Micro-CT Scans Provide 3-D Proof of Estrogen's Bone Benefit

December 03, 2002

Peggy Peck

Dec. 3, 2002 (Chicago) -- A three-dimensional glimpse of bone micro-architecture suggests that estrogen replacement is an effective treatment for osteoporosis because it "protects and retains bone structure, rather than laying down new bone," according to results of small observational study using new micro-computed tomography (CT) technology.

The results were presented here at the 88th Scientific Assembly and Annual Meeting of the Radiological Society of North America.

Harry K. Genant, MD, professor of radiology and medicine at the University of California, San Francisco, said that after two years of estrogen replacement therapy, "trabecular bone appears to retain most of its plate structure," which suggests that the resorption process associated with osteoporosis is slowed or halted.

Dr. Genant and colleagues developed a computer-generated structural model index based on the relative numbers of plates and rods present in the bone before and after estrogen replacement. They recruited 20 postmenopausal women who had been diagnosed with osteoporosis or osteopenia. The women underwent baseline procedures that biopsied fragments taken from one side of the iliac crest. After two years of estrogen replacement, a second biopsy was performed with a sample taken from the other side of the iliac crest.

"By analyzing these specimens in a side-by-side manner we were able to determine the true effect of estrogen on the micro-architecture," Genant told Medscape.

He said that after menopause bone begins to erode until finally the plate structures are worn down and begin to take on a rod-like appearance. Therefore, an increase in trabecular plates would indicate an increase in bone strength and fracture resistance, he said. After two years of estrogen replacement "the women in this study had a 14% change in the ratio of plates to rods," he said. Moreover, this change occurred even though there was no significant increase in bone volume.

"Bone is really like the Eiffel Tower -- there is really not much structure there but it is very stable because of the way it is put together rather than because of the mass involved," said Thomas Link, MD, associate professor of radiology at the Technical University of Munich, Germany. "If you changed the structure even slightly the Eiffel Tower would fall. That's what happens with bone when osteoporosis takes hold." He added that the micro-CT images provide evidence that the bone is "still vital, which suggests that strength can be maintained."

Dr. Link, who was not involved in the study, said the study by Dr. Genant suggests that all "new osteoporosis drugs should be assessed using micro-CT so that we can see if they are really effective at the structural level."

Although Dr. Genant said the study provides additional proof of estrogen's value to bone health, "these findings don't address the larger controversy surrounding hormone replacement," he said.

The Women's Health Initiative was halted last summer after the study's safety monitoring board determined that women taking the estrogen-progestin combination (Prempro) had an increased risk for breast cancer, stroke, and heart disease. A subset of that study, which is tracking the effect of estrogen alone in women who have had hysterectomies, is still underway.

RSNA 88th Scientific Assembly: Abstract 715. Presented Dec. 2, 2002.

Reviewed by Gary D. Vogin, MD

Peggy Peck is a freelance writer for Medscape.

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