In orthopedic surgery and particularly in the total hip arthroplasty (THP), the stem fixation is performed in general using surgical cement which consists essentially of poly (methyl methacrylate) (PMMA). Fracture of cement and prosthesis loosening appears after high concentrations of stress. This phenomenon origin is due to the presence of micro-cavities in the cement volume due to patient movements. The focus of this study is the modeling using the finite element method of a crack emanating from a cavity. It was assumed several positions and orientations of the crack in the cement to calculate the stress intensity factor (SIF). Results show that the presence of a crack emanating from a cavity in the cement increases the risk of fracture of cement.

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The post-operative period for a carrier of total hip prosthesis (THP), especially in the first months, remains the most difficult period for a patient after each operation, even if traumatologist surgeons want the relief and success of their operations. In this investigation, selected three of the daily activities for a wearer of total hip replacement (THR), such as, sitting in a chair, lifting a chair and going down stairs, and was performed a numerical simulation by finite elements in based on experimental data by Bergmann (Bergmann 2001) in terms of effort for each activity. Different stresses have been extracted, as well as a detailed comparison between two activities with different induced stresses such as normal, tensile and compressive shear stresses.