Friction-induced squeak of ceramic-on-ceramic hip implants: a stability design criteria

Abstract

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. The goal of this study was to investigate the possible factors attributing to the hip squeak, and understand the underlying phenomenon. The investigation involved acoustic, modal, and mathematical analyses. Acoustic analysis involved extracting and analyzing audio data from the videos files of squeaking ceramic hips. The audio data was transformed from the time to frequency domain using Fast Frequency Transform (FFT) using MATLAB. This allowed the identification of the squeal frequencies. Modeling involved 3-D rendering of the hip implant (femoral stem, head, cup liner, and the cup shell) using computer-aided-design software. Mathematical analysis involved the investigation of the role of the frictional stick-slip phenomenon of the metal shell and ceramic liner on squeal using a 2-DOF mathematical model. Mass, stiffness properties, and coefficient of friction of the components were incorporated to study the limit cycle using MATLAB/Simulink, which is an indicator of the stability of the system. Modal (Numerical) analysis involved the evaluation of the modal frequencies of the components using ANSYS, to investigate their contribution to squeal. Acoustic analysis of the squeal frequencies showed that the range of squeal frequencies of the coupled system ranged from 1500–3000 Hz, which concurred well with the literature. Modal Analysis showed the metallic shell’s resonant frequency at 4600 Hz. The parametric analyses using the 2-dof model showed that a stable system was approached as the stiffness of the liner was increased. The increase in mass of the shell resulted in larger limit-cycles. Increased stiffness of the shell proved to stabilize the system for most loading conditions.