New trends in wear assessment of biomechanical components: challenges and achievements

Introduction. Wear strongly affects the long-term performance of biomedical components, as material loss may lead to biological reactions and instability. Recently, 3D optical methods have provided new opportunities for evaluating wear. Nevertheless, the reliability of the results depends on the 3D scanning system, the reference geometry estimation and alignment strategy. This study investigates these aspects to improve the reliability of 3D wear evaluations. 

Methods. Total hip and knee replacements (THR, TKR), including retrieved liners and laboratory-tested components, are analyzed to compare different approaches for 3D wear evaluation. The influence of digitizing systems, reference geometry and surface registration on the wear maps is investigated, through experimental campaigns. Different reference geometries are considered, including reconstructed ideal surfaces, scans of unworn components and nominal CAD models. For each case, suitable procedures are evaluated. The comparison highlights how different combinations of acquisition, reference and alignment methods can affect wear results and supports the definition of appropriate protocols. 

Results. Based on the findings, specific wear assessment protocols are proposed for different categories of case studies. The protocols provide guidance on the most suitable 3D scanning techniques for different biocomponents (laser or structured-light scanning, frames number, fixed or moving scene, and use of targets or artefacts), as well as on the selection or reconstruction of the reference geometry and the alignment procedure (best-fit algorithms or specific geometrical features). Conclusions. The proposed protocols support the selection of the most appropriate approach according to the characteristics and available data of each case study. For example, for retrieved total hip replacements, desktop laser or structured-light scanners with markers or reference artefacts are recommended. Alignment should preferably rely on measured unworn surfaces, while the reference geometry may be obtained from a pre-implantation scan, when available, or reconstructed from the nominal geometry of the retrieved component.