[The action of loads on bone tissue].

This paper analyses the effect of mechanical loading on bone remodelling under both physiological and pathological conditions. The sensitivity and the type of the biological response of bone to the changes in mechanical loading are conditioned by several factors: individual race and age, pattern of stress, systemic and local metabolic conditions, etc. Therefore, bone remodelling following mechanical stress is not only a simple repair process, but a complex mechanism of functional adaptation which is controlled by the strain magnitude of bone structure rather than the extent of the stress. Results show that the skeletal changes induced by mechanical stress involve not only the structural properties but also the material characteristics of bone. For example, the size of hydroxyapatite crystals increases under load. These findings allow us to hypothesize that mechanical stress could directly modify the mineral component of bone. Hydroxyapatite appears to be a highly dynamic structure, able to change its crystallinity in relation to external stimuli. It is thus conceivable that hydroxyapatite crystals gather and arient themselves along bone and improve their crystallinity not only under the influence of biological mechanisms, but also as a reaction to mechanical stimuli.