MODEL RELEASED. Knee replacement surgery. Image 7 of 10. Surgeon inserting a hinge washer into a prosthetic knee implant during knee replacement surgery. This implant is in the femur (thigh bone). 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.