I, too, had an RTA in 1967. Although the knee was shattered (femur, tibia, fibula, femoral condile and patella all broken) the surgeon actually saved my knee which lasted 'til 2000. I had knee joint replacement which has been brilliant.
However, even though I still had the knee there was significant muscle wasting. I had to work very hard to build the muscle on that leg. I suspect that after all these years without a knee joint you will have little or no muscle on that leg and joint replacement wouldn't be very effective at all.