IMPROVED METHOD FOR ANALYSIS OF WHOLE BONE TORSION TESTS

Structural tests, such as whole bone torsion tests, have become widely accepted methods for assessing average bone material properties. To s implify interpretation of these tests, the nonuniform bone geometry is often analyzed as a tube with a constant cross section (prismatic) an d the areal properties of the smallest bone section. This approach may not adequately represent the true torsional behavior of the cross sec tion and does not account for any lengthwise variations in bone geomet ry. The errors introduced by these approximations are particularly sig nificant when comparing bones of different sizes and geometries. In th is paper, we examine the effects of approximating the cross-sectional torsional behavior and of neglecting lengthwise variations in bone geo metry. We then present a simple, standardized procedure utilizing a FO RTRAN computer program for accurate determination of material properti es. We examine first simple idealized bone geometries and then a compl ex three-dimensional model of the femur from a 26-day-old male Sprague -Dawley rat. For these models, the conventional methods for interpreti ng torsion tests introduce errors of up to 42% in the shear modulus an d up to 48% in the maximum shear stress; a straightforward extension o f these methods reduces the errors to within 3%.