MODEL RELEASED. Knee replacement surgery. Image 5 of 10. Surgeons fitting an implant to the femur (thigh bone) of a patient during knee replacement surgery. The implant is being pushed into cement that is inside the bone. Once fitted excess cement will be removed. The skin and soft tissues have been peeled back from the knee to expose the bones of the joint. Another implant is fitted to the tibia (shin bone) to create a hinge joint that articulates in exactly the same way as 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.