of this study, there is a strong rationale that in this research model, high magnesium ion concentration could lead to bone cell activation.

Abstract

It is difficult to fix fractures of the condylar head of the mandible. Several techniques have been described which show satisfactory outcomes,but stability can be questionable, and some can cause irritation of the soft tissues. We describe a technique and first results of treating suchfractures with resorbable magnesium-based headless bone screws (Magnezix®2.7 mm CS; Syntellix AG, Hanover, Germany).

By utilising its rapid corrosion reaction and controlling its degradation process through Zn and Mn alloying, purification and anodization, chemically active magnesium can be developed into a biodegradable biocompatible implant material with a specific biodegradation process and tolerable hydrogen evolution rate, which may replace current problematic biodegradable polymers in applications.

Biodegradable metals are breaking the current paradigm in biomaterial science to develop only corrosion resistant metals. In particular, metals which consist of trace elements existing in the human body are promising candidates for temporary implant materials. These implants would be temporarily needed to provide mechanical support during the healing process of the injured or pathological tissue. Magnesium and its alloys have been investigated recently by many authors as a suitable biodegradable biomaterial. In this investigative review we would like to summarize the latest achievements and comment on the selection and use, test methods and the approaches to develop and produce magnesium alloys that are intended to perform clinically with an appropriate host response.

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.

Conclusion: 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.

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.

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

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.

Einleitung: Ein neuartiges Implantatmaterial zur Herstellung von resorbierbaren Implantaten stellen Magnesiumlegierungen dar. Es bestehen nur wenige Erfahrungen zum Verhalten dieser Implantate im MRT. Die Darstellung des Degradationsvorganges im Menschen mittels MRT ist bisher nicht erfolgt.

Material und Methoden: Vier Patientinnen wurden nach Implantation einer absorbierbaren Magnesium (Mg)-Schraube nach distaler Metatarsale-I-Osteotomie mittels MRT nachuntersucht. Die Untersuchungen fanden nach 3, 6, 12 sowie 36 Monaten statt.

Ergebnisse: In vivo zeigten sich weniger Suszeptibilitätsartefakte bei Verwendung von Magnesium Implantaten vergleichend zu Standardimplantaten aus Stahl- oder Titanlegierungen. Die Knochenheilung verlief zeitgerecht. Der Degradationsprozess des Implantates konnte dokumentiert werden. Es zeigte sich ein begleitendes Knochenödem, dieses stand jedoch in keiner Korrelation zu den klinischen und subjektiven Ergebnissen.

Diskussion: In dieser ersten Studie zeigt sich die Degradation der Mg-Implantate, jedoch auch ein Knochenmarksödem. Weitere Studien und Vergleich mit einem Kollektiv mit Standardimplantaten sind notwendig, um eine abschließende Aussage treffen zu können.

Hintergrund: Die Verwendung eines resorbierbaren Implantates kann die Notwendigkeit einer Reoperation zur Metallentfernung nach Vorfußeingriffen vermeiden helfen. Magnesium-Legierungen stellen ein neuartiges Material zur Herstellung von biodegradierbaren Implantaten dar.

Material und Methoden: In einer prospektiven klinischen Studie wurden Patienten, die ein biodegradierbares Magnesium-Implantat an unserem Haus erhielten, prospektiv nachverfolgt. Im Studienzeitraum von August 2013 bis Februar 2015 wurden 22 Patienten mit distaler Metatarsale-1-Osteotomie bei milder bis mäßiger Hallux valgus-Deformität mit einer MAGNEZIX®-Schraube versorgt.

Ergebnisse: Eine Patientin erlitt eine traumatische Dislokation der Osteotomie, alle anderen zeigten eine sichere knöcherne Heilung nach 6 bis 12 Wochen. Bei einer Patientin trat eine prolongierte Schwellung auf. Die klinischen Ergebnisse waren vergleichbar mit publizierten Serien mit Stahl- oder Titanimplantaten.

Diskussion: Biodegradierbare Mg-Implantate stellen eine Alternative zur Osteosynthese bei distalen metatarsale Osteotomien dar. Aktuell existieren nur kurzbis mittelfristige Ergebnisse, so dass für eine endgültige Beurteilung längerfristige Beobachtungszeiträume und größere Patientenkollektive notwendig bleiben.

