Discriminant capacity of quantitative ultrasound versus dual x-ray absorptiometry to determine cancellous bone loss in ovariectomized rats

The capacity of dual x-ray absorptiometry and quantitative ultrasound to di scriminate bone loss and to predict the mechanical and microarchitectural p roperties of cancellous bone in an animal model of osteopenia was evaluated . Thirty-five female Sprague-Dawley rats (10 months old) were randomized in to three groups: baseline group, 10 rats killed at the beginning of the stu dy ovx group, 15 rats ovariectomized; and sham group, 10 rats sham operated . At the beginning and end of the study, all the animals underwent osteoson ography to record the proximal tail (C3 vertebra) bone speed of sound. Sixt een weeks after surgery, the animals were euthanized and the L5-6 lumbar ve rtebrae of each rat were excised for densitometric, biomechanical (compress ion test), and histomorphometric studies, Significant differences were foun d among the groups for final speed of sound (p = 0.01). The L5 bone mineral density of the ovx group decreased by 12.1% (p = 0.0-19) and 12.6% (p = 0. 035) compared, respectively; with baseline and sham groups. The biomechanic al parameters of the ovx group decreased by 15-47% compared with the other Groups, shelving significant differences between the ovx and sham groups bo th for maximal stress (p = 0.026) and elastic modulus (p = 0.013). Histomor phometric parameters of the ovx group showed significant decreases in compa rison with other groups. Logistic regression analysis showed that dual X-ra y absorptiometry and quantitative ultrasound discriminate ovariectomized an d healthy rats with a similar capacity, classifying correctly all rats used in the model in a range of 61-70%. This similar capacity seems to derive f rom two different capacities to detect bone changes. Dual X-ray absorptiome try, depending on bone mineralization and density, is able to detect modifi cations in bone stiffness and strength, confirmed also by the correlation w ith biomechanical data. On the contrary, quantitative ultrasound seems to d epend more on cancellous bone microarchitecural changes because it is corre lated to histomorphometric parameters. (C) 2000 by Elsevier Science Inc. Al l rights reserved.