STRAIN GRADIENTS CORRELATE WITH SITES OF PERIOSTEAL BONE-FORMATION

We examined the hypothesis that peak magnitude strain gradients are sp atially correlated with sites of bone formation, Ten adult male turkey s underwent functional isolation of the right radius and a subsequent 4-week exogenous loading regimen, Full field solutions of the engender ed strains were obtained for each animal using animal-specific, orthot ropic finite element models, Circumferential, radial, and longitudinal gradients of normal strain were calculated from these solutions, Site -specific bone formation within 24 equal angle pie sectors was determi ned by automated image analysis of microradiographs taken from the mid -diaphysis of the experimental radii, The loading regimen increased me an cortical area (+/-SE) by 32.3 +/- 10.5% (p = 0.01), Across animals, some periosteal bone formation was observed in every sector, The amou nt of periosteal new bone area contained within each sector was not un iform, Circumferential strain gradients (r(2) = 0.36) were most strong ly correlated with the observed periosteal bone formation, SED (a scal ar measure of stress/strain magnitude with minimal relation to fluid f low) was poorly correlated with periosteal bone formation (r(2) = 0.01 ). The combination of circumferential, radial, and longitudinal strain gradients accounted for over 60% of the periosteal new bone area (r(2 ) = 0.63), These data indicate that strain gradients, which are readil y determined given a knowledge of the bone's strain environment and ge ometry, may be used to predict specific locations of new bone formatio n stimulated by mechanical loading.