Biomaterials 25 (2004) 769–778 Investigation of fatigue crack growth in acrylic bone cement using the acoustic emission technique A. Roques a , M. Browne a, *, J. Thompson b , C. Rowland c , A. Taylor a a Bioengineering Sciences Research Group, Engineering Materials, University of Southampton, Highfield, Southampton SO17 1BJ, UK b DePuy International Ltd., St Anthony’s Road, Leeds LS11 8DT, UK c Pancom, Fenstanton, Huntingdon PE18 9QZ, UK Received 17 December 2002; accepted 14 July 2003 Abstract Failure of the bone cement mantle has been implicated in the loosening process of cemented hip stems. Current methods of investigating degradation of the cement mantle in vitro often require sectioning of the sample to confirm failure paths. The present research investigates acoustic emission as a passive experimental method for the assessment of bone cement failure. Damage in bone cement was monitored during four point bending fatigue tests through an analysis of the peak amplitude, duration, rise time (RT) and energy of the events emitted from the damage sections. A difference in AE trends was observed during failure for specimens aged and tested in (i) air and (ii) Ringer’s solution at 37  C. It was noted that the acoustic behaviour varied according to applied load level; events of higher duration and RT were emitted during fatigue at lower stresses. A good correlation was observed between crack location and source of acoustic emission, and the nature of the acoustic parameters that were most suited to bone cement failure characterisation was identified. The methodology employed in this study could potentially be used as a pre-clinical assessment tool for the integrity of cemented load bearing implants. r 2003 Elsevier Ltd. All rights reserved. Keywords: Bone cement; Fatigue; In vitro test; Acoustic emission 1. Introduction Improvements in cementing techniques have resulted in increased success rates for cemented hip implants; however, long-term follow ups of implants using third generation cementing techniques have recently shown that revision rates remain significant [1,2]. At 10 years follow up, a 9.2% revision rate has been reported; aseptic loosening of the femoral component was the major cause for revision [2]. The loosening failure scenario is thought to involve interfacial debonding and subsequent bone cement failure [3]. However, these are difficult to monitor and to date, the standard experimental assessments of cemented hip replacement integrity from in vitro studies require sectioning of the samples to confirm failure paths. A pre-clinical tool that could passively monitor the behaviour of a cemented hip prosthesis would therefore be very useful. The acoustic emission (AE) technique is a non- destructive technique (NDT) which has been used in engineering to detect the onset and progression of failure in structures [4–6]. Two approaches have been applied: the user can either access the frequency content of the signal (Fourier transform) or monitor the acoustic parameters (peak amplitude (PA), duration, rise time (RT), energy). There have been a limited number of studies that have attempted to use this NDT method in orthopaedic research [7], primarily to investigate the failure of composite implants [8,9] or damage accumulation in bone [10]. Only recently has bone cement been studied using time decomposition (wavelet analysis) of the acoustic signal emitted during crack propagation [11–13]. In this instance, whereas tradi- tional crack propagation rate measurements could not differentiate between vacuum mixed and hand mixed bone cement specimens, the use of the wavelet based energy showed that there was a significant difference between the fatigue behaviours of the two types of specimens [11]. ARTICLE IN PRESS *Corresponding author. E-mail address: doctor@soton.ac.uk (M. Browne). 0142-9612/$-see front matter r 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0142-9612(03)00581-7