This is a case series of carpal fracture fixations and intercarpal fusions using the MAGNEZIX® absorbable metallic screw. The MAGNEZIX® screw is an absorbable metallic bone screw that is replaced with “bone-like” tissue on full absorption. The screw is made of a magnesium alloy and as such is able to be metabolised by the body. The screw is cannulated and comes in varying sizes. This implant has been used in Ireland for 18 months now but has been widely used in Europe. Six cases in total are presented using the 3.2 mm MAGNEZIX® screw + three scaphoid fixations (two acute and one revision case) and three inter-carpal fusions (one middle column fusion, one trapezio-trapezoid fusion and a third CMCJ fusion). One screw was used in the acute scaphoid fixations+ two screws were used for the revision fixation of scaphoid with bone grafting + two screws for the first two inter-carpal fusion cases and one screw of the third CMCJ fusion. All procedures were carried out by the author. Follow-up of between 6 months and 18 months is available for all patients. One patient has temporarily been lost to follow-up (an acute scaphoid fixation – partial healing at six weeks was noted on imaging). Of the remaining five cases, four were clinically united on follow-up and imaging showed progression of healing at six weeks and twelve weeks in the remainder. Gas formation and lucency is evident on all post-operative films and is recognised in the use of this implant. No systemic complications are reported. One failure of fixation occurred due to technical issues in the middle column fusion case. This case series presents favourable follow-up series of this “new” absorbable magnesium alloy screw with potential benefits that can be utilised in hand and wrist surgery. The screw shows further promising results in the presented cases other than the failure for technical issues. The screw has added benefits of not needing to be removed also and could show advantageous properties if the “bone-like tissue” produced on full absorption can add strength to fusion masses. Further longer term follow-up is required.

Biodegradable magnesium alloys are suitable osteosynthesis materials. Despite the alloy composition, surface modifications appear to have an influence on the degradation process and biocompatibility. The aim of this study was to investigate the impact of hydrogenation and fluoridation of the surface in a mandibular osteotomy model. Standard-sized plates and screws were implanted in an osteotomy at the mandibular angle in nine miniature pigs. The plates and screws were harvested together with the adjacent tissues at 8 weeks after surgery and were investigated by micro-computed tomography and histological analysis. The bone healing of the osteotomy was undisturbed, independent of the surface properties. The adjacent bone tissue showed new bone formation at the implant surface; however, formation of some lacunae could be observed. The corrosion was between 9.8% and 11.6% (fluoridated < hydrogenated < non-modified) in histological specimens, while radiologically neither the volume nor the density of the osteosynthesis material was reduced in any treatment group. The soft tissues exhibited full biocompatibility with every surface property. In summary, surface modification by hydrogenation and fluoridation did not significantly influence bone healing, biocompatibility, or corrosion kinetics of the magnesium osteosynthesis at the mandibular angle.

Introduction: Tibial spine avulsion fractures are mostly a paediatric injury which appropriate treatment is currently debated in literature. The choice between conservative and surgical treatment is based on the radiographic classification of Meyers-McKeever. The most diffused surgical techniques involve either internal fixation devices (screws) or bone tunnels fixation with resorbable sutures. Today, a third option is represented by resorbable magnesium screws which could combine the best features of the two classical systems. Objective of this study is to investigate the efficacy of these new devices in the surgical treatment of tibial spine avulsions.

Materials and Methods: Since 2014 we have seen seven patients with tibial eminence fracture. Patients underwent clinical and radiological examination (MRI, CT scan) before surgery. Only 3 patients that presented with a grade III or IV lesion were treated surgically with internal fixation with magnesium resorbable screws. In post-operative follow-up, functional recovery was evaluated at 1, 2, 4, 6 and 12 months, clinically and by X-ray. Lysholm and IKDC scores were submitted at 1, 2, 6 and 12 months. MRI was repeated at 6 and 12 months.

Results: All three surgical patients showed progressive clinical and functional improvement during the follow-up period. The first case showed a quicker overall recovery rate, which might be due to the lower grade of the lesion. Radiographs and MRI evaluation showed regular healing of the injury. The devices appeared completely resorbed at the 6 months follow-up and replaced by newly formed bone at the 12 months follow-up.

Conclusion: The treatment of tibial spine avulsion fractures with arthroscopic reduction and internal fixation (ARIF) technique by magnesium resorbable screws seems to result in an excellent functional recovery without complications related to fixation devices, which were completely resorbed after 6 months and replaced by newly formed bone after 12 months. This new method could be considered as an alternative option to classic techniques by non resorbable fixation devices or bone tunnel fixation. Further studies are needed in order to evaluate the efficacy of these new devices in a wider group of patients.

Aims
Biodegradable magnesium-based alloy implants represent a promising option in orthopedic surgery, as the clinical outcomes have been reported to be comparable to those of titanium implants and no surgical interventions are required for removal. To date, little is known about the results of the use of these implants in children and adolescents. Therefore, the aim of the present study was to analyze the safety and performance of these implants in children and adolescents.

Patients and Methods
Eighty-nine patients treated with magnesium-based implants for fracture stabilization, osteotomy and osteochondral refixation were analyzed; 38 were treated by osteosynthesis; 18, osteotomy; and 33, osteochondral refixation. The mean follow-up duration was 8.2 months (range, 1.5–30 months). Clinical and radiographical follow-up examinations were performed at 4–8 weeks and 3–6 months, respectively, to evaluate implant performance and osseous consolidation.

Results
Clinical outcomes were rated as good to very good in all patients. Radiolucent zones were apparent after surgery in all patients but were noted to decrease in size during the follow-up period. Revision surgery was necessary in 1 of 89 patients who had a highly unstable osteochondritis dissecans lesion of the knee. None of the magnesium-based implants required surgical removal.

