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%.