The aim of this study was to investigate the differences in the in vivo degradation behaviour of magnesium implants with various grain sizes and damaged surfaces. For this purpose, three different LAE442 magnesium implants were produced: cast, single and double extruded implants, in order to obtain different grain sizes. Furthermore, defects were positioned on the surfaces of some of the single extruded implants. The initial stability was determined. Four pins of each implant material were implanted into rabbits' tibiae and regularly clinically, radiologically and m-computed tomographically investigated over a period of 27 weeks. Following explantation, investigations were carried out using stereo and scanning electron microscopy including energy-dispersive X-ray analyses. Weight and strength changes were measured. The double extruded implants possessing the finest grains exhibited the highest initial stability (179.18 N). These implants demonstrated the lowest in vivo corrosion rates (0.0134 mm/year) and the least radiologically visible changes. The highest corrosion rate was computed for the implants possessing damaged surfaces. Radiologically discernible bone changes occurred at almost the same time as implant changes for all groups. Based on these results, the aim should be to produce fine-grained magnesium-based alloys for resorbable implants and to avoid any surface damage.

In former studies the magnesium alloy LAE442 showed promising in vivo degradation behavior and biocompatibility. However, reproducibility might be enhanced by replacement of the rare earth composition metal “E” by only a single rare earth element. Therefore, it was the aim of this study to examine whether the substitution of “E” by neodymium (“Nd”) had an influence on the in vivo degradation rate. LANd442 implants were inserted into rabbit tibiae and rabbits were euthanized after 4, 8, 13 and 26 weeks postoperatively. In vivo µCT was performed to evaluate the in vivo implant degradation behaviour by calculation of implant volume, density true 3-D thickness and corrosion rates. Additionally, weight loss, type of corrosion and mechanical stability were appraised by SEM/EDS-analysis and three-point bending tests. Implant volume, density and true 3-D thickness decreased over time, whereas the variance of the maximum diameters within an implant as well as the corrosion rate and weight loss increased. SEM examination revealed mainly pitting corrosion after 26 weeks. The maximum bending forces decreased over time. In comparison to LAE442, the new alloy showed a slower, but more uneven degradation behavior and less mechanical stability. To summarize, LANd442 appeared suitable for low weight bearing bones but is inferior to LAE442 regarding its degradation morphology and strength.

Research on magnesium based degradable implant materials has finally obtained success in orthopaedics. Based on the previous good results with LAE442 magnesium alloy, the new LANd442 alloy was developed. In doing this, the single element neodymium replaces the rare earth compound. The primary objective of this study is to assess the biocompatibility of the new alloy in the rabbit model. During a 26 week period, the animals were investigated using clinical, radiological and in vivo µ‐CT techniques. Following euthanasia, histological, fluorescent microscopy and ex vivo µ‐CT investigations were done. Clinically, additional bone formed at the implant's location and accumulation of small amounts of subcutaneous gas can be observed. Radiological investigations show brightening of the medullary cavity and thickening in the region of the diaphysis. The µ‐computed tomographies reveal a reduction in the bone density from 1226.31 to 1192.95 mg HA/ccm together with increases in bone porosity from 4.55 to 6.6% and bone volume from 1.51 to 2.06 mm3 · slice−1. By means of fluorochrome sequential marking, the determined MARs lie between day 93 and 120 at 3.58 µm · d−1 and between day 120 and 179 at 2.25 µm · d−1. Elevated remodelling processes in the bone are histologically confirmed due to the periosteal and endosteal growths and an increased appearance of osteoclasts. Owing to the established considerable bone remodelling processes following intramedullary implantation, LANd442 appears to be a less suitable degradable implant material for cortical bone applications.

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This study shows that the recurrence of gastric dilatation volvulus after ventral midline gastropexy is low and adhesion of the stomach to the abdominal wall is persistent in almost all dogs that were re-examined. The gastropexy site did not appear to interfere with subsequent coeliotomy.