Finite element analysis on proof testing of ceramic ball heads for total hip replacements: Trauma loading considerations

Trauma related loading of hip prostheses has been reported as a cause of failure of implanted ceramic materials, ball and/or cup. In this study a computer simulated model is made to evaluate contact pressures and stresses in the stem/ball contact pair, as well as stress concentration regions in the ceramic cup. A 3D Non-Linear Finite Element Analysis was performed in a "proof test" scenario. A high peak trauma-like loading of 15 KN was used. 28mm ball heads (in diameter) were modeled and two sizes for taper lock were simulated to report their influence on the contact pressure over the critical areas of the ballhead. It was found that the ball head cone's depth has a major incidence in the stress and contact pressure surrounding the stem when an impact load is applied. The best stress and pressure configurations were found for the case of the stem lying completely inside the ballhead.