Imaging: Osteoporosis Testing: DEXA Method
Osteoporosis may be present in patients for years
during which there are no symptoms while bones are gradually thinning. Often, patients are
diagnosed with osteoporosis only after unexpectedly having sharp pain in the mid to low
back. Others may experience fractures of a femur, hip, or distal radius after a relatively
minor fall or accident.1 The resulting fractures are often very painful and can
take many months to heal and sometimes progress to chronic pain.Vertebral fractures, in
particular, may cause intense pain and muscle spasms that last long after the fracture has
healed.2
As our current population ages and the relative proportion of seniors (>50 yr old) in society increases, the need to find a reliable, safe and inexpensive method in which to test bone strength increases. The premise that bone strength is proportional to the amount of bone mineral content is currently the prevailing assumption underlying the current form of testing. Since there is of yet no viable way to measure living bone strength, we take an indirect measure — that of bone mineral density — and expect that the correlation between the two is linear in both directions. We expect that if bone density is less than optimal, it means that bone strength is also likely less than optimal. The converse is true in situations where bone mineral density is higher than normal, such as in callus formation after a bone fracture. Routine x-rays are insensitive to subtle bone loss and it is thought that one must lose over 30% of bone in a given area before this deficit is noticeable on x-ray. The most popular method of identifying bone loss is “absorptiometry.” Dual energy x-ray absorptiometry or DEXA is one of the most widely used imaging methods for identifying osteoporosis—or low bone mineral density (porous bones). The importance of bone mineral density, or bone mass, testing is made more clear when we examine the devastating effects of primary and secondary osteoporosis in our country.
Osteoporosis — A Global Problem
Osteoporosis threatens millions of persons over the age of 50 and it is estimated that
well over 10 million people already have the disease—approximately 8 million women
and 2 million men. The percentage of persons who have osteoporosis increases progressively
with age. Bone mass is a major determinant of fracture risk with an estimated doubling of
fracture risk for every 10% decline in bone mass. At any age among adults, the amount of
bone tissue that is present in the skeleton is the algebraic sum of skeletal mass
accumulated during growth and development and the subsequent bone loss that occurs with
aging. Therefore, both peak bone mass and the rate and duration of bone loss contribute to
fracture risk.
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