Conclusion
Magnesium-based implants in children and adolescents results in good clinical outcomes when used for fracture stabilization, osteotomy and osteochondral defect refixation. Future studies are needed to further analyze the significance of the transient appearance and temporal development of radiolucent zones in the growing skeleton as well as the long-term performance of these implants.

Purpose: The use of titanium-based implants in mandibular condyle fractures can require implant removal because of screw penetration through the condylar surface. The use of biodegradable implants can avoid a second operation for implant removal and the associated possible complications. We investigated the clinical and radiologic outcomes of osteosynthesis of mandibular condyle fractures (MCFs) with biodegradable magnesium-based compression screws.

Materials and methods: We performed a retrospective observational study of 6 patients who had been treated at our department. We recorded the changes in jaw movements over time, occlusion, and possible complications at defined intervals of 1, 3, 6, and 12 months postoperatively. We also compared the preoperative computed tomography (CT) scans with the postoperative cone-beam CT (CBCT) scans at 6 and 12 months postoperatively to evaluate mandibular condyle healing and screw degradation.

Results: Of the 6 patients, 4 were men and 2 were women, with a mean age of 43.2 years (range, 30 to 66 years). All 6 patients had unilateral MCFs. All the patients showed well-restored function of the temporomandibular joint with significant improvement in mouth opening (46.17 ± 6.49 mm), right (10.67 ± 1.03 mm) and left (10.67 ± 1.97 mm) laterotrusion, and protrusion (10.17 ± 1.33 mm) distances to physiologic values. The CBCT scans showed the remodeling processes of the mandibular condyle and a few radiolucencies indicating the magnesium-based screws. Although penetration of 1 screw tip through the condylar surface had occurred, no implant removal was necessary owing to biodegradation of the implant.

Conclusions: The results of the present study have shown that biodegradable magnesium-based compression screws provide good clinical results and avoid implant removal.

Introduction
Transverse fractures of the olecranon are commonly fixed using tension-band wiring techniques. However the superficial nature of this area leads to high complication rates requiring removal of metalwork. The purpose of this retrospective study is to report and evaluate functional outcomes of polyethylene tension-band and bioabsorbable Magnesium alloy screw fixation of olecranon fractures.

Methods
A retrospective case-control study was undertaken. Demographics, injury type and post-operative details were collected. All patients were treated in the same institution by a single surgeon. Primary outcomes included radiographic healing and post-operative range of motion. Secondary outcome was post-operative complications.

Results
A total of five cases were identified. Mean age was 52.4. The control group was made up of six patients treated with a traditional tension band wire fixation. One patient in study group was lost to follow up. 80% of fractures in study group demonstrated anatomic post-operative radiographic union, compared with 83% of control group. All patients had range of motion above 100°, with full protonation and supination. One patient did have an extension lag of 15°.

Conclusion
Surgical repair of olecranon fractures is often complicated by the need for re-operation. This method provides both intramedullary fixation and conversion of distraction forces to compression forces with bioabsorbable materials, and aims to reduce the high re-operation rates commonly seen by avoiding the use of permanent indwelling metal hardware.

Background: For the treatment of hallux valgus commonly distal metatarsal osteotomies are performed. Persistent problems due to the hardware and the necessity of hardware removal has led to the development of absorbable implants. To overcome the limitations of formerly used materials for biodegradable implants, recently magnesium has been introduced as a novel implant material. This is the first study showing mid-term clinical and radiological (MRI) data after using magnesium implants for fixation of distal metatarsal osteotomies.

Material and methods: 26 patients with symptomatic hallux valgus were included in the study. They were randomly selected to be treated with a magnesium or standard titanium screw for fixation of a modified distal metatarsal osteotomy. The patients had a standardized clinical follow up and MRI investigation 3 years' post-surgery. The clinical tests included the range of motion of the MTP 1, the AOFAS, FAAM and SF-36 scores. Further on the pain was evaluated on a VAS.

Results: Eight patients of the magnesium group and 6 of the titanium group had a full clinical and MRI follow up 3 years postoperatively. One patient was lost to follow-up. All other patients could be interviewed, but denied full study participation. There was a significant improvement for all tested clinical scores (AOFAS, SF-36, FAAM, Pain-NRS) from pre-to postoperative investigation, but no statistically relevant difference between the groups. Magnesium implants showed significantly less artifacts in the MRI, no implant related cysts were found and the implant was under degradation three years postoperatively.

Conclusion: In this study, bioabsorbable magnesium implants showed comparable clinical results to titanium standard implants 3 years after distal modified metatarsal osteotomy and were more suitable for radiologic analysis.

Background: Displaced fractures of the humeral capitellum are commonly treated operatively and fixed by titanium screws (TSs) either directly or indirectly. In the case of direct transcartilaginous fixation, biodegradable screws with the ability to be countersunk can be favorable regarding implant impingement and cartilage destruction. Hence, the goal of this study was to biomechanically compare headless compression screws made from titanium with a biodegradable equivalent made from a magnesium alloy.

