|
In 1991 the World Health Organization (WHO) defined osteoporosis as a "loss of bone mass and micro architectural deterioration of the skeleton leading to increased risk of fracture."1,2 Since microarchitecture can not be measured directly, a panel of the WHO recommended that the diagnosis be made according to a quantifiable surrogate marker, calcium mineral, in bone. Subsequently in 1994, the definition focused on the actual bone "density," giving densitometric technology a central place in establishing the diagnosis of osteoporosis.3,4 But soon it became obvious that there was only limited correlation between bone mineral density (BMD) and actual occurrence of fractures and that decreases in bone mass account for only about 50% of the deterioration of bone strength with aging. In other words only about 60% of bone strength is related to BMD.5 Recent developments in bone research have shown that bone mineral density in itself is not sufficient to accurately predict fracture risk. Bone is composed of inorganic calcium apatite crystals that mineralize an organic type I collagen matrix. The degree of mineralization, the properties of the collagen matrix, crystal size, trabecular orientation, special distribution of the different components and many more factors are all impacting bone strength.6-14 Human cadaver studies have confirmed the correlation between bone density and bone.26 strength.5,15-20 Changes in cancellous bone morphology appear to lead to a disproportionate decrease in bone strength.21-26 When postmenopausal women are stratified by age, obvious differences between BMD and actual fracture risk are observed.24 Felsenberg eloquently summarizes what he calls the "Bone Quality Framework." In great detail he talks about the geometry and micro- architecture of bone and how the different components are related to functional stability.27 Are our current testing modalities appropriately addressing these structural factors? Are we keeping in mind that in screening for osteoporosis the key variable is fragility, not bone density itself? All currently FDA approved and commercially available equipments for the evaluation of bone status claim that they - at least indirectly - assess the biological fracture risk. This review summarizes an extensive current literature research covering FDA approved as well as experimental devices for the evaluation of bone. The pros and cons of the different techniques are discussed in the context of diagnostic accuracies and practical implications.
|
