Research on the Biocompatibility of the New Magnesium Alloy LANd442-An In Vivo Study in the Rabbit Tibia over 26 Weeks

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 mu-CT techniques. Following euthanasia, histological, fluorescent microscopy and ex vivo mu-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 mu-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 mm(3) . slice(-1). By means of fluorochrome sequential marking, the determined MARs lie between day 93 and 120 at 3.58 mu m . d(-1) and between day 120 and 179 at 2.25 mu m . 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.