Biomechanical Numerical Simulation Studies On The Effect Of Morphological Features Of Proximal Femur On The Related Strength

Femur, as the most important bone of bearing the weight of upper body andforming gait process, is susceptible to fracture, especially for theelderly people with serious osteoporosis. With the rapid development ofmedical standards, people are not satisfied with curing the fracture onlydepending on the improvement of medical technology. More and more peoplestarted to investigate the factors which can affect the fracture risk andspecified precautions to prevent fractures. Mechanical properties andmorphological features of bones are two most important factors that affectthe fracture risk. However, in vivo mechanical experiments for livingskeleton could not be performed by mechanical test machine. This problemcan be solved by incorporating reverse engineering technology withnon-linear finite element analysis technology. Accordingly, in this studya suite of new measurement of3D proximal femoral morphological parameterswas established and the damage processes of proximal femurs were simulatedwith finite element analysis. Statistical analyses were performed on theproximal femoral morphological parameters and femoral strengths toanalyze the effect of3D morphological parameters on proximal femoralstrengths. In addition, mechanical properties of trabecular bone insidethe femoral heads were investigated by combining micro-CT imagingtechnology with micro-finite element method. The fracture mechanism ofproximal femur was studied at the tissue level. This study was mainlycomposed of three sections:In section one, the method of measuring3D proximal femoral morphologicalparameters was established.51healthy elderly males with the age rangeof66-75were measured with this method, and the effects of age on themorphological parameters were analyzed. First,3D proximal femoral models were reconstructed from QCT images using reverse engineering softwareMIMICS. Models were performed a series of translation and rotation tounify the positions in rapid prototype software MAGICS. Coordinates offeature points were obtained from the surface and interior of the models.In section two, finite element analyses were performed on14randomlyselected proximal femoral models (7samples from group A and7samplesfrom group B) to predict the proximal femoral strength. Complex bonematerial properties, yield criterion and fracture criterion were compiledin UMAT subroutines. As bone was a kind of inhomogeneous and asymmetricalmaterial in tension and compression, at the beginning of each loadincrement, the corresponding yield criterion and fracture criterion weregiven to each element after judging the damage degree and tension orcompression status. A simple load cap was established to make sure thatthe load could be applied to the surface of femoral head uniformly.5mmvertically downward displacement was exerted on the top of the cap.Results revealed that the predicted damage process of proximal femur wasconsistent with experimental data. The predicted strength of proximalfemur significantly related to the morphological parameters TRH, NSA andTOF (P<0.05). There were no statistical difference in strengths betweengroup A and group B.In section three, the strength of cancellous bone inside femoral headsfrom proximal femoral fracture patients were analyzed using micro-CTimaging technology in combination with micro-finite element analysis atthe tissue level, as well as the effects of3D trabecular morphologicalfeatures on the trabecular mechanical properties.7femoral heads fromproximal femoral fracture patients were performed micro-CT scanning toreconstruct the femoral head models. Every femoral head models weredivided into3regions and12sub-regions according to the trabecularorientations. One125mm3trabecular cube was extracted from eachsub-region.6trabecular morphological parameters were measured on each cube including trabecular separation (Tb.Sp), trabecular thickness(Tb.Th), bone volume friction (BV/TV), specific area density (BS/BV),structural model index (SMI) and degree of anisotropy (DA). Twoindependent samples tests were performed on trabecular morphologicalparameters from different regions to analyze regional differences oftrabecular morphological parameters. Finite element analyses wereperformed on each cube along three orthogonal directions, respectively.The apparent Young’s modulus and average von Mises stress were calculatedon each cube along three orthogonal directions. The results showed thatthe mechanical properties along the principal loading direction were muchbetter than the other two non-principal loading directions. There was nosignificant difference between two non-major loading directions. Therewere significant differences in mechanical parameters of cancellous bonealong the principle loading direction between regions. The mechanicalparameters in the lateral region were significantly different from middleregion and medial region.This study improved the measurement of proximal femoral morphologicalparameters and proximal femoral damage algorithm. The effects ofmorphological features on bone strength were elaborated at macro and mesolevels, which provided more evidence for clinicians to prevent fractures.