Cepstrum Analysis for Determining the Fundamental Frequency of Total Hip Replacement Acoustic Emissions

Abstract

Acoustic emission (AE) monitoring of patients with total hip replacement (THR) implants has potential as a non-invasive and inexpensive diagnostic procedure for identifying and monitoring implant complications such as loosening and implant squeaking. AE signals that are generated from implant interactions can provide insight into implant condition and failure modes through signal characteristics such as frequency content. A substantial database of AEs has been collected from 107 THR patients using an AE monitoring prototype diagnostic device. This manuscript presents the use of the relatively unknown signal processing technique of cepstrum analysis as a method for identifying and comparing the frequency content of squeaking THRs from the AE database.It was observed that squeaking AE signals commonly exhibited frequency spectrums with strong harmonic content and fundamental frequencies that varied over time. Cepstrum analysis has the ability to isolate fundamental frequency content in signals that contain harmonics. The position and transient behaviour of the fundamental frequency content can then be used to correlate and categorise particular AE signals. The cepstrum results presented in this manuscript exhibits an ability to successfully isolate the fundamental frequency content for THR AE squeaks from separate patients. The usefulness of a cepstrum analysis for correlating and contrasting THR AE squeaks is demonstrated. However, the results also demonstrated that when strong harmonics were not present in the AE signals, the cepstrum isolated frequency content of no obvious significance and was even unable to simply identify the main frequency content reliably. Nevertheless, the cepstrum analysis is a promising technique to aid in the analysis of THR AE signals and can provide useful insight into the frequency behaviour of these emissions.