Knee replacement surgery. Surgeon removing excess orthopaedic cement after fitting a prosthetic joint components during a total knee replacement operation. The kneecap has been moved aside to expose the knee joint. Orthopaedic cement is a putty-like substance used to bond joint replacements to existing bone in orthopaedic surgery. The component fixed to the end of the thigh bone (femur) is aligned with a component fixed to the end of the shinbone (tibia), forming an 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.