Microarchitecture, the key to bone quality.

Bone has the ability to adapt its shape and size in response to mechanical loads via a process known as modelling in which bones are shaped or reshaped by the independent action of osteoblasts and osteoclasts. Remodelling is a process that maintains mechanical integrity of the skeleton, allowing it to selectively repair and replace damaged bone. During adulthood, bone remodelling is the dominant process; after the age of 40 years, the age-related decline in bone mass increases the risk of fracture, especially in women. Osteoporosis is defined as a reduction in bone mass and an impairment of bone architecture resulting in thinning and increased cortical porosity, bone fragility and fracture risk. As new products and methods have been developed, focusing on bone fragility, effective and sensitive non-invasive means able to detect early changes in bone fragility process have also been developed. Due to limitations in assessing fracture risk and response to therapy, the evaluation of bone mineral contents by bone densitometry is progressively replaced by new non-invasive and/or non-destructive techniques able to estimate bone strength, providing structural information about the pathophysiology of bone fragility by quantitative assessments of macro- and microstructural bone features. DXA and volumetric QCT quantify bone macrostructure, whereas high-resolution CT, microCT, high-resolution MR and microMR assess bone microstructure. Knowledge of bone microarchitecture is a clue for understanding osteoporosis pathophysiology and improving its diagnosis and treatment; the response of microarchitecture parameters to treatment should allow assessment of the real efficacy of the osteoporosis therapy.