MODEL RELEASED. Knee replacement surgery. Image 2 of 10. Patient's knee during surgery to replace the knee joint with a prosthetic (artificial) joint. The skin and soft tissues have been peeled back from the knee to expose the bones of the joint. The heads of the tibia (shin bone, in metal clamp) and femur (thigh bone, to right of tibia) have been removed in preparation for the addition of the prosthesis. 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.