NASHVILLE, TENN. — Three-dimensional, high-resolution peripheral quantitative computed tomography has revealed significant differences in the way that trabecular bone microstructure changes with age in men and women.
The technique allows for in vivo assessment of bone density and trabecular microstructure, Sundeep Khosla, M.D., said at the annual meeting of the American Society for Bone and Mineral Research.
He and his associates at the Mayo Clinic, Rochester, Minn., imaged 278 men and 324 women, aged 21–97 years. The nondominant wrist was scanned to obtain 116 views at the distal end of the radius.
The slice thickness was 89 μm.
Differences in the structure of trabecular bone in men and women are evident in young adulthood. Compared with young women, young men have indices of trabecular structure that predict stronger bones and greater resistance to fractures—higher bone volume/tissue volume (BV/TV) and thicker trabeculae, he said.
Over their lifetimes, men and women have similar reductions in BV/TV, but “the structural basis for this parallel decrease in BV/TV seems to be quite different in women and men,” Dr. Khosla said.
In women aged 20–49 years, trabecular number remains stable, then declines at about the same rate as seen in men aged 50 years and older. Men show no long-term net change in trabecular numbers, because decreases from age 50 on are offset by increases from ages 20 to 49.
Trabecular separation increases by 24% over men's lifetimes, but most of this change occurs after age 50. “Trabeculae actually tend to get closer together in men between the ages of 20 and 50, and then separation increases.” The net effect is that there isn't much change, he said.
Trabecular thickness goes down more than twice as much in men than in women over their lifetimes. “Trabecular thickness goes down fairly linearly over life in women. But in men there is a much more dramatic decrease in trabecular thickness from about age 20 to age 50, and then it looks like it doesn't decrease further,” he said. “In women, aging is associated with loss of trabeculae, whereas in men the primary mechanism of the decrease in BV/TV appears to be trabecular thinning.”
“Losing trabeculae is much more detrimental to bone strength than is thinning trabeculae,” Dr. Khosla noted. A 10% drop in BV/TV due to a reduction in trabecular number results in a twofold to fivefold greater loss of bone strength than the same drop in BV/TV caused by a reduction in trabecular thickness.
In a separate study, investigators used MRI-based virtual bone biopsy (VBB) to track trabecular microarchitecture changes in two groups of postmenopausal women aged 45–55 years—one receiving hormone therapy and the other not receiving the therapy.
A 20-patient treatment group received hormone therapy (0.05 mg/day estradiol transdermal patch); a 27-patient control group did not. All women received supplemental calcium (1,500 mg/day), said Glenn A. Ladinsky, M.D., of the University of Pennsylvania, Philadelphia.
In the control group, VBBs collected at the distal radius and the distal tibia showed conversion from trabecular plate to rod structure, indicating a reduction in bone strength during the 24-month study. Platelike trabecular architecture was preserved in patients who received hormone therapy. There was a 3%–4% reduction in bone mineral density in the control group, as measured by DXA. No changes in BMD were noted in the therapy group.
Dr. Ladinsky is a part owner of MicroMRI Inc., which developed the MRI-based VBB technology. The study was funded in part by Novartis Inc.
Differences in trabecular structure are shown here in two 24-year-olds, male (top left) and female (top right), a 73-year-old man (botton left) and a 71-year-old female. Photos courtesy Dr. Sundeep Khosla
