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Extruded implants (2.5 mm x 25 mm) of the resorbable magnesium alloys MgCa0.8 and LAE442 were implanted into the marrow cavity of both tibiae of 10 New Zealand White rabbits. The animals were in a good general condition over the whole experimental period and showed no signs of lameness. Radiographic examinations could not reveal any generation of gas. The endosteal based bone adhesion to the implant surface was evaluated by l-computed tomography of the right tibia. 53 % of the evaluated slices of the alloy LAE442 showed an adherence of trabecular bone. MgCa0.8 showed trabeculae (38 %), bone clasps (13 %) and -rings (9 %) that covered the whole implant surface. Beside the weight and volume loss, the cross sectional area of the implants were measured to investigate the progress of degradation. Implants of the MgCa0.8 group showed an average loss of more than half of the original implant area (2.18 mm 2 AE 1.03). In contrast LAE442 implants degraded very regularly (4.7 mm 2 AE 0.07). Weight and volume measurements revealed a volume loss of 64.13 % AE 15.92 in the MgCa0.8 group and a lesser volume loss of 45.63 % AE 0.89 in the LAE442. The mechanical properties were tested by a three point bending test. It showed a decrease of the maximal force of 71.2 % AE 2.88 for LAE442 implants and of 85.6 % for MgCa0.8 implants, each compared to the initial condition.Key words: magnesium, long term study, resorbable implants, three point bending, rabbit Stranggepresste Implantate (2,5 mm x 25 mm) der resorbierbaren Magnesiumlegierungen MgCa0,8 und LAE442 wurden in die Markhöhlen beider Tibiae von 10 New Zealand White Kaninchen implantiert. Die Tiere wiesen über den gesamten Versuchszeitraum ein gutes Allgemeinbefinden auf und zeigten keine Lahmheiten. Röntgenologisch konnte keine Gasbildung festgestellt werden. Mit Hilfe von l-computertomographischen Untersuchungen der rechten Tibiae wurde das Knochenanwachsverhalten vom Endost ausgehend an die Implantatoberfläche beurteilt. 53 % der ausgewerteten Schnittbilder der Legierung LAE442 zeigten ein Anhaften trabekulären Knochens an die Implantatoberfläche. Bei MgCa0,8 wurden Trabekel (38 %), Knochenspangen (13 %) und -ringe (9 %), die der gesamten Oberfläche des Implantates auflagen, detektiert. Zur Ermittlung des Degradationsgrades wurde neben der Ermittlung des Gewichts-und Volumenverlustes die Querschnittsfläche der Implantate vermessen. Die Implantate der MgCa0,8-Gruppe hatten im Mittel mehr als die Hälfte der ursprünglichen Implantatfläche verloren (2,18 mm 2 AE 1,03). Die LAE442-Implantate waren hingegen sehr regelmäßig degradiert (4,7 mm 2 AE 0,07). Die Gewichtsmessung und Volumenbestimmung ergab innerhalb der MgCa0,8-Gruppen einen Volumenverlust von 64,13 % AE 15,92. Die Gruppe LAE442 zeigte einen geringeren mittleren Volumenverlust von 45,63 % AE 0,89. Die mechanischen Eigenschaften wurden im Dreipunktbiegeversuch geprüft und ergaben bei LAE442 einen Abfall der maximalen Kraft von 71,2 % AE 2,88, bei MgCa0,8 von 85,6 % im Vergleich zum Initialzustand.

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MgCa0.8 cylinders (2.5 x 25 mm(2)) were coated with a magnesium-fluoride layer and implanted in the marrow cavities of both tibiae of 10 New Zealand White rabbits. The implantation duration was 3 and 6 months. The implants were clinically well tolerated. Micro-computed tomography revealed a new bone formation at the edges of the implants as well as an endosteal and periosteal remodeling. Using EDX-analysis, a calcium and phosphorus rich degradation layer could be found on the implant surface. It was covered by an incomplete layer containing fluoride. The analysis by weight before implantation and after 3 and 6 months, respectively, showed a slight decrease in volume in comparison to uncoated implants. When compared with uncoated implants, the mechanical properties of the coated implants exhibited a reduction in strength after 3 months. After 6 months, the strength of the coated implants was higher than that of uncoated cylinders.

In magnesium alloys, the components used modify the alloy properties. For magnesium implants in contact with bone, rare earths alloys are commonly examined. These were shown to have a higher corrosion resistance than other alloys and a high mechanical strength, but their exact composition is hard to predict. Therefore a reduction of their content could be favorable. The alloys ZEK100 and AX30 have a reduced content or contain no rare earths at all. The aim of the study was to investigate their in vivo degradation and to assess the suitability of the in vivo µCT for the examination of their corrosion. Implants were inserted in rabbit tibiae. Clinical examinations, X-rays and in vivo µCT scans were done regularly. Afterwards implants were analyzed with REM, electron dispersive X-ray (EDX), weighing and mechanical testing. The in vivo µCT is of great advantage, because it allows a quantification of the corrosion rate and qualitative 3D assessment of the corrosion morphology. The location of the implant has a remarkable effect on the corrosion rate. Due to its mechanical characteristics and its corrosion behavior, ZEK100 was judged to be suitable, while AX30, which displays favorable degradation behavior, has too little mechanical strength for applications in weight bearing bones.