Knee replacement surgery. Surgeon performing a total knee replacement operation. During this operation, the kneecap is moved aside to expose the knee joint. The ends of the thigh bone (femur) and shinebone (tibia) are shaped to be fitted with artificial components. A prosthetic component is fixed to the end of the femur and aligned with another component fixed to the end of the tibia, forming the artificial knee joint. Knee joints need replacing when the protective cartilage that lines them is lost. Cartilage can be lost due to injury or arthritis. See clips K004 6229 - K004 6255 for entire sequence.