MECHANICAL VALIDATION OF A TOMOGRAPHIC (PQCT) INDEX FOR NONINVASIVE ESTIMATION OF RAT FEMUR BENDING STRENGTH

Cross-sectional moment of inertia (CSMI) and volumetric cortical bone mineral density (vCtBMD) were assessed by peripheral quantitative comp uted tomography (pQCT) at femur midshafts from 103 Wistar female rats receiving 0 (n = 12) or 15-1000 mu g/kg/day sc of dexamethasone (n = 4 6) from 5 to 9 weeks of age, or 0 or 80 mg/kg 3/wk of AI(OH)(3) IP (n = 23,22) from 4 to 10 months of age, A bone strength index (BSI), calc ulated as the product CSMI x vCtBMD, was found to closely correlate (r = 0.94, R(2) = 0.89, p much less than 0.001) with the actual, mechani cally tested bending breaking force of all bones. Correlation and dete rmination coefficients obtained were higher than those usually reporte d employing different long-bone strength predictive formulae. The curv e approached the origin and was linear throughout the wide range of CS MI, vCtBMD and BSI achieved because of age- and treatment-induced diff erences, showing a very low standard error of the estimate, Instead, d ifferent curve slopes and/or intercepts were found in separate analysi s between data from each of the experiments when breaking force was co rrelated with CSR;II or vCtBMD alone, or with the DEXA-assessed BMD of the mechanically assayed bone portion, Results suggest that noninvasi ve assessment of the BSI by means of pQCT technology provides an origi nal tool for a precise and accurate estimation of long-bone bending st rength that can be advantageously applied in cross-sectional as well a s longitudinal, in vivo studies employing animal models.