Methods: This biomechanical in vitro study was conducted on 13 pairs of fresh-frozen human cadaveric humeri, in which a standardized Bryan-Morrey type I fracture was fixed using 2 magnesium screws (MSs) or 2 TSs. First, construct stiffness was measured during 10 cycles of static loading between 10 and 50 N. Second, continuous loading was applied at 4 Hz between 10 and 50 N, increasing the maximum load every 10,000 cycles by 25 N until construct failure occurred. This was defined by fragment displacement >3 mm.

Results: Comparison of the 2 screw types showed no differences related to construct stiffness (0.50 ±  0.25 kN/mm in MS group and 0.47 ± 0.13 kN/mm in TS group, P = .701), failure cycle (43,944 ±  21,625 and 41,202 ±  16,457, respectively; P = .701), and load to failure (152 ±  53 N and 150 ±  42 N, respectively; P = .915).

Conclusion: Biomechanical comparison showed that simple capitellar fractures are equally stabilized by headless compression screws made from titanium or a biodegradable magnesium alloy. Therefore, in view of the advantages of biodegradable implants for transcartilaginous fracture stabilization, their clinical application should be considered and evaluated.

The reconstruction of the anterior cruciate ligament is, for the most part, currently performed with interference screws made of titanium or degradable polymers. The aim of this study was to investigate the use of biodegradable magnesiuminterference screws for such a procedure because of their known biocompatibility and reported osteoconductive effects. The left tibiae of each of 18 rabbitswere implanted with amagnesium-based (MgYREZralloy) screw, and another 18 with a titanium-based control. Each group was divided into observation periods of 4, 12 and 24 weeks. After sacrifice, μCT scans were acquired to assess the amount of the gas liberated and the degradation rate of the implant. Histological evaluations were performed to investigate the local tissue response adjacent to the implant and to assess the status of the attachment between the tendon and the bone tissue. The μCT scans showed that liberation of gas wasmost prominent 4weeks after implantation andwas significantly decreased by 24 weeks. All screws remained in situ and formed a sufficient connection with the tendon and sufficient osseous integration at 24 weeks. Histological evaluations showed neither inflammatory reactions nor necrosis of the tendon. The results of this pilot study in rabbits indicate that thismagnesium-based interference screw should be considered as an alternative to conventional implant materials.

MAGNEZIX^® CS (Syntellix AG, Hanover, Germany) is a bioabsorbable compression screw made of a magnesium alloy (MgYREZr). Currently there are only two clinical studies reporting on a limited number of elective patients who received this screw in a hallux valgus operation. We applied MAGNEZIX^® CS for fixation of distal fibular fracture in a trauma patient who had sustained a bimalleolar fracture type AO 44-B2.3. Clinical course was uneventful, fracture healing occurred within three months. Follow-up X-rays showed a radiolucent area around the implant for some months, yet this radiolucent area had disappeared in the 17-months follow-up X-ray.

Abstract

Orthopedic implants containing biodegradable magnesium have been used for fracture repair with considerable efficacy; however, the underlying mechanisms by which these implants improve fracture healing remain elusive. Here we show the formation of abundant new bone at peripheral cortical sites after intramedullary implantation of a pin containing ultrapure magnesium into the intact distal femur in rats. This response was accompanied by substantial increases of neuronal calcitonin gene-related polypeptide-α (CGRP) in both the peripheral cortex of the femur and the ipsilateral dorsal root ganglia (DRG). Surgical removal of the periosteum, capsaicin denervation of sensory nerves or knockdown in vivo of the CGRP-receptor-encoding genes Calcrl or Ramp1substantially reversed the magnesium-induced osteogenesis that we observed in this model. Overexpression of these genes, however, enhanced magnesium-induced osteogenesis. We further found that an elevation of extracellular magnesium induces magnesium transporter 1 (MAGT1)-dependent and transient receptor potential cation channel, subfamily M, member 7 (TRPM7)-dependent magnesium entry, as well as an increase in intracellular adenosine triphosphate (ATP) and the accumulation of terminal synaptic vesicles in isolated rat DRG neurons. In isolated rat periosteum-derived stem cells, CGRP induces CALCRL- and RAMP1-dependent activation of cAMP-responsive element binding protein 1 (CREB1) and SP7 (also known as osterix), and thus enhances osteogenic differentiation of these stem cells. Furthermore, we have developed an innovative, magnesium-containing intramedullary nail that facilitates femur fracture repair in rats with ovariectomy-induced osteoporosis. Taken together, these findings reveal a previously undefined role of magnesium in promoting CGRP-mediated osteogenic differentiation, which suggests the therapeutic potential of this ion in orthopedics.

Background: Several types of fixation materials may be used for the radial styloid fractures such as Kirschner wire fixation, screw fixation, volar plate fixation, and fragment-specific radial buttress plate fixation. However, each of these Fixation techniques has certain complications usually related to either the surgical dissection or the application of fixation and symptomatic permanent hardware. Implant removal secondary to irritation of prominent screw heads or bulky plates is not uncommon after radial styloid fracture fixation.

Case Description: Herein, two patients with an isolated radial styloid fracture who were treated with bioabsorbable magnesium (alloy: MgYREZr) screws are presented. In both patients, the fracture union was achieved without any complication and need for implant removal.

