In vivo precision of dual-energy X-ray absorptiometry-derived hip structural analysis in adults

Precision is integral to the monitoring of bone mineral density (BMD) change using dual-energy X-ray absorptiometry (DXA). Hip structural analysis (HSA) is a relatively recent method of assessing cross-sectional geometrical strength from the 2-dimensional images produced by DXA scans. By performing serial scans, we evaluated the in vivo precision of DXA-derived HSA in adults using a GE Lunar iDXA absorptiometer (GE Medical Systems, Madison, WI) in males and females (n=42), mean age of 34.5 (standard deviation [SD]: 8.5; range: 19.3-52.6)yr with a heterogeneous sample. Two consecutive intelligent DXA (iDXA) scans with repositioning of both femurs were conducted for each participant. The coefficient of variation, root-mean-square (RMS) averages of SD, and hence the least significant change (95%) were calculated. We found a high level of precision for BMD measurements of both the total hip and femoral neck, with RMS-SD=0.006 and 0.010 g/cm(2) and percent coefficient of variation (%CV)=0.52% and 0.94%, respectively. We also found good precision for HSA-derived geometrical properties, including sectional modulus, cross-sectional moment of inertia, and cross-sectional area, with %CV (average of the left and right sides) at 4.48%, 3.78%, and 3.13%, respectively. Precision was poorer for buckling ratio and femoral strength index with %CV 28.5% and 9.25%, respectively. The iDXA provides high precision for BMD measurements and with varying levels of precision for HSA geometrical properties.