The acoustic emission technique in orthopaedics - a review

Traditionally, orthopaedic research has focused upon the assessment of individual components in an implanted construct. A great deal of research has investigated the durability of the metallic stem, even though this is the most robust component in the implanted system. Standards have been developed for the structural assessment of the implant and even the bone cement which holds the implant in place in the bone. However, the construct as a whole, and its short- and long-term structural integrity, are rarely assessed, and few methods have been established to monitor and predict the mechanisms leading to failure. These are necessary to ensure that any new implants entering the market will perform satisfactorily and prevent premature revision surgery.

The acoustic emission (AE) technique offers the capability of monitoring structural degradation passively and in real time, and can distinguish failure mechanisms and their location through the analysis of AE parameters. In the present paper, the use of acoustic emission in orthopaedics, in particular for the evaluation of hip replacement constructs, is reviewed. Following this, three case studies undertaken at the University of Southampton are presented, in which acoustic emission on-line monitoring has been used to evaluate the performance of simulated artificial hip replacement constructs and their constituents during static and fatigue testing. In Case Study 1, the fatigue behaviour of bone cement is characterized; in Case Study 2, the residual stresses induced in the construct as a result of bone cement cure are investigated; in Case Study 3, the mechanisms leading to failure of a carbon fibre reinforced plastic hip stem during fatigue testing are characterized.