Meeting Abstract
8.10 Jan. 4 Reconstructing the loading environment of long bones from in vivo strain data DEMES, Brigitte; Stony Brook University bdemes@ms.cc.sunysb.edu
The in vivo strain measurement method has proven to be an important tool for exploring the interface between skeletal loading and bone shape. Strains recorded from multiple sites around the circumference of long bone shafts can be used to characterize the normal strain distribution in bone cross sections and determine the position of the zero-strain neutral axis. To correctly reconstruct the direction of the external bending moment from such data, the geometry of the cross section must also be considered. Using primate long bones as an example, angular discrepancy between bending axis and neutral axis is explored. If the principal moments of area are similar (Imax ~ Imin), orientations of bending and neutral axes are similar, no matter in which plane the external moment acts. With Imax >> Imin, bending and neutral axes are concordant only in bending around the principal or symmetry axes. Bending around other axes (asymmetric bending) results in a shift of the bending axis away from the neutral axis, towards the minor or weaker principal axis. For many primate long bones, with Imax/Imin ratios <1.5, the concordance between bending axis and neutral axis will be high, independent from the direction of the applied moment. At Imax/Imin = 1.5, the discrepancy in angles is 10o at most. At Imax/Imin > 1.5, however, asymmetric bending becomes an issue and must be considered when reconstructing the external bending moments from in vivo strain data. Fortunately, standard engineering equations are available that describe the directional relationship between the bending axis and the neutral axis, and can be used for axis �corrections� in highly asymmetric bones. The bone biology literature has paid little attention to asymmetric bending, despite its potential for producing erroneous results when reconstructing bone loading environments. Supported by NSF BCS 0548892
