Bone Disease: Osteoporosis

Osteoporosis used to mean fractures caused by thin bones. About a decade ago, however, the definition changed. Now the term osteoporosis encompasses not only those who have had fractures caused by thin bones but those who have thin bones and are at increased risk for fracture. This change made the risk factor for the disease (thin bones) equivalent to the disease (osteoporosis) itself. It also meant that many more women suddenly had osteoporosis.

The definition of osteoporosis changed to include those who have had fractures caused by thin bones and those who have thin bones and are at increased risk for fracture

The catalyst for the new definition was the development of the dual-energy X-ray absorptiometry (DEXA) scan, a machine that measures bone density at the hip and spine, where fractures are most likely to occur. Before the machine was put into widespread use, an international group of medical experts met to determine a consistent method for using DEXA scan readings. They decided to use a T score, which uses a statistical term called standard deviation. Standard deviation measures how far something is away from the norm; in this case, the “norm” selected was the bone density of a healthy, average woman in her mid-20s. They also decided that a –2.5 standard deviation below the norm would be used as the definition for osteoporosis.

But not all women with a –2.5 on a DEXA scan have the same risk for breaking a bone. “Bone density is only one part of a complex part of risk factors that indicate whether someone will have fractures in the next few years, and I put it last on the list,” says bone health expert Bruce Ettinger, MD, a senior investigator at Kaiser Permanente in Oakland, California.

Risk factors for fractures incude not only bone density but a woman’s age and if she has previous fractures in her wrist, upper arm or spine

The first two factors that need to be taken into account, he says, are a woman’s age (an older woman is at greater risk of experiencing a fracture) and whether a woman has previously fractured her wrist, upper arm, or spine (fractures in these areas quadruple the risk of a future fracture).

Next, it’s important to assess whether the woman is thin, smokes, or has a family history of osteoporosis, all of which increase risk. Then, the DEXA scan measurement comes into play. “After looking at all of these things,” Ettinger says, “adding bone density modifies risk a little bit, but it doesn’t change it all that much.”

In essence, says Ettinger, most people think about this backwards: They start with the DEXA scan. But the other factors are equally, if not more, critical in assessing fracture risk and making treatment decisions.

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