Mechanical Property Distributions in the Cancellous Bone of the Human Proximal Femur

Abstract

Proximal femurs obtained at routine autopsy were sectioned into large numbers of 5 mm cubic specimens, in order to obtain detailed quantitative information about the spatial and directional variations of the material properties of the cancellous bone. Low strain rate compression tests were performed, evaluating the apparent elastic modulus and yield strength, in three perpendicular testing directions, for each cube. A computer contouring program was used to assemble the experimental data into smoothed distribution plots across sections of interest. The results revealed stiffness and strength elevations/reductions which clearly correspond to roentgenographic features. Especially prominent stiffness elevations (160 to 400 percent above the overall cancellous bone average) were found in the regions traversed by the primary trabeculation system, although the modulus of the bone samples was substantially reduced when measured in directions other than those of habitual weight-bearing. Similar but less pronounced effects were observed for the arcuate trabeculation system. Conversely, Wards triangle and the intertrochanteric regions exhibited significant (as much as 40 to 90 percent below average) stiffness and strength reductions. There was close qualitative agreement between the stiffness and yield strength distributions for all sections examined. This phenomenon was found to be a corollary of the remarkably linear proportionality between the modulus and yield strength values for individual compression tests.