[Determining factors of bone mechanical resistance]

Bone strength is determined by bone geometry, cortical thickness and porosity, trabecular bone morphology and the intrinsic properties of bony tissue. The major complication of osteoporosis, i.e. fracture, is due to a lower bone strength. Thus, any treatment of osteoporosis implies an improvement in bone strength. Bone strength is indirectly estimated by bone mineral density (BMD) using Dual-Energy X-ray Absorptiometry (DXA). Since, DXA-measured BMD accounts for part of the variance in bone strength, some important factors are not captured by DXA, in terms of the effects of anti-osteoporotic treatment and the progression of osteoporosis. Geometry and trabecular microarchitecture have also to be taken into account. Thus, the assessment of the intrinsic mechanical quality of bony tissue should provide a better understanding of the role of tissue quality in determining bone strength. The careful investigation of all the determinants of bone strength (bone tissue included) should be considered in the pathophysiology of osteoporosis and in the mechanisms of action of anti-osteoporotic drugs.