Faculty Mentor: Manish Paliwal
Student: Mark Sidebottom
Ceramic-on-Ceramic (CoC) bearings are an ideal choice for a total hip replacement because the ceramic bearings long wear life than Metal-on-Metal or Metal-on-Polyethylene bearings. Recently CoC hips have been reported to squeak in 1-10% of the patients. A study by Chevilotte et al. showed that in vitro testing of CoC hip implants material transfer (titanium wear particles as a result from impingement of the femoral stem on the acetabular liner) attributed to squeaking in lubricated conditions. This influences the coupling stiffness property of the hip implant and may cause instability which is a precursor to noise.
An explanted Stryker Trident® CoC hip bearing that had been removed due to squeaking was analyzed visually and by computer simulation. Grey marks on the femoral head of the implant showed material transfer of titanium alloy onto the alumina head. A 3-D computer model of the implant was developed using PRO-E (PTC, MA) and analyzed using ANSYS (ANSYS Inc.,PA). Using modal analysis, the natural frequencies of all the components of the implant were determined. The results from the modal analysis and calculated stiffness and damping coefficients were used in the mathematical two degree-of-freedom (DOF) model to calculate the velocity and position of the two masses in the system. To simulate material transfer, the contact stiffness between the two masses was varied and State-Space plots of the parametric analysis were used to evaluate the stability of the system.
Results from the plots show that a variation in contact stiffness has an influence on the behavior of the system. A complete hip implant, including femoral stem and acetabular cup would allow for more DOF and may allow for a better understanding of the stability of the system.