Three-dimensional modeling of in vitro hip kinematics under micro-separation regime for ceramic on ceramic total hip prosthesis: an analysis of vibration and noise.

Micro-separation corresponds to a medial-lateral hip laxity after total hip replacement (THR). This laxity has been shown to generate higher wear rates and a specific pattern of stripe wear caused by edge loading of the head on the rim of the cup. Recently some authors have implicated edge loading as a source of noise generation and in particular squeaking. The goal of this study was to model hip kinematics under the micro-separation regime in a computational simulation of total hip prosthesis including joint laxity and to analyze the vibration frequencies and the potential for noise generation. A three-dimensional computer model of the Leeds II hip simulator was developed using ADAMS((R)) software, simulating a controlled micro-separation during the swing phase of the walking cycle and replicating the experimental conditions previously reported. There was an excellent correlation between the theoretical values and the experimental values of the medial-lateral separation during the walking cycle. Vibratory frequencies were in the audible zone but were lower in magnitude than those reported clinically in relation to squeaking. Micro-separation and rim loading may explain the generation of some sounds from noisy hips after THR. However, the computational model, and the experimental model of micro-separation were unable to replicate the higher frequency squeaking reported clinically. In contrast, other experimental studies involving normal kinematics in combination with third-body particles have replicated clinically relevant frequencies and noises. Copyright 2009 Elsevier Ltd. All rights reserved.