Literature Review: This is the first report on the use of magnesium screws for this indication.

Clinical Relevance: Magnesium bioabsorbable compression screw fixation may be an alternative solution that eliminates removal operations due to symptomatic Hardware in radial styloid fractures.

MAGNEZIX^® (Syntellix AG, Hanover, Germany) is a biodegradable magnesium-based alloy (MgYREZr) which is currently used to manufacture bioabsorbable compression screws. To date, there are very few studies reporting on a limited number of elective foot surgeries using this innovative implant. This case report describes the application of this screw for osteochondral fracture fixation at the humeral capitulum next to a loose radial head prosthesis, which was revised at the same time. The clinical course was uneventful. Degradation of the magnesium alloy did not interfere with fracture healing. Showing an excellent clinical result and free range-of-motion, the contour of the implant was still visible in a one-year follow-up.

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).

Material 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.

Biodegradable magnesium-based implants are currently being developed for use in orthopedic applications. The aim of this study was to investigate the acute, subacute, and chronic local effects on bone tissue as well as the systemic reactions to a magnesium-based (MgYREZr-alloy) screw containing rare earth elements. The upper part of the screw was implanted into the marrow cavity of the left femora of 15 adult rabbits (New Zealand White), and animals were euthanized 1 week, 12 weeks, and 52 weeks postoperatively. Blood samples were analyzed at set times, and radiographic examinations were performed to evaluate gas formation. There were no significant increased changes in blood values compared to normal levels. Histological examination revealed moderate bone formation with direct implant contact without a fibrous capsule. Histopathological evaluation of lung, liver, intestine, kidneys, pancreas, and spleen tissue samples showed no abnormalities. In summary, our data indicate that these magnesium-based screws containing rare earth elements have good biocompatibility and osteoconductivity without acute, subacute, or chronic toxicity.

Degradable magnesium alloys are promising biomaterials for orthopedic applications. The aim of this study was to evaluate the potential effects on both the synovial membrane (synovialis) and the synovial fluid (synovia) of the degradation products of a MgYREZr-pin implanted in the intercondylar femoral notch in a rabbit model. Thirty-six animals were randomized into two groups (MgYREZr or Ti6Al4V alloy) of 18 animals each. Each group was then divided into three subgroups with implantation periods of 1, 4, and 12 weeks, with six animals in each subgroup. The initial inflammatory reaction caused by the surgical trauma declined after 12 weeks of implantation, and elucidated a progressive recovery of the synovial membrane. Compared with control Ti6Al4V pins, there were no significant differences between the groups. However, after 12 weeks, recovery of the synovial membrane was more advanced in the titanium group, in which 92% showed no signs of synovitis, than in the magnesium group. A cytotoxicity test with L929 cells and human osteoblasts (HOB) was also conducted, according to EN ISO 10993-5/12, and no toxic leachable products were observed after 24 h of incubation. In conclusion, the MgYREZr alloy seems to be a suitable material for intra-articular degradable implants.

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.

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.

Background: It is still unknown whether bioabsorbable magnesium (Mg) screws provide an advantage over titanium screws in the treatment of medial malleolar (MM) fractures. The purpose of this retrospective study is to compare the clinical and radiological outcomes of MM fractures fixed with either bioabsorbable Mg screws or conventional titanium screws.

Materials and methods: A cohort of 48 patients with MM fractures who underwent compression screw fixation was retrospectively reviewed. Twenty-three patients (16 male, 7 female; mean age: 37.9 ± 17.7 years) were treated with bioabsorbable Mg screws, and 25 patients (14 male, 11 female; mean age: 45.0 ± 15.7 years) were treated with conventional titanium screw fixation. All patients were followed up for at least 1 year, with a mean time of 24.6 ± 10.5 months (12–53 months). The American Orthopedic Foot and Ankle Society (AOFAS) scale was used to evaluate the clinical results. The Kellgren–Lawrence (KL) osteoarthritis grading was used to evaluate posttraumatic osteoarthritis on final ankle radiographs. Fracture union, rate of implant removal, and complications were recorded. Comparative analysis of two independent groups was performed using the chi-squared test and the Mann–Whitney U-test.

Results: The two groups were comparable concerning demographic and clinical characteristics. Age (p = 0.146), sex (p = 0.252), side (p = 0.190), MM fracture type (p = 0.500), associated fractures (p = 0.470), and follow-up period (p = 0.903) were similar between the groups. At final follow-up examination, AOFAS score (p = 0.191) was similar between groups. Fracture union was achieved in all cases. Grade of posttraumatic osteoarthritis, according to KL, was equally distributed in both groups (p = 0.074). No deep infection or osteomyelitis was seen. Five patients in the titanium screw group underwent implant removal, due to pain in three of them and difficulty in wearing shoes in the other two (p = 0.031). Implant removal was performed after a mean of 14.2 ± 3.1 months (12–19 months).

