Experimental Validation of a Finite Element Model of the Proximal Femur Using Digital Image Correlation and a Composite Bone Model

Abstract

Computational biomechanical models are useful tools for supporting orthopedic implant design and surgical decision making, but because they are a simplification of the clinical scenario they must be carefully validated to ensure that they are still representative. The goal of this study was to assess the validity of the generation process of a structural finite element model of the proximal femur employing the digital image correlation (DIC) strain measurement technique. A finite element analysis model of the proximal femur subjected to gait loading was generated from a CT scan of an analog composite femur, and its predicted mechanical behavior was compared with an experimental model. Whereas previous studies have employed strain gauging to obtain discreet point data for validation, in this study DIC was used for full field quantified comparison of the predicted and experimentally measured strains. The strain predicted by the computational model was in good agreement with experimental measurements, with R(2) correlation values from 0.83 to 0.92 between the simulation and the tests. The sensitivity and repeatability of the strain measurements were comparable to or better than values reported in the literature for other DIC tests on tissue specimens. The experimental-model correlation was in the same range as values obtained from strain gauging, but the DIC technique produced more detailed, full field data and is potentially easier to use. As such, the findings supported the validity of the model generation process, giving greater confidence in the model's predictions, and digital image correlation was demonstrated as a useful tool for the validation of biomechanical models.

Full-field in vitro measurements and in silico predictions of strain shielding in the implanted femur after total hip arthroplasty

“…25,[28][29][30] Tayton et al 26 employed DIC to find the differences in 2-D strain patterns generated in the medial cortex of composite femurs implanted with femoral prostheses of different material stiffness. Dickinson et al 14 tested one composite femur bone in quasi-static loading, and measured the strain distribution using DIC in order to validate a corresponding FE model. DIC data were averaged within 25 different 5 mm 2 areas, and compared to equivalent strain magnitude predictions from the FE model.…”

“…[10][11][12][13] However, the restricted area of interrogation associated with strain gauges is considered to be a limitation of the technique and recently, non-destructive optical measurement methods such as Digital Image Correlation (DIC) have gained popularity because of their full-field data-rich strain measurement capability. [14][15][16] DIC is a well-established non-contact optical metrology method that extracts full-field deformation measurements of objects subjected to external loads. 17,18 It is particularly useful for measuring deformations in complex geometries with inhomogeneous material properties, like human bone, by finding spatial correspondences between different digital images.…”

“…[20][21][22] Recently, a series of investigations has been carried out using DIC to measure strains over bone surfaces. [14][15][16][23][24][25] Despite its strong potential, the use of DIC has largely been restricted to FE validation purposes in experimental biomechanics. Moreover, only a few such investigations were carried out on the femur, either using composite 14,19,26,27 or cadaver specimens.…”

“…[14][15][16][23][24][25] Despite its strong potential, the use of DIC has largely been restricted to FE validation purposes in experimental biomechanics. Moreover, only a few such investigations were carried out on the femur, either using composite 14,19,26,27 or cadaver specimens. 25,[28][29][30] Tayton et al 26 employed DIC to find the differences in 2-D strain patterns generated in the medial cortex of composite femurs implanted with femoral prostheses of different material stiffness.…”

About the inevitable compromise between spatial resolution and accuracy of strain measurement for bone tissue: A 3D zero-strain study

“…However, little is known about the local distribution of stress and strain of bone under certain loads, information necessary to study how bone structure and its local mechanical competence are related. At the organ level strain gages (Cristofolini et al, 2010;Trabelsi and Yosibash, 2011) and digital image correlation (DIC) techniques (Amin Yavari et al, 2013;Dickinson et al, 2011) have been used to perform strain measurement on a limited portion of the external surface of the tested bone. However, these methods can not be used at the biopsy level, where the space is limited and 3D volumetric information becomes essential due to the complex microstructure.…”