Radiopaque markers for enhanced radiographic visibility and wear detection in total knee arthroplasty inserts: a...

Standard x-ray radiography is routinely used to monitor total knee arthroplasty (TKA) postoperatively for complications such as loosening, malpositioning and insert wear. However, the radiolucency of the polyethylene insert makes quantitative wear assessment challenging. This study investigates the integration of radiopaque markers into standard ultra-high molecular weight polyethylene (UHMWPE) inserts to enhance their radiographic visibility and enable quantitative wear assessment from standard radiographs. Preliminary experiments established suitable process parameters for micro-milling cavities into UHMWPE. Final inserts were machined with varying microstructure configurations comprising grooves and holes. These microstructures were filled with a radiopaque composite of high-density polyethylene (HDPE) +20 wt.% barium sulphate (BaSO₄) composite via extrusion. HDPE was employed as a substitute for UHMWPE due to processability challenges resulting from the latter's high melt viscosity. The marker-integrated inserts were successively fitted on a phantom knee setup fitted together with TKA components and radiographed in the anteroposterior view. A weighted scoring model was created to identify optimal marker geometries based on edge visibility, dimensional measurability, homogeneity, and implant-induced obscuration of the marker projections in standard radiographs. Vertical groove markers i.e. those oriented in parallel to the central ray exhibited superior radiographic visibility and measurability compared to horizontal grooves. Hole markers exhibited a higher homogeneity and were easier to fill, but showed slightly reduced radiographic edge definition in comparison to the vertical grooves. Overall, the vertical grooves were identified as the most favourable marker geometry, followed by the holes, whereas horizontal markers performed the poorest. The findings of this study provide a proof of concept for incorporating radiopaque markers into TKA inserts, establishing a methodological framework for futurein vitrowear measurement based on dimensional marker change analysis. Further research into the development of a UHMWPE-compatible marker material is required before clinical relevance can be achieved.