Conclusions: Bioabsorbable Mg and titanium screws had similar therapeutic efficacy in MM fracture fixation regarding functional and radiological outcomes. However, the rate of implant removal was higher with titanium screws. Bioabsorbable Mg screws may be a favorable fixation option since secondary implant removal procedures can be prevented.

Level of evidence: Level IV, Retrospective case series.

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 invitro 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.

Background: Biodegradable implants reduce the likelihood of further surgery for hardware removal and reduce the risks of associated infection and allergy. The purpose of this study is to evaluate the clinical efficacy and determine the comparability of biodegradable magnesium alloy MgYREZr (MAGNEZIX® CS) compression screw fixation compared with standard titanium screw fixation in the surgical treatment of hallux valgus deformity.

Methods: Eleven patients undergoing corrective surgery for hallux valgus utilising biodegradable magnesium screws and a control group of 25 patients undergoing corrective hallux valgus surgery with standard titanium screws were reviewed at a median of 19months (range 12–30months). PROM scores (Manchester-Oxford Foot Questionnaire (MOXFQ), Foot and Ankle Outcomes Instrument (FAOI) and the EQ-5D-3L) were recorded preoperatively and at latest follow-up.

Results: The results between the two groups were broadly similar, with the Magnesium and Titanium patients showing similar patterns in the various domains in the MOXFQ, the FAOI and the EQ-5D-3L. Most patients reported a near full shoe comfort score, and EQ-5D-3L scores were significantly improved in both patient groups (with most patients reporting a full score). Foot pain and foot function improved irrespective of the scoring systems and patients in both groups demonstrated significantly improved scores following the surgery (p <0.05). Notably, there were no significant differences when comparing the post-operative scores between the groups for any individual scoring parameter. No impairment to quality of life was recorded. There were no intra or post-operative complications. There were no problems encountered through the use of the bioabsorbable screws.

Conclusion: Biodegradable magnesium-based compression screws appeared to be safe in this study and are an effective fixation device in the treatment of hallux valgus deformity with clinical outcomes similar to standard titanium screw fixation.

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.

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.

Zielsetzung: Biodegradierbare Implantate aus Magnesiumverbindungen gehören zu den aktuellsten Entwicklungen in der muskuloskelettalen Chirurgie. Diese Studie untersucht das Bildverhalten von Magnesiumimplantaten in verschiedenen bildgebenden Modalitäten im Vergleich zu konventionellen Titanimplantaten.

Material und Methodik: Eine CE-zertifizierte Magnesium Herbert Schraube (MAGNEZIX^®) und eine Titanschraube mit den gleichen Dimensionen (3,2 × 20 mm) wurden in den folgenden Modalitäten untersucht: Konventionelle Radiografie (CR), Multidetektor Computertomografie (MDCT), hochauflösende Flachdetektor Computertomografie (FPCT) und Magnetresonanztomografie (MRT). Die Schrauben wurden sowohl in vitro als auch nach Implantation in eine frische Hühnertibia untersucht. Die Auswertung der Bilddaten erfolgte quantitativ bezüglich Bildqualität sowie Ausmaß und Intensität der Artefakte.

Ergebnisse: In allen bildgebenden Modalitäten hatten die Artefakte der Magnesiumschraube ein kleineres Ausmaß und waren weniger beeinträchtigend im Vergleich zur Titanschraube (Mittelwert der Differenz der Artefaktgröße im CR: 0,7 mm, MDCT: 6,2 mm, FPCT: 5,9 mm und MRT: 4,73 mm; p < 0,05). In der multiplanaren Reformation und 3D Rekonstruktion der MDCT und FPCT war die Magnesiumschraube der Titanschraube ebenfalls überlegen. Die Metall-Knochen Grenze konnte deutlich besser unterschieden werden.

Schlussfolgerungen: Magnesiumimplantate generieren signifikant weniger Artefakte in den gängigen bildgebenden Verfahren im Vergleich zu konventionellen Titanimplantaten und sind daher gut für post-operative Kontrollen geeignet.

The goal of this review is to bring to the attention of the readership of Magnesium Research another facet of the importance of magnesium, i.e. magnesium-based biomaterials. A concise history of biomaterials and magnesium are thus presented. In addition, historical and current, clinical magnesium-based applications are presented.

Magnesium and magnesium-based alloys in biomaterial applications have shifted again into the focus of the biomedical industry. Thanks to the first CE mark approvals of magnesium-based implants interest will increase further, as the hurdles for approval by e.g. the FDA have been lowered. One important aspect is the understanding/improvement of the production processes of the materials, and their quality. The other, even more important aspect is a deeper understanding of the underlying biological cell and tissue mechanisms in the targeted tissues, which is a prerequisite for facilitating future regulatory applications. Therefore, it is of the utmost importance to establish the correlations between the biological, biochemical, mechanical and microstructural properties of magnesium-based implants. This demands a highly interdisciplinary approach, requiring specialist input from each discipline.

Background and aim: Metallic screws are commonly used to fix tibial tubercle osteotomies (TTO). However, hardware removal late after osteotomy union is one of the most common causes of reoperation following TTOs. The use of bioabsorbable screws may eliminate secondary surgeries, but there is no study on their use in this indication. The purpose of this retrospective study was to evaluate the safety and efficacy of bioabsorbable magnesium (Alloy: MgYREZr) screws in tibial tubercle osteotomy (TTO) fixation.

