Prediction of vertebral strength by dual photon absorptiometry and quantitative computed tomography.

We measured the lumbar bone mineral of 19 cadavers (10 women, 9 men) by dual photon absorptiometry (DPA) and quantitative computed tomography (QCT). In addition, we determined the ultimate load and stress of each vertebra, and finally ash content and volumetric ash density of the vertebral body. We found that single energy QCT was inferior to DPA and dual energy QCT in the prediction of the ultimate load or stress of vertebrae (P less than 0.001). The ultimate stress was best predicted by using the dual energy QCT results (r = 0.71; SEE = 36.3 N/cm2) whereas the ultimate vertebral load was best predicted by using the DPA (BMC) results (r = 0.80; SEE = 740 N). If the QCT finding was multiplied with the surface area of the vertebral body it could be used to predict the ultimate load with good accuracy (r = 0.74; SEE = 841 N). All the above correlations were higher in women than in men. The frequency of vertebral compression fractures in the material was well correlated with the bone mineral findings. A nonlinear (third degree) relationship between mineral content and mechanical characteristics is proposed but within the area of measurement used in clinical practice a linear (first degree) equation is preferred.