MODEL RELEASED. Knee replacement surgery. Image 10 of 10. Surgeon sewing up the incision in a patient's knee after knee replacement surgery. The prosthesis consists of two implants; one attached to the head of the femur (thigh bone) and one attached to the head of the tibia (shin bone). This creates 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.