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Taller women, lighter bones and increased fracture risk
Bjørnerem et al. investigated the structural bone factors that might explain why taller women are more prone to fractures than shorter women, even though their wider bones tolerate bending more successfully.
They obtained in vivo 3D high-resolution quantitative peripheral CT scans of the radius, fibula and distal tibia of female subjects from a twin study. A total of 345 women were included (age 40–61 years); 93 had one or more fractures. For every standard deviation (SD) increase in height, there was a corresponding SD increase of the larger tibia cross sectional area (CSA), the larger medullary CSA and the ratio of the higher medullary CSA to the total CSA.
Each SD of greater cortical porosity was significantly associated with fracture independently of height. The odds ratios found were: distal tibia 1.55 (95% CI: 1.11–2.15); distal fibula 1.47 (95% CI 1.14–1.88); and distal radius 1.22 (95% CI 0.96–1.55).
Editor’s comment: The authors conclude that women of greater height develop bones that are wider but have thinner and more porous cortices because of greater excavation of more intracortical canals. As well as needing sufficient strength for muscle attachment and successful locomotion, bones of larger individuals also need to be lighter. This, however, predisposes them to fracture.
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