The effect of modelling and remodelling on human vertebral body architecture.

Vertebral bone strength is determined by several factors: cortical thickness, bone size, trabecular bone density, and microarchitecture. All these factors change with age as a result of the two dynamic processes: remodelling and modelling. When the changes become pronounced, osteoporotic fractures occur. There is a different aging pattern for men and women: 1. Men achieve a higher peak bone mass than women (mainly because of a larger cross-sectional area of their bones); 2. Men have no accelerated bone loss in middle age; and 3. Men seem to be able to compensate for their loss of cancellous bone strength by increasing their vertebral cross-sectional area with age. The general pattern, for both men and women is, though, that of an extreme (70-80%) decline in whole vertebral body strength during normal aging. The accompanying decline in bone density is much less pronounced (35-45%). This clearly illustrates the power relationship between bone density and strength. However, the role of changes in trabecular bone microarchitecture for vertebral bone strength during aging still needs to be determined.