Influence of the frequency of the external mechanical stimulus on bone healing: a computational study

The mechanical environment considerably affects the evolution of the bone healing process. However, the effect of an external cyclic stimulation on the process has not yet been fully clarified. The aim of the present work is to evaluate the distribution of different mechanical variables in the fracture callus when an external cyclic stimulation is applied at different frequencies, in order to investigate those stimuli most likely to regulate bone healing. To perform this analysis an axisymmetric poroelastic finite element model of a sheep metatarsus fracture has been developed and several mechanical variables quantified within the callus: deviatoric strain, octahedral strain, pore pressure and fluid flow velocity. The applied mechanical stimulus corresponds to a compression displacement of 0.02 mm at frequencies of 1, 50 and 100Hz. The fluid flow velocity experiences considerable variations in amplitude and peak value when the frequency of the external stimulus changes, while the rest of the mechanical variables are not significatively modified. We conclude that the change in the frequency of the external mechanical stimulus directly affects the interstitial fluid flow velocity in the fracture callus. This change in the fluid flow velocity may induce movement of wastes, feeds or growth factors, as well as stimulating cellular differentiation and proliferation by means of changes in the mechanical environment of the callus. In addition, the results of this work suggest that, to obtain a more significant effect of cyclic stimulation, higher frequencies with lower amplitude than those normally used in previous experimental works are needed.