MODEL RELEASED. Knee replacement surgery. Image 1 of 10. Jig attached to a patient's lower leg. This jig will keep the drill steady 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. 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.