I might offer a suggestion, based on my experience. I had to abruptly retire when my knees went bad. I've had one replaced and am about to have the other one replaced. I'm not too agile at present. The situation presented itself when my father-in-law, who has been flying full size and model airplanes since in the late 1930's had a stroke and lost control of his left side. He can walk, but his left hand is for the most part useless. Radio controled models is a 2 handed sport, requiring coordination of both hands. I considered what was available and modified a radio control transmitter to provide a 3 axis control stick (roll, pitch, & yaw) and fabricated a foot pedal throttle control to use with the transmitter. He now has full control of model airplanes, and I learned a lot myself. I haven't attempted to fly models, because I had a subdural hematoma in 1996 and my coordination is not fast enough for 100MPH + airplanes. My success was reported around by ofhers to people and I am very busy adapting model airplane controls to work with the person's abilities. It's quite a thrill to see a person fly a model airplane again and see the big grin on their face. It's worth every minute of it.
Jim