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The load-carrying capacity of cortical bone is closely related to its geometry and to its fundamental material properties, including mineral content (BMC). Together these determine the bending stiffness EI, where I is the cross-sectional moment of inertia and E is Young's modulus of elasticity. To assess the relationship of BMC and bone width (BW) to EI in healthy women, we used mechanical response tissue analysis (MRTA), a noninvasive method that involves analysis of tissue responses to ulnar vibration. A total of 48 healthy women were enrolled into an older (64 +/- 1y, n = 25) and a younger (25 +/- 0.6y, n = 23) group. BMC and BW of the dominant ulna were measured by single-photon absorptiometry (SPA). EI was determined by MRTA. BMC (0.75 +/- 0.02 versus 0.63 +/- 0.02 g/cm), BMC/BW (0.75 +/- 0.02 versus 0.63 +/- 0.02 g/cm2), and EI (27.7 +/- 1.3 versus 21.3 +/- 1.1 N.m2) were significantly greater (p less than 0.005) in the young subjects. BW did not change with age (1.00 +/- 0.01 versus 1.01 +/- 0.01 cm). In young women, simple correlations of BMC and BW with EI were both significant. By multiple regression analysis only BW independently predicted EI (EI = -0.35 + 39.1 x BMC, R2 = 0.52). In older women BMC and BW correlated with EI, but in multiple regression only BMC was significant (EI = -34.5 + 62.1 x BW; R2 = 0.45). When this analysis of older women included only those whose BMC values were within 2 SD of the young mean, BMC remained the only significant predictor of EI.(ABSTRACT TRUNCATED AT 250 WORDS)

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