Various types of knee arthroplasty implants are available depending on the number of knee compartments to be replaced and ligament stability. Unlike unicompartmental arthroplasty, the aim of total knee replacement is to maintain normal knee alignment. EOS X-ray imaging in the coronal and sagittal planes is the best modality for measuring the reference axes of the knee, but may by complemented by CT scans in the transverse plane. In addition to implant-related complications such as loosening and polyethylene wear, complications of the knee extensor mechanism are sometimes observed. Conventional radiography remains the first-line diagnostic modality in the event of post-knee replacement pain or instability. Ultrasound and CT imaging may also be helpful to make diagnosis.