Development of Experimental and Finite Element Modelling Techniques for Investigation of Human Femurs
thesisposted on 02.05.2017, 14:39 by Caroline Elizabeth Meakin
The aim of the work presented in this thesis was to develop a finite element model and experiment to simulate the loading conditions caused by a fall on the proximal femur. Investigations were carried out with a PVC surrogate human femur and a sheep's femur. The results of the model and experiment were used to assess the effect of the orientation of the femur at time of impact on the strain distribution. The finite element model was based on data obtained from computed tomography scans of the samples, which were used to characterise their geometry and material properties, and included a simulation of the contact mechanics in the hip joint. The experiment involved the use of strain gauges to measure strain at a number of locations on the samples. Apparatus was developed to support the samples at a range of orientations with respect to the direction of an applied load. Trilateration was used to identify the model coordinates of the strain gauges. The accuracy of the model, assessed by comparison with the results of the experiment, was found to be limited by restrictions in the resolution of the CT data. An investigation into the effect of multiple freeze-thaw cycles on strain gauge measurements showed that the accuracy of strain readings taken after four cycles could not be guaranteed. The use of different materials to simulate the acetabular surface through which the load is applied to the femoral head was determined to have a significant effect on the strain, as was the difference between using a foam soft tissue surrogate and a hard PMMA cap to protect the greater trochanter. The effect of changing the angle of rotation about the shaft of the femur was assessed. It was found that the largest strains per unit force were associated with posterolateral falls.