Dual photon absorptiometry in lumbar vertebrae. Evaluation of the baseline error.

In connection with determination of the bone mineral content in the third lumbar vertebra by dual photon absorptiometry, the fat in the adipose capsules of the kidneys is assumed to cause erroneous positioning of the baseline, leading to overestimation of the bone mineral content. The bone mineral content in L3 was measured in situ (BMC1) and vitro (BMC2) in 14 cadavers. The difference between BMC1 and BMC2 was significantly greater than zero, the median value being 0.32 g/cm at the confidence level of 94.4 per cent. It is concluded that at correlation between bone mineral content and compressive strength in vitro, the in vivo strength is overestimated by about 250 N.