Acoustic emission in orthopaedics: A state of the art review
Introduction
The phenomenon of sonic and ultrasonic wave generation by materials undergoing deformation and fracture processes is termed Acoustic Emission (AE). AE results from the rapid release of energy during crack formation and propagation within a material and can be detected using specialist sensors. AE technology has been widely applied within civil and mechanical engineering to provide a highly sensitive and non-destructive method to monitor the health of structures. The technique enables both the detection and the location of structural flaws as they develop and, as such, the technology has proven invaluable in investigating the dynamic behaviour of materials (Ono, 2011).
A typical AE system consists of sensors, preamplifiers and a data acquisition system. AE sensors used in biomechanical engineering are typically piezoelectric, employing ceramic elements to generate electric signals in response to mechanical strain. Sensors are typically attached to the surface of the material under investigation using a thermo-plastic adhesive, with multiple sensors required to allow AE source triangulation. The analog signals detected by the sensors are amplified using preamplifiers and fed into a data acquisition system. The signals are converted into digital data, filtered and useful signals (“hits”) registered according to pre-defined parameters. The most common method for AE signal detection is based on threshold discrimination, where an amplitude threshold is defined and any signal exceeding this amplitude triggers a “hit” measurement (Muravin, 2009).
Fig. 1 demonstrates a typical AE signal triggering a “hit”. Annotations outline the standardised terms relating to the relevant parameters of AE signals and hits (MISTRAS, 1992).
Due to the large amounts of data generated through AE measurement research in this field has historically been limited and has principally centred on uses in engineering. Recent advances in computational power and digital data storage have, however, led to a marked expansion in AE research and to the development of increasingly widespread applications of the technology (Rashid and Pullin, 2014).
An area of recent particular interest is the application of AE technology to Orthopaedic surgery, where the non-destructive and highly sensitive nature of AE analysis make it ideally suited.
Section snippets
AE in Orthopaedics
Early applications of AE within Orthopaedics involved its use in vitro to characterise the structural and biomechanical properties of bone (Katz, 1979). It was established that the technique is particularly well suited to the dynamic analysis of bone deformation and fracture processes to which it was, and still is, frequently applied.
Subsequent work has seen AE technology applied within the field of arthroplasty research, with researchers taking advantage of its capability to monitor structural
Discussion
Acoustic Emission technology has been widely used in Orthopaedic research as a tool to assess micro-damage accumulation. More recently, however, there has been increased interest in the possible clinical application of the technology and an appreciation of the potential benefits of applying AE analysis during both the diagnosis and treatment of Orthopaedic pathology. This progression has led to an increased appreciation of, and interest in, the breadth of data available during AE monitoring.
Conclusion
Acoustic Emission technology has yet to find widespread clinical application within the field of Orthopaedic surgery. The technology has, however, been widely used in research where it has mostly been adopted as a research tool using AE signals as a surrogate marker for damage accumulation.
The technology has proven invaluable in the evaluation of the biomechanical properties of bone where it has been widely applied during bending and torsional testing (Aggelis et al., 2015) as well as
Perspectives - The future of AE in orthopaedics
Despite the promise shown in vitro, translation of AE techniques to in vivo applications faces many challenges. In addition to the complex structure of bone interfering with AE transmission, AE technology suitable for clinical application needs to be developed. When considering remote data collection, for example, AE sensors that are wireless and lightweight would be required. Identifying the relevant AE signals amongst extraneous noise is also a substantial challenge (Agcaoglu and Akkus, 2013).
Conflict of Interest
The author declares no conflict of interest associated with this article.
No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article.
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