Methods: Ten patients with objective patellar instability who underwent distal realignment procedure using Fulkerson TTO were retrospectively reviewed. The osteotomy was secured with two parallel 4.8 mm magnesium screws in all patients. Kujala score and Lysholm knee score were used to assess the functional outcomes before and after the operation. Union of the osteotomy, displacement, and other imaging findings were evaluated with serial knee radiographs during the follow-up.

Results: There were five male and five female patients with a mean age of 23.4±9.2 years (range, 15-45). The mean follow-up duration was 11.5±3.2 months (range,6-17 months). The osteotomy united in all cases at an average of 3 months. No infection or wound healing problems were seen. A significant increase in Kujala (p:.005) and Lysholm knee scores (p:.005) were recorded in all patients.

Conclusion: The findings support that bioabsorbable magnesium screws can be safely used as an alternative fixation technique in TTO. Furthermore, it provides the advantage to eliminate the need for implant removal.

Fragestellung: Derzeit werden zur operativen Fixierung des rupturierten vorderen Kreuzbandes Interferenzschrauben aus Titan oder bioresorbierbaren Polymeren eingesetzt. Permanente Implantate aus Stahl oder Titan bedingen in der Regel eine zweite Operation zur Entfernung des Osteosynthesematerials. Daher werden hier vorrangig resorbierbare Implantate eingesetzt. Die Nachteile bei bioresorbierbaren Polymeren sind häufig Fremdkörperreaktionen und Entzündungen der Synovialmembran, welche den Erfolg der Operation erheblich verringern. Magnesiumlegierungen sind eine vielversprechende Alternative, da diese einerseits resorbierbar sind und als biokompatibel gelten und ihnen außerdem eine osteokonduktive Wirkung zugeschrieben wird.

Ziel dieser Studie war es, die Auswirkungen der Korrosionsprodukte der eingesetzten Magnesiumlegierung (MAGNEZIX®, Syntellix AG) auf die Synovia und die Synovialmembran des Kniegelenks zu untersuchen. Aufbauend auf den Ergebnissen dieses Versuches wird in einer Folgestudie die Testung mit einer Interferenzschraube erfolgen.

Methodik: Als Versuchstiere dienten 36 weibliche Kaninchen der Rasse New Zealand White Rabbit. Die Tiere wurden in 3 Gruppen mit unterschiedlichen Implantationszeiten (1, 4, 12 Wochen) unterteilt, mit jeweils 12 Tieren in jeder Gruppe. Bei jedem Tier wurde in den linken Femur interkondylär ein Pin implantiert. 6 Tiere jeder Gruppe bekamen einen Magnesiumpin implantiert und die anderen 6 Tiere einen Titanpin als Kontrollgruppe. Jeweils prä- und postoperativ wurden Röntgenaufnahmen angefertigt und Blutproben entnommen. Am Ende der Versuchsdauer wurden die Tiere euthanasiert und beide Kniegelenke punktiert. Außerdem wurden Gewebeproben von der Synovialmembran des operierten und des kontralateralen Kniegelenks entnommen und histopathologisch untersucht. Zur Beurteilung der Synovia-Punktate wurde ein semiquantitativer Score angewandt. Die Proben der Synovialmembran wurden ebenfalls mittels semiquantitativem Synovialitis-Score nach Krenn ausgewertet.

Ergebnisse und Schlussfolgerung: Zu keinem Zeitpunkt wurde röntgenologisch sowie klinisch eine Gasentwicklung beobachtet. Die Blutwerte von Kreatinin, Harnstoff, AST und ALT lagen im Referenzbereich. Sowohl in der Magnesiumgruppe als auch in der Titangruppe traten histopathologisch vergleichbare Veränderungen der Synovialmembran auf, welche sich in einer geringgradigen Verbreiterung der synovialen Deckzellschicht manifestierten.

Histopathologie, Blutanalyse, klinische und röntgenologische Untersuchungen zeigten keine pathologischen Veränderungen, weder in der Kontrollgruppe noch in der Magnesiumgruppe. Die zu Beginn vorliegende geringgradige Synovialitis trat bei beiden Gruppen in gleichem Maße auf und ist auf den traumatischen Eingriff zurückzuführen. Die vorliegenden Ergebnisse zeigen eine gute Biokompatibilität und Verträglichkeit der eingesetzten Magnesiumlegierung in Bezug auf die Synovialmembran.

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.

