Increase of Compact Bone Thickness in Rat Tibia after Implanting MgO into the Bone Marrow Cavity

The effect of implanting MgO paste into the bone marrow of rat tibia, was studied by light microscopy, time of flight-secondary ion mass spectrometry (ToF-SIMS), and environmental scanning electron microscopy (ESEM), and energy dispersive X-ray (EDX) analysis. After three weeks of implantation, the thickness of compact bone increased by 25% compared to sham-operated controls, while no effect was seen on the trabecular bone. In order to further elucidate the mechanism of the Mg-induced increase in bone mass, EDX and ToF-SIMS analysis of the bone samples was made at two weeks. At this time-point, no detectable difference in the thickness of the compact bone in Mg-treated and non-treated animals was observed. The Mg-content of the bone marrow and bone tissue of the Mg-exposed animals did not differ from that of sham-operated controls, implying that there are no traces of the implanted MgO when the mass of compact bone increases, between two and three weeks after surgery. The ratio of Mg/Ca content was higher in the bone of Mg-treated animals, indicating an altered structure of the bone mineral, which was confirmed by the ToF-SIMS analysis, showing increased levels of MgCO3, phosphate ions and CaF in the bone of MgO-exposed animals. Possible cellular activities behind the effect of MgO on compact bone thickness are discussed.