Acoustic Emission Monitoring of Total Hip Arthroplasty Implants

Abstract

Acoustic Emission (AE) monitoring of patients with Total Joint Replacement (TJR) implants uses an array of four passive ultrasonic receivers to undertake in-vivo monitoring of the acoustic events created by patients with TJR implants. This manuscript presents and compares the results of in-vivo and in-vitro measurements of the acoustic signature created by a range of Total Hip Replacement (THR) implants. A major focus of this investigation is in the characterization of squeaking of hard-on-hard bearing surface combinations. The presence of an audible squeak of the bearing surface can cause significant embarrassment and potential discomfort to patients. It has been identified that squeaking is primarily identified at the main bearing interface and the fundamental peak falls in the range of 2-5kHz, with multiple higher harmonics also observed. The frequency of the primary squeak is seen to vary based on bearing surface type of both the acetabular liner and femoral head (ceramic-on-ceramic, metal-on- metal bearing combinations)Comparison is also drawn between in-vivo and in-vitro testing through the use of implant components retrieved during revision surgery of patients previously subjected to in-vivo testing. In the trials presented within this manuscript, strong correlation was achieved between the two test methods. In-vivo signal magnitudes were substantially smaller than those recorded from bench tests directly on the implant. However, characteristic frequencies were very similar in both cases, indicating that tissue attenuation reduces signal magnitude, but the influence of any period shifting of signals through the soft tissue were minimal. These initial results provide an important base for future testing and provide useful insight into the underlying cause of audible squeaking of total hip replacement patients with hard-on-hard bearing surfaces.