Endochondral Growth in Growth Plates of Three Species at Two Anatomical Locations Modulated by Mechanical Compression and Tension

Sustained mechanical loading alters longitudinal growth of bones, and this growth sensitivity to load has been implicated in progression of skeletal deformities during growth. The objective of this study was to quantify the relationship between altered growth and different magnitudesofsustainedalteredstressinadiversesetofnonhumangrowthplates.Thesensitivityof endochondral growth to differing magnitudes of sustained compression or distraction stress was measured in growth plates of three species of immature animals (rats, rabbits, calves) at two anatomicallocations(caudalvertebraandproximaltibia)withtwodifferentagesofratsandrabbits. An external loading apparatus was applied for 8 days, and growth was measured as the distance between fluorescent markers administered 24 and 48 h prior to euthanasia. An apparently linear relationship between stress and percentage growth modulation (percent difference between loaded andcontrolgrowthplates)wasfound,withdistractionacceleratinggrowthandcompressionslowing growth. The growth-rate sensitivity to stress was between 9.2 and 23.9% per 0.1 MPa for different growth plates and averaged 17.1% per 0.1 MPa. The growth-rate sensitivity to stress differed between vertebrae and the proximal tibia (15 and 18.6% per 0.1 MPa, respectively). The range of control growth rates of different growth plates was large (30 microns/day for rat vertebrae to 366 microns/day for rabbit proximal tibia). The relatively small differences in growth-rate sensitivityto stressfora diverse setof growthplatessuggestthat theseresultsmight be generalized toothergrowthplates,includinghuman.Thesedatamaybeapplicabletoplanningthemanagement