I rode with a damaged right knee for a long time. I walked with a cane, it was excruciatingly painful to put weight on the knee while bent, straight leg it wasn't so bad.
Riding was easy, I did adjust the rear brake pedal a bit and I wore short boots so I could move my ankle to push the brake instead of moving my whole leg like I used to, but it was less painfull to ride than it was to push the brake pedal in the car. Swinging the leg over took a bit of time to figure out an elegant way to get on, once figured it was no worse than how I would fall into the car and roll out of it.
The worst part is stowing the cane. I used an adjustable aluminum cane so I could collapse it and just layed it across the bars, the brake line and cables held it reasonably tight against the windshield, it never went anywhere.
Yes I had a handicap placard that I hung off the bar end. I got questioned a lot about it, especially on good days that I went out without the cane.
Thankfully I've healed enough that the doctor would no longer sign the form letting me use the handicap spots