| Total hip arthroplasty is a highly successful treatment for osteoarthritis and rheumatoid arthritis, with a 90% success rate after ten years of implantation in patients over sixty years of age but a lower success rate for longer durations or younger patients. Mechanical failure at the interface between cement and bone is considered to be one of the most important causes of loosening of cemented arthroplasties, but the cement-bone interface has not been studied extensively. Fracture toughness KIc is a material property that describes resistance to propagation of a pre-existing flaw, and using fracture toughness for this application is sensible because the bone-cement interface contains many voids and pores. Previous studies on cortical bone and bone cement concluded that fracture toughness testing yields more consistent results than tensile or shear strength tests with lower variance between specimens of different sizes and configurations. Because the use of acrylic bone cement depends on its ability to form an interdigitating network with highly-porous trabecular bone, it is necessary to develop fracture toughness tests of trabecular bone and cement to be able to evaluate this interface mechanically.; The work presented in this dissertation addresses the fracture toughness of the cement/trabecular bone interface in order to measure effects of several variables related to bone architecture, cement insertion, and test conditions. Specimens of compact tension geometry were prepared and tested using bovine proximal femoral bone and commercial bone cement. First, relationships between KIc and volume fraction, trabecular orientation, and cement pressure were determined. Next, testing was combined with microcomputed tomography (μCT) to measure cement penetration depth within trabecular bone and relate this depth to the fracture resistance. Stable crack propagation experiments were performed to measure effects of initial crack length and monitor the evolution of fracture toughness with increasing crack growth. Finally, scanning electron microscopy was used to examine fracture surfaces of cement and bone to look for evidence of cement pullout and other failure mechanisms. This work should assist the clinician in understanding failure of the cement-bone interface, and aid the engineer in developing standardized test methods useful for evaluating interfaces between various bone and cement formulations. |
