Bone Size Matters in Predicting Fractures

A woman's chances of breaking a bone depends not only on the make-up of the bone, but also on the size, new research suggests.

Typically, doctors use a measure of bone make-up, known as the bone mineral density (BMD), to estimate the risk of fracture. After menopause, the BMD usually falls making the bones more brittle and likely to break.

However, as the current findings show, size changes happen as the BMD drops and this compensates, to some degree, for the loss in bone strength. Therefore, in predicting a woman's odds of fracture, doctors probably should consider not only the BMD but also the size changes.

These results, which are reported in The New England Journal of Medicine, are based on a study of 108 women who had a bone in the forearm tested for BMD and changes in size. This testing began at menopause and was performed every other year for 15 years, on average.

Each year, the women's BMD fell by 1.9%, Dr. Henrik G. Ahlborg, from Malmo University Hospital in Sweden, and colleagues note. At the same time, however, the diameter of two important bone regions increased. In fact, the more the BMD dropped, the thicker these two regions became.

In order to predict the odds of a fracture, the researchers combined the BMD changes with the size changes into something called the strength index. Women with a strength index below normal were much more likely than others to break a bone.

The new findings shed light on important bone changes that are "likely to advance our thinking and the therapeutic options available for the prevention and treatment" of fragile bones, Dr. Ego Seeman, from the University of Melbourne in Australia, states in a related commentary.

SOURCE: The New England Journal of Medicine, July 23, 2003.

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