Flexural and fatigue properties of a bone cement based upon polyethylmethacrylate and hydrxyapatite

Polymethylmethacrylate (PMMA) bone cement is commonly used in surgery to fix joint replacements into the bone. Although the operations are generally successful, loosening of the prosthesis does occur with fracture of the bone cement treated as the source of failure in some instances. Polyethylmethacrylate (PEMA) bone cement offers a promising alternative to PMMA due to its high ductility, low toxicity and low exotherm. In addition, hydroxyapatite (HA) particles can be added, while retaining the ductile properties of the material. In this study, the flexural and fatigue properties of this experimental cement, with and without HA reinforcement, have been examined. It was found that up to 40wt.% HA could be added with increases in both flexural strength and modulus. Specimens were subjected to tension-tension cyclic loading at a number of stress levels until catastrophic failure occurred. In comparison with a commercial PMMA cement, tested at relatively high stresses, the PEMA cement failed at lower cycles to failure. However, the data converged at the lower stresses employed which are closer to the physiological loading situation. With the addition of HA, although the cycles to failure were decreased, the deformation experienced by the PEMA-HA cement whilst being cycled was reduced.