Finite Element Models of Osteocytes and Their Load-Induced Activation

Purpose of Review Osteocytes are the conductors of bone adaptation and remodelling. Buried inside the calcified matrix, they sense mechanical cues and signal osteoclasts in case of low activity, and osteoblasts when stresses are high. How do osteocytes detect mechanical stress? What physical signal do they perceive? Finite element analysis is a useful tool to address these questions as it allows calculating stresses, strains and fluid flow where they cannot be measured. The purpose of this review is to evaluate the capabilities and challenges of finite element models of bone, in particular the osteocytes and load-induced activation mechanisms. Recent Findings High-resolution imaging and increased computational power allow ever more detailed modelling of osteocytes, either in isolation or embedded within the mineralised matrix. Over the years, homogeneous models of bone and osteocytes got replaced by heterogeneous and microstructural models, including, e.g. the lacuno-canalicular network and the cytoskeleton. The lacuno-canalicular network induces strain amplifications and the osteocyte protrusions seem to be stimulated much more than the cell body, both by strain and fluid flow. More realistic cell geometries, like minute constrictions of the canaliculi, increase this effect. Microstructural osteocyte models describe the transduction of external stimuli to the nucleus. Supracellular multiscale models (e.g. of a tunnelling osteon) allow to study differential loading of osteocytes and to distinguish between strain and fluid flow as the pivotal stimulatory cue. In the future, the finite element models may be enhanced by including chemical transport and intercellular communication between osteocytes, osteoclasts and osteoblasts.

Automated summary

This article discusses the role of osteocytes in bone adaptation and remodelling, and explores the application of finite element analysis in studying the capabilities and challenges of osteocytes. Recent advancements in high-resolution imaging and computational power have allowed for more detailed modelling of osteocytes, including the lacuno-canalicular network and the cytoskeleton. Microstructural osteocyte models describe how external stimuli are transmitted to the nucleus. Supracellular multiscale models enable the study of differential loading of osteocytes and the differentiation between strain and fluid flow as the key stimulatory cue.