CRACK LENGTH ESTIMATION FROM THE DAMAGE MODELISATION AROUND A CAVITYI IN THE ORTHOPEDIC CEMENT OF THE TOTAL HIP PROSTHESIS

In orthopedic surgery and particularly in the total hip arthroplasty, the stem fixation is performed in general using a surgical cement which consists essentially of polymer(PMMA). Fracture of cement and prosthesis loosening appears after a high-stress level. This phenomenon origin is due to the presence of micro-cavities in the PMMA volume. The focus of our study is the modeling using the finite-element method of the cement damage around these cavities, the cavities' sizes and shapes effect on the damage risk, and the crack length estimation due to this damage. A small Fortran schedule was incorporated with the Abaqus code to calculate the damage zone. Results show that the presence of a cavity in the cement increases the damage parameter. The damage appears when the cavity is located in cement on the loading axis. If the cavity changes its shape from circular to elliptical, the size of the damage zone increases. One can predict the initiation of a crack in cement with a maximal length of 70 mu m.