He tore his quadricept tendons in his leg. These attach to the knee. . I did this two years ago. They reattach the tendons by drilling holes thru the knee and joining the bottom tendon with the top tendon via wires. You can’t bend your knee for several weeks after the surgery. They put this big ol brace on your leg from the hip to the ankle. (It is like sleeping on a bicycle.) after several weeks there’s a dial that allows 15 percent, 30 percent etc of bend. Then there’s p.t. It’s a long process but most people do ok if they follow orders. This is different than a knee replacement.