Prediction of vertebral and femoral strength in vitro by bone mineral density measured at different skeletal sites.

The aim of the present study was to investigate the prediction of vertebral and femoral strength in vitro by bone mineral density (BMD) measured at different skeletal sites. The third lumbar vertebral body, the right proximal femur, and the right calcaneus were removed from 38 male and 32 female cadavers (mean age 69 years, range 23-92 years). Areal BMD of all bone specimens was determined by dual-energy X-ray absorptiometry (DXA). The failure load of the vertebral body and the femur was determined by mechanical testing. Vertebral and femoral strength were both greater in males than females (p < 0.01), as was BMD at all sites (p < 0.01). Vertebral strength correlated well with vertebral BMD (r2 = 0.64) but was only moderately correlated with BMD measured at the femur (r2 = 0.36) or the calcaneus (r2 = 0.18). Femoral strength showed the highest correlations with femoral BMD (r2 = 0.88) and somewhat weaker relationships with BMD at the vertebra (r2 = 0.50) and the calcaneus (r2 = 0.54). BMD values at the vertebra, femur, and calcaneus were only moderately interrelated (r2 = 0.31-0.65), and vertebral strength correlated only modestly with the strength of the femur (r2 = 0.36). These in vitro results support the concept that optimal prediction of vertebral or femoral strength by DXA requires site-specific assessments.