MODEL RELEASED. Knee replacement surgery. Surgeons carrying out an operation to replace a knee joint. The patient's leg is at lower left, with the knee area opened up to show layers of fat and other tissues. The surgeon is using a tool on the new knee joint. Artificial knee joints are used to restore mobility in those whose knees have been injured or affected by severe arthritis. This operation is being carried out at an NHS (National Health Service) hospital, St Richard's Hospital in Chichester, West Sussex, England.