Cortical bone adaptation to mechanical environment: Strain energy density versus fluid motion

Abstract

This chapter presents an in silico study to compare the osteogenic potentials of normal strain-derived strain energy density (SED) and fluid shear. In vivo studies reported that mechanical loading promotes osteogenesis (i.e., new bone formation) at the sites elevated normal strain magnitude. Accordingly, in silico models assumed normal strain-derived SED as an osteogenic stimulus to predict the sitespecific new bone formation. Nevertheless, there are in vivo studies where new bone formation is noticed at the sites of minimal normal strain magnitude especially near the neutral axis of bending. It is anticipated that SED as stimulus will have limited success in explaining such new bone distribution. Thus, there is no unifying principle that can relate the new bone formation to mechanical environment. A secondary component of mechanical environment, i.e., canalicular fluid flow derived shear, is reported as a potential stimulus of osteogenesis in the literature; however, their exact role is not well established. Therefore, this chapter presents an in silico model which studies site-specific new bone formation as a function of SED and fluid shear, individually and in their combination. The model simulates experimental new bone formation reported in different in vivo animal loading studies. The chapter also concludes that fluid shear closely fits the new bone formation near the minimal strain sites, and both SED and fluid shear contribute collectively to new bone formation. The findings presented in the chapter may be useful in the design of biomechanical strategies to cure bone loss and also in the improvement of the design of orthopedic implants.