Differences in Mechanical Properties of the Human and Monkey Tibia
A method which uses an instrument that detects the response of a long bone to a vibratory stimulus to quantify mechanical properties non-invasively was revised and validated for use in the tibia. Stored data from healthy men was reanalyzed and compared with values from non-human primates. The analysis uses the relationship K(sub b) = 48 EI/L(sup 3) where K(sub b) is the lateral stiffness of a beam with force applied midspan, E is the elastic modulus, I the geometric moment of inertia and L, the limb length. Values for stiffness (EI, Nm(sup2)), the Euler buckling load (P(sub cr) = EI (pi/L)(sup 2)), and bone sufficiency (S) which represents the axial load the bone can support, adjusted to BW (S=P(sub cr)/BW) were obtained. The interest precision of the method in relaxed men, 5.8%, and in sedated male monkeys, 4.3%, was based on repeated measures in the same subjects at 1 month intervals. The R tibias of 40 men, aged 38.6 +/- 7.3 yrs with BW 78.9 +/- 7.9 kg, showed average (+/- SD) L to be 35 +/- 2 cm, EI 222 +/- 71 Nm(sup 2), P(sub cr) 18.1 +/- 4.9 kN, and S 23.4 +/- 5.7 N. The R tibias of 24 Rhesus monkeys ranging in age from 2-12 years, BW 4.9 +/- 3 kg, showed L to be 14.7 +/- 1.9 cm, EI 6.0 +/- 4.8 Nm(sup 2), P(sub cr) 2.51 +/- 1.2 kN and S 57.3 N. These measurements indicate that the tibia of a terrestrial non-human primate, M. mulatta, has higher load carrying capacity for the level of body weights in the species than the human bone.