This lecture covers the non-invasive real-time monitoring of knee prosthesis motion, including the types of knee implants, post-surgery monitoring to avoid complications, and the use of smart knee implants for data gathering and analysis. It also delves into the background of knee motion tracking techniques, such as fluoroscopy, tantalum beads, and biplane radiographs, and presents results from trials with small metallic tags. The lecture concludes with ongoing research on miniaturizing sensors, clinical tests, and potential future applications in joint motion modeling.