Normalized BMD as a predictor of bone strength

Rationale and Objectives. In the noninvasive evaluation of bone quality, bo ne mineral density (BMD) has been shown to be the single most important pre dictor of bone strength and osteoporosis-related fracture. Among the method s of measuring BMD, dual x-ray absorptiometry (DXA) has widespread acceptan ce due to its low radiation, low cost, and high precision. However, DXA mea sures. area BMD instead of true volumetric density; thus, a larger bone wil l tend to have a high BMD than will a smaller bone. Therefore, the comparis on of BMDs of bones of different sizes can be misleading. In this study, th e authors tried to compensate for the size effect by normalizing the area B MD with bone size as measured from a standard pelvic radiograph. Materials and Methods. The overall method for calculation of normalized BMD included conventional area-based BMD from DXA and the extraction of geomet ric measures from pelvic radiographs. The database for analysis included 34 femoral neck specimens. Regression analysis was performed between the norm alized volumetric BMD, measured from femoral neck region, and the mechanica l propel ties obtained from trabecular bone cubes machined from the same re gion. Results. After normalization of the area BRID, the coefficient of determina tion increased from 0.30 to 0.43 for the Young modulus and from 0.27 to 0.3 7 for bone compressive strength. Conclusion. A noninvasive method of normalizing BMD can improve the predict ion of bone mechanical properties and has potential in monitoring changes i n growing skeletons and in the clinical evaluation of bone quality.