Santana Artiles, María Ester (2019) Numerical investigation of femoral augmentation. (PhD thesis), Kingston University, .
Abstract
Femoral augmentation is a minimally invasive procedure involving injection of bone cement into osteoporotic femora in order to enhance their load capacity. However, this treatment poses significant risks such as bone thermal necrosis or embolism when large amounts of bone cement are injected in the femur. This thesis presents methods developed to find the ideal bone cement volume and distribution needed to restore the load capacity of osteoporotic femora depending on their level of osteoporosis. Material properties of augmented tissue were modelled using a proposed scheme that combines Voigt-Reuss-Hill average and bone cement porosity. These ideal bone cement distributions were used as a reference to propose several feasible and generalised augmentation strategies, which comprised placing bone cement in up to three spheres or in up to two pre-drilled channels. Bone cement location was found to be more significant in the augmentation result than bone cement volume or augmentation strategy. Fracture analysis of augmented femora was also conducted, demonstrating that approximately 7ml of bone cement can result in an increase of 74% in yield load, 62% in fracture load, and 117% in energy to fracture. After finding the optimum bone cement volume and distribution, the bone cement injection and polymerisation process was studied in a 2D femur model, and results suggest that risk of thermal necrosis was limited to the regions in the bone-PMMA interface while stress levels required to develop debonding between the materials were not reached. However, results were obtained from a 2D model and the bone-PMMA interface was not modelled in detail. Some other limitations involved in the present study are the use of a single femur, with virtually introduced osteoporosis that only represents senile osteoporosis and a single set of boundary conditions. Additionally, despite results were compared against experiments in the literature, an experimental validation may be necessary to ensure the validity of the model. Despite the limitations of the present study and lack of direct experimental validation, the methods presented in this thesis can be applied to any femur to evaluate the requirements of femoral augmentation and the risks that it may entail. When applied to the studied femur, we conclude that femoral augmentation can increase significantly the femur yield and fracture load and only present risk of thermal necrosis in the bone-PMMA interface.
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