Finite Element Models of Osteocytes and Their Load-Induced Activation

Abstract

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. Summary 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.

Multiscale morphological analysis of bone microarchitecture around Mg-10Gd implants

“…Finite element fluid flow techniques and computational fluid flow dynamics (CFD) such as fluid-structure interaction (FSI) could offer promising approach for predicting the mechanical strain near implants [ 102 ]. By integrating the morphological architecture of the implant as well as that of the surrounding bone eg: ECM, LCN and vascular architectures in a FSI model, valuable insights on the impact of flow velocities and pressure regulation on the mechanical adaptation of the bone such as maximal principal strain, fluid shear stress and extent of osteocyte deformation upon perception of shear stress and the distribution of forces within the ECM can be obtained [ 103 , 104 ]. Alternatively, an approach would be to build a comprehensive multiscale model that incorporates the actual mechanical stress experienced by the bone during gait cycles [ 105 ].…”

Predicting Cortical Bone Resorption in Disuse Condition Caused by Transient Muscle Paralysis

“…However, in-vivo studies have been unable to measure exact fluid velocity due to the inaccessibility of the LCN. Hence, the finite element method have been used to quantify the fluid velocity (Meslier and Shefelbine, 2023) (Steck et al, 2003) (Pereira et al, 2015)(Smit, 2022) (Kumar et al, 2011) (Van Tol et al, 2020) (Teresa et al, 2020). Recently, one study confirmed that Botox-induced muscle paralysis significantly affects the bone’s morphology (Gatti et al, 2019), leading to decreased fluid velocity around the osteocyte (Gatti et al, 2021), which motivates us to consider the loss of fluid flow for modelling bone loss.…”