STRUCTURAL AND MATERIAL MECHANICAL-PROPERTIES OF HUMAN VERTEBRAL CANCELLOUS BONE

The structural Young's modulus (i.e. that of the cancellous framework) was determined by non-destructive compressive mechanical testing in t he the ee orthogonal ax es of 48 vertebral bone cubes. In addition, th e material Young's modulus (i.e. of the trabeculae themselves) was est imated using an ultrasonic technique. Apparent and true density were d etermined by direct physical measurements. Significant mechanical anis otropy was observed: mean structural Young's modulus varied from 165 M Pa in the supero-inferior direction to 43 MPa in the lateral direction . Structural Young's modulus correlated with apparent density, with po wer-law regression models giving the best correlations (r(2) = 0.52-0. 88). Mechanical anisotropy increased as a function of decreasing appar ent density (p < 0.001). Material Young's modulus was 10.0 +/- 1.3 GPa , and was negatively correlated with apparent density (p < 0.001). In multiple regression models, material Young's modulus was a significant independent predictor of structural Young's modulus only in the super o-inferior direction. The data suggest the presence of two effects in vertebral bone associated with decreasing apparent density and, by imp lication, bone loss in general: (a) increased mechanical anisotropy su ch that there is relative conservation of stiffness in the axial direc tion compared with the transverse directions; and (b) increased stiffn ess of the trabeculae themselves. (C) 1997 IPEM Published by Elsevier Science Ltd.