Third body damage and wear in arthroplasty bearing materials: A review of laboratory methods.

Third body wear of arthroplasty bearing materials can occur when hard particles such as bone, bone cement or metal particles become trapped between the articulating surfaces. This can accelerate overall implant wear, potentially leading to early failure. With the development of novel bearing materials and coatings, there is a need to develop and standardise test methods which reflect third body damage seen on retrieved implants. Many different protocols and approaches have been developed to replicate third body wear in the laboratory but there is currently no consensus as to the optimal method for simulating this wear mode, hence the need to better understand existing methods. The aim of this study was to review published methods for experimental simulation of third body wear of arthroplasty bearing materials, to discuss the advantages and limitations of different approaches, the variables to be considered when designing a method and to highlight gaps in the current literature. The methods were divided into those which introduced abrasive particles into the articulating surfaces of the joint and those whereby third body damage is created directly to the articulating surfaces. However, it was found that there are a number of parameters, for example the influence of particle size on wear, which are not yet fully understood. The study concluded that the chosen method or combination of methods used should primarily be informed by the research question to be answered and risk analysis of the device.