Ceramic-on-Ceramic (CoC) bearings are an ideal choice for a total hip replacement because of the ceramic bearings’ longer wear life than Metal-on-Metal or Metal-on-Polyethylene bearings. Friction-induced squeaking has been reported in 1–10% of patients who have a ceramic-on-ceramic total hip replacement, which is a subject of annoyance. Many mechanisms have been proposed to address the squeaking phenomena in CoC hip replacements, but there is no consensus among researchers on the root cause behind the squeaking of hip implants. The goal of this study was to investigate the possible factors attributing to the hip squeak, and understand the underlying phenomenon based on the coupling stiffness of the bearing surface. Boundary conditions for the CoC hip bearing to produce audible noise were also identified. 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. Using modal analysis, the natural frequencies of all the components of the implant were determined. Random vibration analysis was conducted to identify the ideal boundary conditions for the CoC hip bearing.
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. State-Space plots of the parametric analysis were used to evaluate the stability of the system. Mathematical Analysis involved the investigation of the role of the frictional stick-slip phenomenon of the metal shell and ceramic liner on squeal. The size of the limit cycle provides an indication of the degree of severity of a noisy condition.
With only metallic shell affixed to the acetabulum constrained, the modal natural frequency was 3600 Hz which was very close to the free vibration results of the bearing. The Power Spectral Densities displayed the audible frequencies at 11.4 kHz. The limit cycle plots show that a variation in coupling contact stiffness has an influence on the behavior/stability of the system. The study underscored the relevance of material transfer on the bearing surface using the mathematical analysis by varying the coupling stiffness of the bearing surface. In addition, random vibration analysis in conjunction with the parametric analysis identified the ideal boundary condition to produce the squeal frequencies as observed by others.