the existence of bone spurs in the knee

 pulled muscles or tendons

hairline fractures of the femur and tibia

 lack of cartilage between the bones of the knee

 by measuring the angle between the end of the femur and the hip bone

by drilling a hole in the femur and inserting an alignment device

by attaching a cutting jig

by checking sight lines between the femur and tibia

 by measuring the angle between the end of the tibia and the ankle

by drilling a hole in the tibia and inserting an alignment device down the center of the bone 

by attaching an alignment jig that is lined up with the big toe and the highest point of the tibia

by checking sight lines between the femur and tibia

femur, tibia, patella

femur and tibia

 tibia and patella

 femur and patella

to make sure the holes drilled in the bones are in the right places

 to test the fit and range of motion allowed by the components without wasting real ones

to make certain that the patient doesn’t react to the materials used in the real components

 to make certain the bones are cut correctly

to add an extra range of motion to the new knee components 

 to test the anesthesia to see if the patient is waking up

 to make certain that there is not too much space between components

 to make certain the bones are cut correctly