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WEDNESDAY, July 23, 2003 (HealthDayNews) -- When it comes to bones, density is important -- but don't forget about size.
That's the message of a new study, which suggests doctors may want to rethink the way they calculate the risk of fractures in people with a brittle skeleton.
Swedish and American researchers say older women with broader bones are less vulnerable to age-related fractures. These breaks result from thinning bones, or osteoporosis, a condition that affects roughly 8 million women in the United States. Osteoporosis usually follows the drop in estrogen that occurs during menopause, though it also occurs to a lesser degree in men and in younger people taking certain bone-eroding steroids for long periods.
The standard tool for measuring bone strength -- and thus, the risk of a fracture -- is to examine its mineral density. Several devices can perform this test, but in general they use either X-rays or ultrasound to read the mineral content of the interior (or cortical) section of bones in the spine, arm, heel and elsewhere.
Scientists have long known, however, that bone mineral density (BMD) is an imperfect gauge of strength and fracture odds. That's largely because other factors, including bone size and shape, also dictate its soundness under stress.
In the latest study, a team led by Dr. Henrik Ahlborg, an orthopedic surgeon at Malmö University Hospital in Sweden, followed 108 postmenopausal women for an average of 15 years. The women, who were 48 when they began the study, had scans of the radius bone in their forearm every other year. They also had blood drawn to determine their estrogen levels.
Women who lost more bone in the interior of their radius over time tended to gain diameter there. This process, called periosteal apposition, makes bone stiffer, partially compensating for the loss of internal mass.
"The women with the lowest level of [estrogen] after menopause also had the most periosteal apposition," Ahlborg says.
Since both bone mass and bone structure (including size) are independently related to its risk of breaking, the researchers combined the two traits to create a "strength index." Women with better scores on the strength index were less likely to suffer fractured arms over time than those with weaker bones.
Ahlborg's group is now trying to come up with a strength index for bones in the hip -- a common and particularly devastating site of fractures in people with osteoporosis.
Although the study looked only at women, men also undergo periosteal growth -- indeed, more so than women. As a result, they may gain more protection from the widening.
People with osteoporosis have several options to slow the pace of their bone loss, such as estrogen therapy and a variety of drugs. But these treatments don't build new bone or help bone grow in size. To date, parathyroid hormone injections are the only therapy shown to reduce fracture risk by bulking up the skeleton. Eli Lilly & Co. now markets a version of this substance, called Forteo, to people with severe osteoporosis.
More information
Try the National Osteoporosis Foundation or the National Institute on Aging.
