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Christopher E. Cann, PhD; Harry K. Genant, MD
University of California San Francisco

JAMA. 1981;246(20):2322-2323.

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In Reply.—

Dr Mazess has questioned the 10% per annum rate of bone loss we see in the spines of women within the first two years after oophorectomy, as measured using quantitative computed tomography (QCT). His argument centers on the question of compositional changes of the vertebral marrow, where the conversion of hematopoietic marrow to fatty marrow could simulate a reduction of bone mineral content when mineral is measured using single-energy QCT. His calculations are approximately correct; we have shown experimentally that a 10% increase in the fraction of vertebral volume occupied by fat (eg, from 20% to 30%, an increase of 50%) will cause a 3.5% apparent decrease in the mineral.¹ Cross-sectional population data from Heuck² show an absolute increase of 5% per decade in the volume of fat in the vertebral body, but also show that the spine contains substantially less fat than sites in the . . . [Full Text PDF of this Article]

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