Short communicationAccuracy of finite element predictions in sideways load configurations for the proximal human femur
Introduction
Osteoporosis and sideways fall are known to be two of the major determinants of proximal femur fractures among the elderly (Berry and Miller, 2008, Courtney et al., 1995, Greenspan et al., 1998, Parkkari et al., 1999). Current methods for fracture risk evaluation, based on densitometry and epidemiological parameters (Kanis et al., 2005), are not free from limitations (Lekamwasam, 2010, Silverman and Calderon, 2010, Watts et al., 2009). A major concern is that areal bone mineral density is the only bone strength determinant included (Ensrud et al., 2009, Gagnon and Ebeling, 2009). Subject-specific finite element (FE) models of bones from Computed Tomography (CT) data have been proposed to improve fracture risk prediction, since they can take into account the structural determinants of bone strength and the variety of external loads acting on bones (Cody et al., 1999). A preliminary requirement for clinical application is the in-vitro validation of FE models predictions (Viceconti et al., 2005).
The majority of FE validation studies in literature focused on bone strength prediction in quasi-axial loading configurations (e.g. resembling single stance configuration), while few works aimed at validating FE models in sideways fall configurations. Among those who addressed sideways fall (Keyak et al., 2001, Koivumäki et al., 2010, Majumder et al., 2009, Verhulp et al., 2008, Wakao et al., 2009), most of them try to directly predict bone strength, without preliminarily assessing the accuracy in elastic strain prediction, even if using a strain-based elastic limit criterion.
To the authors' knowledge, only one work (Lotz et al., 1991) reported FE strain prediction accuracy in sideways fall configurations. However, this work was limited to one femur and one loading configuration, while falling to the side may give rise to a variety of boundary conditions (Groen et al., 2008, Nankaku et al., 2005, Wakao et al., 2009), and achieved a limited strain prediction accuracy (R2=0.67, calculated from the raw data reported in the paper).
Recently, the authors developed a methodology to generate subject-specific FE models of femurs from CT data (Schileo et al., 2007, Schileo et al., 2008, Taddei et al., 2006). This methodology achieved under quasi-axial loading configurations a high in vitro strain prediction accuracy, comparable to the authors' knowledge only to (Bessho et al., 2007, Trabelsi et al., 2009).
The aim of the present work was to verify if the FE modelling procedure proposed in (Schileo et al., 2008), hereinafter called “reference study”, could accurately predict the strain levels elicited by low magnitude loads applied in vitro in sideways loading conditions.
Section snippets
Materials and methods
Three unpaired cadaver femora showing no deformities were obtained from IIAM (www.iiam.org) and embalmed in a 4% formalin solution (Öhman et al., 2008). They were scanned with CT (HiSpeed GE Co., USA, pixel size 0.59 mm, slice thickness 1 mm from femoral head to lesser trochanter, 5 mm elsewhere) and dual energy X-ray absorptiometry (DXA) (Eclipse, Norland Co., USA) (Table 1).
Experimental measurements
Strain increased linearly with load for each individual strain gauge, and each loading configuration: R2≥0.99 for 98% of the cases where strains reached a value of 100 microstrain or larger. Similarly, displacements measured by LVDTs increased linearly with load (R2≥0.85 for 94% of the cases where displacements reached a value of 50 μm or larger). This confirms that bone can be assumed to behave linearly with good approximation for the strain range and strain rates used in this study.
Comparison between predicted and measured strains
The FE
Discussion
The aim of the present study was to verify if a previously proposed FE modelling procedure (Schileo et al., 2008, Schileo et al., 2007) is capable to accurately predict in-vitro measured strains also in a range of sideways load configurations.
The main outcome of the present study is the achievement of a good strain prediction accuracy for the tested set of sideways load configurations, both in terms of correlation (R2>0.9) and error (RMSE%<10%). These results are comparable to those obtained in
Conflict of interest statement
None of the authors received nor will receive direct or indirect benefits from third parties for the performance of this study.
Acknowledgments
The present study was partially funded by EC Grant VPHOP (FP7-ICT2008-223865) and Emilia Romagna Region-University Research Programme 2007–2009.
References (37)
- et al.
Prediction of proximal femur strength using a CT-based nonlinear finite element method: differences in predicted fracture load and site with changing load and boundary conditions
Bone
(2009) - et al.
Prediction of strength and strain of the proximal femur by a CT-based finite element method
Journal of Biomechanics
(2007) - et al.
Femoral strength is better predicted by finite element models than QCT and DXA
Journal of Biomechanics
(1999) - et al.
Fall direction, bone mineral density, and function: risk factors for hip fracture in frail nursing home elderly
The American Journal of Medicine
(1998) - et al.
The relation between hip impact velocity and hip impact force differs between sideways fall techniques
Journal of Electromyography and Kinesiology
(2008) - et al.
Effect of force direction on femoral fracture load for two types of loading conditions
Journal of Orthopaedic Research
(2001) Application of FRAX model to Sri Lankan postmenopausal women
Clinical Densitometry
(2010)- et al.
Effects of body configuration on pelvic injury in backward fall simulation using 3D finite element models of pelvis–femur–soft tissue complex
Journal of Biomechanics
(2009) - et al.
Trabecular bone modulus–density relationships depend on anatomic site
Journal of Biomechanics
(2003) - et al.
The effects of embalming using a 4% formalin solution on the compressive mechanical properties of human cortical bone
Clinical Biomechanics
(2008)
An accurate estimation of bone density improves the accuracy of subject-specific finite element models
Journal of Biomechanics
Subject-specific finite element models implementing a maximum principal strain criterion are able to estimate failure risk and fracture location on human femurs tested in vitro
Journal of Biomechanics
Subject-specific finite element models can accurately predict strain levels in long bones
Journal of Biomechanics
Subject-specific finite element models of long bones: an in vitro evaluation of the overall accuracy
Journal of Biomechanics
Validation of subject-specific automated p-FE analysis of the proximal femur
Journal of Biomechanics
Load distribution in the healthy and osteoporotic human proximal femur during a fall to the side
Bone
Extracting clinically relevant data from finite element simulations
Clinical Biomechanics (Bristol, Avon)
The effect of impact direction on the fracture load of osteoporotic proximal femurs
Medical Engineering & Physics
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