DXA-derived section modulus and bone mineral content predict long-bone torsional strength

Previous studies have used dual energy x-ray absorptiometry (DXA) scans to calculate the section modulus (Z) of adolescent and adult human femurs. The DXA-derived Values of Z were assumed to be proportional to bone strength i n bending and torsion. in this study we used dog (n 5), pig (n 4), and huma n (n 13) femurs covering a linear bone mineral content (BMCL) range of 0.91 -6.1 g/cm. Using DXA scans, ex vivo torsional strength tests, and torsional finite element models, we assessed the validity of using the DXA-derived Z value as an indicator of strength. The correlation between BMCL and streng th was r(2) = 0.87 and the correlation between Z and strength was r(2) = 0. 86. Based on finite element results, the dog and pig section moduli were ad justed to be comparable to the human data based on cross-sectional shape an d bone tissue shear strength differences. With these adjustments, the corre lation between adjusted section modulus and measured strength did not impro ve (r(2) = 0.87). These data indicate that DXA-derived section modulus can be used to predict strength over a wide range of bone sizes. However, a cle ar advantage of using DXA-derived section modulus rather than BMCL could no t be found.