Comparison of the resorbable magnesium . alloys LAE442 und MgCa0.8 concerning their mechanical properties, their progress of degradation and the bone-implant-contact after 12 months implantation duration in a rabbit model

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 mu-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) +/- 1.03). In contrast LAE442 implants degraded very regularly (4.7 mm(2) +/- 0.07). Weight and volume measurements revealed a volume loss of 64.13 % +/- 15.92 in the MgCa0.8 group and a lesser volume loss of 45.63 % +/- 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 % +/- 2.88 for LAE442 implants and of 85.6 % for MgCa0.8 implants, each compared to the initial condition.