Bending strength of the femur in relation to non-invasive bone mineral assessment

To analyze the importance of bone mineral for the strength of the distal diaphyseal femur, we studied 14 distal cadaver femora by quantitative computed tomography, (QCT) dual energy X-ray (DXA) absorptiometry and three-point bending. The femora were retrieved at autopsy from 10 male and 4 female donors aged median 74 yr (range 59-92 yr). Significant correlations were found between three bone mineral mass related parameters--QCT bone mass (density x slice area), DXA mineral density (BMD) and content (BMC)--and mechanical parameters. Second area moment equivalents correlated significantly with the mechanical properties of the distal femur. QCT density did not show the same high correlations. The results indicate that the structural strength of diaphyseal bone is determined more by its geometry than mineral density. Assessment of bone mass by QCT or DXA may become important not only for assessment of fracture risk but also for planning of internal fixation in the treatment of osteporotic fractures. Further studies are required to investigate the clinical importance of these observations.