I fixed my 'difficult' knee, after twenty years of it grumbling severely for every waking hour, by falling off a motorbike and whacking it very hard off the road.
As it became more mobile, I began cycling again, initially because the car seat wouldn't go back far enough for the stiff leg to operate the clutch.
Eventually, things became manageable and I continued the cycling, more for convenience than exercise.
A good while later, a friend was describing a similar condition and I sympathised, saying how I had suffered for years - then I realised that it had stopped some time ago!
I have had no real issue in the subsequent two decades, bar the odd justifiable twinge for a few seconds, maybe once a month.
The other knee had a similar, but rather less significant issue, and this also 'healed', possibly as a result of not being affected by my efforts to 'unload' the other knee.
I can offer this revolutionary alternative therapy on a private appointment basis, with a minimal wait - just enough time for me to arrange the loan of a van to throw you out the back of.