BONE-STRUCTURE AND MECHANICAL RESISTANCE OF BONE TISSUE

The strength of bone depends on bone structure, both in terms of globa l geometry of the bone and the microscopic pattern of the trabecular n etwork, Modifications in the trabecular organization, often related to the aging process, include altered anisotropy, perforations, loss of connectivity and microfractures, The microscopic architecture of trabe cular bone can be studied on histomorphometric slices, the use of ster eologic techniques on these slices may better reflect the changes occu ring in 3 dimensions. High-resolution tomodensitometry and 3-D magneti c resonance imaging are under further evaluation, An evaluation of the fractal geometry of the trabecular network, performed on the vertebra e, calcaneus, or ulna on standard radiographs has given promising resu lts. Bone strength is determined by resistance tests on bone tissue sa mples, The relationship between the applied force and bone deformation is used to determine a stress-strain curve and resistance parameters. The mechanical behavior of a given bone can be modelized by a Finite Element Analysis, the computerized model being able to predict the rea ction of this bone. Ultra-sound analysis does not directly measure bon e density, nor bone architecture, but would reflect both these propert ies, Velocity and attenuation of ultra-sounds, measured at the calcane us or patella, are useful in distinguishing between controls and osteo porosis cases, and may have predictive value.