DEXA scan

The best correlate with bone fragility is radiographic measurement of bone mineral density (BMD) using DEXA scan.

DEXA scan (dual energy x-ray absorptiometry): the preferred way to measure BMD

1. proximal femur: BMD measurement in this location is the best predictor for future fractures

2. LS spine: best location to assess response to treatment (need AP and lateral views, since AP often overestimates BMD because of superimposition of overlying posterior elements and aortic calcifications)

3. forearm BMD may be used if hip or spine are unsuitable

Interpretation of DEXA scan results:

1. findings are reported as

a) T-score: norms for healthy young adults

b) Z-score: norms of subjects of same age and sex as the patient

2. diagnostic criteria: WHO definitions (with a normal distribution 1 SD below the mean is the low- est 25th percentile, 2 SD below is 2.5th percentile)

a) normal: >–1 standard deviations (SD)

b) osteopenia: from –1 to –2.5 SD

c) osteoporosis:<than –2.5 SD17