There are no efficient treatment options for osteoarthritis (OA) that delay further progression. Besides osteoinduction, there is growing evidence of also anti-inflammatory, angiogenetic and neuroprotective effects of biodegradable magnesium-based biomaterials. Their use for the treatment of cartilage lesions in contrast is not well-evaluated yet.

Mg-cylinders were analysed in an in vitro and in vivo OA model. In vitro, SCP-1 stem cell line was analysed under inflammatory conditions and Mg-impact. In vivo, small Mg- and WE43 alloy-cylinders (1mm × 0,5mm) were implanted into the subchondral bone of the knee joint of 24 NZW rabbits after establishment of OA. As control, another 12 rabbits received only drill-holes. µCT-scan were performed and assessed for changes in bone volume and density. After euthanasia, cartilage was evaluated macroscopically and histologically after Safranin-O-staining. Furthermore, staining with CD271 directed antibody was performed to assess neuro-reactivity.

In vitro, an increased gene expression of extracellular matrix proteins as collagen II or aggrecan even under inflammatory conditions was observed under Mg-impact. In vivo, µCT evaluation revealed twice-elevated values for bone volume in femoral condyles with Mg-cylinders compared to controls while density remained unchanged. Cartilage showed no significant differences between the groups. Mg- and WE-samples showed significantly lower levels of CD271+ cells in the cartilage and bone of the operated joints than in non-operated joints, which was not the case in the Drilling-group. Furthermore, bone in operated knees of Drilling-group showed a strong trend to an increase in CD271+ cells compared to both Cylinder-groups. Counting of CD271+ vessels revealed that this difference was attributable to a higher amount of these vessels.

The in vitro results indicate a potential cartilage regenerative activity of the degradable Mg-based material. While so far there was no positive effect on the cartilage itself in vivo, implantation of Mg-cylinders seemed to reduce pain-mediating vessels.

Acknowledgements: This work is funded by the German Research Foundation (DFG, project number 404534760). We thank Björn Wiese for production of the cylinders.

According to the latest report from the German Arthroplasty Registry, aseptic loosening is the primary cause of implant failure following primary hip arthroplasty. Osteolysis of the proximal femur due to the stress-shielding of the bone by the implant causes loss of fixation of the proximal femoral stem, while the distal stem remains fixed.

Removing a fixed stem is a challenging process. Current removal methods rely on manual tools such as chisels, burrs, osteotomes, drills and mills, which pose the risk of bone fracture and cortical perforation. Others such as ultrasound and laser, generate temperatures that could cause thermal injury to the surrounding tissues and bone. It is crucial to develop techniques that preserve the host bone, as its quality after implant removal affects the outcome of a revision surgery.

A gentler removal method based on the transcutaneous heating of the implant by induction is proposed. By reaching the glass transition temperature (T_G) of the periprosthetic cement, the cement is expected to soften, enabling the implant to be gently pulled out. The in-vivo environment comprises body fluids and elevated temperatures, which deteriorate the inherent mechanical properties of bone cement, including its T_G. We aimed to investigate the effect of fluid absorption on the T_G (ASTM E2716-09) and Vicat softening temperature (VST) (ISO 306) of Palacos R cement (Heraeus Medical GmbH) when dry and after storage in Ringer's solution for up to 8 weeks.

Samples stored in Ringer's solution exhibited lower T_G and VST than those stored in air. After 8 weeks, the T_G decreased from 95.2°C to 81.5°C in the Ringer's group, while the VST decreased from 104.4°C to 91.9°C. These findings will be useful in the ultimate goal of this project which is to design an induction-based system for implant removal.

Acknowledgements: Funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – SFB/TRR-298-SIIRI – Project-ID 426335750

There is no optimal therapy to stop or cure chondral degeneration in osteoarthritis (OA). Beside cartilage, subchondral bone is involved. The often sclerotic bone is mechanically less solid which in turn influences negatively chondral quality. Microfracturing as therapeutic technique aims to enhance bone quality but is applied only in smaller cartilage lesions. The osteoproliferative properties of Magnesium (Mg) have been shown repeatedly^1-3. The present study examined the influence of micro-scaled Mg cylinders compared to sole drilling in an OA model.

Ten New Zealand White rabbits underwent anterior crucial ligament transection. During 12 weeks after surgery, the animals developed OA as previously described⁴. In a second surgery, half of the animals received 20 drill holes (ø 0.5mm) and the other half received 20 drill holes, which were additionally filled with one Mg cylinder each. Extracapsular plication was performed in all animals. During the follow-up of 8 weeks three µ-computed tomographic (µCT) scans were performed: immediately after surgery and after four and eight weeks. Changes of bone volume, trabecular thickness and bone density were calculated and compared.

µCT evaluation showed an increase in bone volume and trabecular thickness in both groups. This increase was significantly higher in rabbits which received Mg cylinders showing thrice as high values for both parameters (bone volume: Mg group +44.5%, drilling group +15.1%, p≤0.025; trabecular thickness: Mg group +53.2%, drilling group +16.9%, p≤0.025). Also bone density increased in both groups, but on a distinctly lower level and with no significant difference.

Although profound higher bone volume was found after implantation of Mg cylinders, µCT showed similar levels of bone density indicating adequate bone quality in this OA model. Macroscopic and histological evaluation of cartilage condition have to reveal possible impact on OA progression. Additionally, current examination implement different alloys and influence on lameness.

Introduction

The treatment osteonecrosis of the femoral head remains uncertain. Core decompression is the standard technique for the early stages (ARCO I and II). A new alternative is core decompression combined with the insertion of an osteonecrosis rod. This implant is supposed to reduce the intraosseous pressure and to give additional structural support. The aim of this study was to evaluate the clinical and radiological outcome via magnetic resonance imaging (MRI) of this new technique.

The ability to predict load-bearing capacity during the consolidation phase in distraction osteogenesis by non-invasive means would represent a significant advance in the management of patients undergoing such treatment. Measurements of stiffness have been suggested as a promising tool for this purpose. Although the multidimensional characteristics of bone loading in compression, bending and torsion are apparent, most previous experiments have analysed only the relationship between maximum load-bearing capacity and a single type of stiffness. We have studied how compressive, bending and torsional stiffness are related to the torsional load-bearing capacity of healing callus using a common set of samples of bone regenerate from 26 sheep treated by tibial distraction osteogenesis.

Our findings showed that measurements of torsional, bending and compressive stiffness were all suitable as predictors of the load-bearing capacity of healing callus. Measurements of torsional stiffness performed slightly better than those of compressive and bending stiffness.