Is ceramic-on-ceramic squeaking phenomenon reproducible in vitro? A long-term simulator study under severe conditions

Clinical and in vitro studies on ceramic hip prostheses correlate cup implant position with hip noise, ceramic wear, or ceramic liner damage. A ceramic cup malposition could lead to edge load, ceramic head wear, and squeaking. A noise of a ceramic hip could also be correlate with implant instability and liner damage. Aim of this study was to investigate the long-term wear behavior of 12 commercial alumina-on-alumina bearings under severe conditions: different angles of inclination (23 degrees, 45 degrees, and 63 degrees) and the addition of third body particles (titanium and alumina powder) to address the effective role of cup position and ceramic particles on wear and hip noise. The study was performed using a 12-stations hip joint wear simulator (Shore Western, Monrovia) under bovine calf serum used as lubricant. Wear was evaluated by gravimetric method and the piezo-spectroscopic technique was used to evaluate the residual stress of the ceramic components and correlate this to the weight loss. After eight million cycles, we found that the inclination of the cup (63 degrees in this study) was the most disadvantaged and it was correlated with a hip noise. Gravimetric measurements showed higher wear than the other configurations and these results were in agreement with the Photoluminescence investigation. In particular, the results obtained in this work revealed a residual stress state greater not only with respect to the other angles of inclination but also to two retrieved alumina acetabular cups with a 10 years follow-up.