MODEL RELEASED. Knee replacement surgery. Image 3 of 10. Prosthetic (artificial) knee joint being fitted during knee replacement surgery. The skin and soft tissues have been peeled back from the knee to expose the bones of the joint. The implants have not been attached yet, the surgeon is ensuring that the parts fit. Implants are fitted to the femur (thigh bone) and tibia (shin bone) to create a hinge joint that articulates in an identical way to a normal knee joint. Joints may need to be replaced after injury, disease, for example arthritis, or deformity. This knee is being replaced because of a valgus instability, which causes an inward facing knee. For a sequence showing the operation see M551/397-M551/406.