Finite element analysis of PMMA reinforced osteoporotic femurs

With increased incidence of hip fractures in osteoporotic patients, it is important to develop preventive treatment options including prophylactic reinforcements and tools to assess treatment efficacy. To increase femoral strength, PMMA was injected in the neck region of cadaveric femurs. From two pairs of osteoporotic femurs, one femur in each pair was augmented while the contralateral was used as control. Finite element models were used to calculate the resulting stress and strain distributions. CT scans of each femur were used to define proximal femur geometry and elastic modulus. To validate the models, both reinforced and contralateral femurs were tested to fracture on an MTS material testing machine. A fifth femur, with normal bone density, was also modeled and tested to fracture to assess the fracture differences between osteoporotic and normal proximal femurs. The fracture events were recorded using a high speed video camera. The von Mises strain distributions calculated using finite element analysis were shown to correlate well with experimental fracture images. This suggests that validated finite element models based on CT scans can be used successfully to investigate different material options for in vivo implants where experimental bone strength testing is not an option.