Biomechanical indices of the femoral neck estimated from the standard DXA output: age- and sex-related differences.

We explored the feasibility of using routine dual-energy X-ray absorptiometry (DXA) to estimate several parameters of femoral neck geometry related to bone strength and to analyze their changes with age. Bone mineral density (BMD) was measured in 871 control men and women and in 19 women with hip fracture. Volumetric BMD (volBMD) and geometrical parameters were estimated from the DXA output with previously published formulas. In young subjects, areal BMD was higher in men than in women, but volBMD was similar in both sexes. However, it showed a more rapid decline with age in women. The femoral neck width and cortical thickness were also higher in young men than in women. Neck width increased and cortical thickness decreased with age in both sexes. The buckling ratio, an index of local cortical instability, increased more rapidly in women. The compressive strength decreased progressively with age in women, whereas it did not change in men after 50 yr of age. Compressive strength and the buckling ratio showed the largest difference between control and hip fracture women (Z=-1.3). This cross-sectional study suggests that data available in the standard DXA output can easily be used to estimate several geometrical parameters of the femoral neck that evolve in a sex- and age-specific manner. Further studies are needed to elucidate whether they add significant information to BMD in the prediction of fracture risk.