Age-related fractures appear to impact cortical bone more than trabecular bone

With much osteoporosis research focusing on vertebral fractures and trabecular bone loss, a team of Australian researchers recently theorized from their cross-sectional study of women’s bones that medications targeting age-related cortical bone loss occurring after age 65 years may ultimately improve the treatment and diagnosis of osteoporosis.

In their study published in the Lancet, Roger M.D. Zebaze, MD, in the Department of Endocrinology, Austin Health, Melbourne, and colleagues, wrote, “Contrary to prevailing views, bone loss at peripheral sites in the first 15 years after menopause makes only a small contribution to total bone loss across life. These findings reconcile the epidemiology and pathogenesis of nonvertebral fractures; most fractures in old age are nonvertebral and occur at predominantly cortical sites after age 65 years, most bone loss occurs after this age, and most bone loss is cortical, not trabecular at peripheral sites.”

Using high-resolution peripheral CT scans, Zebaze and colleagues quantified and compared cortical vs. trabecular bone loss in the distal radius of 122 white women (mean age 62 years). They used scanning electron microscopy to measure the porosity of the subjects’ distal radius.

Additionally, Zebaze and colleagues measured bone density in cross-sections of bone cut from 24 women’s post-mortem femurs at 1 cm below the lesser trochanter, mid-shaft and mid-femoral neck.

Cortical vs. trabecular bone findings

In the women who were 50 to 80 years-old, researchers found that 68% of their overall distal radius bone loss was cortical.

They observed that about 16% of the total bone loss occurred between ages 50 years and 64 years the remainder bone loss occurred after age 65 years.

According to a Lancet press release, between ages 50 years and 80 years and older, trabecular density at the distal radius decreased by 18.2 mg hydroxyapatite per cm³ before exclusion of cortical remnants, but after that it decreased by 68.7 mg hydroxyapatite per cm³. Additionally, cortical density decreased by 127.8 mg hydroxyapatite per cm³ before porosity-producing trabecularization of the cortex was included and 374.3 mg hydroxyapatite per cm³ after it was included.

The researchers speculate that age-related increases in cortical porosity are underestimated by current methods of measuring bone mineral density and assessing fracture risk. They suggest that because of trabecularization of the cortex, cortical remnants that look similar to trabeculae are mistakenly viewed and calculated as trabecular bone loss by current methods, as noted in the release.

Reference:
Zebaze RMD, Ghasem-Zadeh A, Bohte A, et al. Intracortical remodelling and porosity in the distal radius and post-mortem femurs of women: a cross-sectional study. Lancet. 2010;375:1729–1736.
The study was funded by the Australia National Health and Medical Research Council.

[These] findings — namely, that most fractures occur after age 65 years and are attributable to greater loss of cortical than of trabecular bone — have important implications for both identification and treatment of osteoporosis.

– David B. Burr, MD
Department of Anatomy and Cell Biology
Indiana University School of Medicine, Indianapolis
This perspective appeared in an accompanying article in the Lancet.

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