Precision and age-related changes of 3D-DXA reconstructions and FEA of the proximal femur in comparison to DXA

The growing interest in 3D-DXA reconstructions for possible uses in fracture risk prediction or patient follow-up, e.g., in conjunction with finite element analyses, asks for precision data to increase the interpretability of results making use of the 3D-DXA technique. Using two datasets and a total of 2427 DXA scans of the proximal femur we evaluated the short- and long-term precision of standard DXA measurements. All the available scans were reconstructed using 3D-Shaper software and processed through a nonlinear finite element pipeline for femoral strength estimation. Short- and long-term precision were computed for thirty 3D-DXA-based parameters as well as femoral strength in fall and stance configurations. Precision errors were related to change rates of the respective parameters by calculating the trend assessment interval (TAI). Simultaneously, spatially resolved precision errors were computed for cortical parameters and error progression from DXA to 3D-DXA and FEA was considered. Precision errors were amplified through the different processing steps. Long-term precision errors were 1.6%, 2.0% and 7.5% for total hip aBMD, total hip integral vBMD and strength in fall, respectively. Errors between processing steps were only weakly correlated. Higher change rates for vBMD and strength compensated the larger precision errors, resulting in similar TAIs for total hip aBMD (5.5 years), total hip integral vBMD (4.6) and strength (5.8), respectively. Relative local precision errors of cortical parameters were largest in the superior and anterior neck region and above the lesser trochanter. 3D-DXA and thereon based FEA may offer interesting insights into the densitometric and mechanical quality of the proximal femur. The here reported results should offer a help for the interpretation of sequential measurements where these are required.