Meeting Abstract
25.5 Jan. 5 Within-bone Variation in Stiffness Measured by Nanoindentation in High-running Mice MIDDLETON, K.M.*; GARLAND, T., Jr.; GOLDSTEIN, B.D.; GUDURU, P.R.; KELLY, S.A.; SWARTZ, S.M.; Brown Univ.; Univ. Calif., Riverside; Brown Univ.; Brown Univ.; Univ. Calif., Riverside; Brown Univ. kmm@brown.edu
A bone�s loading response is, in part, a reaction to dynamic forces filtered through multiple levels of structure, from micro-scale material properties to macro-scale geometry. Studies of large mammals and the complex shape of the mouse femur, suggest that regions of both compression and tension will be present during loading. We hypothesize that stiffness will vary according to anatomical quadrant in bone�s cortex and that modulus will differ among groups experiencing different levels of exercise. We measured modulus in femora of 48 female mice, half from lines selected for high levels of voluntary wheel running (37 generations) and half from control lines. Additionally, half had access to a wheel for 13-14 weeks beginning at 53-60 days of age, allowing the separation of selection effects from activity effects. Modulus was measured at the mid-shaft via nanoindentation at four quadrants (anterior, posterior, medial, lateral). No significant variation in modulus in any single quadrant was found due to selection, activity, or an interaction. However, when all samples were pooled for a quadrant, significant differences were present. Moduli in the anterior and lateral quadrants were significantly higher (32.1 and 32.4 GPa, respectively) than at the posterior and medial quadrants (30.1 and 29.8 GPa). This pattern of higher modulus in the anterolateral vs. posteromedial cortex agrees with published data for some bones of large mammals (e.g., horse radii and metacarpals, human tibiae), but such a pattern has not previously been demonstrated in small mammals. These data suggest that the long bones of large and small mammals may respond to similarly at the tissue level despite vastly different loads. Supported by NIH 1F32AR053008-01 to K.M., NSF IOB-0543429 to T.G., and NSF CMS-0547032 to P.G.
