Stress concentration regions in ceramic ball heads for total hip replacement considering trauma-like loading

A high stress condition in the hip system may cause fracture of the ball head. This failure may appear after a heavy accident such as sudden fall. The aim of this investigation is to make a computer simulated model of the hip system to evaluate the regions of stress concentration as well as the pressure in the stem-ball junction. 3D Non-Linear Finite Element Analyses were performed taking into consideration a high peak load to simulate trauma conditions. Ball heads from 22 to 36 mm in diameter were modeled, and also two sizes for taper lock were simulated to report their influence on the stresses over the critical areas of the ball head. Two different materials of common ball head ceramics (Alumina and Zirconia) were considered to evaluate its relation to the stresses produced. It was found that the ball head cone's depth has major incidence in the stress concentration surrounding the stem when an impact load is applied, and that a deeper cone may offer a more relieved loading configuration when considering stress related parameters such as Von Mises stress, contact pressure and friction stress.