Fundamental deficits in the bone microarchitecture of trabecular and cortical bone structure, as measured by high-resolution peripheral quantitative computed tomography (CT), can predict the risk of fracture in older men and women even when standard measures of bone mineral density (BMD) are in the normal range, according to new research.

Standard measures of areal BMD (aBMD) are assessed by dual-energy X-ray absorptiometry (DXA), but low BMD is not the only cause of bone fragility, and most older adults who sustain a fragility fracture do not meet the diagnostic criteria for osteoporosis, explain Elizabeth Samelson, Ph.D., of the Institute for Aging Research at Hebrew SeniorLife and Harvard Medical School, in Boston, Massachusetts, and colleagues, in their article published online November 28 in the Lancet Diabetes and Endocrinology.

"As most of our study participants with fractures had femoral neck aBMD T-scores in the osteopenic or normal range, our results indicate that assessment of bone microstructure might be useful in people who would not otherwise be identified as being at risk of fracture,". 

Accurate Fracture Predictors

"Therefore, while femoral neck aBMD and Fracture Risk Assessment Tool (FRAX) score remain the clinical standards for risk stratification, assessment of additional bone traits might improve prediction of fracture risk," they add. Annual costs associated with fragility fractures exceed US$19 billion in the United States and €36 billion in Europe, the researchers explain in their article. "Given the predicted growth in the number of older adults, the number of fractures and associated costs are projected to increase by two to four times worldwide in the next few decades," they state.

But because most older adults who suffer a fragility fracture do not meet the diagnostic criteria for osteoporosis, physicians currently lack validated means of assessing fracture risk in these patients.

Improved methods to identify people at the highest risk of fracture would allow for the treatment of patients who would probably have the greatest benefit-to-risk profiles and might ultimately reduce fracture burden.High-resolution peripheral quantitative CT (HR-pQCT) shows cortical and trabecular bone density and microarchitecture at peripheral skeletal sites with minimum radiation exposure and can differentiate between individuals with and without a history of fracture, often independently of DXA BMD, they explain.

In the largest prospective study of its kind, Samelson and colleagues evaluated data on 7254 older adults with a mean baseline age of 69 years from the Bone Microarchitecture International Consortium, including cohorts in the United States, France, Switzerland, Canada, and Sweden. With a mean follow-up of 4.6 years, 11% (765) of participants sustained incident fractures. Among those with fractures, as many as 86% (633) had femoral neck T-scores greater than –2.5, and therefore did not meet the criteria of "osteoporosis.