Hi, Loosening of the implant is most often the cause of pain years or decades after the knee replacement.Any increase in pain after knee replacement should raise concerns for infection. X-rays and other studies can assess alignment and loosening. Subtle loosening may not show up on a regular ​X-ray, and a bone scan or MRI may be performed. Laboratory studies that are sometimes performed include markers of inflammation such as erythrocyte sedimentation rate (ESR) and a C-reactive protein (CRP) tests. Elevations of these markers of inflammation can indicate an infection or other inflammatory medical conditions. Hope that was helpful. Let me know if I can assist you further. Regards, Dr. Saranya Ramadoss, General and Family Physician