Effect of fixation, soft-tissues, and scan projection on bone mineral measurements with dual energy X-ray absorptiometry (DXA)

The objective of this study was to determine the effect of fixation, soft t issues, and scan projection on bone mineral measurements with dual energy X -ray absorptiometry (DXA). In seven fresh cadavers, DXA scans were obtained within 48 hours of death and after 10 months of fixation with 5% formalin/ 95% ethanol. The measurements showed a high linear relationship (r(2) > 0.9 7; SEE% < 10%), with no significant deviation after fixation (except for to tal body BMD: -3.1%). In 14 specimens, the precision of femoral and spinal analyses was determined under in situ and ex situ conditions. There was no significant difference between ex situ and in situ reproducibility, the coe fficient of variation being <3% for the BMC and <2% for the BMD (except at the greater trochanter). The effect of the soft tissues and scan projection was assessed in 83 cadavers aged 80.4 +/- 10.3 years. The soft tissues had only a small effect on analyses of the total femur (r(2) > 0.90; SEE% <9%) , but led to more substantial deviations in regional femoral analyses and i n the spine (r(2) = 0.78-0.90; SEE% = 8-22%). Comparing lateral with anteri or-posterior (AP) spinal scans, the vertebral bodies were found to occupy 4 0.2 +/- 7.2% of the BMC, and 62.0 +/- 11.2% of the BMD, the ranges being 26 -58%, and 38-91%, respectively. There were large deviations from linearity between in situ AP and ex situ lateral spinal scans with r2 values of 0.63 and 0.73 for BMD and BMC (SEE% = 52% and 27% relative to the vertebral body ), respectively.