 Bone mass, cortical thickness and bone geometry independently contribute to bone strength, all regulated differently. Thus, the regulation must therefore be trait specific studied as to understand the pathophysiology of osteoporosis as osteoporosis may partly be the result of deficits occurring during growth. We must also better discriminate the different traits building the skeleton. Areal bone mineral density aBMD, measured by dual X-ray absorptiometry DXA the clinically used estimation of bone mass, is an estimate only adjusted for the measured area, not the third dimension the depth, but aBMD is often uncritically used as a measurement for the true density. As to predict future fragility fracture, aBMD is acceptable, but for the understanding of reduced bone strength, we must separate the estimation into bone mass, the amount of bone within the skeletal envelope, bone size and skeletal structure architecture as these traits are independent associated with fractures. 