Patient‐specific modelling of bone and bone‐implant systems: the challenges

Abstract

In the past three decades, finite element (FE) modelling has provided considerable understanding to the area of musculoskeletal biomechanics. However, most of this understanding has been generated using generic, standardised or idealised models. Patient-specific modelling (PSM) is almost never used for making clinical decisions. Imaging technologies have made it possible to create patient-specific geometries and FE meshes for modelling. While these have brought us closer to PSM, several challenges associated with the definition of material properties, loads, boundary conditions and interaction between components still need to be overcome. This study reviews the current status of PSM with respect to defining material behaviour and prescribing boundary conditions and interactions. With regard to the constitutive modelling of bone, it is seen that imaging is being increasingly used to define elastic properties (isotropic as well as anisotropic). However, the post-elastic and time-dependent behaviour, important for several modelling situations, is mostly obtained from in vitro experiments. Strain-based plasticity, not commonly available in FE codes, appears to have the potential of reducing an element of patient-specificity in modelling the yielding behaviour of bone. PSM of real boundary conditions that include muscles and ligaments continues to remain a challenge; many clinically relevant questions can be, however, answered without their inclusion. Simulation techniques to undertake PSM of interactions between bone and uncemented implants are available. Interference fit employed in both joint replacement fracture treatments induces considerable preload whose inclusion in models is important for the prediction of interface behaviour.

Minimization of dental implant diameter and length according to bone quality determined by finite element analysis and optimized calculation

“…In this study, trabecular bone was assumed to be homogenous and isotropic, which differs from patient-specific FE models [9,10] using real structures of trabecular bone from computed tomography data, and the anisotropic properties [11] of real bone. It would be clinically useful if patient-specific FE models could routinely be constructed easily for clinical diagnosis of bone 13 quality with a lower cost.…”

“…However, some problems still remain. [9,10] Thus, simplified models applicable to every case are considered to be better to investigate the general influence of bone properties. Because of this simplification, the results of this study should be verified with patient-specific models in the future.…”

Experimental validation of finite element predicted bone strain in the human metatarsal

“…Over the years, the geometry of bones has improved from using generic and idealized two-dimensional models (158-160) to three-dimensional subject-specific models, which are becoming more commonly used (161). Bone geometries for the latter are typically generated using x-ray computed tomography (CT) or magnetic resonance imaging (MRI) scans (162,163).…”

“…One way is to perform mechanical tests on small bone samples in different orientations to obtain the appropriate engineering constants (228)(229)(230), although the mechanics tests are often subject to end effects (100). Ultrasonic methods could also be used to evaluate elastic constants on small bone specimens, but this does not account for the tissue's heterogeneity (162) or post-yield mechanical behavior. Furthermore, it may be impractical to extract such small bone samples from relatively small bones such as the metatarsals.…”

Four decades of finite element analysis of orthopaedic devices: Where are we now and what are the opportunities?

“…FE has been used across the full spectrum of orthopaedic devices and there have been a number of thorough reviews (Huiskes and Chao, 1983;Huiskes and Hollister, 1993;Prendergast, 1997;Viceconti et al, 2009;Laz and Browne, 2010;Erdemir et al, 2012;Pankaj, 2013;Taylor et al, 2013;Carr and Goswami, 2009;Prendergast, 2001). The main focus of this review will be hip and knee replacement, as these have been studied the most, but the issues raised are applicable to the simulation of all orthopaedic devices.…”