In vivo,
bone cement is subject to cyclic loading in a fluid environment. However, little is known about the effect of moisture absorption on the
fatigue crack propagation resistance of
bone cement. The effect of moisture absorption at 37 degrees C on the
fatigue crack propagation resistance of a common
bone cement (Endurance, DePuy, Orthopaedics, Inc.) was examined. Preliminary fracture toughness tests were conducted on disk-shaped, vacuum-mixed cement specimens (compact tension type) that were cyclically pre-cracked. Plain-strain fracture toughness K(IC) (MPa square root(m)) was determined. To study the effect of moisture absorption four treatment groups, with different soaking periods in Ringer's at 37 degrees C, of Endurance cement were tested. The specimens weights prior to and following soaking showed a significant increase in mean weight for specimens soaked for 8 and 12 weeks. Linear regression analysis of log(da/dN) vs. log (deltaK) was conducted on the combined data in each
fatigue test group. Soaking
bone cement in Ringer's at 37 degrees C for 8 and 12 weeks lead to an improvement in
fatigue crack propagation resistance, that may be related to water sorption that increases
polymer chain mobility, with enhanced crack tip blunting. It may be more physiologically relevant to conduct in vitro studies of
fatigue and fracture toughness of
bone cements following storage in a fluid environment.