Comparison of methods for assigning the material properties of the distraction callus in computational models

Abstract

In silico models of distraction osteogenesis and fracture healing usually assume constant mechanical properties for the new bone tissue generated. In addition, these models do not always account for the porosity of the woven bone and its evolution. In this study, finite element analyses based on computed tomography (CT) are used to predict the stiffness of the callus until 69 weeks after surgery using 15 CT images obtained at different stages of an experiment on bone transport, technique in which distraction osteogenesis is used to correct bone defects. Three different approaches were used to assign the mechanical properties to the new bone tissue. First, constant mechanical properties of the hard callus tissue and no porosity were assumed. Nevertheless, this approach did not show good correlations. Second, random variations in the elastic modulus and porosity of the woven bone were taken from previous experimental studies. Finally, the elastic properties of each element were assigned depending on gray scale in CT images. The numerically predicted callus stiffness was compared with previous in vivo measurements. It was concluded firstly that assignment depending on gray scale is the method that provides the best results and secondly that the method that considers a random distribution of porosity and elastic modulus of the callus is also suitable to predict the callus stiffness from 15 weeks after surgery. This finding provides a method for assigning the material properties of the distraction callus, which does not require CT images and may contribute to improve current in silico models.

Biomechanical duality of fracture healing captured using virtual modeling and validated in ovine bones

“…. A literature review led to uncertainty regarding the true mechanical properties of fibrous and cartilaginous constituents of callus (27)(28)(29)(30)(31)(32)(33), so a three orders-of-magnitude variation in soft callus modulus values was tested ( = 0.5, 5, 50, or 500 MPa). After optimization of the density cutoff for applying the soft modulus, we found that the dual-zone models with ≥ 5…”

Mechanobiology of Bone Consolidation During Distraction Osteogenesis: Bone Lengthening Vs. Bone Transport

“…These geometric parameters were calculated with the aid of CT images taken after the slaughter of the animal, and more details are described in the following subsection. Despite the changes in the percentage of mineralized volume reported by Mora-Macı´as et al, 31,35 this strategy is justified by the scarce variation in the total volume of the bone callus (TV), bone volume (BV) plus non-mineralized soft tissue, during the consolidation phase, approximately the first 200 days after surgery. Therefore, the evolution of the mechanical properties of the bone callus during the consolidation phase was estimated as:…”

“…Therefore, the aim of this study is to analyze the evolution of several mechanical parameters during the consolidation of the BL callus, and compare them with the BT results reported by Mora-Macı´as et al. [30][31][32][33][34][35][36] The differences in the evolution of kinetic and kinematics parameters from gait analysis were studied, as well as their possible relationship with the ossification of the resulting bone callus. This comparison was supplemented by quantifying in vivo the mechanical properties of the tissue through indirect non-invasive techniques, instrumented fixator, and CT images.…”

“…8 The application of all these in vivo techniques extends the knowledge of DO processes and provides information for the development of numerical models for the in silico mechanical characterization of the callus as a future clinical tool. 31,[43][44][45][46]55 Extensive literature has recognized the decisive role that several biomechanical factors play in bone regeneration processes. 6,21,23,49 These factors, which affect the quantity and quality of new tissue, have been historically optimized in several DO applications to control the stress and strain distribution through the bone callus, which affect the quantity and quality of new tissue.…”

“…In the literature, most research does not involve several measuring techniques for the analysis of multiple biomechanical parameters under a fixed distraction protocol, fixation system, and animal model. One exception is found in the BT studies of Mora-Macı´as et al, [30][31][32][33][34][35][36] which combine numerous in vivo and ex vivo approaches, resulting in an exhaustive characterization of the BT callus and its regeneration process using an unchanging experimental protocol and animal model. These BT studies, which form the basis of this work, have been reproduced in BL to look at the mechanobiological dissimilitude between both processes.…”