12C-1 High Resolution Acoustic Microscopy: A New Method to Investigate Remodeling Process of Trabecular Bone

In the current study, a 200 MHz scanning acoustic microscope (3.75 mum nominal spatial resolution) has been used to document changes in trabecular bone material properties related to a model of adaptive remodeling. Thirty cylindrical specimens of trabecular bone were extracted from one bovine sternum and one ulna metaphysis. Samples from each bone site (n=15), were separated in 3 groups of 5 samples each. Specimens of C (control) group were immediately fixed after extraction and embedded in methylmetacrylate, NL (no loaded) and L (loaded) groups were maintained viable In a controlled perfusion culture-loading chamber over three weeks. Specimens of L groups underwent a cyclic compressive strain mimicking human jump, whereas NL samples were left free of loading. After the experiment, L and NL samples were fixed and embedded in methylmetacrylate, then all samples were explored with SAM. Z spatial distribution was calculated over the surface of a single trabeculae. Z mean value was estimated for each sample then, averaged over samples of each group. In controls, Z was significantly higher in ulna than in sternum. The sternum appeared to respond more significantly to mechanical loading than ulna and displayed a significant 30% increase in Z for L group when compared to C group and a 13 % increase when compared to NL group. In conclusion, our results suggest that 400 MHz SAM is relevant to map local changes in bone intrinsic material properties resulting from (i) probable local differences in tissue properties exhibited naturally between weight bearing (ulna) and no bearing (sternum) bones, (ii) heterogeneous adaptive remodeling stimulated by cyclic loading.