OBJECTIVE: Ultrasound transmission velocity (UTV) and bone mineral density (BMD) were examined as possible predictors of the bending strength of osteoporotic long bones in ovariectomized rats treated with calcium-depleted diet. BACKGROUND: Changes in cancellous bone quality due to osteoporosis have been well documented, but only a few studies described non-invasive assessment of the biomechanical quality of long bones. METHODS: Forty-three rats were divided into three groups: ovariectomized and calcium-depleted diet, ovariectomized and standard diet, and untreated controls. All femora were scanned by quantitative computed tomography (QCT) to measure BMD and cortical dimensions at the mid-diaphysis. Bending strength was determined from the maximum bending moment and the femoral cortical dimensions at the mid-diaphysis. The UTV of cortical bond at the mid-disphysis of the femur was measured in the proximal/distal direction. RESULTS: It was found that bending strength was significantly different among the groups (p<0.0001). Despite the fact that bending strength of the osteoporotic rat femur significantly decreased, the osteoporotic effect did not produce a significant change in cortical thickness. UTV in the ovariectomized and calcium-depleted diet was lower than in the other groups; however, no significant differences were found betwene those on the standard diet and the untreated controls. The BMD in ovariectomized rats was also significantly lower than in the untreated controls (p<0.05); however, the BMD in those fed with the calcium-depleted diet was not significantly different from those with the standard diet. Both cortical UTV and BMD as a single variable may not predict changes in bending strength of the cortical bone at the mid-diaphysis of the rat femur. However, the combined effect of UTV and BMD was significantly better than a single parameter in the assessment of strength. RELEVANCE: Osteoporotic fracture results from the reduced BMD and the microstructural changes involving the entire skeleton. The ovariectomized rats with calcium-depleted diets may simulate a model for the human postmenopausal osteoporosis. Ultrasound measurements of cortical bone may not be better predictors of osteoporotic fracture risk than those of cancellous bone. The strength of osteoporotic long bone may not be properly predicted by either BMD or UTV as a single determinant, measured at the cortical bone of the rat femur.