For years, we've thought we understood osteoporosis: it's a disease in
which the bones become more and more fragile as they lose density, usually due
to aging, menopause, and other factors like lack of calcium and
vitamin D in the diet.
But today, advances in research are shedding new light on osteoporosis,
which is predicted to affect as many as half of all Americans over age 50 by
the year 2020. From diagnosis to prevention to osteoporosis treatment, new research is turning our old
understanding of osteoporosis upside down.
The National Osteoporosis Foundation estimates that 10 million people in the U.S. have osteoporosis and nearly 34 million more have osteopenia, which puts them at greater risk for osteoporosis.
Bone mineral density
(BMD) is related to bone strength. BMD testing is used to diagnose osteoporosis. BMD is measured with a test called a DXA scan. By measuring BMD, doctors can predict the risk of having a bone fracture.
A bone density scan, or test, should not be confused with a...
The "gold standard" test for diagnosing osteoporosis is the
DEXA scan (dual energy X-ray absorptiometry), which measures bone density in
the spine, hip, or wrist. These are the most common locations for bone
fractures. But this test, as advanced as it is, has limitations.
"Many patients with normal bone density measurements on a DEXA scan still
have fractures, and a substantial number of patients whose DEXA scan shows
osteoporosis don't get fractures," says Sundeep Khosla, MD, a professor of
medicine and osteoporosis researcher at the Mayo Clinic in Rochester, Minn.
"The DEXA tells you how much bone is present, but not much about the internal
structure of that bone." Obviously, doctors would like to be able to predict
fracture risk much more accurately, to fine-tune who is at greatest risk of
fracture and most in need of medication.
Khosla compares the human skeleton to a bridge made of metal. "You could
have two bridges with the same amount of metal in them, but one could be more
sturdy, just because of the way it's constructed," he says. "Similarly, because
the microarchitecture of one person's bones is different from another's, their
actual strength may be quite different."
Khosla and other osteoporosis researchers are studying new imaging and
computer techniques that will allow them to look inside the bone, and
see specific structural characteristics. This will help them to build models of
bone strength that can help predict which patients are most likely to have
One such imaging technique is computed tomography (CT) scanning of the spine
and hip. Researchers take the three-dimensional image of the bone that the CT
scan creates, and use a computer modeling technique that breaks the image down
into tiny pieces. "The density of each piece allows you to estimate the
strength of each piece, and get the overall strength of the structure," says
Khosla. "Depending on where a bone is weakest, it may be more or less prone to
That's taken to a higher level in a new instrument being used to study
osteoporosis, called high-resolution peripheral quantitative tomography.
Because it uses a higher level of radiation, it can't be used at the spine or
near vital organs, but it can be used to image areas like wrist bones. "The
resolution with peripheral scanners is good enough that you can see individual
structural components, which give you much more information about the strength
of the bone," Khosla says.
He predicts that the peripheral scanners, which may not be much more
expensive than today's DEXA, may soon be approved for clinical use. Since CT
scans are significantly more expensive, they may not be used as a stand-alone
screening tool. However, when a patient has a CT scan for another reason, it's
relatively easy to get bone information at the same time.
"We still need to accumulate more data about how these tools predict
fracture risk, but initial results are promising," says Khosla.