Subject-specific FE models of the human femur predict fracture path and bone strength under single-leg-stance loading

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T1 - Subject-specific FE models of the human femur predict fracture path and bone strength under single-leg-stance loading

AU - Gustafsson, Anna

AU - Tognini, Martina

AU - Bengtsson, Frida

AU - Gasser, T. Christian

AU - Isaksson, Hanna

AU - Grassi, Lorenzo

PY - 2021

Y1 - 2021

N2 - Hip fractures are a major health problem with high socio-economic costs. Subject-specific finite element (FE) models have been suggested to improve the fracture risk assessment, as compared to clinical tools based on areal bone mineral density, by adding an estimate of bone strength. Typically, such FE models are limited to estimate bone strength and possibly the fracture onset, but do not model the fracture process itself. The aim of this study was to use a discrete damage approach to simulate the full fracture process in subject-specific femur models under stance loading conditions. A framework based on the partition of unity finite element method (PUFEM), also known as XFEM, was used. An existing PUFEM framework previously used on a homogeneous generic femur model was extended to include a heterogeneous material description together with a strain-based criterion for crack initiation. The model was tested on two femurs, previously mechanically tested in vitro. Our results illustrate the importance of implementing a subject-specific material distribution to capture the experimental fracture pattern under stance loading. Our models accurately predicted the fracture pattern and bone strength (1% and 5% error) in both investigated femurs. This is the first study to simulate complete fracture paths in subject-specific FE femur models and it demonstrated how discrete damage models can provide a more complete picture of fracture risk by considering both bone strength and fracture toughness in a subject-specific fashion.

AB - Hip fractures are a major health problem with high socio-economic costs. Subject-specific finite element (FE) models have been suggested to improve the fracture risk assessment, as compared to clinical tools based on areal bone mineral density, by adding an estimate of bone strength. Typically, such FE models are limited to estimate bone strength and possibly the fracture onset, but do not model the fracture process itself. The aim of this study was to use a discrete damage approach to simulate the full fracture process in subject-specific femur models under stance loading conditions. A framework based on the partition of unity finite element method (PUFEM), also known as XFEM, was used. An existing PUFEM framework previously used on a homogeneous generic femur model was extended to include a heterogeneous material description together with a strain-based criterion for crack initiation. The model was tested on two femurs, previously mechanically tested in vitro. Our results illustrate the importance of implementing a subject-specific material distribution to capture the experimental fracture pattern under stance loading. Our models accurately predicted the fracture pattern and bone strength (1% and 5% error) in both investigated femurs. This is the first study to simulate complete fracture paths in subject-specific FE femur models and it demonstrated how discrete damage models can provide a more complete picture of fracture risk by considering both bone strength and fracture toughness in a subject-specific fashion.

KW - Cohesive traction separation law

KW - Crack propagation

KW - Crack surface

KW - Partition of unity

KW - PUFEM

KW - XFEM

U2 - 10.1016/j.jmbbm.2020.104118

DO - 10.1016/j.jmbbm.2020.104118

M3 - Article

C2 - 33125949

AN - SCOPUS:85093960152

VL - 113

JO - Journal of the Mechanical Behavior of Biomedical Materials

JF - Journal of the Mechanical Behavior of Biomedical Materials

SN - 1751-6161

M1 - 104118

ER -