Osteoporosis and DXA Scans

Osteoporosis and DXA Scans: How is Osteoporosis Detected?

Dual-energy X-ray absorptiometry (DEXA) assess...

Osteoporosis and DXA scans: Dual-energy X-ray absorptiometry (DXA) assessment of bone mineral density of the femoral neck (A) and the lumbar spine (B): T scores of – 4.2 and – 4.3 were found at the hip (A) and lumbar spine (B), respectively in a 53 year-old male patient. (Photo credit: Wikipedia)

Early detection of osteoporosis requires a bone density test. This is because there are no warning signs for osteoporosis in its early stages other then bone fracture. In an effort to avoid osteoporotic or osteopenia related fracture, the testing of bone mass density is required. The most common test is called a central DXA (dual energy x-ray absorptiometry) scan. DXA technology is designed to emit two simultaneous x-ray beams aimed at an individual’s hip or spine. The level of absorption of these x-ray beams is used to determine the density of the bone mass. The beams have differing energy levels, thereby distinguishing them from each other. Typically, women over the age of 65 are at higher risk for loss of bone mass and are prime candidates for an osteoporosis DXA scan.

The DXA scan is reported in both, T-scores and Z-scores. The T-score is the number of standard deviations above or below the average for a young adult at peak bone density, but there can be differences based on reference group. The Z-score is a number of standard deviations below an average person of the same age group. Both scores are valuable for the diagnosis of osteoporosis. Another measure of bone mass density is grams per centimeter squared, (g/cm2), which addresses raw volume of bone mass with no normative comparison. The DXA test emits low levels of radiation, is not painful, and requires only five minutes to complete.

Osteoporosis plagues millions of people, and is largely caused by a lack of axial mechanical loading at a level that will stimulate an adaptive response in osteoblasts. Osteoporosis is induced by a lack of load being placed on the body, which is a requirement for bone mineral absorption. While often associated with the aging process, osteoporosis is also seen in other demographic groups. Children and young adults suffer from this disease if they are immobilized for one reason or another and are unable to load the body. Astronauts who spend extended periods of time without the benefit of the gravitational pull of the earth also experience osteoporosis. All of these groups can have relative recovery from osteoporosis with the appropriate exercise prescription/dose response. With conventional modalities this process becomes more difficult as individuals age. In a study by Tsuzuku, et al. (2001) bone mass density generation was observed with high-intensity resistance training, but was not effective with low-intensity resistance training. Subjects included males in their 20s as both test and control participants. The results showed increases in bone mass with the test group that was using the heaviest mechanical loading possible on the body, whereas results with the control group showed no change in bone mass. Groups were tested via DXA scan testing.

 

Source:

Tsuzuku, S., Shimokata, H., Ikegami, Y., Yabe, K., & Wasnich, R.D. (2001). Effects of high versus low intensity resistance training on bone mineral density in young males. Calcified Tissue International. 68(6):342-347.

Enhanced by Zemanta