The effect of vertebral rotation of the lumbar spine on dual energy X-ray absorptiometry measurements: observational study.

OBJECTIVE To estimate how axial rotation of lumbar vertebrae quantitatively affects bone mineral density, as measured by dual energy X-ray absorptiometry in the anteroposterior plane. DESIGN Observational study. SETTING University teaching hospital, Hong Kong. PATIENTS Cadaver lumbar vertebrae (L2 to L4) were removed from four adults. MAIN OUTCOME MEASURES Using dual energy X-ray absorptiometry, the bone mineral content, bone area, and bone mineral density were measured in the neutral position and with vertebral axial rotation in increments of 7.5 degrees, up to a maximum of 45 degrees. RESULTS Correlation analysis showed a significant positive correlation between the degree of rotation and measured bone area, a significant negative correlation between degree of rotation and bone mineral density measurements, but no significant correlation between degree of rotation and measured bone mineral content. The measured bone area increased approximately 24% and the bone mineral density decreased approximately 19% when the vertebrae were rotated by 45 degrees. CONCLUSIONS These results suggest that for patients with rotational deformity of the spine, such as scoliosis, measurements of lumbar spine bone mineral content by dual energy X-ray absorptiometry is not affected, while bone mineral density measurements are not reliable.