Bone density measurements

BMD measurements of the lumbar spine (L1–L4), left femoral neck, and total hip using DXA (XR-800, Norland, WI, USA) were used in this study. All DXA scans were performed by an experienced technician. As for the variability of BMD, the in vitro coefficient of variance was 0.9% for the spine, 0.8% for L1 to L4 measurements, 1.1% for left femoral neck and 0.8% for total hip. Descriptive statistics were used to summarize the BMD of spine, left femoral neck, and total hip.

T score (comparison with normal, young subjects of the same sex) and Z score (comparison with age-, sex-, and weight-matched controls) were based on the reference values in the DXA machine, expressed as standard deviations (SD). The WHO definition was applied for osteoporosis (T score <–2.5 SD), osteopenia (T score > –2.5 and < –1.0 SD), and normal BMD (T score > –1.0 SD) for female patients and male patients aged over 50 years. The Z score was used in male patients younger than 50 years, and osteopenia was defined as a Z score < –2.^[19]