High resolution CT of the distal radius can reveal high-risk changes in bone architecture that might not be reflected in bone mineral density measurements and help target preventive treatment, according to Professor Ego Seeman from Austin Health in Melbourne.

“The aim of treating bone fragility is to reduce the burden of all fractures, but over 60% of fragility fractures occur in women with osteopenia or normal BMD,” he said.

“Porosity of the cortex, though, can predict fractures independent of both BMD and the FRAX risk score.

“Cortical and trabecular deterioration disproportionately compromise bone strength relative to the amount of bone lost.”

Professor Seeman collaborated with colleagues in Lyon, France, to analyse data from 589 women aged 42 to 94 years.

During 8 years of follow-up 111 women had fractures: 30 of 77 (39%) with osteoporosis diagnosed on the basis of hip BMD, 49 of 295 (17%) with osteopenia and 32 of 216 (16%) with normal BMD.

“Although the relative risk of fracture in women with osteopenia or normal BMD is lower, the absolute numbers of factures are higher in these groups,” he said.

“The challenge is to identify women without clearly-defined osteoporosis who are at high risk.”

Examining bone microstructure provided an important clue, as women having fractures had thinner and more porous cortices and fewer trabeculae than women remaining fracture free.

“A standard deviation increase in porosity increased fracture risk by 28% independent of BMD,” Professor Seeman said.

The presence of osteoporosis alone identified 30 of the 111 women with fractures. Adding a measure of porosity identified another 25, while adding the FRAX score to these two measures identified only another three.

Even with these three assessments, about half of women were still not recognised as being at risk.

“However, we showed that additional women with osteopenia or normal BMD contributing to the fracture burden can be identified before they fracture by measuring bone microstructure,” he concluded.