The effects of the cement thickness on the failure probability of the cemented hip prosthesis

Abstract

Finite element analysis has been widely used to determine the behavior of implants placed in a body. However, uncertainties in loading acting on the implant, material properties and implant geometry are not taken into account during these analyses. Thus, it can result in either an unreliable design or unnecessarily overdesigned implants. Therefore, probabilistic design methods, in which uncertainties related to design variables are taken into account during the solution, have been recently considered as an important approach to design more reliable and long-lasting implant. Since the failure of the cemented hip prostheses mostly occurs at the cement mantle, determining the failure probability becomes more important. Therefore, in this study, the failure probability of the cement mantle which bonds the hip prosthesis into bone was calculated using the reliability methods by considering the uncertainties in the related design variables. In order to calculate the failure probability, three-dimensional solid models of the cement mantle, femur and hip prosthesis was obtained. The same model was used to obtain the maximum principal stress from the deterministic stress analysis in order to compare the failures state of the cemented hip prosthesis using the both approaches. The deterministic stress analysis carried out considering the mean values of the design parameters does not indicate any failure for the cement mantle thickness considered in this study. On the other hand, the probabilistic analysis yields a failure probability up to 0.3. Therefore these results indicate that the probabilistic analysis should be considered to design a more reliable and long-lasting implant.