They looked at bone biopsies taken from the thigh bones of 21 women, all past menopause, who had suffered fractures at the site. Nine had not taken the drugs, while 12 had, for an average of 8.5 years.
"We took bone from close to the fracture site," Lane said. The women on the bisphosphonates, they found, had "old" bone. Normally, Lane said, bone is about 20 percent new, 60 percent middle-age and 20 percent old. "This was 90 percent old bone, suggesting the body is not turning over the bone," Lane said.
When too much of the bone is old bone, Lane said, it lacks the ability to repair microdamage. "What I think is happening is, women keep doing microdamage to the bone," he said. As a result, the unusual fractures of the thigh bone can occur with simple activity, such as climbing stairs.
At least one other expert isn't so sure. Criticizing both studies, Dr. Nelson Watts, director of the University of Cincinnati Bone Health and Osteoporosis Center, said the research has "major flaws" and "major errors in interpretation."
"They're looking at too small a sample size," he said .
Watts, who has been involved in clinical trials with bisphosphonates, said the drug studies typically have thousands of subjects and "we don't see these fractures."
The link could be a chance association, said Watts, who has been a consultant for makers of osteoporosis medications. "If there is a causal association," he said, "it appears to be limited to a small subset."
Neither Rosenwasser nor Lane is suggesting that bisphosphonates be abandoned. Both agree they can help soon after a diagnosis of osteoporosis. But after a certain point, they said women may be better off going off the drug or switching to another type of osteoporosis drug.
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