Prediction of fracture load and stiffness of the proximal femur by CT-based specimen specific finite element analysis: cadaveric validation study

Abstract

BackgroundFinite element analysis (FEA) of the proximal femur has been previously validated with large mesh size, but these were insufficient to simulate the model with small implants in recent studies. This study aimed to validate the proximal femoral computed tomography (CT)-based specimen-specific FEA model with smaller mesh size using fresh frozen cadavers.MethodsTwenty proximal femora from 10 cadavers (mean age, 87.1 years) were examined. CT was performed on all specimens with a calibration phantom. Nonlinear FEA prediction with stance configuration was performed using Mechanical Finder (mesh,1.5 mm tetrahedral elements; shell thickness, 0.2 mm; Poisson’s coefficient, 0.3), in comparison with mechanical testing. Force was applied at a fixed vertical displacement rate, and the magnitude of the applied load and displacement were continuously recorded. The fracture load and stiffness were calculated from force–displacement curve, and the correlation between mechanical testing and FEA prediction was examined.ResultsA pilot study with one femur revealed that the equations proposed by Keller for vertebra were the most reproducible for calculating Young’s modulus and the yield stress of elements of the proximal femur. There was a good linear correlation between fracture loads of mechanical testing and FEA prediction (R2 = 0.6187) and between the stiffness of mechanical testing and FEA prediction (R2 = 0.5499). There was a good linear correlation between fracture load and stiffness (R2 = 0.6345) in mechanical testing and an excellent correlation between these (R2 = 0.9240) in FEA prediction.ConclusionsCT-based specimen-specific FEA model of the proximal femur with small element size was validated using fresh frozen cadavers. The equations proposed by Keller for vertebra were found to be the most reproducible for the proximal femur in elderly people.

Finite element analysis of the femoral diaphysis of fresh-frozen cadavers with computed tomography and mechanical testing

“…The load recorded at the yield point was defined as the fracture load. The stiffness was calculated as the slope of the load-deformation curve between 20 and 80% of the fracture load reference to the previous study that was reported by Miura et al [ 1 ].…”

“…Young’s modulus and yield stress of each tetrahedral element, assumed to be isotropic, were calculated from the equations proposed by Keyak [ 2 , 3 , 14 ], Carter [ 15 ], Keller, and Keller for vertebra [ 16 ] (Table 1 ). Moduli lower than 0.01 MPa were assigned a new value of 0.01 MPa, and those higher than 20 GPa got a new value of 20 GPa, and Young’s modulus and yield stress of the shell element were calculated using a CT value of 1500 HU reference to the previous study that was reported by Miura et al and Matsuura [ 1 , 17 ]. The Drucker-Prager equivalent criterion was adopted for the yield of the element.…”

“…Recently, computed tomography-based finite element analysis (CT-based FEA) has been widely used for mechanical analysis of the femur. Many reports have described fracture models of the femur following traffic accidents and simulations of stress distribution after joint replacement [ 1 – 13 ]. When we consider a femoral diaphyseal fracture and the stress distribution for femoral diaphyseal after prosthesis replacement using FEA, the whole femoral shaft must be evaluated.…”

“…However, there are no reports of FEA models of diaphyseal femoral fractures. Although experimental data can be used to validate CT-based FEA models, most of the fracture models in previous reports were of the proximal femur [ 1 – 6 ]. The proximal of femur have abundant cancellous bone, while the femoral diaphysis mainly consists of cortical bone.…”

Development of a Knee Joint CT-FEM Model in Load Response of the Stance Phase During Walking Using Muscle Exertion, Motion Analysis, and Ground Reaction Force Data

“…This technology is being used to further advancements in orthopedics and dentistry [4][5][6][7]. Furthermore, bone strength can be predicted and evaluated using a 3D bone model for each individual using the corresponding images [8][9][10]. CT-FEM studies have been performed for various parts of the spine and joints [11][12][13], and knee joints [14][15][16][17][18][19] being no exception.…”