Magnesium-based interference screws may be an alternative in anterior/posterior cruciate ligament reconstruction. The well-known osteoconductive effects of biodegradable magnesium alloys may be useful. It was the purpose of this study to evaluate the biomechanical properties of a magnesium based interference screw and compare it to a standard implant. A MgYREZr-alloy interference screw and a standard implant (Milagro®; De Puy Mitek, Raynham, MA, USA) were used for graft fixation. Specimens were placed into a tensile loading fixation of a servohydraulic testing machine. Biomechanical analysis included pretensioning of the constructs at 20 N for 1 min following cyclic pretensioning of 20 cycles between 20 and 60 N. Biomechanical elongation was evaluated with cyclic loading of 1000 cycles between 50 and 200 N at 0.5 Hz. Maximum load to failure was 511.3±66.5 N for the Milagro® screw and 529.0±63.3 N for magnesium-based screw (ns, P=0.57). Elongations after preload, during cyclical loading and during failure load were not different between the groups (ns, P>0.05). Stiffness was 121.1±13.8 N/mm for the magnesium-based screw and 144.1±18.4 for the Milagro® screw (ns, P=0.32). MgYREZr alloy interference screws show comparable results in biomechanical testing to standard implants and may be an alternative for anterior cruciate reconstruction in the future.

Objectives: This study aims to evaluate the mid-term functional and radiological outcomes of magnesium-based screws in the treatment of scaphoid fractures.

Patients and methods: Between February 2015 and February 2018, a total of 21 patients (18 males, 3 females; mean age: 28.5±5.8 years; range, 19 to 39 years) with acute scaphoid waist fractures who underwent fracture fixation with biologically degradable magnesium-based compression screws were retrospectively analyzed. Fractures were classified according to the Herbert and Fisher classification. The absence of pain on palpation and painless active range of motion were accepted as the signs of union.

Results: The mean follow-up was 43.3±5.3 (range, 36 to 52) months. According to the Herbert and Fisher classification, nine patients had type B1 and 12 patients had type B2 scaphoid fractures. Union was achieved in all cases. The mean time to union was 11.2±1.5 (range, 9 to 14) weeks. The mean grip strength, flexion, and extension were 43.57°, 73.57°, and 76.43°, respectively. The grip strength, pinch strength, and range of motion of the operated side were evaluated at the final follow-up visit and compared with the contralateral side (control group). No complication occurred. Any screw was not removed.

Conclusions: Magnesium-based compression screws can be safely used for acute scaphoid fractures considering their favorable functional and radiological results.

Magnesium (Mg) bioabsorbable screws are new biomaterials used in fracture fixation. In the current literature, there is only one case report on the use of magnesium bio-absorbable screws in ankle fractures. Within the present study, a 19-year-old female who sustained an isolated lateral malleolar fracture was treated with open reduction and intramedullary Mg screw fixation and then followed up for two years. Fracture union was achieved without any complication such as failure of fixation, loss of reduction, infection, or any other adverse reaction. Mg bioabsorbable screws are an alternative method of fracture fixation as compared to conventional metallic implants since they eliminate the need for implant removal.

The treatment of comminuted distal humeral fractures with free osteochondral fragments is challenging. Osteochondral fragments should be retained whenever possible and secured with implants buried beneath the articular surface to obtain a uniform articular surface. Headless compression screws and K wires are commonly used for this purpose. However, certain complications have been reported with these fixation implants in case of the non-union and osteolysis of the fragments such as migration and cartilage damage. Fixation of osteochondral fractures in distal humeral fractures using bioabsorbable implants has been rarely reported in the current literature. Herein, a patient who sustained a comminuted distal humeral fracture with multi-fragmentary osteochondral fragments is presented, and treatment with magnesium bioabsorbable compression screws is discussed.

Currently, most of the fracture fixation materials used in orthopedic and trauma surgery are made of non-absorbable metallic implants such as titanium or steel. These implants often need to be removed due to residual pain, irritation or inflammatory reactions. Obviously, a second operation for implant removal has several disadvantages since it is associated with potential complications such as re-fracture, infection, nerve and vascular injuries. Additionally, it bears the risk of anesthesia and creates a significant burden for the health care resources. The idea to use magnesium as basis for degradable biomaterials in medicine exists for more than hundred years. Recently developed bioabsorbable magnesium-based implants are approved and available for patients in orthopedic surgery since 2013. The aim in the development of these innovative implants was an appropriate mechanical strength, good biocompatibility and complete absorption. Magnesium seems to be very beneficial for bioabsorbable orthopedic implants: firstly, it has a remarkable strength and the material is physiologically metabolized. Secondly, the Young’s modulus (“elasticity”) is close to cortical bone. Moreover, the material and its degradation products are non-toxic, and even induce new bone formation and most probably provides resistance to infection. During the first clinical investigations more than hundred years ago surgeons were often faced with challenges related to the magnesium-implants, e. g. different degradation behavior and mechanical properties. With the availability of a new material generation based on the MAGNEZIX®-technology many of the mentioned challenges are solved. 

In current clinical practice implants used in orthopedic surgery normally consist of titanium and its alloys or stainless steel, which are non-degradable materials. Degradable or potentially degradable implants include various ceramics, polymers and metals, such as iron, zinc and magnesium (1). Magnesium-based implants manufactured from a magnesium alloy based on MgYREZr were CE-approved in 2013 for the first time and are used in clinical practice worldwide since then (2). This innovative type of implant has been used in more than 25,000 trauma and orthopedic patients so far.