Aspects of the Fatigue Behaviour of Acrylic Bone Cement

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Abstract

Polymethylmethacrylate bone cement is used to fixate many orthopaedic implants. However, it is a brittle material, prone to damage accumulation leading to cement cracking and prosthesis loosening. The damage accumulation failure scenario has been recognised as the predominant mode of cemented implant loosening, and a combination of finite element analysis and continuum damage mechanics can be used to model this failure scenario; however, the empirical laws used to model the fatigue behaviour of acrylic bone cement are incomplete. The objective of this thesis is to develop empirical laws which accurately describe the fatigue behaviour of acrylic bone cement. Furthermore, this thesis addresses a number of aspects of the fatigue behaviour of acrylic bone cement which are relevant to experimental testing and clinical performance.

Three experimental tests were designed to investigate a number of aspects of the fatigue behaviour of acrylic bone cement. Namely; the mismatch between the in vivo and in vitro performance of vacuum-mixed cement; the relationship between damage accumulation and stress; the effect of an off-axis tensile stress on the fatigue strength of acrylic bone cement.

The results show that the in vivo underperformance of vacuum-mixed cement can be explained by the greater variation in fatigue strength of vacuum-mixed cement, which is caused by occasional large pores. Moreover, the practice of removing specimens with these large pores will lead to an overestimation of the fatigue strength, and in addition the variability associated with a certain mixing technique/cement will be missed. The rate of damage accumulation in bone cement was found to be nonlinear and stress dependent. The effect of an off-axis tensile stress was found to reduce the mean fatigue strength by up to one order of magnitude, showing that the in vivo fatigue strength of acrylic bone cement is presently underestimated.

In conclusion the work of this thesis has developed empirical laws to model the fatigue behaviour of acrylic bone cement and it has also determined a number of key aspects of the fatigue behaviour of acrylic bone cement.

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Cited By (1)

Year	Entry
2003	Lennon AB. A Stochastic Model of Damage Accumulation in Acrylic Bone Cement: Application to Failure Modelling of Cemented Hip Replacement [PhD thesis]. Trinity College Dublin; 2003.