Influence of Region Size on Bone Mineral Measurements along Femoral Stems in THA

The influence of regional size on the precision error in the evaluation of bone mineral changes along femoral components in uncemented THA's was studied methodologically using Dual Energy X-ray Absorptiometry (DEXA) and with a review of the literature. A significant negative relation between region size and precision error was found in experimental studies and the precision error was shown to vary with type of DEXA scanner when reviewing the literature. When using Gruen's zones we found that the precision was best at the tip and poorest in the proximal regions. Guidelines based upon calculations of the approximate percentage changes necessary in a single individual to be statistically significant in a longitudinal study with 95% probability were made for three different types of DEXA scanners.